U.S. patent application number 11/451697 was filed with the patent office on 2007-01-25 for thermoset particles with enhanced crosslinking, processing for their production, and their use in oil and natural gas driliing applications.
This patent application is currently assigned to SUN DRILLING PRODUCTS CORPORATION. Invention is credited to Jozef Bicerano.
Application Number | 20070021309 11/451697 |
Document ID | / |
Family ID | 37532898 |
Filed Date | 2007-01-25 |
United States Patent
Application |
20070021309 |
Kind Code |
A1 |
Bicerano; Jozef |
January 25, 2007 |
Thermoset particles with enhanced crosslinking, processing for
their production, and their use in oil and natural gas driliing
applications
Abstract
Thermoset polymer particles are used in many applications
requiring lightweight particles possessing high stiffness,
strength, temperature resistance, and/or resistance to aggressive
environments. The present invention relates to the use of methods
to enhance the stiffness, strength, maximum possible use
temperature, and environmental resistance of such particles. One
method of particular interest is the application of
post-polymerization process step(s) (and especially heat treatment)
to advance the curing reaction and to thus obtain a more densely
crosslinked polymer network. The most common benefits of said heat
treatment are the enhancement of the maximum possible use
temperature and the environmental resistance. The present invention
also relates to the development of thermoset polymer particles. It
also relates to the further improvement of the key properties (in
particular, heat resistance and environmental resistance) of said
particles via post-polymerization heat treatment. Furthermore, it
also relates to processes for the manufacture of said particles.
Finally, it also relates to the use of said particles in the
construction, drilling, completion and/or fracture stimulation of
oil and natural gas wells; for example, as a proppant partial
monolayer, a proppant pack, an integral component of a gravel pack
completion, a ball bearing, a solid lubricant, a drilling mud
constituent, and/or a cement additive.
Inventors: |
Bicerano; Jozef; (Midland,
MI) |
Correspondence
Address: |
Daniel H. Golub
1701 Market Street
Philadelphia
PA
19103
US
|
Assignee: |
SUN DRILLING PRODUCTS
CORPORATION
BELLE CHASSE
LA
70037
|
Family ID: |
37532898 |
Appl. No.: |
11/451697 |
Filed: |
June 13, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60689899 |
Jun 13, 2005 |
|
|
|
Current U.S.
Class: |
507/219 ;
428/402; 507/117 |
Current CPC
Class: |
C09K 8/92 20130101; C09K
8/035 20130101; C08J 3/28 20130101; Y10T 428/2982 20150115; C08J
3/12 20130101; C04B 16/04 20130101; C09K 8/80 20130101; C08J
2325/04 20130101 |
Class at
Publication: |
507/219 ;
507/117; 428/402 |
International
Class: |
C09K 8/00 20060101
C09K008/00; B32B 5/16 20060101 B32B005/16 |
Claims
1. A polymeric particle having a substantially cured polymer
network; wherein a packing of said particles manifests a static
conductivity of at least 100 mDft after 200 hours at temperatures
greater than 80.degree. F.; made by a method comprising: forming a
polymer by polymerizing a reactive mixture containing at least one
of a monomer, an oligomer, or combinations thereof; said at least
one of a monomer, an oligomer, or combinations thereof having three
or more reactive functionalities capable of creating crosslinks
between polymer chains; and subjecting said particle to at least
one post-polymerizing process that advances curing of a polymer
network.
2. The particle of claim 1, wherein said reactive mixture contains
a crosslinking component comprising at least one of a first
monomer, a first oligomer or a first combination thereof; and
wherein said reactive mixture further contains a non-crosslinking
component comprising at least one of a second monomer, a second
oligomer or a second combination thereof.
3. The particle of claim 1, wherein an amount of crosslinking
component ranges from 1% to 100% by weight of the reactive
mixture.
4. The particle of claim 1, wherein said reactive mixture comprises
at least one of monomer, oligomer or combinations thereof; said at
least one of monomer, oligomer or combinations thereof being used
to synthesize thermoset epoxies, epoxy vinyl esters, polyesters,
phenolics, melamine-based resins, polyurethanes, polyureas,
polyimides, or mixtures thereof.
5. The particle of claim 1, wherein said reactive mixture comprises
a crosslinking monomer selected from the group consisting of:
Divinylbenzene, trimethylolpropane trimethacrylate,
trimethylolpropane triacrylate, trimethylolpropane dimethacrylate,
trimethylolpropane diacrylate, pentaerythritol tetramethacrylate,
pentaerythritol trimethacrylate, pentaerythritol dimethacrylate,
pentaerythritol tetraacrylate, pentaerythritol triacrylate,
pentaerythritol diacrylate, bisphenol-A diglycidyl methacrylate,
ethyleneglycol dimethacrylate, ethyleneglycol diacrylate,
diethyleneglycol dimethacrylate, diethyleneglycol diacrylate,
triethyleneglycol dimethacrylate, and triethyleneglycol diacrylate,
a bis(methacrylamide) having the formula: ##STR1## a
bis(acrylamide) having the formula: ##STR2## a polyolefin having
the formula CH.sub.2.dbd.CH--(CH.sub.2).sub.x--CH.dbd.CH.sub.2
(wherein x ranges from 0 to 100, inclusive), a polyethyleneglycol
dimethylacrylate having the formula: ##STR3## a polyethyleneglycol
diacrylate having the formula: ##STR4## a molecule or a
macromolecule containing at least three isocyanate
(--N.dbd.C.dbd.O) groups, a molecule or a macromolecule containing
at least three alcohol (--OH) groups, a molecule or a macromolecule
containing at least three reactive amine functionalities where a
primary amine (--NH.sub.2) contributes two to the total number of
reactive functionalities while a secondary amine (--NHR--, where R
can be any aliphatic or aromatic organic fragment) contributes one
to the total number of reactive functionalities; and a molecule or
a macromolecule where the total number of reactive functionalities
arising from any combination of isocyanate (--N.dbd.C.dbd.O),
alcohol (--OH), primary amine (--NH.sub.2) and secondary amine
(--NHR--, where R can be any aliphatic or aromatic organic
fragment) adds up to at least three, 1,4-divinyloxybutane,
divinylsulfone, diallyl phthalate, diallyl acrylamide, triallyl
cyanurate, triallyl isocyanurate, triallyl trimellitate or mixtures
thereof.
6. The particle of claim 5, wherein said reactive mixture comprises
a non-crosslinking monomer selected from the group consisting of:
Styrenic monomers, styrene, methylstyrene, ethylstyrene
(ethylvinylbenzene), chlorostyrene, chloromethylstyrene,
styrenesulfonic acid, t-butoxystyrene, t-butylstyrene,
pentylstyrene, alpha-methylstyrene, alpha-methyl-p-pentylstyrene;
acrylic and methacrylic monomers, methyl acrylate, methyl
methacrylate, ethyl acrylate, ethyl methacrylate, 2-ethylhexyl
acrylate, 2-ethylhexyl methacrylate, lauryl acrylate, lauryl
methacrylate, glycidyl acrylate, glycidyl methacrylate,
dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate,
hydroxyethyl acrylate, hydroxyethyl methacrylate, diethylene glycol
acrylate, diethylene glycol methacrylate, glycerol monoacrylate,
glycerol monomethacrylate, polythylene glycol monoacrylate,
polyethylene glycol monomethacrylate, butanediol monoacrylate,
butanediol monomethacrylate; unsaturated carboxylic acid monomers,
acrylic acid, methacrylic acid; alkyl vinyl ether monomers, methyl
vinyl ether, ethyl vinyl ether; vinyl ester monomers, vinyl
acetate, vinyl propionate, vinyl butyrate; N-alkyl substituted
acrylamides and methacrylamides, N-methylacrylamide,
N-methylmethacrylamide, N-ethyl acrylamide, N-ethyl methacrylamide;
nitrile monomers, acrylonitrile, methacrylonitrile; olefinic
monomers, ethylene (H.sub.2C.dbd.CH.sub.2) and the alpha-olefins
(H.sub.2C.dbd.CHR) where R is any saturated hydrocarbon fragment;
vinylic alcohols, vinyl alcohol; vinyl halides, vinyl chloride;
vinylidene halides, vinylidene chloride, or mixtures thereof.
7. The particle of claim 1, said method further comprising using a
formulation including at least one of said reactive mixture, and
additional formulation ingredients wherein said additional
formulation ingredients are selected from the group of ingredients
consisting of initiators, catalysts, inhibitors, dispersants,
stabilizers, rheology modifiers, buffers, antioxidants, defoamers,
impact modifiers, or mixtures thereof.
8. The particle of claim 1, said post-polymerizing process being
performed as a manufacturing process step, as an "in situ" process
step in a hydrocarbon reservoir, or combinations thereof.
9. The particle of claim 8, wherein said post-polymerizing process
further comprises at least one of heat treatment, stirring, flow,
sonication, irradiation, or combinations thereof.
10. The particle of claim 9, wherein said heat treatment is
performed in a medium including a vacuum, a non-oxidizing gas, a
mixture of non-oxidizing gases, a liquid, or a mixture of liquids;
or in a downhole environment of a hydrocarbon reservoir.
11. The particle of claim 1, wherein said particle has a shape
selected from the group of shapes consisting of a powder, a pellet,
a grain, a seed, a short fiber, a rod, a cylinder, a platelet, a
bead, a spheroid, or mixtures thereof.
12. The particle of claim 1, wherein a largest principal axis
dimension of said particle does not exceed 10 millimeters.
13. The particle of claim 2, wherein the crosslinking component
comprises divinylbenzene, wherein the non-crosslinking component
comprises styrene, said divinylbenzene in an amount ranging from 3%
to 35% by weight of the reactive mixture.
14. The particle of claim 13, wherein said non-crosslinking monomer
further comprises ethylvinylbenzene.
15. The particle of claim 13, wherein said polymerizing comprises
suspension polymerizing.
16. The particle of claim 15, wherein said suspension polymerizing
comprises rapid rate polymerizing.
17. The particle of claim 15, wherein said suspension polymerizing
comprises isothermal polymerizing.
18. The particle of claim 13, said method further comprising using
a formulation including at least one of said reactive mixture and
additional formulation ingredients wherein said additional
formulation ingredients comprise at least one of initiators,
catalysts, inhibitors, dispersants, stabilizers, rheology
modifiers, buffers, antioxidants, defoamers, impact modifiers, or
mixtures thereof.
19. The particle of claim 13, said method further comprising
subjecting said particle to at least one post-polymerizing
process.
20. The particle of claim 19, wherein said post-polymerizing
process further comprises at least one of heat treatment, stirring,
flow, sonication, irradiation, or combinations thereof.
21. The particle of claim 19, wherein an unreactive gaseous
environment with nitrogen as the preferred unreactive gas is used
as the heat transfer medium during said post-polymerizing
process.
22. The particle of claim 13, wherein said particle is a spherical
bead having a diameter does not exceed 10 millimeters.
23. The particle of claim 22, wherein said diameter ranges from 0.1
mm to 4 mm.
24. A polymeric particle exhibiting a static conductivity of at
least 100 mDft after 200 hours at temperatures greater than 80 OF;
and comprising a rigid thermoset polymer.
25. The particle of claim 24, wherein said thermoset polymer
comprises a terpolymer.
26. The particle of claim 24, wherein said thermoset polymer
comprises a styrene-ethylvinylbenzene-divinylbenzene
terpolymer.
27. The particle of claim 24, wherein said particle has a shape
selected from the group of shapes consisting of a powder, a pellet,
a grain, a seed, a short fiber, a rod, a cylinder, a platelet, a
bead, a spheroid, or mixtures thereof.
28. The particle of claim 24, wherein a largest principal axis
dimension of said particle does not exceed 10 millimeters.
29. The particle of claim 24, wherein said particle is a spherical
bead having a diameter that does not exceed 10 millimeters.
30. The particle of claim 29, wherein said diameter ranges from 0.1
mm to 4 mm.
31. An assembly of particles comprising a rigid thermoset polymer;
said polymer having a substantially cured polymer network, and
wherein a packing of said particles manifests a static conductivity
of at least 100 mDft after 200 hours at temperatures greater than
80.degree. F., wherein the particles in said assembly have sizes
that do not exceed 10 millimeters in any principal axis
direction.
32. The assembly of particles of claim 31, wherein said thermoset
polymer comprises a terpolymer.
33. The assembly of particles of claim 31, wherein said thermoset
polymer comprises a styrene-ethylvinylbenzene-divinylbenzene
terpolymer.
34. The assembly of particles of claim 31, wherein said particle is
a spherical bead having a diameter that does not exceed 10
millimeters.
35. The assembly of particles of claim 34, wherein said diameter
ranges from 0.1 mm to 4 mm.
36. A method for producing substantially cured polymeric particles,
comprising: (a) forming polymeric particles by polymerizing a
reactive mixture, dispersed within a liquid medium, containing at
least one of an initiator; and at least one of a monomer, an
oligomer or combinations thereof, said at least one of a monomer,
an oligomer, or combinations thereof having three or more reactive
functionalities capable of creating crosslinks between polymer
chains; wherein a packing of particles resulting from step (a)
manifests a first static conductivity when measured after 200 hours
under a given compressive stress and at a given temperature greater
than 80.degree. F.; and (b) subjecting the particles polymerized in
step (a) to at least one post-polymerizing process, wherein said
post-polymerizing process advances curing of a polymer network of
the polymeric particles forming the substantially cured polymeric
particles, wherein a packing of the substantially cured polymeric
particles manifests a second static conductivity when measured
after 200 hours under the given compressive stress and at the given
temperature; wherein the second static conductivity is greater than
the first static conductivity.
37. The method of claim 36, wherein said reactive mixture contains
a crosslinking component comprising at least one of a first
monomer, a first oligomer or a first combination thereof; and
wherein said reactive mixture further contains a non-crosslinking
component comprising at least one of a second monomer, a second
oligomer or a second combination thereof.
38. The method of claim 37, wherein an amount of crosslinking
component ranges from 1% to 100% by weight of the reactive
mixture.
39. The method of claim 36, wherein said reactive mixture comprises
at least one of monomer, oligomer or combinations thereof, said at
least one of monomer, oligomer or combinations thereof being used
to synthesize thermoset epoxies, epoxy vinyl esters, polyesters,
phenolics, melamine-based resins, polyurethanes, polyureas,
polyimides, or mixtures thereof.
40. The method of claim 36, wherein said reactive mixture comprises
a crosslinking monomer selected from the following list, or
mixtures thereof: Divinylbenzene, trimethylolpropane
trimethacrylate, trimethylolpropane triacrylate, trimethylolpropane
dimethacrylate, trimethylolpropane diacrylate, pentaerythritol
tetramethacrylate, pentaerythritol trimethacrylate, pentaerythritol
dimethacrylate, pentaerythritol tetraacrylate, pentaerythritol
triacrylate, pentaerythritol diacrylate, bisphenol-A diglycidyl
methacrylate, ethyleneglycol dimethacrylate, ethyleneglycol
diacrylate, diethyleneglycol dimethacrylate, diethyleneglycol
diacrylate, triethyleneglycol dimethacrylate, and triethyleneglycol
diacrylate, a bis(methacrylamide) having the formula: ##STR5## a
bis(acrylamide) having the formula: ##STR6## a polyolefin having
the formula CH.sub.2.dbd.CH--(CH.sub.2).sub.x--CH.dbd.CH.sub.2
(wherein x ranges from 0 to 100, inclusive), a polyethyleneglycol
dimethylacrylate having the formula: ##STR7## a polyethyleneglycol
diacrylate having the formula: ##STR8## a molecule or a
macromolecule containing at least three isocyanate
(--N.dbd.C.dbd.O) groups, a molecule or a macromolecule containing
at least three alcohol (--OH) groups, a molecule or a macromolecule
containing at least three reactive amine functionalities where a
primary amine (--NH.sub.2) contributes two to the total number of
reactive functionalities while a secondary amine (--NHR--, where R
can be any aliphatic or aromatic organic fragment) contributes one
to the total number of reactive functionalities; and a molecule or
a macromolecule where the total number of reactive functionalities
arising from any combination of isocyanate (--N.dbd.C.dbd.O),
alcohol (--OH), primary amine (--NH.sub.2) and secondary amine
(--NHR--, where R can be any aliphatic or aromatic organic
fragment) adds up to at least three, 1,4-divinyloxybutane,
divinylsulfone, diallyl phthalate, diallyl acrylamide, triallyl
cyanurate, triallyl isocyanurate, triallyl trimellitate.
41. The method of claim 36, wherein said reactive mixture comprises
a non-crosslinking monomer selected from the following list, or
mixtures thereof: Styrenic monomers, styrene, methylstyrene,
ethylstyrene (ethylvinylbenzene), chlorostyrene,
chloromethylstyrene, styrenesulfonic acid, t-butoxystyrene,
t-butylstyrene, pentylstyrene, alpha-methylstyrene,
alpha-methyl-p-pentylstyrene; acrylic and methacrylic monomers,
methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl
methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate,
lauryl acrylate, lauryl methacrylate, glycidyl acrylate, glycidyl
methacrylate, dimethylaminoethyl acrylate, dimethylaminoethyl
methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate,
diethylene glycol acrylate, diethylene glycol methacrylate,
glycerol monoacrylate, glycerol monomethacrylate, polythylene
glycol monoacrylate, polyethylene glycol monomethacrylate,
butanediol monoacrylate, butanediol monomethacrylate; unsaturated
carboxylic acid monomers, acrylic acid, methacrylic acid; alkyl
vinyl ether monomers, methyl vinyl ether, ethyl vinyl ether; vinyl
ester monomers, vinyl acetate, vinyl propionate, vinyl butyrate;
N-alkyl substituted acrylamides and methacrylamides,
N-methylacrylamide, N-methylmethacrylamide, N-ethyl acrylamide,
N-ethyl methacrylamide; nitrile monomers, acrylonitrile,
methacrylonitrile; olefinic monomers, ethylene
(H.sub.2C.dbd.CH.sub.2) and the alpha-olefins (H.sub.2C.dbd.CHR)
where R is any saturated hydrocarbon fragment; vinylic alcohols,
vinyl alcohol; vinyl halides, vinyl chloride; vinylidene halides,
vinylidene chloride or mixtures thereof.
42. The method of claim 36, said method further comprising using a
formulation including at least one of said reactive mixture, and
additional formulation ingredients wherein said additional
formulation ingredients are selected from the group of ingredients
consisting of initiators, catalysts, inhibitors, dispersants,
stabilizers, rheology modifiers, buffers, antioxidants, defoamers,
impact modifiers, or mixtures thereof.
43. The method of claim 36, said post-polymerizing process being
performed as a manufacturing process step, as an "in situ" process
step in a hydrocarbon reservoir, or combinations thereof.
44. The method of claim 43, wherein said post-polymerizing process
further comprises at least one of heat treatment, stirring, flow,
sonication, irradiation, or combinations thereof.
45. The method of claim 44, wherein said heat treatment is
performed in a medium including a vacuum, a non-oxidizing gas, a
mixture of non-oxidizing gases, a liquid, or a mixture of liquids;
or in a downhole environment of a hydrocarbon reservoir.
46. The method of claim 36, wherein said particle has a shape;
selected from the group of shapes consisting of a powder, a pellet,
a grain, a seed, a short fiber, a rod, a cylinder, a platelet, a
bead, a spheroid, or mixtures thereof.
47. The method of claim 36, wherein a largest principal axis
dimension of said particle does not exceed 10 millimeters.
48. The method of claim 36, wherein the crosslinking component
comprises divinylbenzene, wherein the non-crosslinking component
comprises styrene, said divinylbenzene in an amount ranging from 3%
to 35% by weight of the reactive mixture.
49. The method of claim 48, wherein said non-crosslinking monomer
further comprises ethylvinylbenzene.
50. The method of claim 36, said polymerizing comprises suspension
polymerizing.
51. The method of claim 50, wherein said suspension polymerizing
comprises rapid rate polymerizing.
52. The method of claim 50, wherein said suspension polymerizing
comprises isothermal polymerizing.
53. The method of claim 48, said method further comprising
subjecting said particle to at least one post-polymerizing
process.
54. The method of claim 53, wherein said post-polymerizing process
further comprises at least one of heat treatment, stirring, flow,
sonication, irradiation, or combinations thereof.
55. The method of claim 53, wherein said post polymerizing process
occurs in an unreactive gaseous environment with nitrogen as the
preferred unreactive gas.
56. The method of claim 48, said method further comprising using a
formulation including at least one of said reactive mixture and
additional formulation ingredients wherein said additional
formulation ingredients comprise at least one of initiators,
catalysts, inhibitors, dispersants, stabilizers, rheology
modifiers, buffers, antioxidants, defoamers, impact modifiers, or
mixtures thereof.
57. The method of claim 48, wherein said particle is a spherical
bead having a diameter that does not exceed 10 millimeters.
58. The method of claim 57, wherein said diameter ranges from 0.1
mm to 4 mm.
59. A method of producing an assembly of particles comprising: (a)
forming polymeric particles by polymerizing a reactive mixture,
dispersed within a liquid medium, containing at least one of an
initiator; and at least one of a monomer, an oligomer or
combinations thereof, said at least one of a monomer, an oligomer,
or combinations thereof having three or more reactive
functionalities capable of creating crosslinks between polymer
chains; wherein a packing of particles resulting from step (a)
manifests a first static conductivity when measured after 200 hours
under a given compressive stress and at a given temperature greater
than 80.degree. F.; and (b) subjecting the particles polymerized in
step (a) to at least one post-polymerizing process, wherein said
post-polymerizing process advances curing of a polymer network of
the polymeric particles forming the substantially cured polymeric
particles, wherein a packing of the substantially cured polymeric
particles manifests a second static conductivity when measured
after 200 hours under the given compressive stress and at the given
temperature; wherein the second static conductivity is greater than
the first static conductivity. (c) separating the particles by
shape and size range, wherein the particles in said assembly have
sizes that do not exceed 10 millimeters in any principal axis
direction.
60. The method of claim 59, wherein the crosslinking component
comprises divinylbenzene, wherein the non-crosslinking component
comprises styrene, said divinylbenzene in an amount ranging from 3%
to 35% by weight of the reactive mixture.
61. The method of claim 59, wherein said non-crosslinking monomer
further comprises ethylvinylbenzene.
62. The method of claim 60, said method further comprising
subjecting said particle to at least one post-polymerizing
process.
63. The method of claim 62, wherein said post-polymerizing process
further comprises at least one of heat treatment, stirring, flow,
sonication, irradiation, or combinations thereof.
64. The method of claim 59, wherein said particle is a spherical
bead having a diameter that does not exceed 10 millimeters.
65. The method of claim 64, wherein said diameter ranges from 0.1
mm to 4 mm.
66. A method for fracture stimulation of a subterranean formation
having a wellbore, comprising: injecting into the wellbore a slurry
at sufficiently high rates and pressures such that said formation
fails and fractures to accept said slurry; said slurry comprising a
fluid and a proppant, wherein said proppant comprises a particle
comprising a rigid thermoset polymer; and emplacing said proppant
within the fracture network in a packed mass or a partial monolayer
of particles within the fracture, which packed mass or partial
monolayer props open the fracture; thereby allowing produced gases,
fluids, or mixtures thereof, to flow towards the wellbore.
67. A method for lightening a load of cement comprising: mixing an
uncured cement composition with an effective amount of a particle
comprising a rigid thermoset polymer; and placing the mixture in a
selected location.
68. A method for treating a well penetrating a subterranean
formation comprising: providing an effective amount of a particle
comprising a rigid thermoset polymer; and introducing said
polymeric particle into said well.
69. A method for treating a well penetrating a subterranean
formation comprising: mixing into a drilling mud formulation an
effective amount of a particle comprising a rigid thermoset
polymer; and introducing said drilling mud formulation with said
effective amount of the polymeric particle into said well.
70. A method for reducing friction in a well penetrating a
subterranean formation comprising: mixing into a drilling fluid
formulation as a solid lubricant an effective amount of a particle
comprising a rigid thermoset polymer; and introducing said drilling
fluid formulation with said effective amount of the polymeric
particle into said well.
71. A method for reducing friction in a well penetrating a
subterranean formation comprising: mixing into a drilling fluid
formulation as a ball bearing an effective amount of a particle
comprising a rigid thermoset polymer; and introducing said drilling
fluid formulation with said effective amount of the polymeric
particle into said well.
72. A method for forming a gravel pack within a wellbore
comprising: blending into the gravel pack formulation an effective
amount of a particle comprising a rigid thermoset polymer; and
introducing the gravel pack formulation with said effective amount
of the polymeric particle into the wellbore.
73. The method of claims 66, 67, 68, 69, 70, 71 or 72, wherein said
thermoset polymer has a substantially cured polymer network,
wherein a packing of said particles manifests a static conductivity
of at least 100 mDft after 200 hours at temperatures greater than
80.degree. F.
74. The method of claims 66, 67, 68, 69, 70, 71, 72 or 73 wherein
said thermoset polymer comprises at least one of a thermoset epoxy,
a thermoset epoxy vinyl ester, a thermoset polyester, a thermoset
phenolic, a thermoset melamine-based resin, a thermoset
polyurethane, a thermoset polyurea, a thermoset polyimide, or
mixtures thereof.
75. The method of claims 66, 67, 68, 69, 70, 71, 72 or 73 wherein
said thermoset polymer comprises a terpolymer.
76. The method of claims 66, 67, 68, 69, 70, 71, 72 or 73 wherein
said thermoset polymer matirx comprises a
styrene-ethylvinylbenzene-divinylbenzene terpolymer.
77. The method of claims 66, 67, 68, 69, 70, 71, 72 or 73 wherein
said particle has a shape; selected from the group of shapes
consisting of a powder, a pellet, a grain, a seed, a short fiber, a
rod, a cylinder, a platelet, a bead, a spheroid, or mixtures
thereof.
78. The method of claims 66, 67, 68, 69, 70, 71, 72 or 73, wherein
a largest principal axis dimension of said particle does not exceed
10 millimeters.
79. The method of claim 66, 67, 68, 69, 70, 71, 72 or 73 wherein
said particle is a spherical bead having a diameter that does not
exceed 10 millimeters.
80. The method of claim 66, 67, 68, 69, 70, 71, 72 or 73 wherein
said diameter ranges from 0.1 mm to 4 mm.
81. The method of claim 66, 67, 68, 69, 70, 71, 72 or 73 wherein
said polymeric particle is blended with other solid particles
including at least one of sand, resin-coated sand, ceramic and
resin-coated ceramic.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/689,899 filed Jun. 13, 2005.
FIELD OF THE INVENTION
[0002] The present invention relates to lightweight thermoset
polymer particles, to processes for the manufacture of such
particles, and to applications of such particles. It is possible to
use a wide range of thermoset polymers as the main constituents of
the particles of the invention, and to produce said particles by
means of a wide range of fabrication techniques. Without reducing
the generality of the invention, in its currently preferred
embodiments, the thermoset polymer consists of a terpolymer of
styrene, ethyvinylbenzene and divinylbenzene; suspension
polymerization is performed to prepare the particles, and
post-polymerization heat treatment is performed with the particles
placed in an unreactive gaseous environment with nitrogen as the
preferred unreactive gas to further advance the curing of the
thermoset polymer. When executed in the manner taught by this
disclosure, many properties of both the individual particles and
packings of the particles can be improved by the practice of the
invention. The particles exhibit enhanced stiffness, strength, heat
resistance, and resistance to aggressive environments; as well as
the improved retention of high conductivity of liquids and gases
through packings of the particles in aggressive environments under
high compressive loads at elevated temperatures. The thermoset
polymer particles of the invention can be used in many
applications. These applications include, but are not limited to,
the construction, drilling, completion and/or fracture stimulation
of oil and natural gas wells; for example, as a proppant partial
monolayer, a proppant pack, an integral component of a gravel pack
completion, a ball bearing, a solid lubricant, a drilling mud
constituent, and/or a cement additive.
BACKGROUND
[0003] The background of the invention can be described most
clearly, and hence the invention can be taught most effectively, by
subdividing this section in three subsections. The first subsection
will provide some general background regarding the role of
crosslinked (and especially stiff and strong thermoset) particles
in the field of the invention. The second subsection will describe
the prior art that has been taught in the patent literature. The
third subsection will provide additional relevant background
information selected from the vast scientific literature on polymer
materials science and chemistry, to further facilitate the teaching
of the invention.
A. General Background
[0004] Crosslinked polymer (and especially stiff and strong
thermoset) particles are used in many applications requiring high
stiffness, high mechanical strength, high temperature resistance,
and/or high resistance to aggressive environments. Crosslinked
polymer particles can be prepared by reacting monomers or oligomers
possessing three or more reactive chemical functionalities, as well
as by reacting mixtures of monomers and/or oligomers at least one
ingredient of which possesses three or more reactive chemical
functionalities.
[0005] The intrinsic advantages of crosslinked polymer particles
over polymer particles lacking a network consisting of covalent
chemical bonds in such applications become especially obvious if an
acceptable level of performance must be maintained for a prolonged
period (such as many years, or in some applications even several
decades) under the combined effects of mechanical deformation,
heat, and/or severe environmental insults. For example, many
high-performance thermoplastic polymers, which have excellent
mechanical properties and which are hence used successfully under a
variety of conditions, are unsuitable for applications where they
must maintain their good mechanical properties for many years in
the presence of heat and/or chemicals, because they consist of
assemblies of individual polymer chains. Over time, the deformation
of such assemblies of individual polymer chains at an elevated
temperature can cause unacceptable amounts of creep, and
furthermore solvents and/or aggressive chemicals present in the
environment can gradually diffuse into them and degrade their
performance severely (and in some cases even dissolve them). By
contrast, the presence of a well-formed continuous network of
covalent bonds restrains the molecules, thus helping retain an
acceptable level of performance under severe use conditions over a
much longer time period.
[0006] Oil and natural gas well construction activities, including
drilling, completion and stimulation applications (such as
proppants, gravel pack components, ball bearings, solid lubricants,
drilling mud constituents, and/or cement additives), require the
use of particulate materials, in most instances preferably of as
nearly spherical a shape as possible. These (preferably
substantially spherical) particles must generally be made from
materials that have excellent mechanical properties. The mechanical
properties of greatest interest in most such applications are
stiffness (resistance to deformation) and strength under
compressive loads, combined with sufficient "toughness" to avoid
the brittle fracture of the particles into small pieces commonly
known as "fines". In addition, the particles must have excellent
heat resistance in order to be able to withstand the combination of
high compressive load and high temperature that normally becomes
increasingly more severe as one drills deeper. In other words,
particles that are intended for use deeper in a well must be able
to withstand not only the higher overburden load resulting from the
greater depth, but also the higher temperature that accompanies
that higher overburden load as a result of the nature of geothermal
gradients. Finally, these materials must be able to withstand the
effects of the severe environmental insults (resulting from the
presence of a variety of hydrocarbon and possibly solvent molecules
as well as water, at simultaneously elevated temperatures and
compressive loads) that the particles will encounter deep in an oil
or natural gas well. The need for relatively lightweight high
performance materials for use in these particulate components in
applications related to the construction, drilling, completion
and/or fracture stimulation of oil and natural gas wells thus
becomes obvious. Consequently, while such uses constitute only a
small fraction of the applications of stiff and strong materials,
they provide fertile territory for the development of new or
improved materials and manufacturing processes for the fabrication
of such materials.
[0007] We will focus much of the remaining discussion of the
background of the invention on the use of particulate materials as
proppants. One key measure of end use performance of proppants is
the retention of high conductivity of liquids and gases through
packings of the particles in aggressive environments under high
compressive loads at elevated temperatures.
[0008] The use of stiff and strong solid proppants has a long
history in the oil and natural gas industry. Throughout most of
this history, particles made from polymeric materials (including
crosslinked polymers) have been considered to be unsuitable for use
by themselves as proppants. The reason for this prejudice is the
perception that polymers are too deformable, as well as lacking in
the ability to withstand the combination of elevated compressive
loads, temperatures and aggressive environments that are commonly
encountered in oil and natural gas wells. Consequently, work on
proppant material development has focused mainly on sands, on
ceramics, and on sands and ceramics coated by crosslinked polymers
to improve some aspects of their performance. This situation has
prevailed despite the fact that most polymers have densities that
are much closer to that of water so that in particulate form they
can be transported much more readily into a fracture by low-density
fracturing or carrier fluids such as unviscosified water.
[0009] Nonetheless, the obvious practical advantages [see a review
by Edgeman (2004)] of developing the ability to use lightweight
particles that possess almost neutral buoyancy relative to water
have stimulated a considerable amount of work over the years.
However, as will be seen from the review of the prior art provided
below, progress in this field of invention has been very slow as a
result of the many technical challenges that exist to the
successful development of cost-effective lightweight particles that
possess sufficient stiffness, strength and heat resistance.
B. Prior Art
[0010] The prior art can be described most clearly, and hence the
invention can be placed in the proper context most effectively, by
subdividing this section into two subsections. The first subsection
will describe prior art related to the development of
"as-polymerized" thermoset polymer particles. The second subsection
will describe prior art related to the development of thermoset
polymer particles that are subjected to post-polymerization heat
treatment.
1. "As-Polymerized" Thermoset Polymer Particles
[0011] As discussed above, particles made from polymeric materials
have historically been considered to be unsuitable for use by
themselves as proppants. Consequently, their past uses in proppant
materials have focused mainly on their placement as coatings on
sands and ceramics, in order to improve some aspects of the
performance of the sand and ceramic proppants.
[0012] Significant progress was made in the use of crosslinked
polymeric particles themselves as constituents of proppant
formulations in prior art taught by Rickards, et al. (U.S. Pat. No.
6,059,034; U.S. Pat. No. 6,330,916). However, these inventors still
did not consider or describe the polymeric particles as proppants.
Their invention only related to the use of the polymer particles in
blends with particles of more conventional proppants such as sands
or ceramics. They taught that the sand or ceramic particles are the
proppant particles, and that the "deformable particulate material"
consisting of polymer particles mainly serves to improve the
fracture conductivity, reduce the generation of fines and/or reduce
proppant flowback relative to the unblended sand or ceramic
proppants. Thus while their invention differs significantly from
the prior art in the sense that the polymer is used in particulate
form rather than being used as a coating, it shares with the prior
art the limitation that the polymer still serves merely as a
modifier improving the performance of a sand or ceramic proppant
rather than being considered for use as a proppant in its own
right.
[0013] Bienvenu (U.S. Pat. No. 5,531,274) disclosed progress
towards the development of lightweight proppants consisting of
high-strength crosslinked polymeric particles for use in hydraulic
fracturing applications. However, embodiments of this prior art,
based on the use of styrene-divinylbenzene (S-DVB) copolymer beads
manufactured by using conventional fabrication technology and
purchased from a commercial supplier, failed to provide an
acceptable balance of performance and price. They cost far more
than the test standard (Jordan sand) while being outperformed by
Jordan sand in terms of the liquid conductivity and liquid
permeability characteristics of their packings measured according
to the industry-standard API RP 61 testing procedure. [This
procedure is described by the American Petroleum Institute in its
publication titled "Recommended Practices for Evaluating Short Term
Proppant Pack Conductivity" (first edition, Oct. 1, 1989).] The
need to use a very large amount of an expensive crosslinker (50 to
80% by weight of DVB) in order to obtain reasonable performance
(not too inferior to that of Jordan Sand) was a key factor in the
higher cost that accompanied the lower performance.
[0014] The most advanced prior art in stiff and strong crosslinked
"as-polymerized" polymer particle technologies for use in
applications in oil and natural gas drilling was developed by
Albright (U.S. Pat. No. 6,248,838) who taught the concept of a
"rigid chain entanglement crosslinked polymer". In summary, the
reactive formulation and the processing conditions were modified to
achieve "rapid rate polymerization". While not improving the extent
of covalent crosslinking relative to conventional isothermal
polymerization, rapid rate polymerization results in the "trapping"
of an unusually large number of physical entanglements in the
polymer. These additional entanglements can result in a major
improvement of many properties. For example, the liquid
conductivities of packings of S-DVB copolymer beads with
w.sub.DVB=0.2 synthesized via rapid rate polymerization are
comparable to those that were found by Bienvenu (U.S. Pat. No.
5,531,274) for packings of conventionally produced S-DVB beads at
the much higher DVB level of w.sub.DVB=0.5. Albright (U.S. Pat. No.
6,248,838) thus provided the key technical breakthrough that
enabled the development of the first generation of crosslinked
polymer beads possessing sufficiently attractive combinations of
performance and price characteristics to result in their commercial
use in their own right as solid polymeric proppants.
2. Heat-Treated Thermoset Polymer Particles
[0015] There is no prior art that relates to the development of
heat-treated thermoset polymer particles that have not been
reinforced by rigid fillers or by nanofillers for use in oil and
natural gas well construction applications. One needs to look into
another field of technology to find prior art of some relevance
related to such "unfilled" heat-treated thermoset polymer
particles. Nishimori, et. al. (JP1992-22230) focused on the
development of particles for use in liquid crystal display panels.
They taught the use of post-polymerization heat treatment to
increase the compressive elastic modulus of S-DVB particles at room
temperature. They only claimed compositions polymerized from
reactive monomer mixtures containing 20% or more by weight of DVB
or other crosslinkable monomer(s) prior to the heat treatment. They
stated explicitly that improvements obtained with lower weight
fractions of the crosslinkable monomer(s) were insufficient and
that hence such compositions were excluded from the scope of their
patent.
C. Scientific Literature
[0016] The development of thermoset polymers requires the
consideration of a vast and multidisciplinary range of polymer
materials science and chemistry challenges. It is essential to
convey these challenges in the context of the fundamental
scientific literature.
[0017] Bicerano (2002) provides a broad overview of polymer
materials science that can be used as a general reference for most
aspects of the following discussion. Additional references will
also be provided below, to other publications which treat specific
issues in greater detail than what could be accommodated in
Bicerano (2002).
[0018] 1. Selected Fundamental Aspects of the Curing of Crosslinked
Polymers
[0019] It is essential, first, to review some fundamental aspects
of the curing of crosslinked polymers, which are applicable to such
polymers regardless of their form (particulate, coating, or
bulk).
[0020] The properties of crosslinked polymers prepared by standard
manufacturing processes are often limited by the fact that such
processes typically result in incomplete curing. For example, in an
isothermal polymerization process, as the glass transition
temperature (T.sub.g) of the growing polymer network increases, it
may reach the polymerization temperature while the reaction is
still in progress. If this happens, then the molecular motions slow
down significantly so that further curing also slows down
significantly. Incomplete curing yields a polymer network that is
less densely crosslinked than the theoretical limit expected from
the functionalities and relative amounts of the starting reactants.
For example, a mixture of monomers might contain 80% DVB by weight
as a crosslinker but the final extent of crosslinking that is
attained may not be much greater than what was attained with a much
smaller percentage of DVB. This situation results in lower
stiffness, lower strength, lower heat resistance, and lower
environmental resistance than the thermoset is capable of
manifesting when it is fully cured and thus maximally
crosslinked.
[0021] When the results of the first scan and the second scan of
S-DVB beads containing various weight fractions of DVB (w.sub.DVB),
obtained by Differential Scanning Calorimetry (DSC), as reported by
Bicerano, et al. (1996) (see FIG. 1) are compared, it becomes clear
that the low performance and high cost of the "as purchased" S-DVB
beads utilized by Bienvenu (U.S. Pat. No. 5,531,274) are related to
incomplete curing. This incomplete curing results in the
ineffective utilization of DVB as a crosslinker and thus in the
incomplete development of the crosslinked network. In summary,
Bicerano, et al. (1996), showed that the T.sub.g of typical
"as-polymerized" S-DVB copolymers, as measured by the first DSC
scan, increased only slowly with increasing w.sub.DVB, and
furthermore that the rate of further increase of T.sub.g slowed
down drastically for w.sub.DVB>0.08. By contrast, in the second
DSC scan (performed on S-DVB specimens whose curing had been driven
much closer to completion as a result of the temperature ramp that
had been applied during the first scan), T.sub.g grew much more
rapidly with w.sub.DVB over the entire range of up to
w.sub.DVB=0.2458 that was studied. The more extensively cured
samples resulting from the thermal history imposed by the first DSC
scan can, thus, be considered to provide much closer approximations
to the ideal theoretical limit of a "fully cured" polymer
network.
[0022] 2. Effects of Heat Treatment on Key Properties of Thermoset
Polymers
[0023] a. Maximum Possible Use Temperature
[0024] As was illustrated by Bicerano, et al. (1996) for S-DVB
copolymers with w.sub.DVB of up to 0.2458, enhancing the state of
cure of a thermoset polymer network can increase T.sub.g very
significantly relative to the T.sub.g of the "as-polymerized"
material. In practice, the heat distortion temperature (HDT) is
used most often as a practical indicator of the softening
temperature of a polymer under load. As was shown by Takemori
(1979), a systematic understanding of the HDT is possible through
its direct correlation with the temperature dependences of the
tensile (or equivalently, compressive) and shear elastic moduli.
For amorphous polymers, the precipitous decrease of these elastic
moduli as T.sub.g is approached from below renders the HDT
well-defined, reproducible, and predictable. HDT is thus closely
related to (and usually slightly lower than) T.sub.g for amorphous
polymers, so that it can be increased significantly by increasing
T.sub.g significantly.
[0025] The HDT decreases gradually with increasing magnitude of the
load used in its measurement. For example, for general-purpose
polystyrene (which has T.sub.g=100.degree. C.), HDT=95.degree. C.
under a load of 0.46 MPa and HDT=85.degree. C. under a load of 1.82
MPa are typical values. However, the compressive loads deep in an
oil well or natural gas well are normally far higher than the
standard loads (0.46 MPa and 1.82 MPa) used in measuring the HDT.
Consequently, amorphous thermoset polymer particles can be expected
to begin to deform significantly at a lower temperature than the
HDT of the polymer measured under the standard high load of 1.82
MPa. This deformation will cause a decrease in the conductivities
of liquids and gases through the propped fracture, and hence in the
loss of effectiveness as a proppant, at a somewhat lower
temperature than the HDT value of the polymer measured under the
standard load of 1.82 MPa.
[0026] b. Mechanical Properties
[0027] As was discussed earlier, Nishimori, et. al. (JP1992-22230)
used heat treatment to increase the compressive elastic modulus of
their S-DVB particles (intended for use in liquid crystal display
panels) significantly at room temperature (and hence far below
T.sub.g). Deformability under a compressive load is inversely
proportional to the compressive elastic modulus. It is, therefore,
important to consider whether one may also anticipate major
benefits from heat treatment in terms of the reduction of the
deformability of thermoset polymer particles intended for oil and
natural gas drilling applications, when these particles are used in
subterranean environments where the temperature is far below the
T.sub.g of the particles. As explained below, the enhancement of
curing via post-polymerization heat treatment is generally expected
to have a smaller effect on the compressive elastic modulus (and
hence on the proppant performance) of thermoset polymer particles
when used in oil and natural gas drilling applications at
temperatures far below their T.sub.g.
[0028] Nishimori, et. al. (JP1992-22230) used very large amounts of
DVB (w.sub.DVB>>0.2). By contrast, in general, much smaller
amounts of DVB (w.sub.DVB.ltoreq.0.2) must be used for economic
reasons in the "lower value" oil and natural gas drilling
applications. The elastic moduli of a polymer at temperatures far
below T.sub.g are determined primarily by deformations that are of
a rather local nature and hence on a short length scale. Some
enhancement of the crosslink density via further curing (when the
network junctions created by the crosslinks are far away from each
other to begin with) will hence not normally have nearly as large
an effect on the elastic moduli as when the network junctions are
very close to each other to begin with and then are brought even
closer by the enhancement of curing via heat treatment.
Consequently, while the compressive elastic modulus can be expected
to increase significantly upon heat treatment when w.sub.DVB is
very large, any such effect will normally be less pronounced at low
values of w.sub.DVB. In summary, it can thus generally be expected
that the enhancement of the compressive elastic modulus at
temperatures far below T.sub.g will probably be small for the types
of formulations that are most likely to be used in the synthesis of
thermoset polymer particles for oil and natural gas drilling
applications.
SUMMARY OF THE INVENTION
[0029] The present invention involves a novel approach towards the
practical development of stiff, strong, tough, heat resistant, and
environmentally resistant ultralightweight particles, for use in
the construction, drilling, completion and/or fracture stimulation
of oil and natural gas wells.
[0030] The disclosure is summarized below in three key aspects: (A)
Compositions of Matter (thermoset particles that exhibit improved
properties compared with prior art), (B) Processes (methods for
manufacture of the compositions of matter), and (C) Applications
(utilization of the compositions of matter in the construction,
drilling, completion and/or fracture stimulation of oil and natural
gas wells).
[0031] The disclosure describes lightweight thermoset polymer
particles whose properties are improved relative to prior art. The
particles targeted for development include, but are not limited to,
terpolymers of styrene, ethyvinylbenzene and divinylbenzene. The
particles exhibit any one or any combination of the following
properties: enhanced stiffness, strength, heat resistance, and/or
resistance to aggressive environments; and/or improved retention of
high conductivity of liquids and/or gases through packings of the
particles when the packings are placed in potentially aggressive
environments under high compressive loads at elevated
temperatures.
[0032] The disclosure also describes processes that can be used to
manufacture the particles. The fabrication processes targeted for
development include, but are not limited to, suspension
polymerization to prepare the "as-polymerized" particles, and
post-polymerization process(es) to further advance the curing of
the polymer. The post-polymerization process(es) may optionally
comprise heat treatment. The particles during the heat treatment
are placed in an unreactive gaseous environment with nitrogen as
the preferred unreactive gas.
[0033] The disclosure finally describes the use of the particles in
practical applications. The targeted applications include, but are
not limited to, the construction, drilling, completion and/or
fracture stimulation of oil and natural gas wells; for example, as
a proppant partial monolayer, a proppant pack, an integral
component of a gravel pack completion, a ball bearing, a solid
lubricant, a drilling mud constituent, and/or a cement
additive.
A. Compositions of Matter
[0034] The compositions of matter of the present invention are
thermoset polymer particles. Any additional formulation
component(s) familiar to those skilled in the art can also be used
during the preparation of the particles; such as initiators,
catalysts, inhibitors, dispersants, stabilizers, rheology
modifiers, buffers, antioxidants, defoamers, impact modifiers,
plasticizers, pigments, flame retardants, smoke retardants, or
mixtures thereof. Some of the the additional component(s) may also
become either partially or completely incorporated into the
particles in some embodiments of the invention. However, the only
required component of the particles is a thermoset polymer.
[0035] Any rigid thermoset polymer may be used as the polymer of
the present invention. Rigid thermoset polymers are, in general,
amorphous polymers where covalent crosslinks provide a
three-dimensional network. However, unlike thermoset elastomers
(often referred to as "rubbers") which also possess a
three-dimensional network of covalent crosslinks, the rigid
thermosets are, by definition, "stiff". In other words, they have
high elastic moduli at "room temperature" (25.degree. C.), and
often up to much higher temperatures, because their combinations of
chain segment stiffness and crosslink density result in a high
glass transition temperature.
[0036] Some examples of rigid thermoset polymers that can be used
as materials of the invention will be provided below. It is to be
understood that these examples are being provided without reducing
the generality of the invention, merely to facilitate the teaching
of the invention.
[0037] Commonly used rigid thermoset polymers include, but are not
limited to, crosslinked epoxies, epoxy vinyl esters, polyesters,
phenolics, melamine-based resins, polyurethanes, and polyureas.
Rigid thermoset polymers that are used less often because of their
high cost despite their exceptional performance include, but are
not limited to, crosslinked polyimides. These various types of
polymers can, in different embodiments of the invention, be
prepared by starting either from their monomers, or from oligomers
that are often referred to as "prepolymers", or from suitable
mixtures of monomers and oligomers.
[0038] Many additional types of rigid thermoset polymers can also
be used in particles of the invention, and are all within the scope
of the invention. Such polymers include, but are not limited to,
various families of crosslinked copolymers prepared most often by
the polymerization of vinylic monomers, of vinylidene monomers, or
of mixtures thereof.
[0039] The "vinyl fragment" is commonly defined as the
CH.sub.2.dbd.CH-- fragment. So a "vinylic monomer" is a monomer of
the general structure CH.sub.2.dbd.CHR where R can be any one of a
vast variety of molecular fragments or atoms (other than hydrogen).
When a vinylic monomer CH.sub.2.dbd.CHR reacts, it is incorporated
into the polymer as the --CH.sub.2--CHR-- repeat unit. Among rigid
thermosets built from vinylic monomers, the crosslinked styrenics
and crosslinked acrylics are especially familiar to workers in the
field. Some other familiar types of vinylic monomers (among others)
include the olefins, vinyl alcohols, vinyl esters, and vinyl
halides.
[0040] The "vinylidene fragment" is commonly defined as the
CH.sub.2.dbd.CR''-- fragment. So a "vinylidene monomer" is a
monomer of the general structure CH.sub.2.dbd.CR'R'' where R' and
R'' can each be any one of a vast variety of molecular fragments or
atoms (other than hydrogen). When a vinylidene monomer
CH.sub.2.dbd.CR'R'' reacts, it is incorporated into a polymer as
the --CH.sub.2--CR'R''-repeat unit. Among rigid thermosets built
from vinylidene polymers, the crosslinked alkyl acrylics [such as
crosslinked poly(methyl methacrylate)] are especially familiar to
workers in the field. However, vinylidene monomers similar to each
type of vinyl monomer (such as the styrenics, acrylates, olefins,
vinyl alcohols, vinyl esters and vinyl halides, among others) can
be prepared. One example of particular interest in the context of
styrenic monomers is .quadrature.-methyl styrene, a vinylidene-type
monomer that differs from styrene (a vinyl-type monomer) by having
a methyl (--CH.sub.3) group serving as the R'' fragment replacing
the hydrogen atom attached to the .quadrature.-carbon.
[0041] Thermosets based on vinylic monomers, on vinylidene
monomers, or on mixtures thereof, are typically prepared by the
reaction of a mixture containing one or more non-crosslinking
(difunctional) monomer and one or more crosslinking (three or
higher functional) monomers. All variations in the choices of the
non-crosslinking monomer(s), the crosslinking monomers(s), and
their relative amounts [subject solely to the limitation that the
quantity of the crosslinking monomer(s) must not be less than 1% by
weight], are within the scope of the invention.
[0042] Without reducing the generality of the invention, in its
currently preferred embodiments, the thermoset polymer particles
consist of a terpolymer of styrene (non-crosslinking),
ethyvinylbenzene (also non-crosslinking), and divinylbenzene
(crosslinking), with the weight fraction of divinylbenzene ranging
from 3% to 35% by weight of the starting monomer mixture.
B. Processes
[0043] If a suitable post-polymerization process step is applied to
thermoset polymer particles, in many cases the curing reaction will
be driven further towards completion so that T.sub.g (and hence
also the maximum possible use temperature) will increase. This is
the most commonly obtained benefit of applying a
post-polymerization process step. In some instances, there may also
be further benefits, such as an increase in the compressive elastic
modulus even at temperatures that are far below T.sub.g, and an
increase of such magnitude in the resistance to aggressive
environments as to enhance significantly the potential range of
applications of the particles.
[0044] Processes that may be used to enhance the degree of curing
of a thermoset polymer include, but are not limited to, heat
treatment (which may be combined with stirring, flow and/or
sonication to enhance its effectiveness), electron beam
irradiation, and ultraviolet irradiation. FIG. 2 provides an
idealized schematic illustration of the benefits of implementing
such methods. We focused mainly on the use of heat treatment in
order to increase the T.sub.g of the thermoset polymer.
[0045] The processes that may be used for the fabrication of the
thermoset polymer particles of the invention comprise two major
steps. The first step is the formation of the particles by means of
a polymerization process. The second step is the use of an
appropriate postcuring method to advance the curing reaction and to
thus obtain a thermoset polymer network that approaches the "fully
cured" limit. Consequently, this subsection will be further
subdivided into two subsections, dealing with polymerization and
with postcure respectively.
[0046] 1. Polymerization and Network Formation
[0047] Any method for the fabrication of thermoset polymer
particles known to those skilled in the art may be used to prepare
embodiments of the particles of the invention. Without reducing the
generality of the invention, our preferred method will be discussed
below to facilitate the teaching of the invention.
[0048] It is especially practical to prepare the particles by using
methods that can produce the particles directly in the desired
(usually substantially spherical) shape during polymerization from
the starting monomers. (While it is a goal of this invention to
create spherical particles, it is understood that it is exceedingly
difficult as well as unnecessary to obtain perfectly spherical
particles. Therefore, particles with minor deviations from a
perfectly spherical shape are considered perfectly spherical for
the purposes of this disclosure.) Suspension (droplet)
polymerization is the most powerful method available for
accomplishing this objective.
[0049] Two main approaches exist to suspension polymerization. The
first approach is isothermal polymerization which is the
conventional approach that has been practiced for many decades. The
second approach is "rapid rate polymerization" as taught by
Albright (U.S. Pat. No. 6,248,838) which is incorporated herein by
reference in its entirety. Without reducing the generality of the
invention, suspension polymerization as performed via the rapid
rate polymerization approach taught by Albright (U.S. Pat. No.
6,248,838) is used in the current preferred embodiments of the
invention.
[0050] 2. Post-Polymerization Advancement of Curing and Network
Formation
[0051] As was discussed earlier and illustrated in FIG. 1 with the
data of Bicerano, et al. (1996), typical processes for the
synthesis of thermoset polymers may result in the formation of
incompletely cured networks, and may hence produce thermosets with
lower glass transition temperatures and lower maximum use
temperatures than is achievable with the chosen formulation of
reactants. Consequently, the use of a post-polymerization process
step (or a sequence of such process steps) to advance the curing of
a thermoset polymer particle of the invention is an aspect of the
invention. Suitable methods include, but are not limited to, heat
treatment (also known as "annealing"), electron beam irradiation,
and ultraviolet irradiation.
[0052] Post-polymerization heat treatment is a very powerful method
for improving the properties and performance of S-DVB copolymers
(as well as of many other types of thermoset polymers) by helping
the polymer network approach its "full cure" limit. It is, in fact,
the most easily implementable method for advancing the state of
cure of S-DVB copolymer particles. However, it is important to
recognize that another post-polymerization method (such as electron
beam irradiation or ultraviolet irradiation) may be the most
readily implementable one for advancing the state of cure of some
other type of thermoset polymer. The use of any suitable method for
advancing the curing of the thermoset polymer that is being used as
a particle of the present invention after polymerization is within
the scope of the invention.
[0053] Without reducing the generality of the invention, among the
suitable methods, heat treatment is used as the post-polymerization
method to enhance the curing of the thermoset polymer in the
preferred embodiments of the invention. Any desired thermal history
can be imposed; such as, but not limited to, isothermal annealing
at a fixed temperature; nonisothermal heat exposure with either a
continuous or a step function temperature ramp; or any combination
of continuous temperature ramps, step function temperature ramps,
and/or periods of isothermal annealing at fixed temperatures. In
practice, while there is great flexibility in the choice of a
thermal history, it must be selected carefully to drive the curing
reaction to the maximum final extent possible without inducing
unacceptable levels of thermal degradation.
[0054] Any significant increase in T.sub.g by means of improved
curing will translate directly into an increase of comparable
magnitude in the practical softening temperature of the polymer
particles under the compressive load imposed by the subterranean
environment. Consequently, a significant increase of the maximum
possible use temperature of the thermoset polymer particles is the
most common benefit of advancing the extent of curing by heat
treatment.
[0055] A practical concern during the imposition of heat treatment
is related to the amount of material that is being subjected to
heat treatment simultaneously. For example, very small amounts of
material can be heat treated uniformly and effectively in vacuum;
or in any inert (non-oxidizing) gaseous medium, such as, but not
limited to, a helium or nitrogen "blanket". However, heat transfer
in a gaseous medium is generally not nearly as effective as heat
transfer in an appropriately selected liquid medium. Consequently,
during the heat treatment of large quantities of the particles of
the invention (such as, but not limited to, the output of a run of
a commercial-scale batch production reactor), it is usually
necessary to use a liquid medium, and furthermore also to stir the
particles vigorously to ensure that the heat treatment is applied
as uniformly as possible. Serious quality problems may arise if
heat treatment is not applied uniformly; for example, as a result
of the particles that were initially near the heat source being
overexposed to heat and thus damaged, while the particles that were
initially far away from the heat source are not exposed to
sufficient heat and are thus not sufficiently postcured.
[0056] If a gaseous or a liquid heat treatment medium is used, the
medium may contain, without limitation, one or a mixture of any
number of types of constituents of different molecular structure.
However, in practice, the medium must be selected carefully to
ensure that its molecules will not react with the crosslinked
polymer particles to a sufficient extent to cause significant
oxidative and/or other types of chemical degradation. In this
context, it must also be kept in mind that many types of molecules
which do not react with a polymer at ambient temperature may react
strongly with the polymer at elevated temperatures. The most
relevant example in the present context is that oxygen itself does
not react with S-DVB copolymers at room temperature, while it
causes severe oxidative degradation of S-DVB copolymers at elevated
temperatures where there would not be much thermal degradation in
its absence.
[0057] Furthermore, in considering the choice of medium for heat
treatment, it is also important to keep in mind that the molecules
constituting a molecular fluid can swell organic polymers,
potentially causing "plasticization" and thus resulting in
undesirable reductions of T.sub.g and of the maximum possible use
temperature. The magnitude of any such detrimental effect increases
with increasing similarity between the chemical structures of the
molecules in the heat treatment medium and of the polymer chains.
For example, a heat transfer fluid consisting of aromatic molecules
will tend to swell a styrene-divinylbenzene copolymer particle. The
magnitude of this detrimental effect will increase with decreasing
relative amount of the crosslinking monomer (divinylbenzene) used
in the formulation. For example, a styrene-divinylbenzene copolymer
prepared from a formulation containing only 3% by weight of
divinylbenzene will be far more susceptible to swelling in an
aromatic liquid than a copolymer prepared from a formulation
containing 35% divinylbenzene.
[0058] Geothermal gradients determine the temperature of the
downhole environment. The temperature can be sufficiently high in
some downhole environments to become effective in the postcuring of
some compositions of matter covered by the invention. Consequently,
the "in situ" postcuring of the polymer particles, wherein the
particles are placed in the downhole environment of a hydrocarbon
reservoir without heat treatment and the heat treatment then takes
place in the environment as a result of the elevated temperature of
the environment, is also within the scope of the invention.
[0059] It is important to note that the polymer particles are kept
in the downhole environment of a hydrocarbon reservoir for a very
long time in many applications. Consequently, temperatures which
may be too low to provide a reasonable cycle time in postcuring as
a manufacturing step may often be adequate for the "in situ"
postcuring of the particles in the downhole environment during use.
On the other hand, the implementation of postcuring as a
manufacturing step often has the advantage of providing for better
quality control and greater uniformity of particle properties.
While each of these two approaches may hence be more suitable than
the other one for use in different situations, they both fall
within the scope of the invention. Furthermore, their combination
by (a) applying a postcuring step during manufacture to advance
polymerization and network formation, followed by (b) the "in situ"
completion of the postcuring in the downhole environment, is also
within the scope of the invention.
[0060] Various means known to those skilled in the art, including
but not limited to the stirring, flow and/or sonication of an
assembly of particles being subjected to heat treatment, may also
be optionally used to enhance further the effectiveness of the heat
treatment. The rate of thermal equilibration under a given thermal
gradient, possibly combined with the application of any such
additional means, depends on many factors. These factors include,
but are not limited to, the amount of polymer particles being heat
treated simultaneously, the shapes and certain key physical and
transport properties of these particles, the shape of the vessel
being used for heat treatment, the medium being used for heat
treatment, whether external disturbances (such as stirring, flow
and/or sonication) are being used to accelerate equilibration, and
the details of the heat exposure schedule. Simulations based on the
solution of the heat transfer equations may hence be used
optionally to optimize the heat treatment equipment and/or the heat
exposure schedule.
[0061] Without reducing the generality of the invention, in its
currently preferred embodiments, the thermoset polymer particles
are placed in an unreactive gaseous environment with nitrogen as
the preferred unreactive gas during heat treatment. Appropriately
chosen equipment is used, along with simulations based on the
solution of the heat transfer equations, to optimize the heat
exposure schedule so that large batches of particles can undergo
thermal exposure to an extent that is sufficient to accomplish the
desired effects of the heat treatment without many particles
undergoing detrimental overexposure. This embodiment of the heat
treatment process works especially well (without adverse effects
such as degradation that could occur if an oxidative gaseous
environment such as air were used and/or swelling that could occur
if a liquid environment were used) in enhancing the curing of the
thermoset polymer. It is, however, important to reemphasize the
much broader scope of the invention and the fact that the
particular currently preferred embodiments summarized above
constitute just a few among the vast variety of possible
qualitatively different classes of embodiments.
C. Applications
[0062] The obvious practical advantages [see a review by Edgeman
(2004)] of developing the ability to use lightweight particles that
possess almost neutral buoyancy relative to water have stimulated a
considerable amount of work over the years. However, progress in
this field of invention has been very slow as a result of the many
technical challenges that exist to the successful development of
cost-effective lightweight particles that possess sufficient
stiffness, strength and heat resistance. The present invention has
resulted in the development of such stiff, strong, tough, heat
resistant, and environmentally resistant ultralightweight
particles; and also of cost-effective processes for the fabrication
of the particles. As a result, a broad range of potential
applications can be envisioned and are being pursued for the use of
the thermoset polymer particles of the invention in the
construction, drilling, completion and/or fracture stimulation of
oil and natural gas wells. Without reducing the generality of the
invention, in its currently preferred embodiments, the specific
applications that are already being evaluated are as a proppant
partial monolayer, a proppant pack, an integral component of a
gravel pack completion, a ball bearing, a solid lubricant, a
drilling mud constituent, and/or a cement additive.
[0063] The use of assemblies of the particles as proppant partial
monolayers and/or as proppant packs generally requires the
particles to possess significant stiffness and strength under
compressive deformation, heat resistance, and resistance to
aggressive environments. Enhancements in these properties result in
the ability to use the particles as proppants in hydrocarbon
reservoirs that exert higher compressive loads and/or possess
higher temperatures.
[0064] The most commonly used measure of proppant performance is
the conductivity of liquids and/or gases (depending on the type of
hydrocarbon reservoir) through packings of the particles. A minimum
liquid conductivity of 100 mDft is often considered as a practical
threshold for considering a packing to be useful in propping a
fracture that possesses a given closure stress at a given
temperature. It is also a common practice in the industry to use
the simulated environment of a hydrocarbon reservoir in evaluating
the conductivities of packings of particles. The API RP 61 method
is currently the commonly accepted testing standard for
conductivity testing in the simulated environment of a hydrocarbon
reservoir. As of the date of this filing, however, work is underway
to develop alternative testing standards.
[0065] It is also important to note that the current selection of
preferred embodiments of the invention has resulted from our focus
on application opportunities in the construction, drilling,
completion and/or fracture stimulation of oil and natural gas
wells. Many other applications can also be envisioned for the
compositions of matter that fall within the scope of thermoset
polymer particles of the invention, extending far beyond their uses
by the oil and natural gas industry.
BRIEF DESCRIPTION OF THE DRAWINGS
[0066] The accompanying drawings, which are included to provide
further understanding of the invention and are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention and, together with the description, serve to explain
the principles of the invention.
[0067] FIG. 1 shows the effects of advancing the curing reaction in
a series of isothermally polymerized styrene-divinylbenzene (S-DVB)
copolymers containing different DVB weight fractions via heat
treatment. The results of scans of S-DVB beads containing various
weight fractions of DVB (w.sub.DVB), obtained by Differential
Scanning Calorimetry (DSC), and reported by Bicerano, et al.
(1996), are compared. It is seen that the T.sub.g of typical
"as-polymerized" S-DVB copolymers, as measured by the first DSC
scan, increased only slowly with increasing w.sub.DVB, and
furthermore that the rate of further increase of T.sub.g slowed
down drastically for w.sub.DVB>0.08. By contrast, in the second
DSC scan (performed on S-DVB specimens whose curing had been driven
much closer to completion as a result of the temperature ramp that
had been applied during the first scan), T.sub.g grew much more
rapidly with w.sub.DVB over the entire range of up to
w.sub.DVB=0.2458 that was studied.
[0068] FIG. 2 provides an idealized schematic illustration, in the
context of the resistance of thermoset polymer particles to
compression as a function of the temperature, of the most common
benefits of using the methods of the present invention. In most
cases, the densification of the crosslinked polymer network via
post-polymerization heat treatment will have the main benefit of
increasing the softening (and hence also the maximum possible use)
temperature, along with improving the environmental resistance. In
some instances, enhanced stiffness and strength at temperatures
that are significantly below the softening temperature may be
additional benefits.
[0069] FIG. 3 provides a process flow diagram depicting the
preparation of the example. It contains four major blocks;
depicting the preparation of the aqueous phase (Block A), the
preparation of the organic phase (Block B), the mixing of these two
phases followed by suspension polymerization (Block C), and the
further process steps used after polymerization to obtain the
"as-polymerized" and "heat-treated" samples of particles (Block
D).
[0070] FIG. 4 shows the variation of the temperature with time
during polymerization.
[0071] FIG. 5 shows the results of differential scanning
calorimetry (DSC) scans. Sample AP manifests a large exothermic
curing peak region instead of a glass transition region when it is
heated. Sample AP is, hence, partially (and in fact only quite
poorly) cured. On the other hand, while the DSC curve of Sample
IA20mG170C is too featureless for the software to extract a precise
glass transition temperature from it, there is no sign of an
exothermic peak. Sample IA20mG170C is, hence, very well-cured. The
DSC curves of Sample AP/406h6000psi and Sample
IA20mG170C/406h6000psi, which were obtained by exposing Sample AP
and Sample IA20mG170C, respectively, to 406 hours of heat at a
temperature of 250.degree. F. under a compressive stress of 6000
psi during the liquid conductivity experiments, are also shown.
Note that the exothermic peak is missing in the DSC curve of Sample
AP/406h6000psi, demonstrating that "in situ" postcuring via heat
treatment under conditions simulating a downhole environment has
been achieved.
[0072] FIG. 6 provides a schematic illustration of the
configuration of the conductivity cell.
[0073] FIG. 7 compares the measured liquid conductivities of
packings of particles of 14/16 U.S. mesh size (diameters ranging
from 1.19 mm to 1.41 mm) from Sample IA20mG 170C and Sample AP, at
a coverage of 0.02 lb/ft.sup.2, under a closure stress of 5000 psi
at a temperature of 220.degree. F., and under a closure stress of
6000 psi at a temperature of 250.degree. F., as functions of the
time.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0074] Because the invention will be understood better after
further discussion of its currently preferred embodiments, further
discussion of the embodiments will now be provided. It is
understood that the discussion is being provided without reducing
the generality of the invention, since persons skilled in the art
can readily imagine many additional embodiments that fall within
the full scope of the invention as taught in the SUMMARY OF THE
INVENTION section.
A. Nature, Attributes and Applications of Currently Preferred
Embodiments
[0075] The currently preferred embodiments of the invention are
lightweight thermoset polymer particles possessing high stiffness,
strength, temperature resistance, and resistance to aggressive
environments. These attributes, occurring in combination, make the
particles especially suitable for use in many challenging
applications in the construction, drilling, completion and/or
fracture stimulation of oil and natural gas wells. The applications
include the use of the particles as a proppant partial monolayer, a
proppant pack, an integral component of a gravel pack completion, a
ball bearing, a solid lubricant, a drilling mud constituent, and/or
a cement additive.
[0076] In one embodiment, the polymeric particle has a
substantially cured polymer network; wherein a packing of the
particles manifests a static conductivity of at least 100 mDft
after 200 hours at temperatures greater than 80.degree. F. The
particles are made by a method including the steps of: forming a
polymer by polymerizing a reactive mixture containing at least one
of a monomer, an oligomer, or combinations thereof. The at least
one of a monomer, an oligomer, or combinations thereof have three
or more reactive functionalities capable of creating crosslinks
between polymer chains. The particle is subjected to at least one
post-polymerizing process that advances the curing of a polymer
network.
B. Compositions of Matter
[0077] The preferred embodiments of the particles of the invention
consist of terpolymers of styrene (S, non-crosslinking),
ethyvinylbenzene (EVB, also non-crosslinking), and divinylbenzene
(DVB, crosslinking).
[0078] The preference for such terpolymers instead of copolymers of
S and DVB is a result of economic considerations. To summarize, DVB
comes mixed with EVB in the standard product grades of DVB, and the
cost of DVB increases rapidly with increasing purity in special
grades of DVB. EVB is a non-crosslinking (difunctional) styrenic
monomer. Its incorporation into the thermoset polymer does not
result in any significant changes in the properties of the polymer,
compared with the use of S as the sole non-crosslinking monomer.
Consequently, it is far more cost-effective to use a standard
(rather than purified) grade of DVB, thus resulting in a terpolymer
where some of the repeat units originate from EVB.
[0079] The amount of DVB in the terpolymer ranges from 3% to 35% by
weight of the starting mixture of the three reactive monomers (S,
EVB and DVB) because different applications require different
maximum possible use temperatures. Even when purchased in standard
product grades where it is mixed with a large weight fraction of
EVB, DVB is more expensive than S. It is, hence, useful to develop
different product grades where the maximum possible use temperature
increases with increasing weight fraction of DVB. Customers can
then purchase the grades of the particles that meet their specific
application needs as cost-effectively as possible.
C. Polymerization
[0080] Suspension polymerization is performed via rapid rate
polymerization, as taught by Albright (U.S. Pat. No. 6,248,838)
which is incorporated herein by reference in its entirety, for the
fabrication of the particles. Rapid rate polymerization has the
advantage, relative to conventional isothermal polymerization, of
producing more physical entanglements in thermoset polymers (in
addition to the covalent crosslinks).
[0081] The most important additional formulation component (besides
the reactive monomers) that is used during polymerization is the
initiator. The initiator may consist of one type molecule or a
mixture of two or more types of molecules that have the ability to
function as initiators. Additional formulation components, such as
catalysts, inhibitors, dispersants, stabilizers, rheology
modifiers, buffers, antioxidants, defoamers, impact modifiers,
plasticizers, pigments, flame retardants, smoke retardants, or
mixtures thereof, may also be used when needed. Some of the
additional formulation component(s) may become either partially or
completely incorporated into the particles in some embodiments of
the invention.
D. Attainable Particle Sizes
[0082] Suspension polymerization produces substantially spherical
polymer particles. (While it is a goal of this invention to create
spherical particles, it is understood that it is exceedingly
difficult as well as unnecessary to obtain perfectly spherical
particles. Therefore, particles with minor deviations from a
perfectly spherical shape are considered perfectly spherical for
the purposes of this disclosure.) The particles can be varied in
size by means of a number of mechanical and/or chemical methods
that are well-known and well-practiced in the art of suspension
polymerization. Particle diameters attainable by such means range
from submicron values up to several millimeters. Hence the
particles may be selectively manufactured over the entire range of
sizes that are of present interest and/or that may be of future
interest for applications in the oil and natural gas industry.
E. Optional Further Selection of Particles by Size
[0083] Optionally, after the completion of suspension
polymerization, the particles can be separated into fractions
having narrower diameter ranges by means of methods (such as, but
not limited to, sieving techniques) that are well-known and
well-practiced in the art of particle separations. The narrower
diameter ranges include, but are not limited to, nearly
monodisperse distributions. Optionally, assemblies of particles
possessing bimodal or other types of special distributions, as well
as assemblies of particles whose diameter distributions follow
statistical distributions such as gaussian or log-normal, can also
be prepared.
[0084] The optional preparation of assemblies of particles having
diameter distributions of interest from any given "as polymerized"
assembly of particles can be performed before or after the heat
treatment of the particles. Without reducing the generality of the
invention, in the currently most preferred embodiments of the
invention, any optional preparation of assemblies of particles
having diameter distributions of interest from the product of a run
of the pilot plant or production plant reactor is performed after
the completion of the heat treatment of the particles.
[0085] The particle diameters of current practical interest for
various uses in the construction, drilling, completion and/or
fracture stimulation of oil and natural gas wells range from 0.1 to
4 millimeters. The specific diameter distribution that would be
most effective under given circumstances depends on the details of
the subterranean environment in addition to depending on the type
of application. The diameter distribution that would be most
effective under given circumstances may be narrow or broad,
monomodal or bimodal, and may also have other special features
(such as following a certain statistical distribution function)
depending on both the details of the subterranean environment and
the type of application.
F. Heat Treatment
[0086] The particles are placed in an unreactive gaseous
environment with nitrogen as the preferred unreactive gas during
heat treatment in the currently preferred embodiment of the
invention. The inreactive gas thus serves as the heat treatment
medium. This approach works especially well (without adverse
effects such as degradation that could occur if an oxidative
gaseous environment such as air were used and/or swelling that
could occur if a liquid environment were used) in enhancing the
curing of the particles.
[0087] Gases are much less effective than liquids as heat transfer
media. The use of a gaseous rather than a liquid environment hence
presents engineering challenges to the heat treatment of very large
batches of particles. However, these challenges to practical
implementation are overcome by means of the proper choice of
equipment and by the use of simulation methods.
[0088] Detailed and realistic simulations based on the solution of
the heat transfer equations are hence often used optionally to
optimize the heat exposure schedule. It has been found that such
simulations become increasingly useful with increasing quantity of
particles that will be heat treated simultaneously. The reason is
the finite rate of heat transfer. The finite rate results in slower
and more difficult equilibration with increasing quantity of
particles and hence makes it especially important to be able to
predict how to cure most of the particles further uniformly and
sufficiently without overexposing many of the particles to
heat.
[0089] In performing heat treatment as a manufacturing step as
described above, which is the preferred embodiment of the
invention, the useful temperature range is from 120.degree. C. to
250.degree. C., inclusive. The duration of the exposure will, in
practice, decrease with the maximum temperature of exposure. More
specifically, if the heat treatment temperature is 120.degree. C.,
at least four hours of exposure to that temperature will be
required. On the other hand, if the heat treatment temperature is
250.degree. C., the duration of exposure to that temperature will
not exceed 20 minutes. In the most preferred embodiments of the
invention, the particles undergo a total exposure to temperatures
in the range of 150.degree. C. to 200.degree. C. for a duration of
10 minutes to 90 minutes, inclusive.
[0090] In other embodiments of the invention, where heat treatment
is performed "in situ" in the downhole environment, the minimum
downhole temperature is 80.degree. C. and the minimum dwell time in
the downhole environment is one week. In practice, the minimum
required amount of time for adequate postcuring in the downhole
environment will decrease with increasing temperature of the
environment. In more preferred embodiments of this class, the
temperature of the downhole environment is at least 100.degree. C.
In the most preferred embodiments of this type, the temperature of
the downhole environment is at least 120.degree. C.
EXAMPLE
[0091] The currently preferred embodiments of the invention will be
understood better in the context of a specific example. It is to be
understood that the example is being provided without reducing the
generality of the invention. Persons skilled in the art can readily
imagine many additional examples that fall within the scope of the
currently preferred embodiments as taught in the DETAILED
DESCRIPTION OF THE INVENTION section. Persons skilled in the art
can, furthermore, also readily imagine many alternative embodiments
that fall within the full scope of the invention as taught in the
SUMMARY OF THE INVENTION section.
A. Summary
[0092] The thermoset matrix was prepared from a formulation
containing 20% DVB by weight of the starting monomer mixture. The
DVB had been purchased as a mixture where only 63% by weight
consisted of DVB. The actual polymerizable monomer mixture used in
preparing the thermoset matrix consisted of roughly 68.73% S,
11.27% EVB and 20% DVB by weight.
[0093] Suspension polymerization was performed in a pilot plant
reactor, via rapid rate polymerization as taught by Albright (U.S.
Pat. No. 6,248,838) which is incorporated herein by reference in
its entirety. The "single initiator" approach was utilized in
applying this method. The "as-polymerized" particles obtained from
this run of the pilot plant reactor (by removing some of the slurry
and allowing it to dry at ambient temperature) are designated as
Sample AP.
[0094] Some other particles were then removed from the of the
slurry, washed, spread very thin on a tray, and heat-treated for
ten minutes at 170.degree. C. in an oven under an unreactive gas
(nitrogen) blanket. These heat-treated particles will be designated
as Sample IA20mG170C.
[0095] FIG. 3 provides a process flow diagram depicting the
preparation of the example. It contains four major blocks;
depicting the preparation of the aqueous phase (Block A), the
preparation of the organic phase (Block B), the mixing of these two
phases followed by suspension polymerization (Block C), and the
further process steps used after polymerization to obtain the
"as-polymerized" and "heat-treated" samples of particles (Block
D).
[0096] Particles from each of the two samples were then sent to
independent testing laboratories. Differential scanning calorimetry
(DSC) was performed on each sample by Impact Analytical, in
Midland, Michigan. The liquid conductivities of packings of the
particles of each sample were measured by FracTech Laboratories, in
Surrey, United Kingdom.
[0097] The following subsections will provide further details on
the formulation, preparation and testing of this working example,
to enable persons who are skilled in the art to reproduce the
example.
B. Formulation
[0098] An aqueous phase and an organic phase must be prepared prior
to suspension polymerization. The aqueous phase and the organic
phase, which were prepared in separate beakers and then used in the
suspension polymerization of the particles of this example, are
described below.
[0099] 1. Aqueous Phase
[0100] The aqueous phase used in the suspension polymerization of
the particles of this example, as well as the procedure used to
prepare the aqueous phase, are summarized in TABLE 1.
TABLE-US-00001 TABLE 1 The aqueous phase was prepared by adding
Natrosol Plus 330 and gelatin (Bloom strength 250) to water,
heating to 65.degree. C. to disperse the Natrosol Plus 330 and the
gelatin in the water, and then adding sodium nitrite and sodium
carbonate. Its composition is listed below. INGREDIENT WEIGHT (g) %
Water 1493.04 98.55 Natrosol Plus 330 (hydroxyethylcellulose) 7.03
0.46 Gelatin (Bloom strength 250) 3.51 0.23 Sodium Nitrite
(NaNO.sub.2) 4.39 0.29 Sodium Carbonate (Na.sub.2CO.sub.3) 7.03
0.46 Total Weight in Grams 1515.00 100.00
[0101] 2. Organic Phase
[0102] The organic phase used in the suspension polymerization of
the particles of this example, as well as the procedure used to
prepare the organic phase, are summarized in TABLE 2.
TABLE-US-00002 TABLE 2 The organic phase was prepared by placing
the monomers and benzoyl peroxide (an initiator) together and
agitating the resulting mixture for 15 minutes. Its composition is
listed below. After taking the other components of the 63% DVB
mixture into account, the polymerizable monomer mixture actually
consisted of roughly 68.73% S, 11.27% EVB and 20% DVB by weight.
The total polymerizable monomer weight of was 1355.9 grams.
INGREDIENT WEIGHT (g) % Styrene (pure) 931.90 67.51 Divinylbenzene
(63% DVB, 430.44 31.18 98.5% polymerizable monomers) Benzoyl
peroxide (75% active) 18.089 1.31 Total Weight in Grams 1380.429
100.00
C. Preparation of Particles from Formulation
[0103] Once the formulation is prepared, its aqueous and organic
phases are mixed, polymerization is performed, and "as-polymerized"
and "heat-treated" particles are obtained, as described below.
[0104] 1. Mixing
[0105] The aqueous phase was added to the reactor at 65.degree. C.
The organic phase was introduced 15 minutes later with agitation at
the rate of 90 rpm. The mixture was held at 65.degree. C. with
stirring at the rate of 90 rpm for 11 minutes, by which time proper
dispersion had taken place as manifested by the equilibration of
the droplet size distribution.
[0106] 2. Polymerization
[0107] The temperature was ramped from 65.degree. C. to 78.degree.
C. in 10 minutes. It was then further ramped from 78.degree. C. to
90.degree. C. very slowly over 80 minutes. It was then held at
90.degree. C. for one hour to provide most of the conversion of
monomer to polymer, with benzoyl peroxide (half life of one hour at
92.degree. C.) as the initiator. The actual temperature was
monitored throughout the process. The highest actual temperature
measured during the process (with the set point at 90.degree. C.)
was 93.degree. C. The thermoset polymer particles were thus
obtained in an aqueous slurry which was then cooled to 40.degree.
C. FIG. 4 shows the variation of the temperature with time during
polymerization.
[0108] 3. "As-Polymerized" Particles
[0109] The "as-polymerized" sample obtained from the run of the
pilot plant reactor described above will be designated as Sample
AP. In order to complete the preparation of Sample AP, some of the
aqueous slurry was poured onto a 60 mesh (250 micron) sieve to
remove the aqueous reactor fluid as well as any undesirable small
particles that may have formed during polymerization. The
"as-polymerized" beads of larger than 250 micron diameter obtained
in this manner were then washed three times with warm (40.degree.
C. to 50.degree. C.) water and allowed to dry at ambient
temperature. A small quantity from this sample was sent to Impact
Analytical for DSC experiments.
[0110] Particles of 14/16 U.S. mesh size were isolated from Sample
AP by some additional sieving. This is a very narrow size
distribution, with the particle diameters ranging from 1.19 mm to
1.41 mm. This nearly monodisperse assembly of particles was sent to
FracTech Laboratories for the measurement of the liquid
conductivity of its packings.
[0111] After the completion of the liquid conductivity testing, the
particles used in the packing that was exposed to the most extreme
conditions of temperature and compressive stress were recovered and
sent to Impact Analytical for DSC experiments probing the effects
of the conditions used during the conductivity experiments on the
thermal properties of the particles.
[0112] 4. "Heat-Treated" Particles Postcured in Nitrogen
[0113] The as-polymerized particles were removed from some of the
slurry. These particles were then poured onto a 60 mesh (250
micron) sieve to remove the aqueous reactor fluid as well as any
undesirable small particles that may have formed during
polymerization. The "as-polymerized" beads of larger than 250
micron diameter obtained in this manner were then washed three
times with warm (40.degree. C. to 50.degree. C.) water, spread very
thin on a tray, and heat-treated isothermally for twenty minutes at
170.degree. C. in an oven in an inert gas environment (nitrogen).
The heat-treated particles that were obtained by using this
procedure will be designated as Sample IA20mG 170C. A small
quantity from this sample was sent to Impact Analytical for DSC
experiments.
[0114] Particles of 14/16 U.S. mesh size were isolated from Sample
IA20mG170C by some additional sieving. This is a very narrow size
distribution, with the particle diameters ranging from 1.19 mm to
1.41 mm. This nearly monodisperse assembly of particles was sent to
FracTech Laboratories for the measurement of the liquid
conductivity of its packings.
[0115] After the completion of the liquid conductivity testing, the
particles used in the packing that was exposed to the most extreme
conditions of temperature and compressive stress were recovered and
sent to Impact Analytical for DSC experiments probing the effects
of the conditions used during the conductivity experiments on the
thermal properties of the particles.
D. Differential Scanning Calorimetry
[0116] DSC experiments (ASTM E1356-03) were carried out by using a
TA Instruments Q100 DSC with nitrogen flow of 50 mL/min through the
sample compartment. Roughly eight to ten milligrams of each sample
were weighed into an aluminum sample pan, the lid was crimped onto
the pan, and the sample was then placed in the DSC instrument. The
sample was then scanned from 5.degree. C. to 225.degree. C. at a
rate of 10.degree. C. per minute. The instrument calibration was
checked with NIST SRM 2232 indium. Data analysis was performed by
using the TA Universal Analysis V4.1 software.
[0117] The DSC data are shown in FIG. 5. Sample AP manifests a
large exothermic curing peak region 510 instead of a glass
transition region when it is heated. Sample AP is, hence, partially
(and in fact only quite poorly) cured. On the other hand, while the
DSC curve of Sample IA20mG 170C 520 is too featureless for the
software to extract a precise glass transition temperature from it,
there is no sign of an exothermic peak. Sample IA20mG 170C is,
hence, very well-cured. The DSC curves of Sample AP/406h6000psi 530
and Sample IA20mG170C/406h6000psi 540, which were obtained by
exposing Sample AP and Sample IA20mG170C, respectively, to 406
hours of heat at a temperature of 250.degree. F. under a
compressive stress of 6000 psi during the liquid conductivity
experiments described below, are also shown. Note that the
exothermic peak is missing in the DSC curve of Sample
AP/406h6000psi, demonstrating that "in situ" postcuring via heat
treatment under conditions simulating a downhole environment has
been achieved. For the purposes of this application the term
"substantially cured" means the absence of an exothermic curing
peak in the DSC plot.
E. Liquid Conductivity Measurement
[0118] A fracture conductivity cell allows a particle packing to be
subjected to desired combinations of compressive stress (simulating
the closure stress on a fracture in a downhole environment) and
elevated temperature over extended durations, while the flow of a
fluid through the packing is measured. The flow capacity can be
determined from differential pressure measurements. The
experimental setup is illustrated in FIG. 6.
[0119] Ohio sandstone, which has roughly a compressive elastic
modulus of 4 Mpsi and a permeability of 0.1 mD, was used as a
representative type of outcrop rock. Wafers of thickness 9.5 mm
were machined to 0.05 mm precision and one rock was placed in the
cell. The sample was split to ensure that a representative sample
is achieved in terms of its particle size distribution and then
weighed. The particles were placed in the cell and leveled. The top
rock was then inserted. Heated steel platens were used to provide
the correct temperature simulation for the test. A thermocouple
inserted in the middle port of the cell wall recorded the
temperature of the pack. The packings were brought up to the
targeted temperature gradually and equilibrated at that
temperature. Consequently, many hours of exposure to elevated
temperatures had already taken place by the inception of the
collection of conductivity data points, with the time at which the
fully equilibrated cells were obtained being taken as the time=zero
reference. A servo-controlled loading ram provided the closure
stress. The conductivity of deoxygenated silica-saturated 2%
potassium chloride (KCl) brine of pH 7 through the pack was
measured.
[0120] The conductivity measurements were performed by using the
following procedure:
1. A 70 mbar full range differential pressure transducer was
activated by closing the bypass valve and opening the low pressure
line valve.
2. When the differential pressure appeared to be stable, a tared
volumetric cylinder was placed at the outlet and a stopwatch was
started.
3. The output of the differential pressure transducer was fed to a
data logger 5-digit resolution multimeter which logs the output
every second during the measurement.
[0121] 4. Fluid was collected for 5 to 10 minutes, after which time
the flow rate was determined by weighing the collected effluent.
The mean value of the differential pressure was retrieved from the
multimeter together with the peak high and low values. If the
difference between the high and low values was greater than the 5%
of the mean, the data point was disregarded.
[0122] 5. The temperature was recorded from the inline thermocouple
at the start and at the end of the flow test period. If the
temperature variation was greater than 0.5.degree. C., the test was
disregarded. The viscosity of the fluid was obtained from the
measured temperature by using viscosity tables. No pressure
correction is made for brine at 100 psi. The density of brine at
elevated temperature was obtained from these tables.
[0123] 6. At least three permeability determinations were made at
each stage. The standard deviation of the determined permeabilities
was required to be less than 1% of the mean value for the test
sequence to be considered acceptable.
[0124] 7. The end of the permeability testing, the widths of each
of the four corners of the cell were determined to 0.01 mm
resolution by using vernier calipers.
[0125] The test results are summarized in TABLE 3. TABLE-US-00003
TABLE 3 Measurements on packings of 14/16 U.S. mesh size of Sample
AP and Sample IA20mG170C at a coverage of 0.02 lb/ft.sup.2. The
conductivity of deoxygenated silica-saturated 2% potassium chloride
(KCl) brine of pH 7 through each sample was measured at a
temperature (T) of 190.degree. F. (87.8.degree. C.) under a
compressive stress (.quadrature..sub.c) of 4000 psi (27.579 MPa),
at a temperature of 220.degree. F. (104.4.degree. C.) under a
compressive stress of 5000 psi (34.474 MPa), and at a temperature
of 250.degree. F. (121.1.degree. C.) under a compressive stress of
6000 psi (41.369 MPa). The time (t) is in hours. The liquid
conductivity (J) is in mDft. T = 220.degree. F., .quadrature..sub.c
= 5000 psi J of T = 250.degree. F., .quadrature..sub.c = 6000 psi t
J of AP IA20mG170C t J of AP J of IA20mG170C 29 558 669 22 232 225
61 523 640 46 212 199 113 489 584 70 198 187 162 468 562 118 154
176 213 455 540 182 142 159 259 444 527 230 137 147 325 418 501 264
135 145 407 390 477 326 128 145 357 122 139 379 120 139 406 118
137
[0126] These results are shown in FIG. 7.
[0127] The liquid conductivity of the partial monolayer of the
heat-treated particles under a closure stress of 5000 psi at a
temperature of 220.degree. F. is seen to be distinctly higher than
that of the partial monolayer of the "as polymerized" particles
that were postcured via "in situ" heat treatment in the
conductivity cell at a temperature of only 220.degree. F.
[0128] It is also seen that partial monolayers of both particles
that were heat-treated in a discrete additional post-polymerization
process step and "as polymerized" particles that were kept for a
prolonged period in the elevated temperature environment of the
conductivity cell manifest useful levels of liquid conductivity
(above 100 mDft) even under a closure stress of 6000 psi at a
temperature of 250.degree. F. The difference in liquid conductivity
between the partial monolayers of these two types of particles is
very small under a closure stress of 6000 psi at a temperature of
250.degree. F., where long-term exposure to this rather high
temperature is highly effective in advancing the postcuring of the
"as polymerized" particles via "in situ" heat treatment as was
shown in FIG. 5.
[0129] The present disclosure may be embodied in other specific
forms without departing from the spirit or essential attributes of
the disclosure. Accordingly, reference should be made to the
appended claims, rather than the foregoing specification, as
indicating the scope of the disclosure. Although the foregoing
description is directed to the preferred embodiments of the
disclosure, it is noted that other variations and modification will
be apparent to those skilled in the art, and may be made without
departing from the spirit or scope of the disclosure.
* * * * *