U.S. patent application number 13/349738 was filed with the patent office on 2012-07-19 for disintegrating ball for sealing frac plug seat.
This patent application is currently assigned to UTEX INDUSTRIES, INC.. Invention is credited to William James Costello, Thomas Allen Goedrich, Mark Henry Naedler, Patrick Lawrence Prosser.
Application Number | 20120181032 13/349738 |
Document ID | / |
Family ID | 46489904 |
Filed Date | 2012-07-19 |
United States Patent
Application |
20120181032 |
Kind Code |
A1 |
Naedler; Mark Henry ; et
al. |
July 19, 2012 |
DISINTEGRATING BALL FOR SEALING FRAC PLUG SEAT
Abstract
A composition for a ball that disintegrates, dissolves,
delaminates or otherwise experiences a significant degradation of
its physical properties over time in the presence of hydrocarbons
and formation heat. The ball may be used in methods and apparatus
for hydraulically fracturing a subterranean zone in a wellbore.
Inventors: |
Naedler; Mark Henry;
(Cypress, TX) ; Prosser; Patrick Lawrence;
(Houston, TX) ; Goedrich; Thomas Allen; (Bastrop,
TX) ; Costello; William James; (Houston, TX) |
Assignee: |
UTEX INDUSTRIES, INC.
Houston
TX
|
Family ID: |
46489904 |
Appl. No.: |
13/349738 |
Filed: |
January 13, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61433011 |
Jan 14, 2011 |
|
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61540353 |
Sep 28, 2011 |
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Current U.S.
Class: |
166/308.1 ;
166/193 |
Current CPC
Class: |
E21B 43/26 20130101 |
Class at
Publication: |
166/308.1 ;
166/193 |
International
Class: |
E21B 43/26 20060101
E21B043/26; E21B 33/12 20060101 E21B033/12 |
Claims
1. A fracturing system for a wellbore, said system comprising: a
tube having a wall comprising an interior surface and an exterior
surface; a ball seat carried by the tube, the ball seat comprising
an opening of a first diameter; and a ball having a second diameter
larger than the first diameter, the ball comprising a first
material, wherein the first material is disintegrated by
hydrocarbons.
2. The system of claim 1, wherein the first material comprises
polystyrene.
3. The system of claim 2, wherein the first material comprises
general purpose polystyrene.
4. The system of claim 2, wherein the ball further comprises a
second material, wherein the second material comprises fibers or
particles of at least one member selected from the group consisting
of aramid, glass, carbon, boron, polyester, cotton and
ceramics.
5. The system of claim 2, wherein the ball further comprises a
second material, wherein the second material comprises one or more
layers of a composite fabric material, said composite fabric
material comprising at least one member selected from the group
consisting of aramid, glass, carbon, boron, polyester, cotton and
ceramic fibers.
6. The system of claim 2, wherein the ball comprises from about 30
percent to about 90 percent by weight of the first material.
7. The system of claim 2, wherein the ball comprises from about 50
percent to about 70 percent by weight of the first material.
8. The system of claim 2, wherein the ball comprises about 60
percent by weight of the first material.
9. The system of claim 4, wherein the ball comprises about 60
percent by weight of the first material and about 40 percent by
weight of the second material.
10. The system of claim 1, wherein the ball is seated in the
opening of the ball seat so that a first portion of the ball is
exposed above the opening and a second portion of the ball is
exposed below the opening, the system further comprising a volume
of hydrocarbon disposed in the tube and in contact with the first
portion of the ball.
11. The system of claim 1, wherein the ball is seated in the
opening of the ball seat and prevents fluid communication between a
first portion of the tube above the ball and a second portion of
the tube below the ball.
12. The system of claim 11, wherein the ball prevents fluid
communication between the first and second portions of the tube at
a pressure of up to about 10,000 psi.
13. The system of claim 1, wherein the ball seat comprises a flange
disposed around the interior surface of the tube wall.
14. The system of claim 1, wherein the ball seat comprises a sleeve
slidingly mounted within the tube between a first position and a
second position.
15. The system of claim 14, wherein the sleeve has an interior
surface and an exterior surface, and further comprises a shoulder
defined adjacent the interior surface.
16. The system of claim 15, wherein the ball seat further comprises
a collar abutting the shoulder and in which the opening is
defined.
17. The system of claim 14, wherein the tube further comprises a
plurality of apertures disposed in the tube wall, wherein the
sleeve in the first position is adjacent the apertures so as to
impede fluid flow therethrough.
18. The system of claim 14, further comprising a plurality of ball
seats, wherein each of the plurality of ball seats has an opening
of a diameter different from those of the other ball seats; and a
plurality of balls, each disposed to seat within one of the
openings of the ball seats, wherein each of the plurality of balls
has a diameter different from those of the other balls.
19. The system of claim 18, further comprising a pipe string in
which the seats are disposed, wherein the plurality of seats are
arranged consecutively along the pipe string from the seat with the
largest diameter opening to the seat with the smallest diameter
opening.
20. A fracturing system for a wellbore, said system comprising: a
tube having a wall comprising an interior surface and an exterior
surface; a ball seat carried by the tube, the ball seat comprising
an opening of a first diameter; and a ball having a second diameter
larger than the first diameter, the ball comprising a first
material, wherein the first material degrades at a temperature
greater than 150.degree. F.
21. The system of claim 20, wherein the first material degrades at
a temperature range of from about 150.degree. F. to about
350.degree. F.
22. The system of claim 20, wherein the first material degrades at
a temperature range of from about 150.degree. F. to about
220.degree. F.
23. The system of claim 20, wherein the first material degrades at
a temperature range from about 150.degree. F. to about 200.degree.
F.
24. The system of claim 20, wherein the ball does not deform at a
pressure of up to about 10,000 psi.
25. The system of claim 20, wherein the first material is selected
from the group consisting of thermosetting polymers, thermoplastic
polymers, elastomers and adhesives.
26. The system of claim 20, wherein the first material comprises a
thermosetting polymer selected from the group consisting of
phenolic resins, urea-formaldehyde resins, epoxy resins, melamine
resins, crosslinked polyesters, polyimides, polyurethanes, cyanate
esters, polycyanurates and melamine formaldehyde.
27. The system of claim 20, wherein the first material comprises a
thermoplastic polymer selected from the group consisting of
acrylonitrile butadiene styrene, acrylates such as poly methyl
methacrylate, polyoxymethylene, polyamides, polybutylene
terephthalate, polyethylene terephthalate, polycarbonate,
polyester, polyethylene, polyetheretherketone, polypropylene,
polystyrene, polyvinylidene chloride and styrene-acrylonitrile.
28. The system of claim 20, wherein the first material comprises an
elastomer selected from the group consisting of ethylene propylene,
polyisoprene, polybutadiene, chloroprene rubber, butyl rubber,
styrene-butadiene rubber and nitrile rubber.
29. The system of claim 20, wherein the first material comprises an
adhesive selected from the group consisting of acrylates,
methacrylates, and cyanoacrylate.
30. The system of claim 20, wherein the first material is selected
from the group consisting of polystyrene, tert-butyl vinyl ether,
3-chlorostyrene, cyclohexyl methacrylate, cyclohexyl vinyl ether,
N,N-dimethylacrylamide, 4-ethoxystyrene, ethylene terephthalate,
ethyl methacrylate, 4-fluorostyrene, 2-hydropropyl methacrylate,
indene, isobornyl acrylate, N-isopropylacrylamide, isopropyl
methacrylate, phenylene vinylene, phenyl vinyl ketone, atactic
styrene, isotactic styrene, trimethylsilyl methacrylate, vinyl
alcohol, vinyl benzoate, vinyl chloride, vinylcyclohexanoate and
vinyl pivalate.
31. The system of claim 20, wherein the ball further comprises a
second material, wherein the second material comprises fibers or
particles of at least one member selected from the group consisting
of aramid, glass, carbon, boron, polyester, cotton and
ceramics.
32. The system of claim 20, wherein the ball further comprises a
second material, wherein the second material comprises one or more
layers of a composite fabric material, said composite fabric
material comprising at least one member selected from the group
consisting of aramid, glass, carbon, boron, polyester, cotton and
ceramic fibers.
33. A method for fracturing the formation around a wellbore, the
method comprising: deploying a pipe string into a wellbore, the
pipe string having perforations disposed in a wall of the pipe
string and a ball seat positioned in the interior of the pipe
string; setting packers above and below the perforations to seal
the annulus formed between the pipe string and the formation;
introducing a disintegratable ball comprised of a first material
into the pipe string; seating the ball on the ball seat by applying
a fluid pressure to the ball, which fluid pressure is greater than
the pressure of the wellbore, wherein the ball when seated, has an
upstream portion and a downstream portion; introducing fracturing
fluids into the wellbore to initiate fracturing of the formation
adjacent the perforations; cooling the upstream portion of the
disintegratable ball during fracturing of the formation to inhibit
disintegration of the ball; upon completion of the fracturing,
introducing a hydrocarbon pad into the pipe string; contacting the
upstream portion of the ball with the hydrocarbon pad to promote
disintegration of the ball by the hydrocarbon pad; and allowing
disintegration of the ball to continue until the ball unseats from
the ball seat.
34. The method of claim 33, wherein a pressure differential across
the ball is maintained during fracturing.
35. The method of claim 34, wherein the upstream pressure applied
to the ball is greater than the downstream pressure applied to the
ball.
36. The method of claim 35, wherein the upstream pressure is up to
10,000 psi.
37. The method of claim 33, wherein a temperature differential
across the ball is maintained during fracturing.
38. The method of claim 37, wherein the upstream temperature
applied to the ball is less than the downstream temperature applied
to the ball.
39. The method of claim 33, wherein the fracturing fluid has a
fluid temperature less than the temperature of the wellbore
fluid;
40. The method of claim 39, wherein the fracturing fluid is used to
cool the ball during fracturing.
41. The method of claim 33, wherein the hydrocarbon pad is
diesel.
42. The method of claim 33, wherein the heat of the formation is
used to accelerate degradation.
43. The method of claim 33, wherein the first material comprises a
thermosetting polymer selected from the group consisting of
phenolic resins, urea-formaldehyde resins, epoxy resins, melamine
resins, crosslinked polyesters, polyimides, polyurethanes, cyanate
esters, polycyanurates and melamine formaldehyde.
44. The method of claim 33, wherein the first material comprises a
thermoplastic polymer selected from the group consisting of
acrylonitrile butadiene styrene, acrylates such as poly methyl
methacrylate, polyoxymethylene, polyamides, polybutylene
terephthalate, polyethylene terephthalate, polycarbonate,
polyester, polyethylene, polyetheretherketone, polypropylene,
polystyrene, polyvinylidene chloride and styrene-acrylonitrile.
45. The method of claim 33, wherein the first material comprises an
elastomer selected from the group consisting of ethylene propylene,
polyisoprene, polybutadiene, chloroprene rubber, butyl rubber,
styrene-butadiene rubber and nitrile rubber.
46. The method of claim 33, wherein the first material comprises an
adhesive selected from the group consisting of acrylates,
methacrylates, and cyanoacrylate.
47. The method of claim 33, wherein the first material is selected
from the group consisting of polystyrene, tent-butyl vinyl ether,
3-chlorostyrene, cyclohexyl methacrylate, cyclohexyl vinyl ether,
N,N-dimethylacrylamide, 4-ethoxystyrene, ethylene terephthalate,
ethyl methacrylate, 4-fluorostyrene, 2-hydropropyl methacrylate,
indene, isobornyl acrylate, N-isopropylacrylamide, isopropyl
methacrylate, phenylene vinylene, phenyl vinyl ketone, atactic
styrene, isotactic styrene, trimethylsilyl methacrylate, vinyl
alcohol, vinyl benzoate, vinyl chloride, vinylcyclohexanoate and
vinyl pivalate.
48. The method of claim 33, wherein the ball further comprises a
second material, wherein the second material comprises fibers or
particles of at least one member selected from the group consisting
of aramid, glass, carbon, boron, polyester, cotton and
ceramics.
49. The method of claim 33, wherein the ball further comprises a
second material, wherein the second material comprises one or more
layers of a composite fabric material, said composite fabric
material comprising at least one member selected from the group
consisting of aramid, glass, carbon, boron, polyester, cotton and
ceramic fibers.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of the filing date of
(i) U.S. Provisional Application No. 61/433,011 filed on Jan. 14,
2011 and entitled "Disintegrating Ball for Sealing Frac Plug Seat,"
and (ii) U.S. Provisional Application No. 61/540,353 filed on Sep.
28, 2011 and entitled "Disintegrating Ball for Sealing Frac Plug
Seat," such provisional applications being hereby incorporated
herein by reference in their entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to a ball used in well
stimulation to create a seal when dropped down a wellbore onto a
frac plug seat. More specifically, it relates to a ball that has
sufficient rigidity to resist deformation and withstand the high
pressure differentials, typically up to 10,000 psi, that are
required during well stimulation, but is capable of disintegrating,
dissolving, delaminating or otherwise experiencing a significant
degradation of its physical properties in the presence of
hydrocarbons and latent heat following well stimulation. Extraction
from the hole or milling the ball is not necessary upon completion
of the well fracturing process.
BACKGROUND
[0003] In well stimulation, the ability to perforate multiple zones
in a single well and then fracture each zone independently,
referred to as "zone fracturing", has increased access to potential
reserves. Many gas wells are drilled with zone fracturing planned
at the well's inception. Zone fracturing helps stimulate the well
by creating conduits from the formation for the hydrocarbons to
reach the well. A well drilled with planned fracturing zones will
be equipped with a string of piping below the cemented casing
portion of the well. The string is segmented with packing elements
and frac plugs containing ball seats to isolate zones. A ball is
dropped or pumped down the well and seats in the frac plug, thereby
isolating pressure from above. Typically, a ball seat has an axial
opening of a select diameter. To the extent multiple frac plugs are
disposed along a string, the diameter of these seats in the
respective frac plugs becomes progressively smaller with the depth
of the string. This permits a plurality of balls having a
progressively increasing diameter, to be dropped (or pumped),
smallest to largest diameter, down the well to isolate the various
zones, starting from the toe of the well and moving up. When the
well stimulation in a particular zone is complete, pressure from
within the formation should return the ball utilized in a
particular zone to the surface, carrying the ball upward in the
flow of return fluids. In order to maximize the number of zones and
therefore the efficiency of the well, the diameter of the balls and
the corresponding ball seats are very close in size from one zone
to another. One-eighth inch increments are common. This means that
a given ball has very little diametrical interference with the seat
supporting it since a ball with a diameter of one-eighth inch
smaller than the seat's axial opening must pass through that
seat.
[0004] Conventional prior art frac balls are typically made of a
non-metallic material, such as reinforced epoxies and phenolics,
that may be removed by milling in the event the balls become stuck.
Such conventional prior art frac balls are made of materials that
are designed to remain intact when exposed to hydraulic fracturing
temperatures and pressures and are not significantly dissolved or
degraded by the hydrocarbons or other media present within the
well. When one of these prior art balls does not return to the
surface and prevents lower balls from purging, coiled tubing must
be lowered into the wellbore to mill the stuck ball and remove it
from the seat. In addition, smaller-sized prior art balls that are
not stuck in their seats still might not return to the surface
because the pressure differential across the ball due to the
uprising current in the large diameter casing might not be
significant enough to overcome gravity. Consequently, while such
smaller-sized balls may not completely block a zone, they are still
likely to impede production by partially blocking the wellbore.
[0005] Dissolvable balls are sometimes used in a frac process know
as perf and plug, where fracturing pressures are not as high. This
fracturing process is used when preinstalled perforated casing
string is not available and the zones are created through existing
casing by perforating the casing to create formation flow paths
therethrough. Specifically, using explosives, a relatively large
number of small, radial holes are cut through the casing and
cement. Typically, these holes have an irregular shape with rough
or jagged edges and varying sizes due to the manner in which they
are cut. Once the holes are created, the pumping process begins at
the surface and the frac fluid fractures that zone through the
newly cut radial holes. Upon completion of the zone, relatively
small balls are carried in high quantities in fluid pumped from the
surface in order to plug the perforated holes. These small balls
must be malleable enough to block the irregular perforated holes in
the casing. In this regard, these perf and plug balls typically
have a high elongation and a low flexural modulus, the reason being
that they must deform to plug the irregular shapes of the casing
perforations. These balls require a large ratio of ball diameter to
seat diameter to withstand the pressure from fracturing the zone
above. Perf and plug balls must remain intact under latent heat and
pressure conditions for long periods of time and are often designed
to dissolve in water.
DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 illustrates a ball of the present invention seated in
a frac plug.
[0007] FIG. 2 illustrates a frac plug before the ball has become
seated.
[0008] FIG. 3 shows a non-dissolving, prior art ball after becoming
stuck in the seat of a frac plug.
[0009] FIG. 4 illustrates perf and plug style balls of the prior
art.
[0010] FIG. 5 illustrates a cut-away side view of a composite ball
of the present invention in which a fabric is layered in parallel
planes.
[0011] FIG. 6 illustrates a cut-away side view of a composite ball
of the present invention in which multiple fabric layers are
wrapped around a central axis.
[0012] FIG. 7 illustrates a cut-away side view of a ball of the
present invention in which a strengthening material is embedded in
a base material.
DETAILED DESCRIPTION
[0013] The method and apparatus of the present invention provides a
ball that disintegrates, dissolves, delaminates or otherwise
experiences a significant degradation of its physical properties
over time in the presence of hydrocarbons and formation heat. The
term "disintegrate" with respect to the frac ball of the present
invention is defined to refer generically to various processes by
which the physical properties of the frac ball are significantly
degraded such that the frac ball can no longer maintain a seal with
respect to its corresponding ball seat, such processes including
but not limited to disintegration, dissolution and
delamination.
[0014] The composition of the ball of the present invention permits
it to maintain its strength and shape for the time period required
to fracture its assigned zone. In one embodiment, this time period
is approximately 10 hours.
[0015] The ball of the present invention is dropped down a wellbore
onto a frac plug seat whereupon it is caused to seat in the frac
plug as described above. Since the ball is immersed in frac fluid
and dropped from the surface, when it lands in the frac plug seat,
the ball is at approximately the same temperature as the frac
fluid. Ambient temperatures on the surface including heat generated
from the pumps used the pump the frac fluid down hole, typically
heat the frac fluid and consequently the balls of the present
invention to a temperature of no greater than 150.degree. F.
[0016] Frac fluid is then pumped into the frac zone in a
conventional manner to initiate formation fracturing. During the
hydraulic fracturing process, the convective frac fluid from the
surface pumped to fracture the zone also serves as a coolant for
the ball relative to latent high temperatures. Since frac fluid
must be continuously pumped to the ball to maintain the ball's
position in the seat, the flow of frac fluid will keep the ball at
nearly the temperature of the frac fluid. Latent heat from the
earth is transferred by convection to the ball and is in turn
transferred and removed from the ball by convection to the frac
fluid. In addition, the frac fluid displaces hydrocarbons within
the well minimizing hydrocarbon contact with the ball, thereby
inhibiting disintegration of the ball during the hydraulic
fracturing process.
[0017] Once the frac zone is complete, a column of hydrocarbons,
such as diesel fuel, is pumped onto the top or upper portion of the
ball. This column of fluid, sometimes referred to as a pad,
effectively "soaks" the portion of the ball exposed to the frac
zone and initiates the disintegration of the ball. The next larger
ball is then dropped or pumped into place on the frac plug
immediately above the disintegrating ball, and hydraulic fracturing
procedures in the respective zone are initiated. The newly seated
ball functions to block frac fluid flow from reaching the now
disintegrating lower ball. Thus, the lower ball sits in its seat
and continues to disintegrate in the presence of the pad while the
zones above it are fractured. Without the relatively cool frac
fluid reaching the lower ball, the lower ball's temperature will
climb to the latent temperature in the well bore. The latent
temperature in the well bore can reach, for example, in excess of
200.degree. F., in excess of 220.degree. F., or in excess of
350.degree. F. The latent formation heat and pressure, the
hydrocarbon pad pumped from the top of the well, and to a lesser
extent, hydrocarbons from the formation function to disintegrate
the ball and initially soften its exterior, stripping the ball of
its rigidity and reducing the likelihood that it could become stuck
in the seat. As time elapses, the ball continues to disintegrate
and soften towards the core. When the well begins to backflow, the
currents effectively disintegrate the ball.
[0018] It should be noted that for several reasons, the ball will
not disintegrate in this controlled manner simply in the presence
of formation hydrocarbons acting on the exposed lower surface of
the ball, i.e., that portion of the ball that extends below the
frac seat. First, the ball is intentionally cooled by the frac
fluid pumped down the well. Second, the hydrocarbon pad that is
pumped down the well is specifically selected to yield a controlled
disintegration of the ball. In one embodiment, the pad is diesel
fuel, which has a composition that ranges from approximately
C.sub.10H.sub.20 to C.sub.15H.sub.28.
[0019] In addition to being subject to controlled disintegration in
the presence of hydrocarbons at temperatures in excess of
150.degree. F. as described above, and in contrast to the pert and
plug balls described above, the disintegrating balls of the present
invention are designed for strength, rigidity and hardness
sufficient to withstand the high pressure differentials required
during well stimulation, which typically range from about 1,000
pounds per square inch (psi) to about 10,000 psi. According to
certain embodiments, the ball of the present invention is formed of
a material or combination of materials having sufficient strength,
rigidity and hardness at a temperature of from about 150.degree. F.
to about 350.degree. F., from about 150.degree. F. to about
220.degree. F. or from about 150.degree. F. to about 200.degree. F.
to seat in the frac plug and then withstand deformation under the
high pressure ranging from about 1,000 psi to about 10,000 psi
associated with hydraulic fracturing processes. For this reason,
according to some embodiments of the present invention the ball is
formed of a material having a Rockwell Hardness of M 75 or
greater.
[0020] According to one embodiment, the disintegrating ball of the
present invention comprises polystyrene. Polystyrene is a
relatively high strength, rigid, high modulus resin that is not
compatible with hydrocarbons and disintegrates in the presence of a
hydrocarbon, such as diesel, particularly at elevated temperatures,
such as temperatures above 150.degree. F. and/or pressures, such as
1,000 psi to 10,000 psi where the hydrocarbon acts as a
solvent.
[0021] According to one embodiment, the ball of the present
invention is made of general purpose (GP) polystyrene, which may be
substantially pure without other significant additives. According
to another embodiment, the ball of the present invention is made of
high impact polystyrene (HIP) which may include additives. The
following chain represents a suitable polystyrene for making the
ball of the present invention:
##STR00001##
[0022] With respect to degradation at latent temperatures in the
wellbore, the disintegrating ball of the present invention can be
formed of any base material or combination of base materials that
is sufficiently strong and rigid to support and not deform at a
pressure of from 1,000 psi to 10,000 psi at a temperature of less
than 150.degree. F., but that undergoes a significant degradation
of physical properties at temperatures in excess of 150.degree. F.,
such that the disintegrating ball breaks apart into a plurality of
particles, fragments or pieces that may easily be pumped to the
surface. For example, the base material may undergo a significant
degradation of physical properties at a temperature range of from
about 150.degree. F. to about 350.degree. F., from about
150.degree. F. to about 220.degree. F., or from about 150.degree.
F. to about 200.degree. F. This can include polystyrene, as
indicated above. Other base materials that have suitable strength
and rigidity while also being subject to physical degradation at
the appropriate temperatures, include thermosetting polymers,
thermoplastic polymers, elastomers and adhesives. Suitable
thermosetting polymer materials include phenolic resins,
urea-formaldehyde resins, epoxy resins, melamine resins,
crosslinked polyesters, polyimides, polyurethanes, cyanate esters,
polycyanurates and melamine formaldehyde. Suitable thermoplastic
polymer materials include acrylonitrile butadiene styrene,
acrylates such as poly methyl methacrylate, polyoxymethylene,
polyamides, polybutylene terephthalate, polyethylene terephthalate,
polycarbonate, polyester, polyethylene, polyetheretherketone,
polypropylene, polystyrene, polyvinylidene chloride and
styrene-acrylonitrile. Suitable elastomer materials include
ethylene propylene, polyisoprene, polybutadiene, chloroprene
rubber, butyl rubber, styrene-butadiene rubber and nitrile rubber.
Suitable adhesives include acrylates, methacrylates, and
cyanoacrylate.
[0023] In certain embodiments, the disintegrating ball of the
present invention may be formed of a material having a glass
transition temperature (the temperature at which the amorphous
phase of a polymer is converted between glassy and rubbery states)
or a melting point temperature (the temperature at which a material
transitions from a solid state to a liquid state) in the
appropriate temperature range, that is, in excess of 150.degree. F.
(65.5.degree. C.), for example in the range of from about
150.degree. F. to about 350.degree. F. (about 65.5.degree. C. to
about 176.7.degree. C.), from about 150.degree. F. to about
220.degree. F. (about 65.5.degree. C. to about 104.4.degree. C.),
or from about 150.degree. F. to about 200.degree. F. (about
65.5.degree. C. to about 93.3.degree. C.). Such materials may
include, but are not limited to, the materials listed in Table 1
below.
TABLE-US-00001 TABLE 1 Example Polymeric Materials Glass Transition
Melting Point Repeating Unit Temperature (T.sub.g) (.degree. C.)
(T.sub.m) (.degree. C.) tent-Butyl vinyl ether 88 250
3-Chlorostyrene 90 Cyclohexyl methacrylate 92 Cyclohexyl vinyl
ether 81 N,N-Dimethylacrylamide 89 4-Ethoxystyrene 86 Ethylene
terephthalate 72 265 Ethyl methacrylate 65 4-Fluorostyrene 95
2-Hydropropyl methacrylate 76 Indene 85 Isobornyl acrylate 94
N-Isopropylacrylamide 85-130 Isopropyl methacrylate 81 Phenylene
vinylene 80 380 Phenyl vinyl ketone 74 Styrene, atactic 100
Styrene, isotactic 100 240 Trimethylsilyl methacrylate 68 Vinyl
alcohol 85 220 Vinyl benzoate 71 Vinyl chloride 81 227
Vinylcyclohexanoate 76 Vinyl pivalate 86
[0024] In another embodiment of the present invention, reinforcing
material can be added to the base material of the ball to increase
the strength and rigidity of the ball so it can support higher
pressures, such as from about 1,000 psi to about 10,000 psi when
plugging a seat in a frac plug. Specifically, relatively high
percentages of aramid, glass, carbon, boron, polyester, cotton and
ceramic fibers or particles can elevate the pressure threshold the
ball can sustain. Such fillers do not dissolve in hydrocarbons, but
when the base material disintegrates, these fillers become
inconsequential silt in the wellbore fluid. According to other
embodiments of the present invention, the ball can include
composite fabric layers made of aramid, glass, carbon, boron,
polyester, cotton or ceramic fibers disposed within the base
material. Such composite fabric layers enable the ball to retain
high strength at high pressures, such as from about 1,000 psi to
about 10,000 psi when plugging a seat in a frac plug.
[0025] According to certain embodiments, the ball of the present
invention may include one or more of (a) imbedded aramid, glass,
carbon, boron, polyester, cotton or ceramic fibers, (b) one or more
layers of fabric formed of aramid, glass, carbon, boron, polyester,
cotton or ceramic fibers wrapped around the core of the ball, and
(c) one or more layers of fabric formed of aramid, glass, carbon,
boron, polyester, cotton or ceramic fibers disposed in adjacent
parallel planes.
[0026] According to certain embodiments, the ball of the present
invention includes about 30 to about 90 percent by weight of the
base material and about 10 to about 70 percent by weight of fibers,
particles or layers of fabric. According to certain other
embodiments, the ball of the present invention includes about 50 to
about 70 percent by weight of the base material and about 30 to
about 50 percent by weight of fibers, particles or layers of
fabric. In still other embodiments, the ball of the present
invention includes about 60 percent by weight of the base material
and about 40 percent by weight of fibers, particles or layers of
fabric.
[0027] Additionally, aluminum may be used to strengthen the
disintegrating ball since the corrosive environment in the well
hole causes the aluminum to disintegrate as well.
[0028] FIG. 1 illustrates a polymeric, disintegratable frac ball 10
of the present invention in service. Frac ball 10 is seated on a
frac plug seat 12 which is sealably housed in a sleeve 14 carried
in a tube 16 of a pipe string 18. Sleeve 14 is slidable between a
second position (illustrated in FIG. 1) and a first position
(illustrated in FIG. 2). Those of ordinary skill in the art will
appreciate that as fluid, such as frac fluid, is pumped down the
well as shown by the directional arrow 20, a pressure differential
between the upstream fluid 22 and the downstream formation fluids
24 as applied across the ball 10 and seat 12 urges sleeve 14 into
the second position. In this second position, sleeve 14 abuts
shoulder 26 of the tube 16. The tube 16 is provided with a
plurality of radial apertures or holes 28 that serve as a conduit
from the interior 30 of tube 16 to the formation 32, thereby
permitting frac fluid pumped from the surface to infiltrate the
annulus 34 between the pipe string 18 and the formation 32.
Moreover, as will be appreciated in FIG. 2, when sleeve 14 is in
the second position, apertures 28 are fully open to permit fluid
flow therethrough. Packing element 36 is one of many packing
elements that partition annulus 34 into zones. A second packing
element (not shown) is disposed down stream of perforations 28 so
that the packing elements straddle the frac zone and seal the frac
zone from the remainder of annulus 34.
[0029] In FIG. 2, sleeve 14 is shown in a first position, where a
ball has not been dropped and the upstream fluid pressure from the
frac pumps has not been applied to a seated ball to shift sleeve 14
to the second position. Radial apertures 28 are sealed from
communication with interior 30.
[0030] In FIG. 3, a prior art ball 38 not capable of disintegrating
is illustrated as distorted and wedged in seat 12 from the upstream
pump pressure during the frac process. When the frac process is
complete and the upstream pump pressure is relieved, frac fluid and
hydrocarbons with accumulated pressure from the fracturing process
and formation pressure purge from the zones below. The wedged ball
38 restricts the return flow from the formations below, requiring
expensive milling to remove the ball.
[0031] FIG. 4 illustrates the prior art where pert and plug balls
40 shown disposed in radial apertures 42 formed in casing 44 and
cement 46 adjacent formation 32 by perforation procedures. Prior
art balls 40 must distort in order to plug the perforated apertures
42 and typically have a large ball diameter to aperture diameter
ratio. Fluid from inside the casing 44 is normally passed through
the perforated apertures 42 and into the formation 32 while
fracturing that zone. Typically, a large number of balls 40 are
dropped into the stream from above with the hope of blocking the
apertures 42.
[0032] FIGS. 5 and 6 illustrate embodiments of a ball 10 of the
present invention where fabric layers 46 partition material 48 for
enhanced strength. In FIG. 5, fabric layers 46 have a horizontal
lay-up, while in FIG. 6, fabric layers 46 are wrapped around a
center axis.
[0033] FIG. 7 illustrates an embodiment of ball 10 of the present
invention in which reinforcing material, such as glass, ceramic or
carbon fibers or particles 50 is embedded in material 48.
[0034] While the ball 10 of the present invention has been
described in the foregoing embodiments as including certain
specific materials and the pad utilized to initiate degradation of
the ball as diesel, those of ordinary skill in the art will
appreciate that other ball material and pad solvent combinations
may be utilized so long as they satisfy the requirements of the
system described herein. In this regard, styrene is known to have a
solubility parameter of 8.7 .delta.(cal/cm.sup.3).sup.1/2. Although
a pad of diesel is a preferred embodiment for a ball made of
polystyrene as described herein, solvents with the same or similar
solubility parameters as polystyrene may also be satisfactory for
the purposes of the present invention, such as for example, other
hydrocarbons, oils, ketones, esters and inorganic acids. In one
embodiment, hydrocarbons are preferred because hydrocarbons are
generally acceptable fluids under various regulatory standards for
pumping into a wellbore and are typically readily available at a
well site, and are present naturally in the well. In any event,
materials with similar solubility parameters may also be
satisfactory for ball 10 of the present invention. Finally, so long
as the material used to form the ball of the present invention
satisfies the other criteria set forth herein, particularly
strength and rigidity, the ball may be formed of other polymeric or
other materials with a pad selected to have the same or similar
solubility parameters as the polymeric or other material of the
ball.
[0035] Similarly, with respect to degradation at latent
temperatures of the wellbore, so long as the material used to form
the ball of the present invention satisfies the other criteria set
forth herein, particularly strength and rigidity, the ball may be
formed of other polymeric materials with a glass transition
temperature and/or melting temperature in the appropriate
temperature range such that the materials undergo significant
physical degradation at temperatures in excess of 150.degree. F.,
such as from about 150.degree. F. to about 350.degree. F., from
about 150.degree. F. to about 220.degree. F., or from about
150.degree. F. to about 200.degree. F.
* * * * *