U.S. patent application number 10/663415 was filed with the patent office on 2005-03-17 for method and apparatus for temporarily maintaining a downhole foam element in a compressed state.
Invention is credited to Grigsby, Tommy F., Procyk, Alexander D., Todd, Bradley L..
Application Number | 20050056425 10/663415 |
Document ID | / |
Family ID | 34274373 |
Filed Date | 2005-03-17 |
United States Patent
Application |
20050056425 |
Kind Code |
A1 |
Grigsby, Tommy F. ; et
al. |
March 17, 2005 |
Method and apparatus for temporarily maintaining a downhole foam
element in a compressed state
Abstract
The present invention is directed to a degradable wrap and
method for temporarily maintaining a downhole foam element in a
compressed state. The degradable wrap is fitted around the foam
element and temporarily maintains the foam element in a compressed
state against an outer surface of a downhole sand control device.
It is provided to keep the foam element in the compressed state
while a production assembly comprising the downhole sand control
device and foam element mounted thereon is placed downhole in a
well bore adjacent to a production zone. The degradable wrap is
permeable to the production fluid and degrades over time. Once the
degradable wrap has degraded the foam element fills the annulus
between the production screen and casing string or well bore wall.
The foam element acts to inhibit the flow of water along the
annulus and is useful in zone isolation.
Inventors: |
Grigsby, Tommy F.; (Houma,
LA) ; Procyk, Alexander D.; (Houston, TX) ;
Todd, Bradley L.; (Duncan, OK) |
Correspondence
Address: |
Robert A. Kent
Halliburton Energy Services, Inc.
2600 S. 2nd Street
Duncan
OK
73536
US
|
Family ID: |
34274373 |
Appl. No.: |
10/663415 |
Filed: |
September 16, 2003 |
Current U.S.
Class: |
166/296 ;
166/227 |
Current CPC
Class: |
E21B 33/1208 20130101;
E21B 43/12 20130101 |
Class at
Publication: |
166/296 ;
166/227 |
International
Class: |
E21B 043/10 |
Claims
What is claimed is:
1. A method for temporarily maintaining a compressible foam element
in a compressed state against an outer surface of a downhole sand
control device, comprising the steps of: (a) installing a
production assembly downhole within a casing string or well bore,
the production assembly comprising a degradable wrap securely
fitted around the compressible foam element so as to cause the
compressible foam element to assume a compressed configuration
against the downhole sand control device; and (b) degrading the
degradable downhole wrap thereby causing the compressible foam
element to expand into contact with the casing string or well
bore.
2. The method according to claim 1, further comprising the step of
isolating a a section of the production assembly.
3. The method according to claim 2, wherein the isolating step
comprises the steps of installing an isolation pipe having a top
end and a bottom end inside the production assembly and sealing the
isolation pipe to the production assembly.
4. The method according to claim 3, wherein the step of installing
the isolation pipe inside the production assembly is performed
after the step of installing the production assembly downhole in
the casing string or well bore and production has been flowing for
a period of time.
5. The method according to claim 3, wherein a coil tubing is
employed to install the isolation pipe inside of the production
assembly and to seal the top and bottom ends of the isolation pipe
to the production assembly.
6. The method according to claim 1, wherein the degradable wrap is
biodegradable and gradually degrades by thermal hydrolysis in the
presence of the aqueous solution.
7. The method according to claim 6, wherein the biodegradable wrap
is in the form of a string or tape, which is helically wound around
the compressible foam element.
8. The method according to claim 7, wherein the biodegradable wrap
is formed into a tubular sheath.
9. The method according to claim 8, wherein the biodegrable tubular
sheath is formed of a woven cloth.
10. The method according to claim 1, wherein the degradable wrap
comprises a degradable polymer selected from the group consisting
of homopolymers, random, block, graft, and star- and hyper-branched
aliphatic polyesters.
11. The method according to claim 1, wherein the degradable wrap
comprises a degradable polymer selected from the group consisting
of polysaccharides; chitins; chitosans; proteins; aliphatic
polyesters; poly(lactides); poly(glycolides);
poly(.epsilon.-caprolactones); poly(hydroxybutyrates);
poly(anhydrides); aliphatic polycarbonates; poly(orthoesters);
poly(amino acids); poly(ethylene oxides); and polyphosphazenes.
12. The method according to 11, wherein the degradable wrap
comprises an aliphatic polyester having the general formula of
repeating units shown below: 4where n is an integer between 75 and
10,000 and R is selected from the group consisting of hydrogen,
alkyl, aryl, alkylaryl, acetyl, heteroatoms, and mixtures
thereof.
13. The method according to claim 11, wherein the degradable wrap
further comprises a plasticizer.
14. The method according to claim 13, wherein the plasticizer
comprises a derivative of oligomeric lactic acid, selected from the
group defined by the formula: 5where R is a hydrogen, alkyl, aryl,
alkylaryl, acetyl, heteroatom, or a mixture thereof and R is
saturated, where R' is a hydrogen, alkyl, aryl, alkylaryl, acetyl,
heteroatom, or a mixture thereof and R' is saturated, where R and
R' cannot both be hydrogen, where q is an integer and
2.ltoreq.q.ltoreq.75; and mixtures thereof.
15. The method according to claim 1, wherein the degradable wrap is
permeable enabling a production fluid to pass through the
compressible foam element and the sand control device.
16. A production assembly, comprising: a base pipe; a sand control
device incorporated within, or mounted to, the base pipe; a
compressible foam element mounted to the sand control device; and a
degradable wrap securely fitted around the compressible foam
element so as to cause the compressible foam element to assume a
compressed configuration.
17. The production assembly according to claim 16, wherein the
degradable wrap is biodegradable and gradually degrades by thermal
hydrolysis in the presence of an aqueous solution.
18. The production assembly according to claim 17, wherein the
biodegradable wrap is in the form of a string or tape, which is
helically wound around the compressible foam.
19. The production assembly according to claim 17, wherein the
biodegradable wrap is formed into a tubular sheath.
20. The production assembly according to claim 19, wherein the
biodegrable tubular sheath is formed of a woven cloth.
21. The production assembly according to claim 16, wherein the
degradable wrap comprises a degradable polymer selected from the
group consisting of homopolymers, random, block, graft, and star-
and hyper-branched aliphatic polyesters.
22. The production assembly according to claim 16, wherein the
degradable wrap comprises a degradable polymer selected from the
group consisting of polysaccharides; chitins; chitosans; proteins;
aliphatic polyesters; poly(lactides); poly(glycolides);
poly(.epsilon.-caprolactones); poly(hydroxybutyrates);
poly(anhydrides); aliphatic polycarbonates; poly(orthoesters);
poly(amino acids); poly(ethylene oxides); and polyphosphazenes.
23. The production assembly according to claim 22, wherein the
degradable wrap comprises an aliphatic polyester having the general
formula of repeating units shown below: 6where n is an integer
between 75 and 10,000 and R is selected from the group consisting
of hydrogen, alkyl, aryl, alkylaryl, acetyl, heteroatoms, and
mixtures thereof.
24. The production assembly according to claim 22, wherein the
degradable wrap further comprises a plasticizer.
25. The production assembly according to claim 24, wherein the
plasticizer comprises a derivative of oligomeric lactic acid,
selected from the group defined by the formula: 7where R is a
hydrogen, alkyl, aryl, alkylaryl, acetyl, heteroatom, or a mixture
thereof and R is saturated, where R' is a hydrogen, alkyl, aryl,
alkylaryl, acetyl, heteroatom, or a mixture thereof and R' is
saturated, where R and R' cannot both be hydrogen, where q is an
integer and 2.ltoreq.q.ltoreq.75; and mixtures thereof.
26. The production assembly according to claim 16, wherein the
degradable wrap is permeable enabling a production fluid to pass
through the compressible foam element and the downhole sand control
device.
27. An apparatus for temporarily maintaining a compressible foam
element in a compressed state against an outer surface of a
downhole sand control device, comprising a degradable wrap securely
fitted around the compressible foam element.
28. The apparatus according to claim 27, wherein the degradable
wrap is biodegradable and gradually degrades by thermal hydrolysis
in the presence of an aqueous solution.
29. The apparatus according to claim 28, wherein the biodegradable
wrap is in the form of a string or tape, which is helically wound
around the compressible foam element.
30. The apparatus according to claim 28, wherein the biodegradable
wrap is formed into a tubular sheath.
31. The apparatus according to claim 30, wherein the biodegrable
tubular sheath is formed of a woven cloth.
32. The apparatus according to claim 27, wherein the degradable
wrap comprises a degradable polymer selected from the group
consisting of homopolymers, random, block, graft, and star- and
hyper-branched aliphatic polyesters.
33. The apparatus according to claim 27, wherein the degradable
wrap comprises a degradable polymer selected from the group
consisting of polysaccharides; chitins; chitosans; proteins;
aliphatic polyesters; poly(lactides); poly(glycolides);
poly(.epsilon.-caprolactones); poly(hydroxybutyrates);
poly(anhydrides); aliphatic polycarbonates; poly(orthoesters);
poly(amino acids); poly(ethylene oxides); and polyphosphazenes.
34. The apparatus according to claim 33, wherein the degradable
wrap comprises an aliphatic polyester having the general formula of
repeating units shown below: 8where n is an integer between 75 and
10,000 and R is selected from the group consisting of hydrogen,
alkyl, aryl, alkylaryl, acetyl, heteroatoms, and mixtures
thereof.
35. The apparatus according to claim 33, wherein the degradable
wrap further comprises a plasticizer.
36. The apparatus according to claim 35, wherein the plasticizer
comprises a derivative of oligomeric lactic acid, selected from the
group defined by the formula: 9where R is a hydrogen, alkyl, aryl,
alkylaryl, acetyl, heteroatom, or a mixture thereof and R is
saturated, where R' is a hydrogen, alkyl, aryl, alkylaryl, acetyl,
heteroatom, or a mixture thereof and R' is saturated, where R and
R' cannot both be hydrogen, where q is an integer and
2.ltoreq.q.ltoreq.75; and mixtures thereof.
37. The apparatus according to claim 27, wherein the degradable
wrap is permeable enabling a production fluid to pass through the
compressible foam and the downhole sand control device.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to methods and
apparatuses for controlling fluid flow in a downhole annulus, and
more particularly to a method and apparatus for temporarily
maintaining a downhole foam element in a compressed state until it
needs to expand and fill the annulus to thereby inhibit fluid flow
therein.
[0002] Very often during recovery of hydrocarbons from a
subterranean formation water is produced along with the
hydrocarbons. This is undesirable because it necessitates having to
remove the water from the production fluid, which is typically
expensive. It also creates the problem of having to dispose of the
contaminated water, which is particularly problematic in offshore
applications. To alleviate the problem, techniques have been
developed to isolate regions of the production zone where the water
enters the well. These techniques are commonly known as zone
isolation. Zone isolation is generally accomplished in long,
extended or horizontal completions by installing a section of pipe
inside of the production screen section and sealing the isolation
pipe both above and below the screen section. This prevents the
water from entering the production tubing through the screen in the
region of concern.
[0003] One drawback of the zone isolation technique, however, is
that water can still enter the production tubing. In many cases,
water enters the production tubing through the annulus formed
between the outer surface of the isolated production assembly
section and the inside wall of the casing string (or well bore
wall). The annulus acts as a conduit for the water by channeling it
to adjacent production screens and in turn into the production
tubing.
[0004] Recently, a solution to this problem has been proposed. It
involves installing a tubular foam element over the outer surface
of the production assembly. The tubular foam element fills the
annulus between the outer surface of the production assembly and
the inside wall of the casing string (or well bore wall). Indeed,
the tubular foam element is sized to have an outer diameter that is
larger than the inner diameter of the casing string or inner well
bore wall so as to cause an interference fit. This allows the
tubular foam element to block the annulus from the flow of water in
the region of the isolated zone. Although the tubular foam element
is permeable, it offers enough flow resistance in the axial
direction to significantly reduce, and in some cases nearly
eliminate, the seepage of water along the annulus.
[0005] The challenge that this proposed solution has presented,
however, is how to install the tubular foam element downhole
without damaging the element given that its outer diameter exceeds
the inner diameter of the inner wall of the well bore.
SUMMARY OF THE INVENTION
[0006] The present invention provides an apparatus for temporarily
maintaining a compressible tubular foam element in a compressed
state against an outer surface of a downhole sand control device,
which comprises a degradable wrap securely fitted around the
compressible tubular foam element. The apparatus keeps the
compressible tubular foam element in a compressed state so that a
production assembly comprising the sand control device and
compressible tubular foam element mounted on the sand control
device can be placed downhole in a production zone. Once the
production assembly is in place adjacent to the production zone,
the degradable wrap degrades, thereby causing the compressible
tubular foam element to expand filling the annulus formed between
the production assembly and the casing string or well bore.
[0007] The compressible tubular foam element is permeable to the
hydrocarbons and thus during normal operation permits production to
flow radially into the production assembly. When water starts to
enter a particular zone, a zone isolation step can be performed by
installing an isolation pipe inside of the production assembly and
sealing at its ends. Although as those of ordinary skill in the art
will appreciate other zone isolation techniques may be performed.
The compressible tubular foam element remains in the annulus formed
between the production assembly and the casing string or well bore
and operates to inhibit the normal flow of the water along the
annulus.
[0008] The degradable wrap according to the present invention is
preferably biodegradable and gradually degrades by thermal
hydrolysis in the presence of an aqueous solution. It may take the
form of a string or tape, which is helically wound around the
compressible tubular foam element, but is preferably a tubular
sheath made of a woven degradable polymer. The degradable wrap can
be permeable to production fluid by incorporating a material having
pores, such as a woven or nonwoven cloth.
[0009] In another embodiment, the present invention is directed to
a method of maintaining the compressible foam element in a
compressed state. The method commences with the step of installing
a production assembly downhole within the well bore. The present
invention is also directed to the structure of the production
assembly, which comprises a base pipe, a sand control device
incorporated within, or mounted to, the outer surface of the base
pipe, the compressible tubular foam element coaxially mounted to
the outer surface of the sand control device, and the degradable
wrap securely fitted around the compressible tubular foam element
so as to cause the compressible tubular foam element to assume a
compressed configuration.
[0010] In normal operation, the degradable wrap degrades in the
presence of a downhole aqueous solution as more fully explained
below, thereby causing the compressible tubular foam element to
expand into contact with the casing string or well bore wall. In
the event water is detected in a zone adjacent to a section of the
production assembly, the method continues with the step of
installing an isolation pipe having a top end and a bottom end
inside a blank section of the production assembly. Finally, the
isolation pipe is sealed to the production assembly at its top end
and bottom end or by expanding the isolation pipe so as to cause it
to form an interference fit with the production assembly.
Preferably, a coil tubing is employed to install the isolation pipe
inside of the production assembly and to seal the top and bottom
ends of the isolation pipe to the production assembly. However, as
those of ordinary skill in the art will appreciate, other
techniques may be employed to carry out the steps of the present
invention.
[0011] Other and further objects, features and advantages of the
present invention will be readily apparent to those skilled in the
art upon a reading of the description of preferred embodiments
which follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The present invention is better understood by reading the
following description of non-limitative embodiments with reference
to the attached drawings, which are briefly described as
follows:
[0013] FIG. 1 is a cross-sectional view of a production assembly
that employs a biodegradable tubular sheath to temporarily contain
a compressible tubular foam element against a sand control device
in accordance with the present invention.
[0014] FIG. 2 is a cross-section view of the production assembly
shown in FIG. 1 after the biodegradable sheath has degraded and the
foam element has expanded filling the annulus between the
production assembly and the casing string.
[0015] FIG. 3 is a cross-section view of the production assembly
shown in FIG. 2 illustrating the condition where water is entering
the production tubing through the production assembly and a coil
tubing installing an isolation pipe inside of the production
assembly.
[0016] FIG. 4 is a cross-sectional view of the production assembly
shown in FIG. 2 illustrating the condition where the isolation pipe
has been sealed at both ends to the inner surface of the production
assembly thereby preventing the water from entering into the
production tubing.
[0017] FIG. 5 is a perspective view of the production assembly
shown in FIG. 1.
[0018] FIG. 6 is a perspective view of a production assembly
employing a degradable string helically wrapped around the
compressible tubular foam element in accordance with another
embodiment of the present invention.
[0019] FIG. 7 is a perspective view of a production assembly
employing a degradable tape helically wrapped around the foam
element in accordance with another embodiment of the present
invention.
[0020] It is to be noted, however, that the appended drawings
illustrate only typical embodiments of this invention and are
therefore not to be considered limiting of its scope, as the
invention may admit to other equally effective embodiments.
DETAILED DESCRIPTION OF THE INVENTION
[0021] The details of the present invention will now be discussed
with reference to the figures. Turning to FIG. 1, a multi-sectional
production assembly in accordance with the present invention is
shown generally by reference numeral 10. The production assembly 10
is shown disposed downhole inside of a casing string 12, which in
turn is cemented to the wall of the well bore. The casing string 12
is perforated in the production zone, which is referred to
generally by reference numeral 1. As those of ordinary skill in the
art will recognize, the present invention has application in open
holes as well as those lined with casing string. An annulus 13 is
formed between the production assembly 10 and the casing string
12.
[0022] The production assembly 10 is formed of a base pipe 14,
which is preferably a steel pipe, which has a plurality of openings
to allow a production fluid to flow from the production zone 1 into
the base pipe 14. The production assembly 10 comprises a sand
control device 16, which is mounted to the exterior surface of the
base pipe 14 in the region of the openings. The sand control device
16 is generally tubular in shape and is preferably formed of one or
more layers of sintered or diffusion-bonded wire mesh screens.
However, other known downhole sand control devices may be
employed.
[0023] The production assembly 10 further includes a compressible
tubular foam element 18, which may be formed of any number of
materials, including for example, an open cell polyurethane foam.
The compressible tubular foam element 18 is preferably permeable
enough in the radial direction to permit hydrocarbons to flow
through it under normal production conditions, but impermeable
enough in the axial direction to offer enough flow resistance to
significantly reduce, and in some cases nearly eliminate, the
seepage of water along the annulus 13.
[0024] The production assembly 10 further comprises a degradable
wrap 20, which is securely fit around the outer surface of the
compressible tubular foam element 18. In FIGS. 1-5, the degradable
wrap is shown as a tubular sheath, preferably formed of a woven
cloth. It may also take the form of a string 120 or tape 220
helically wound around the compressible tubular foam element 18, as
shown in FIGS. 6 and 7, respectively, or be formed of a non-woven
material. As those of ordinary skill in the art will appreciate,
however, the degradable wrap 20 may take many other forms. Indeed,
any configuration capable of temporarily maintaining the foam
element 18 in a compressed state is intended to be encompassed by
the present invention.
[0025] In the embodiment where the degradable wrap 20 takes the
form of a tubular sheath, the tubular sheath is pulled over the
foam element 18 by way of a tubular mandrel (not shown). The
tubular mandrel is preferably designed to collapse the compressible
tubular foam element 18 around the sand control device 16 while at
the same time pulling the tubular sheath into place.
[0026] Nonlimiting examples of degradable materials that may be
used in forming the degradable wrap 20 include but are not limited
to degradable polymers. Such degradable materials are capable of
undergoing an irreversible degradation downhole. The term
"irreversible" as used herein means that the degradable material,
once degraded downhole, should not recrystallize or reconsolidate
while downhole, e.g., the degradable material should degrade in
situ but should not recrystallize or reconsolidate in situ. The
terms "degradation" or "degradable" refer to both the two
relatively extreme cases of hydrolytic degradation that the
degradable material may undergo, i.e., heterogeneous (or bulk
erosion) and homogeneous (or surface erosion), and any stage of
degradation in between these two. This degradation can be a result
of, inter alia, a chemical reaction, thermal reaction, a reaction
induced by radiation, or by an enzymatic reaction. The
degradability of a polymer depends at least in part on its backbone
structure. For instance, the presence of hydrolyzable and/or
oxidizable linkages in the backbone often yields a material that
will degrade as described herein. The rates at which such polymers
degrade are dependent on the type of repetitive unit, composition,
sequence, length, molecular geometry, molecular weight, morphology
(e.g., crystallinity, size of spherulites, and orientation),
hydrophilicity, hydrophobicity, surface area, and additives. Also,
the environment to which the polymer is subjected may affect how it
degrades, e.g., temperature, presence of moisture, oxygen,
microorganisms, enzymes, pH, and the like.
[0027] Suitable examples of degradable polymers that may be used in
accordance with the present invention include but are not limited
to those described in the publication of Advances in Polymer
Science, Vol. 157 entitled "Degradable Aliphatic Polyesters" edited
by A.-C. Albertsson. Specific examples include homopolymers,
random, block, graft, and star- and hyper-branched aliphatic
polyesters. Polycondensation reactions, ring-opening
polymerizations, free radical polymerizations, anionic
polymerizations, carbocationic polymerizations, coordinative
ring-opening polymerization, and any other suitable process may
prepare such suitable polymers. Specific examples of suitable
polymers include polysaccharides such as dextran or cellulose;
chitins; chitosans; proteins; aliphatic polyesters; poly(lactides);
poly(glycolides); poly(.epsilon.-caprolactones);
poly(hydroxybutyrates); poly(anhydrides); aliphatic polycarbonates;
poly(orthoesters); poly(amino acids); poly(ethylene oxides); and
polyphosphazenes. Of these suitable polymers, aliphatic polyesters
and polyanhydrides are preferred.
[0028] Aliphatic polyesters degrade chemically, inter alia, by
hydrolytic cleavage. Hydrolysis can be catalyzed by either acids or
bases. Generally, during the hydrolysis, carboxylic end groups are
formed during chain scission, and this may enhance the rate of
further hydrolysis. This mechanism is known in the art as
"autocatalysis," and is thought to make polyester matrices more
bulk eroding.
[0029] Suitable aliphatic polyesters have the general formula of
repeating units shown below: 1
[0030] where n is an integer between 75 and 10,000 and R is
selected from the group consisting of hydrogen, alkyl, aryl,
alkylaryl, acetyl, heteroatoms, and mixtures thereof. Of the
suitable aliphatic polyesters, poly(lactide) is preferred.
Poly(lactide) is synthesized either from lactic acid by a
condensation reaction or more commonly by ring-opening
polymerization of cyclic lactide monomer. Since both lactic acid
and lactide can achieve the same repeating unit, the general term
poly(lactic acid) as used herein refers to formula I without any
limitation as to how the polymer was made such as from lactides,
lactic acid, or oligomers, and without reference to the degree of
polymerization or level of plasticization.
[0031] The lactide monomer exists generally in three different
forms: two stereoisomers L- and D-lactide and racemic D,L-lactide
(meso-lactide). The oligomers of lactic acid, and oligomers of
lactide are defined by the formula: 2
[0032] where m is an integer 2.ltoreq.m.ltoreq.75. Preferably m is
an integer and 2.ltoreq.m.ltoreq.10. These limits correspond to
number average molecular weights below about 5,400 and below about
720, respectively. The chirality of the lactide units provides a
means to adjust, inter alia, degradation rates, as well as physical
and mechanical properties. Poly(L-lactide), for instance, is a
semicrystalline polymer with a relatively slow hydrolysis rate.
This could be desirable in applications of the present invention
where a slower degradation of the degradable particulate is
desired. Poly(D,L-lactide) may be a more amorphous polymer with a
resultant faster hydrolysis rate. This may be suitable for other
applications where a more rapid degradation may be appropriate. The
stereoisomers of lactic acid may be used individually or combined
to be used in accordance with the present invention. Additionally,
they may be copolymerized with, for example, glycolide or other
monomers like .epsilon.-caprolactone, 1,5-dioxepan-2-one,
trimethylene carbonate, or other suitable monomers to obtain
polymers with different properties or degradation times.
Additionally, the lactic acid stereoisomers can be modified to be
used in the present invention by, inter alia, blending,
copolymerizing or otherwise mixing the stereoisomers, blending,
copolymerizing or otherwise mixing high and low molecular weight
polylactides, or by blending, copolymerizing or otherwise mixing a
polylactide with another polyester or polyesters.
[0033] Plasticizers may be present in the polymeric degradable
materials of the present invention. The plasticizers may be present
in an amount sufficient to provide the desired characteristics, for
example, (a) more effective compatibilization of the melt blend
components, (b) improved processing characteristics during the
blending and processing steps, and (c) control and regulation of
the sensitivity and degradation of the polymer by moisture.
Suitable plasticizers include but are not limited to derivatives of
oligomeric lactic acid, selected from the group defined by the
formula: 3
[0034] where R is a hydrogen, alkyl, aryl, alkylaryl, acetyl,
heteroatom, or a mixture thereof and R is saturated, where R' is a
hydrogen, alkyl, aryl, alkylaryl, acetyl, heteroatom, or a mixture
thereof and R' is saturated, where R and R' cannot both be
hydrogen, where q is an integer and 2.ltoreq.q.ltoreq.75; and
mixtures thereof. Preferably q is an integer and
2.ltoreq.q.ltoreq.10. As used herein the term "derivatives of
oligomeric lactic acid" includes derivatives of oligomeric lactide.
In addition to the other qualities above, the plasticizers may
enhance the degradation rate of the degradable polymeric materials.
The plasticizers, if used, are preferably at least intimately
incorporated within the degradable polymeric materials.
[0035] Aliphatic polyesters useful in the present invention may be
prepared by substantially any of the conventionally known
manufacturing methods such as those described in U.S. Pat. Nos.
6,323,307; 5,216,050; 4,387,769; 3,912,692; and 2,703,316, the
relevant disclosures of which are incorporated herein by
reference.
[0036] Polyanhydrides are another type of particularly suitable
degradable polymer useful in the present invention. Polyanhydride
hydrolysis proceeds, inter alia, via free carboxylic acid
chain-ends to yield carboxylic acids as final degradation products.
The erosion time can be varied over a broad range of changes in the
polymer backbone. Examples of suitable polyanhydrides include
poly(adipic anhydride), poly(suberic anhydride), poly(sebacic
anhydride), and poly(dodecanedioic anhydride). Other suitable
examples include but are not limited to poly(maleic anhydride) and
poly(benzoic anhydride).
[0037] The physical properties of degradable polymers depend on
several factors such as the composition of the repeat units,
flexibility of the chain, presence of polar groups, molecular mass,
degree of branching, crystallinity, orientation, etc. For example,
short chain branches reduce the degree of crystallinity of polymers
while long chain branches lower the melt viscosity and impart,
inter alia, elongational viscosity with tension-stiffening
behavior. The properties of the material utilized can be further
tailored by blending, and copolymerizing it with another polymer,
or by a change in the macromolecular architecture (e.g.,
hyper-branched polymers, star-shaped, or dendrimers, etc.). The
properties of any such suitable degradable polymers (e.g.,
hydrophobicity, hydrophilicity, rate of degradation, etc.) can be
tailored by introducing select functional groups along the polymer
chains. For example, poly(phenyllactide) will degrade at about
{fraction (1/5)}th of the rate of racemic poly(lactide) at a pH of
7.4 at 55.degree. C. One of ordinary skill in the art with the
benefit of this disclosure will be able to determine the
appropriate degradable polymer to achieve the desired physical
properties of the degradable polymers.
[0038] In choosing the appropriate degradable material, one should
consider the degradation products that will result, which in this
case is a degradable sheath. These degradation products should not
adversely affect other operations or components. The choice of
degradable material also can depend, at least in part, on the
conditions of the well, e.g., well bore temperature. For instance,
low molecular weight aliphatic polyesters (e.g., 2,000-10,000 mw)
have been found to be suitable for lower temperature wells,
including those within the range of 60.degree. F. to 150.degree.
F., and high molecular weight (e.g., 50,000-70,000) have been found
to be suitable for well bore temperatures above this range. Some
stereoisomers of poly(lactide) or mixtures of such stereoisomers
may be suitable for even higher temperature applications.
[0039] Turning to FIGS. 1-5, a method of controlling the fluid
flow, and more specifically water, in the annulus 13 in accordance
with the present invention will now be described. The production
assembly 10 in accordance with the present invention is placed
downhole in the well bore inside casing string 12 in the region of
interest, namely production zone 1, as shown in FIG. 1. As also
shown in FIG. 1, when the production assembly 10 is first placed
downhole it has the degradable wrap 20 securely fit around the foam
element 18 keeping it in its compressed state.
[0040] Over time, as the degradable wrap 20 is exposed to the
downhole environment, in particular the aqueous fluids present
downhole, it begins to degrade. As the degradable wrap degrades,
the compressible tubular foam element begins to expand until it
completely fills the annulus 13 between the production assembly 10
and the inside of the well bore, which in this case is lined with
casing string 12, as shown in FIG. 2. When both the degradable wrap
20 and the compressible tubular foam element 18 are both permeable
to the production fluids, the production fluids can be recovered as
soon as the production assembly 10 is installed. This is
illustrated by the arrows in FIGS. 1 and 2, which indicate the
direction of flow of the production fluids.
[0041] In the event that water starts to seep into the production
fluid to the point where it detrimentally effects production, the
production zone 1 can be isolated from the rest of the well using
conventional isolation techniques, which are incorporated into the
present invention as follows. A coil tubing 30 lowers an isolation
pipe 40 into the inside of the production assembly 10, as shown in
FIG. 3 in the region of interest. The isolation pipe 40 is
basically a section of steel pipe that has an outer diameter
smaller than the inner diameter of the base pipe 14. Once the
isolation pipe 40 is lowered into the desired position, each of its
ends are sealed to the inside of the base pipe 14 using known
techniques. The completely installed isolation pipe 40 is shown in
FIG. 4, which illustrates how the isolation pipe 40 blocks the flow
of water into the production tubing. The compressible tubular foam
element 18 creates flow resistance in the axial direction and
thereby retards the flow of water along the annulus 13.
[0042] Therefore, the present invention is well adapted to carry
out the objects and attain the ends and advantages mentioned as
well as those that are inherent therein. While numerous changes may
be made by those skilled in the art, such changes are encompassed
within the spirit of this invention as defined by the appended
claims.
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