U.S. patent application number 16/074443 was filed with the patent office on 2019-02-28 for deformable pouches for zonal isolation.
The applicant listed for this patent is SCHLUMBERGER TECHNOLOGY CORPORATION. Invention is credited to Olga Petrovna ALEKSEENKO, Svetlana Viktorovna NESTEROVA, Dmitriy Ivanovich POTAPENKO, Alexey Alexandrovich SOVA.
Application Number | 20190063181 16/074443 |
Document ID | / |
Family ID | 59499987 |
Filed Date | 2019-02-28 |
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United States Patent
Application |
20190063181 |
Kind Code |
A1 |
NESTEROVA; Svetlana Viktorovna ;
et al. |
February 28, 2019 |
DEFORMABLE POUCHES FOR ZONAL ISOLATION
Abstract
A method for plugging or sealing voids in a formation may
include introducing deformable pouches enclosing solid particulate
materials into a fluid being pumped down the well; and injecting
the deformable pouches into the voids of the formation; wherein at
least one dimension of the deformable pouches may be between about
1 mm and 100 mm.
Inventors: |
NESTEROVA; Svetlana Viktorovna;
(Novosibirsk, RU) ; POTAPENKO; Dmitriy Ivanovich;
(Sugar Land, TX) ; ALEKSEENKO; Olga Petrovna;
(Novosibirsk, RU) ; SOVA; Alexey Alexandrovich;
(Novosibirsk, RU) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SCHLUMBERGER TECHNOLOGY CORPORATION |
Sugar Land |
TX |
US |
|
|
Family ID: |
59499987 |
Appl. No.: |
16/074443 |
Filed: |
February 1, 2016 |
PCT Filed: |
February 1, 2016 |
PCT NO: |
PCT/RU2016/000035 |
371 Date: |
August 1, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09K 8/035 20130101;
C09K 8/80 20130101; C09K 8/665 20130101; C09K 8/805 20130101; C04B
40/0028 20130101; C09K 8/68 20130101; C04B 2103/0077 20130101; C09K
8/426 20130101; E21B 33/138 20130101; E21B 43/261 20130101; E21B
43/11 20130101 |
International
Class: |
E21B 33/138 20060101
E21B033/138; E21B 43/26 20060101 E21B043/26; E21B 43/11 20060101
E21B043/11 |
Claims
1. A method for plugging or sealing voids in a formation,
comprising: introducing deformable pouches enclosing solid
particulate materials into a fluid being pumped down the well; and
injecting the deformable pouches into the voids of the formation;
wherein at least one dimension of the deformable pouches may be
between about 1 mm and 100 mm.
2. The method of claim 1, wherein a shell of the deformable pouches
are made of a film or fabric that is partially or completely
destroyed in the downhole environment.
3. The method of claim 2, wherein the film or fabric is at least
partially degradable, soluble, reactible, or meltable in the
downhole environment.
4. The method of claim 2, wherein the film or fabric include at
least one of polylactic acid, polyesters, polyamides, polyglycolic
acid, polyurethanes, polyethers, anhdyrides, and copolymers
thereof.
5. The method of claim 2, wherein the thickness of the film or
fabric ranges from about 0.01 mm to about 5 mm.
6. The method of claim 1, wherein the deformable pouches include at
least one pin hole fluidly connecting the outside of the pouch to
the interior portion of the pouch.
7. The method of claim 1, wherein the solid particulate materials
enclosed by the deformable pouches includes at least one of fibers,
flakes, platelets, ribbons, rods, precipitated material from
chemical reactions, grains, pellets, spherical materials.
8. The method of claim 1, wherein the solid particulate materials
enclosed by the deformable pouches includes at least one of plastic
beads, sand, ceramic beads, glass, wax beads, oil-soluble resins,
benzoic acid flakes, cellophane flakes, crushed nut shells, crushed
shells, ceramic proppant, silica flour, granulated polylactic acid
(PLA), polyglycolic acid (PGA), rock salt, alumina, and calcium
carbonate, polyethylene beads, glass beads, resin coated ceramic
proppant including curable and procured resin coated ceramic, resin
coated sand including curable and procured resin coated sand.
9. The method of claim 1, wherein the solid particulate material
enclosed by the deformable pouches is partially or completely
destroyed in the downhole environment.
10. The method of claim 1, wherein the solid particulate material
enclosed by the deformable pouches is substantially stable in the
downhole environment.
11. The method of claim 1, wherein at least one dimension of the
deformable pouches is between about 1 mm and 50 mm.
12. The method of claim 1, wherein at least one dimension of the
deformable pouches is between about 1 mm and 25 mm.
13. The method of claim 1, wherein at least one dimension of the
deformable pouches is between about 1 mm and 10 mm.
14. The method of claim, further comprising: pre-soaking the
deformable pouches in a fluid prior to the introducing.
15. A method for fracturing a wellbore, comprising: perforating a
wellbore casing to form a perforation cluster in a first zone of a
wellbore casing; subjecting the perforation cluster in the first
zone to a fracturing treatment; pumping a fluid including
deformable pouches downhole; and injecting the deformable pouches
into voids in the formation behind the first zone of the wellbore
casing.
16. The method for fracturing a wellbore of claim 15, further
comprising: repeating the perforating the wellbore casing to form a
perforation cluster in a wellbore casing, subjecting the formed
perforation cluster to a fracturing treatment, pumping a fluid
including deformable pouches downhole, and injecting the deformable
pouches into voids in the formation until a plurality of zones in
the wellbore casing are fractured.
17. The method of claim 15, wherein a shell of the deformable
pouches are made of a film or fabric that is partially or
completely destroyed in the downhole environment.
18. A method for plugging or sealing voids in a formation,
comprising: introducing deformable pouches enclosing solid
particulate materials into a fluid being pumped down the well; and
injecting the deformable pouches into the voids of the formation
located behind the wellbore casing; wherein at least one dimension
of the deformable pouches may be between about 1 mm and 100 mm; and
wherein the deformable pouches are partially or completely
destroyable in the downhole environment.
19. A method for plugging or sealing voids in a formation,
comprising: introducing deformable pouches enclosing solid
particulate materials into a fluid being pumped down the well; and
packing the deformable pouches into the voids of the formation;
wherein at least one dimension of the deformable pouches may be
between about 1 mm and 100 mm; and wherein the deformable pouches
are substantially stable in the downhole environment.
20. The method of claim 19, wherein the plugging or sealing voids
in a formation occurs during a drilling or cementing process.
Description
BACKGROUND
[0001] Treatments of horizontal oil and gas wells as well as
vertical or declined wells in multi-layered formations frequently
require using diverting techniques in order to enable the
redirection of applied treatments between different zones. Some
commonly used diverting methods include, but are not limited to,
using mechanical isolation devices such as packers and wellbore
plugs, setting bridge plugs, pumping wellbore fluids containing
ball sealers, or pumping wellbore fluids containing blends of
particles with fibers/flakes.
[0002] The use of wellbore fluids containing ball sealers for
treatment diversion includes introducing ball-shaped sealers into
the well, where they are delivered by the pumping fluid to the
perforation holes in the casing where they become lodged or seated.
Once seated, a ball sealer prevents the fluid penetration from the
wellbore into the zone behind casing. That blockage increases
pressure in the wellbore and enables the redirection of applied
treatments to another unblocked zone(s) where no or little
stimulation activity has happened. Although ball sealers provide
efficient and cost-effective solution there are still some problems
with their sealing and seating effectiveness. For example, the
deviation of actual geometry of the perforation entry from the
shape of an ideal circle may lead to incomplete stopping of
wellbore fluid penetration into the sealed zone. Another problem
can be the early release of the ball sealers from the perforations,
often due to a temporary reduction of wellbore pressure during a
treatment, resulting in the unintended opening of the sealed
zone.
[0003] Using particulate materials (e.g., particle blends and/or
fibers/flakes) for treatment diversion is based on the bridging of
the particulates in narrow voids behind the casing, typically in
fractures or wormholes within the formation, with subsequent
accumulation of particles on the created bridge to form a plug
within the void/fracture. However, it is difficult to predict the
distance from the wellbore where particles will eventually bridge,
making it difficult to estimate the volume of particulate materials
required for successful diversion. Further, there can be a reduced
bridging ability of the diverting particulate slurry during pumping
because of its dilution with wellbore fluid during the pumping
downhole (interface mixing). Additionally, when using a blend of
particles of different sizes a higher than expected permeability of
the formed plugs is often observed because of the separation of
particles during pumping into groups of particles of specific
sizes. FIG. 1 depicts a graphical representation (not to scale) of
how an initially homogenously blended particulate slurry 10 can
become a size-segmented fluid 12 during pumping downhole. The
size-segmentation effect may be more noticeable when the pumping of
the particle blend occurs over longer wellbore lengths in order to
arrive at the void/fracture needing to be plugged for treatment
diversion.
SUMMARY
[0004] In one aspect, embodiments disclosed herein relate to a
method for plugging or sealing voids in a formation that includes
introducing deformable pouches enclosing solid particulate
materials into a fluid being pumped down the well; and injecting
the deformable pouches into the voids of the formation; wherein at
least one dimension of the deformable pouches may be between about
1 mm and 100 mm.
[0005] In another aspect, embodiments disclosed herein relate to a
method for fracturing a wellbore that includes perforating a
wellbore casing to form a perforation cluster in a first zone of a
wellbore casing; subjecting the perforation cluster in the first
zone to a fracturing treatment; pumping a fluid including
deformable pouches downhole; and injecting the deformable pouches
into voids in the formation behind the first zone of the wellbore
casing.
[0006] In yet another aspect, embodiments disclosed herein relate
to a method for plugging or sealing voids in a formation that
includes introducing deformable pouches enclosing solid particulate
materials into a fluid being pumped down the well; and injecting
the deformable pouches into the voids of the formation located
behind the wellbore casing; wherein at least one dimension of the
deformable pouches may be between about 1 mm and 100 mm; and
wherein the deformable pouches are partially or completely
destroyable in the downhole environment.
[0007] In yet another aspect, embodiments disclosed herein relate
to a method for plugging or sealing voids in a formation that
includes introducing deformable pouches enclosing solid particulate
materials into a fluid being pumped down the well; and packing the
deformable pouches into the voids of the formation; wherein at
least one dimension of the deformable pouches may be between about
1 mm and 100 mm; and wherein the deformable pouches are
substantially stable in the downhole environment.
[0008] Other aspects and advantages of the invention will be
apparent from the following description and the appended
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0009] FIG. 1 shows a graphical representation of the
size-segmentation of a blended particulate slurry during pumping
downhole.
[0010] FIG. 2 shows an illustration of a use of deformable pouches
according to an embodiment of the present disclosure.
[0011] FIG. 3 shows a schematic of a modified flow injector.
[0012] FIG. 4 depicts a flow chart for a multi-stage hydraulic
fracturing treatment using the deformable pouches for fluid
diversion between the treatment stages.
[0013] FIG. 5 depicts the laboratory setup to mimic a void in a
formation and test its plugging by deformable pouches.
[0014] FIG. 6 shows the results obtained for the pressure drop
across the plug formed during the experiment of Example 2.
DETAILED DESCRIPTION
[0015] Embodiments disclosed herein relate to generally relates to
using deformable pouches for wellbore operations. More
specifically, embodiments of the present disclosure may relate to
using deformable pouches for isolating perforated zones in cased
and cemented wells during a multi-stage hydraulic fracturing
treatment. During a multi-stage hydraulic fracturing treatment,
zonal isolation may be required for diverting stimulating fluid
away from certain perforated zones (e.g., already treated zones) so
that the stimulating fluid may act upon and stimulate other
perforated zones within the wellbore. Although some of the
following discussion emphasizes diversion using deformable pouches
in fracturing, a skilled artisan would readily recognize that the
deformable pouches and methods of employing them described herein
may be used prior to, during, or after many other wellbore
operations (e.g., drilling, cementing, etc.). Some embodiments
shall be described in terms of treatment of horizontal wells, but
are equally applicable to wells of any orientation. Some
embodiments shall be described for hydrocarbon production wells,
but it is to be understood that they may be used for wells for
production of other fluids, such as water or carbon dioxide, or,
for example, for injection or storage wells.
[0016] In general, embodiments of the deformable pouches include an
impermeable or moderately permeable shell (the pouch) enclosing a
particulate filling material. The deformable pouches are included
in a wellbore fluid which may then carry the deformable pouches
downhole. The wellbore fluid that acts as a carrier fluid for the
deformable pouches may be aqueous, oleaginous, or emulsions
thereof--either of which may be optionally viscosified with a
gelling agent. The size of the deformable pouches is a primary
consideration for embodiments according to this disclosure and the
overall size should be such that the deformable pouches are small
enough, or in some instances deformable enough, to be able to pass
through the perforations within the wellbore casing, but large
enough to lodge into or plug the voids in the formation behind the
casing, while not penetrating too deeply into the formation. In
practice, two mechanisms may exist for the plugging of a void
within the formation by the application of deformable pouches
downhole: (1) the jamming of a void by a single pouch with a larger
cross section than that of a point in the void (e.g., may jam at
the throat or entrance of the void or may jam at a point further
within the void); or (2) the formation of a bridge by the
simultaneous arrival and agglomeration of multiple pouches within
the void.
[0017] For example, FIG. 2 depicts a top-down sectional view of a
wellbore illustrating the lodging/plugging that may occur after
deformable pouches proceed past a perforation in the wellbore
casing and accumulate in the void(s) of the formation.
Specifically, FIG. 2 shows a formation 304 having a wellbore 312
formed therein. A casing 310 that lines wellbore 312 has a
perforation 308 therein, exposing a void 302 (specifically a
fracture in this embodiment) in the formation 304. A plug 300
comprised of a plurality of deformable pouches 306 forms within the
void 302 in the formation 304 when the deformable pouches are small
enough or deformable enough to pass through the perforation 308.
While the illustrated embodiment shows the void as a fracture, it
will be understood that in one or more embodiments, a void in the
formation may include wormholes, perforation tunnels, hydraulic
fractures, vugs, pores, or the like.
[0018] The deformability of the pouches renders the actual initial
shape of the pouch somewhat irrelevant and in general, there are no
limitations upon the shape of the deformable pouch as long as the
deformable pouch is sized, shaped, and/or deformable enough to seal
or plug a void from within the void (as opposed to on the wall of
the wellbore). For example, and as the top-down sectional view of a
wellbore shown in FIG. 2 depicts, once the deformable pouches 306
pass through the casing perforation and void opening 308 and
encounter a restriction in the void space 302 of the formation 304,
the pouches will be stressed and their shape will be deformed under
the pressure imposed upon them by the wellbore fluid pushing the
deformable pouches 306 against the formation 304 lodging them
therein to form a plug 300. Indeed, the ability of the pouches to
deform may actually facilitate the formation of a tighter seal or
plug with a smaller volume of open space or open volume (e.g.,
smaller pores and lower permeability) in the formation voids than
what can be achieved by a similar volume of rigid particulates that
are not applied within the confines of a deformable pouch. In one
or more embodiments, the permeability of the obtained seals or
plugs in the voids may be from about 0.05-10 Darcy, or more
specifically about 0.8 Darcy. This sealing effect may be likened to
the ability of stacked sandbags to prevent the ingress of rising
water due to the ability of the sandbags to deform under the
pressure exerted by their stacking. Conveniently, methods using the
deformable pouches may be capable of forming plugs that are
adaptable to the size and shape heterogeneity of the voids
encountered downhole and therefore may be successful in a wider
variety of applications and/or in a smaller overall volume than
particulates on their own (e.g., not enclosed in a pouch). Indeed,
in some embodiments, a total bulk volume of deformable pouches,
including their fluid and/or particulate content, needed for the
isolation of a perforation cluster with 12 perforations may be as
low as about 2 liters with a total weight of less than 1 kg. This
is significantly less than for traditional free form particulate
diverters such as rock salt or benzoic acid flakes which may
require pumping over 25 kg of diverting material per perforated
cluster.
[0019] In one or more embodiments, at least one dimension of the
deformable pouches may be between about 1 mm and 100 mm. In more
specific embodiments, at least one dimension of the deformable
pouches may be between about 1 mm and 50 mm. In even more specific
embodiments, at least one dimension of the deformable pouches may
be between about 1 mm and 25 mm. In some embodiments, at least one
dimension of the deformable pouches may be between about 1 mm and
10 mm. Further, the deformable pouches may possess at least two
dimensions or each of its dimensions between one of the ranges
presented above.
[0020] In one or more embodiments, the shell of the deformable
pouches may be fabricated from a film or a fabric that is flexible
and deformable, while also being impermeable or substantially
impermeable to fluid flow therethrough. However, in one or more
embodiments, the pouches may be moderately permeable. In some
embodiments, the film or the fabric may be partially or completely
destroyed in the downhole environment. For example, the film or
fabric may be a material that is at least partially degradable,
soluble, reactible, meltable or otherwise destroyable in the
downhole environment as a result of the conditions inherent therein
or as a result of the addition of a species (e.g., chemical
reactant, pH modifier, etc.) to induce their destruction. Partial
destruction of the film or fabric making up the deformable pouches
may occur when at least 5%, or in some embodiments at least 50%, of
the film or fabric is destroyed. Further, in some embodiments, the
destruction of the deformable pouches may be engineered to occur
over predetermined amount of time, thereby allowing the deformable
pouches to be emplaced within voids of the formation intact prior
to experiencing substantial destruction, or in some instances, any
destruction. Some examples of dissolvable or degradable materials
that may be used to create the deformable pouches include
polylactic acid (PLA), polyesters and copolymers thereof,
polyamides and copolymers thereof, polyglycolic acid, anhdyrides,
polyethers and copolymers thereof, polyurethanes and the like.
[0021] Non-limiting examples of degradable materials that may be
used include certain polymer materials that are capable of
generating acids upon degradation. These polymer materials may
herein be referred to as "polymeric acid precursors"; they can be
used as destructible deformable pouch materials or as degradable
diverting particulate materials, depending on their properties.
These materials are typically solids at room temperature. The
polymeric acid precursor materials include the polymers and
oligomers that hydrolyze or degrade in certain chemical
environments under known and controllable conditions of
temperature, time, and pH to release organic acid molecules that
may be referred to as "monomeric organic acids." As used herein,
the expression "monomeric organic acid" or "monomeric acid" may
also include dimeric acid or acid with a small number of linked
monomer units that function similarly to monomer acids composed of
only one monomer unit, in that they are fully in solution at room
temperature.
[0022] Polymer materials may include those polyesters obtained by
polymerization of hydroxycarboxylic acids, such as the aliphatic
polyesters of lactic acid, referred to as polylactic acid; of
glycolic acid, referred to as polyglycolic acid; of 3-hydroxbutyric
acid, referred to as polyhydroxybutyrate; of 2-hydroxyvaleric acid,
referred to as polyhydroxyvalerate; of epsilon caprolactone,
referred to as polyepsilon caprolactone or polycaprolactone; the
polyesters obtained by esterification of hydroxyl amino acids such
as serine, threonine and tyrosine; and the copolymers obtained by
mixtures of the monomers listed above. A general structure for the
above described homopolyesters is:
H--{O--[C(R1,R2)].sub.x--[C(R3,R4)].sub.y--C.dbd.O}.sub.z--OH
[0023] Where R1, R2, R3, and R4 are either H, linear alkyl, such as
CH3, CH.sub.2CH.sub.3 (CH.sub.2).sub.nCH.sub.3, branched alkyl,
aryl, alkylaryl, a functional alkyl group (bearing carboxylic acid
groups, amino groups, hydroxyl groups, thiol groups, or others) or
a functional aryl group (bearing carboxylic acid groups, amino
groups, hydroxyl groups, thiol groups, or others); x is an integer
between 1 and 11; y is an integer between 0 and 10; and z is an
integer between 2 and 50,000.
[0024] Under appropriate conditions (pH, temperature, water
content) polyesters such as those described here may hydrolyze and
degrade to yield hydroxycarboxylic acids and compounds such as
those acids referred to in the foregoing as "monomeric acids."
[0025] One example of a suitable degradable polymeric acid
precursor, as mentioned above, is the polymer of lactic acid,
sometimes called polylactic acid, "PLA," polylactate or
polylactide. Lactic acid is a chiral molecule and has two optical
isomers. These are D-lactic acid and L-lactic acid. The
poly(L-lactic acid) and poly(D-lactic acid) forms are generally
crystalline in nature. Polymerization of a mixture of the L- and
D-lactic acids to poly(DL-lactic acid) results in a polymer that is
more amorphous in nature. In one or more embodiments, poly(L-lactic
acid) and poly(D-lactic acid) may be used separately or may be used
as a mixture of both optical isomers. The polymers described herein
are essentially linear. The degree of polymerization of the linear
polylactic acid can vary from as few units as necessary to make
them solids under downhole conditions to several thousand monomeric
units (e.g., 2000-5000). Cyclic structures may also be used. The
degree of polymerization of these cyclic structures may be smaller
than that of the linear polymers. These cyclic structures may
include cyclic dimmers if they are solids under storage and
wellsite ambient conditions.
[0026] Another example is the polymer of glycolic acid
(hydroxyacetic acid), also known as polyglycolic acid ("PGA"), or
polyglycolide. Other materials suitable as polymeric acid
precursors (destructible deformable pouch materials or degradable
diverting particulate materials, depending on their properties) are
all those polymers of glycolic acid with itself or with other
hydroxy-acid-containing moieties.
[0027] The polylactic acid and polyglycolic acid may each be used
as homopolymers, which may contain less than about 0.1% by weight
of other comonomers. As used with reference to polylactic acid,
"homopolymer(s)" is meant to include polymers of D-lactic acid,
L-lactic acid and/or mixtures or copolymers of pure D-lactic acid
and pure L-lactic acid. Additionally, random copolymers of lactic
acid and glycolic acid and block copolymers of polylactic acid and
polyglycolic acid may be used. Combinations of the described
homopolymers and/or the above-described copolymers may also be
used.
[0028] Other examples of polyesters of hydroxycarboxylic acids that
may be used as polymeric acid precursors are the polymers of
hydroxyvaleric acid (polyhydroxyvalerate), hydroxybutyric acid
(polyhydroxybutyrate) and their copolymers with other
hydroxycarboxylic acids. Polyesters resulting from the ring opening
polymerization of lactones such as epsilon caprolactone
(polyepsiloncaprolactone) or copolymers of hydroxyacids and
lactones may also be used as polymeric acid precursors.
[0029] Polyesters obtained by esterification of other
hydroxyl-containing acid-containing monomers such as hydroxyamino
acids may be used as polymeric acid precursors. Naturally occurring
amino acids are L-amino acids. The three most common amino acids
that contain hydroxyl groups are L-serine, L-threonine, and
L-tyrosine. These amino acids may be polymerized to yield
polyesters at the appropriate temperature and using appropriate
catalysts by reaction of their alcohol and their carboxylic acid
groups. D-amino acids are less common in nature, but their polymers
and copolymers may also be used as polymeric acid precursors
(destructible deformable pouch or degradable diverting particulate
materials, depending upon properties). NatureWorks, LLC,
Minnetonka, Minn., USA, produces solid cyclic lactic acid dimer
called "lactide" and from it produces lactic acid polymers, or
polylactates, with varying molecular weights and degrees of
crystallinity, under the generic trade name NATUREWORKS.TM. PLA.
The PLAs currently available from NatureWorks, LLC have number
average molecular weights (M.sub.n) of up to about 100,000 and
weight averaged molecular weights (M.sub.w) of up to about 200,000,
although any polylactide (made by any process by any manufacturer)
may be used. Those available from NatureWorks, LLC typically have
crystalline melt temperatures of from about 120 to about
170.degree. C., but others are obtainable. Poly(d,l-lactide) of
various molecular weights is also commercially available from
Bio-lnvigor, Beijing and Taiwan. Bio-lnvigor also supplies
polyglycolic acid (also known as polyglycolide) and various
copolymers of lactic acid and glycolic acid, often called
"polygalactin" or poly(lactide-co-glycolide).
[0030] The extent of the crystallinity can be controlled by the
manufacturing method for homopolymers and by the manufacturing
method and the ratio and distribution of lactide and glycolide for
the copolymers. Additionally, the chirality of the lactic acid used
also affects the crystallinity of the polymer. Polyglycolide can be
made in a porous form. Some of the polymers dissolve very slowly in
water before they hydrolyze.
[0031] Amorphous polymers may be useful in certain applications. An
example of a commercially available amorphous polymer is that
available as NATUREWORKS 4060D PLA, available from NatureWorks,
LLC, Which is a poly(DL lactic acid) and contains approximately 12%
by Weight of D-lactic acid and has a number average molecular
weight (M.sub.n) of approximately 98,000 g/mol and a weight average
molecular weight (M.sub.w) of approximately 186,000 g/mol.
[0032] Other polymer materials that may be useful are the
polyesters obtained by polymerization of polycarboxylic acid
derivatives, such as dicarboxylic acid derivatives With
polyhydroxy-containing compounds, in particular dihydroxy
containing compounds. Polycarboxylic acid derivatives that may be
used are those of dicarboxylic acids such as oxalic acid,
propanedioic acid, malonic acid, fumaric acid, maleic acid,
succinic acid, glutaric acid, pentanedioic acid, adipic acid,
phthalic acid, isophthalic acid, terphthalic acid, aspartic acid,
or glutamic acid; polycarboxylic acid derivatives are those such as
of citric acid, poly and oligo acrylic acid and methacrylic acid
copolymers; other materials that may be used if they are solids, or
may be used as starting materials for polymerization if they are
liquids, are dicarboxylic acid anhydrides, such as, maleic
anhydride, succinic anhydride, pentanedioic acid anhydride, adipic
acid anhydride, phthalic acid anhydride; dicarboxylic acid halides,
primarily dicarboxylic acid chlorides, such as propanedioic acyl
chloride, malonyl chloride, fumaroyl chloride, maleyl chloride,
succinyl chloride, glutaroyl chloride, adipoyl chloride, and
phthaloyl chloride. Useful polyhydroxy containing compounds for
making useful degradable polymers are those dihydroxy compounds
such as ethylene glycol, propylene glycol, 1,4butanediol,
1,5pentanediol, 1,6hexanediol, hydroquinone, resorcinol, bisphenols
such as bisphenol acetone (bisphenol A) or bisphenol formaldehyde
(bisphenol F); and polyols such as glycerol. When both a
dicarboxylic acid derivative and a dihydroxy compound are used, a
linear polyester results. It is understood that when one type of
dicarboxylic acid is used, and one type of dihydroxy compound is
used, a linear homopolyester is obtained. When multiple types of
polycarboxylic acids and/or polyhydroxy containing monomers are
used, copolyesters are obtained. According to the Flory Stockmayer
kinetics, the "functionality" of the polycarboxylic acid monomers
(number of acid groups per monomer molecule) and the
"functionality" of the polyhydroxy containing monomers (number of
hydroxyl groups per monomer molecule) and their respective
concentrations, determine the configuration of the polymer (linear,
branched, star, slightly crosslinked or fully crosslinked). All
these configurations can be hydrolyzed or "degraded" to carboxylic
acid monomers, and therefore can be considered as polymeric acid
precursors (solids that can be used as destructible deformable
pouch components or as degradable diverting particulate material
components). As one non-limiting example, not descriptive all the
possible polyester structures that can be used, but providing an
indication of the general structure of the most simple cases
encountered, the general structure for the linear homopolyesters
useful is:
H--{O--R1-O--C.dbd.O--R2-C.dbd.O}.sub.z--OH
[0033] Where R1 and R2 are linear alkyl, branched alkyl, aryl, and
alkylaryl groups; and z is an integer between 2 and 50,000.
[0034] Other examples of suitable polymeric acid precursors are the
polyesters derived from phthalic acid derivatives such as
polyethylene terephthalate (PET), polybutylene terephthalate (PBT),
polyethylene naphthalate (PEN), and the like.
[0035] Under the appropriate conditions (for example pH,
temperature, and water content) polyesters such as those described
herein can "hydrolyze" and "degrade" to yield polycarboxylic acids
and polyhydroxy compounds, regardless of the original polyester
synthesized from any of the polycarboxylic acid derivatives listed
above. The polycarboxylic acid compounds yielded by the polymer
degradation process are also considered monomeric acids.
[0036] Other examples of polymer materials that may be used are
those obtained by the polymerization of sulfonic acid derivatives
with polyhydroxy compounds, such as polysulphones or phosphoric
acid derivatives with polyhydroxy compounds, such as
polyphosphates.
[0037] Such solid polymeric acid precursor material may be capable
of undergoing an irreversible breakdown into fundamental acid
products downhole. As referred to herein, the term "irreversible"
will be understood to mean that the solid polymeric acid precursor
material, once broken downhole, does not reconstitute downhole,
e.g., the material breaks down in situ but does not reconstitute in
situ. The term "breakdown" refers to both of the two extreme cases
of hydrolytic degradation that the solid polymeric acid precursor
material may undergo, e.g., bulk erosion and surface erosion, and
any stage of degradation in between these two. This degradation can
be a result of, inter alia, a chemical reaction. The rate at which
the chemical reaction takes place may depend on, inter alia, the
chemicals added, temperature and time. The breakdown of solid
polymeric acid precursor materials may or may not depend, at least
in part, on their structure. For instance, the presence of
hydrolyzable and/or oxidizable linkages in the backbone often
yields a material that will breakdown as described herein. The
rates at which such polymers breakdown are dependent on factors
such as, but not limited to, 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. The manner in which the polymer breaks down also may be
affected by the environment to which the polymer is exposed, e. g.,
temperature, presence of moisture, oxygen, microorganisms, enzymes,
pH, and the like.
[0038] Another class of suitable solid polymeric materials that may
be used as destructible deformable pouches and/or degradable
diversion particulate materials inside such pouches includes
polyamides and polyimides. Such polymers may comprise hydrolyzable
groups in the polymer backbone that may hydrolyze under the
conditions that exist downhole. Non-limiting examples of suitable
polyamides include proteins, polyamino acids, nylon, and
poly(caprolactam). Another class of polymers that may be suitable
for use is those polymers that may contain hydrolyzable groups, not
in the polymer backbone, but as pendant groups. Hydrolysis of the
pendant groups may generate a water soluble polymer and other
byproducts. A non-limiting example of such a polymer is
polyvinylacetate, which upon hydrolysis forms water-soluble
polyvinylalcohol and acetate salts. Other suitable materials
include polysaccharides, chitins, chitosans, orthoesters,
polyanhydrides, polycarbonates, poly(orthoesters), poly(ethylene
oxdides), and poly phosphazenes.
[0039] In other embodiments, the film or the fabric may be
substantially stable and non-degradable under downhole conditions.
In one or more embodiments, the film or fabric that is
substantially stable and non-degradable under downhole conditions
may be made from at least one of polyethylene, polyester,
polyamide, polyethylene terephthalate, polysaccharides, cotton,
wool, steel fabric, glass fabric, and asbestos fabric. Skilled
artisans would understand that in order to keep films or fabric
comprising polymeric materials substantially stable and
non-degradable under downhole conditions, it may be useful to use
those materials in specific conditions (e.g. certain temperatures
and/or pH values). For example, in order to limit the hydrolysis
and degradations of some of the polymers it may be useful to use
them solely in situations where a downhole temperature will be
below about 120.degree. C. or in some embodiments below about
80.degree. C. Further, in order to limit the hydrolysis and
degradation of some of the polymers it may be useful to use them
solely in situations where the downhole pH is from about 6-8.
[0040] The thickness and mechanical/chemical properties of the
sheet, film or fabric used to make the deformable pouches may
optionally be designed so that the premature
destruction/degradation/dissolution is prevented or reduced during
the pumping downhole and in the downhole conditions. In some
embodiments, the thickness of the film or fabric that is formed
into the deformable pouches may range from about 0.01 mm to about 5
mm, or from about 0.05 mm to about 2 mm, and potentially from about
0.1 mm to about 1 mm. Optionally, the deformable pouches may be
made with several layers of film or fabric, for example up to about
10 layers, which may be the same or different material. The use of
multiple layers may increase the mechanical stability of the
deformable pouches and/or allow for better control of the
dissolution time of the deformable pouch. Additionally, in some
embodiments, the deformable pouch may include at least one pin hole
fluidly connecting the outside of the pouch to the interior portion
of the pouch. The at least one pin hole may serve to equalize the
pressure between the inside of the pouches and wellbore during the
pumping of the pouches downhole, thereby preventing or reducing
their premature destruction due to differential pressure effects
(e.g., by bursting or otherwise opening and emptying the contents
therein).
[0041] The particulate materials enclosed within the deformable
pouches may be described here in terms of solid diverting materials
used in fracturing, but the deformable pouches may enclose any
inert or reactive solids, fluids, or combinations of solids and
fluids (e.g., a slurry) to any desired downhole location for any
purpose, such as diversion, fluid loss control, etc. The deformable
pouches are generally either a pre-formed pouch or bag that is then
filled with particulate material or it may be a similarly
structured pouch that is fashioned around the material to be
contained (e.g., a shrinkable film enclosing the material); either
way, it may be sealed or otherwise closed after it is filled with
particulate or other material. The deformable pouch may be referred
to as a shell, envelope, etc. In one or more embodiments, the
particulate materials that are enclosed by the deformable pouches
may be at least one of various fibers, flakes, platelets, ribbons,
rods, precipitated material from chemical reactions, grains,
pellets, spherical materials etc. Non-limiting examples of
particulate materials that may be included within the deformable
pouches include plastic beads, sand, ceramic beads, glass, wax
beads, oil-soluble resins, benzoic acid flakes, cellophane flakes,
crushed nut shells, crushed shells, ceramic proppant, silica flour,
granulated polylactic acid (PLA), polyglycolic acid (PGA), rock
salt, alumina, and calcium carbonate, polyethylene beads, glass
beads, resin coated ceramic proppant including curable and procured
resin coated ceramic, resin coated sand including curable and
procured resin coated sand and mixtures thereof. The particulate
materials enclosed within the deformable pouch may be of any size
as long as they may be enclosed within the deformable pouch and may
include mixtures of particulates of differing sizes and/or
differing shapes (e.g., a mixture of spherical particles and fibers
or flakes).
[0042] In some embodiments, the ability of the deformable pouches
filled with particulate materials to conform to a variety of void
size and shapes under the pressure applied by the wellbore fluid
may facilitate the use of non-uniformly sized and shaped
particulate materials. When enclosed within the deformable pouches,
these solid particulate materials may effectively plug voids within
a formation including, such as vugs, fluid loss pathways, hydraulic
fractures, wormholes etc. In one or more embodiments, the solid
particulate material may be degradable or otherwise destroyable
under downhole conditions as described above for the film or fabric
that makes up the deformable pouch. The use of degradable or
otherwise destroyable particulates may facilitate the clearance of
the plug or seal in the formation, which may be necessary in order
for efficient production from the wellbore. Further, in some
embodiments where the deformable pouches have pin holes, the film
or fabric making up the deformable packages may be substantially
stable under the downhole conditions while the particulate
materials therein may be degradable or otherwise destroyable. In
these instances, the degradation of the particulate materials
within the stable deformable pouch may effectively loosen the seal
or plug formed by the deformable pouches allowing for the clearance
of the plug or seal in the formation without the destruction of the
deformable pouch enclosure. In other embodiments, the solid
particulate material may be substantially stable and maintain their
seal indefinitely under downhole conditions, even if the film or
fabric making up the deformable pouch is eventually destroyed under
the downhole conditions. In some embodiments of deformable pouches,
the use of a stable film or fabric and/or stable particulate
material may be particularly useful for cementing or drilling
applications where plug or seal removal is not completely
necessary.
[0043] Indeed, in some embodiments, the shell of the deformable
pouches may be specifically designed to be degradable downhole
after forming a temporary seal in a void, while the particulate
materials within the pouch remain stable and packed within the void
to leave a highly permeable granulated filler within the void,
allowing the voids to be open for production. For example, in a
more specific embodiment, the shell of the deformable pouches may
be made of degradable or otherwise destroyable materials and may be
filled with non-degradable ceramic proppant. In this embodiment,
the amount of degradable shell material that needs to degrade for
increasing the conductivity within the temporarily sealed zone is
much lower than the volume of the created plug or seal. However, in
other embodiments, the shell and its particulate contents may be
specifically designed to be degradable downhole after forming a
temporary seal in a void, thereby increasing the conductivity of
the near-wellbore zone.
[0044] The deformable pouches are intended to be introduced into a
wellbore and pumped down to a target zone for sealing or plugging a
void in the formation behind the wellbore casing. To introduce the
deformable pouches into the fluid for pumping into the wellbore, a
standard or modified flow injector, for example those used for ball
sealers may be placed in the high pressure line. Such devices are
typically used for injection of larger deformable pouches (those
with a dimension greater than about 10 mm) and the injector is
commonly installed after the pumping units so the deformable
pouches are not subjected to forces that would break or damage them
in the surface equipment. A schematic is shown in FIG. 3.
Deformable pouches (not shown) are loaded into the accumulator 40
via a plug valve 42. The accumulator 40 is isolated from the main
treating line 44 by two remotely operated valves 46. Then the plug
valve 42 to the accumulator 40 is closed, the remotely operated
valves 46 are opened and the deformable pouches are flushed from
the accumulator 40 by the pumping fluid. A simple flow-through
injection apparatus may also be used or the deformable pouches may
be delivered downhole on bailers.
[0045] In one or more embodiments, before pumping the deformable
pouches downhole, they may be pre-soaked in a fluid. This may be
particularly useful when the deformable pouches are provided with
pin holes that may allow the fluid to enter into the pouch and wet
the particulate materials therein. In some embodiments, the
pre-soaking may be used to initiate the dissolution/degradation
processes of the film or fabric making up the deformable pouches
and/or of the particulate materials therein. In some embodiments,
the pre-soaking may be used to reduce the friction between the
particulate materials enclosed within the deformable pouches. The
reduction in friction accomplished by pre-soaking the deformable
pouches may lead to a tighter packing of the pouches in the voids
behind the wellbore casing and may also reduce the risk of the
deformable pouches being destroyed during their pumping
downhole.
[0046] For some applications, such as treatment diversion,
deformable pouches may be used for setting temporary seals or plugs
formed by the pouches and their contents. There are several
mechanisms that may be used or occur during the removal of the
seals formed: (1) self-degradation; (2) reaction with chemical
agents; (3) melting at least one component of a deformable pouch or
its contents; (4) dissolution of at least one component of the
deformable pouches (i.e., the shell or the pouch contents); and (5)
disintegration of at least one component of the deformable pouches
(i.e., the shell or the pouch contents). These mechanisms will be
explained below in further detail.
[0047] Self-degradation may occur when the shell and/or the
particulate materials therein are unstable and degrade under the
temperatures and conditions present downhole. Some examples of
degradable materials are polyesters, including esters of lactic
acid, glycolic acid, other hydroxy acids and copolymers thereof;
polyamides and copolymers thereof; polyethers and copolymers
thereof; polyurethanes, etc. Other examples of degradable materials
which may encompass the film or fabric of the deformable pouches or
their particulate contents were described above.
[0048] In some embodiments, an induced reaction with chemical
agents may occur to chemically react with and thereby remove the
seals or plugs formed by the deformable pouches and/or their
particulate contents. In these instances, chemical agents may be
pumped downhole after the treatment process that necessitated the
sealing or plugging of the formation has completed with the express
purpose of reacting with the deformable pouch and/or its
particulate contents in order to clear the seal or plug. Some
examples of materials that may be removed by reacting with other
agents are carbonates including calcium and magnesium carbonates
and mixtures thereof (reactive to acids and chelating agents); acid
soluble cement (reactive to acids); polyesters including
polyglycolic acid, polylactic acid, esters of lactic acid, glycolic
acid, other hydroxyl acids, and copolymers thereof (can be
hydrolyzed with acids and bases); active metals such as magnesium,
aluminum, zinc and their alloys (reactive to water, acids and
bases), etc.
[0049] In some embodiments, the melting of at least one component
of the deformable pouch (i.e., the shell or pouch contents) may
facilitate the removal of a plug or seal. When the shell or its
contents contains a meltable component, its melting may results in
a reduction of the mechanical stability of the plug, making it
easier to be cleared. Examples of materials that may melt under
downhole conditions include hydrocarbons having 30 or more carbon
atoms; polycaprolactones; paraffins and waxes; carboxylic acids
such as benzoic acid and its derivatives; etc.
[0050] In some embodiments, plug or seal removal may also be
achieved through physical dissolution of at least one of the
components of the deformable pouch (i.e., the shell and/or its
particulate material contents) into the surrounding fluid. The
solubility of the component(s) may depend significantly on the
temperature. In this case, post-treatment temperature recovery in
the sealed zone can trigger the removal of the seal. Materials that
dissolve in water or water-based fluids may include water-soluble
polymers, water-soluble elastomers, carbonic acids, rock salt,
amines, and inorganic salts. Materials that may dissolve in oil or
oil-based fluids may include oil-soluble polymers, oil-soluble
resins, oil-soluble elastomers, polyethylene, carbonic acids,
amines, and waxes.
[0051] In some embodiments, plug or seal removal may be achieved
through the disintegration of the shell or its particulate material
contents into smaller pieces that may be more readily flushed away.
Materials that can disintegrate include plastics such as PLA,
polyamides and composite materials comprising degradable plastics
and non-degradable fine solids. It should be noted that some
degradable materials pass through a disintegration stage during the
degradation process. An example is PLA, which turns into a fragile
material before complete degradation.
[0052] FIG. 4 depicts a flow chart 500 for a multi-stage hydraulic
fracturing treatment using the deformable pouches for fluid
diversion between the treatment stages. In 502, the multi-stage
treatment is initiated by perforating the wellbore casing to form a
perforation cluster. During the perforation the wellbore casing is
perforated and perforation tunnels (formation voids) may be formed
a depth into the formation. In 504, the perforation cluster is
subjected to a fracturing treatment. In 506, a calculated amount of
deformable pouches are pumped downhole for sealing the treated
zone. In 508, the deformable pouches are injected into the
perforation cluster and seal it. In 510, after the plugs or seals
are formed in the treated zone in 508, the perforation gun is moved
for perforating a new zone of the wellbore. The stages may then
repeat for treating other wellbore zones until the desired number
of a plurality of wellbore zones are treated. Further, if no
increase in wellbore pressure is observed after injection of the
deformable pouches, then a plug might not have been formed by the
deformable pouches, and it may be desirable to repeat pumping of
another volume of the pouches or use a different method of
diversion and/or isolation to form a sufficient plug.
[0053] The delivery of solid particulate materials downhole in the
form of deformable pouches may allow for the use of significantly
less solid particulate materials to accomplish a diversion or to
form a plug or seal than by simply adding the particulate materials
to the fluid itself. This is due to the conventional downhole
dilution of the particulate materials being eliminated by their
confinement in the deformable pouch. Further, the use of less
amounts of solid particulate materials downhole reduces the risk of
wellbore plugging during diversion stages or other treatments.
Additionally, not only would using a lower amount of solid
particulate materials downhole save money, it may also reduce the
risk of formation damage from the application of large amounts of
materials downhole, while also enabling more efficient
post-treatment clean-up as a negligible amount of particulate
material would likely remain in the wellbore, thereby eliminating
additional wellbore cleaning that is commonly required after the
application of materials downhole.
EXAMPLES
Example 1
[0054] To demonstrate that deformable pouches can form a plug or
seal with low permeability 20 mm.times.10 mm deformable pouches (a
shell of polyethylene film filled with polylactic acid
particulates) were utilized in a test using the setup shown in FIG.
5 to mimic a void in a formation. The setup includes a tube 80,
which serves as an accumulator for a plug. There is a 6 mm slot 82
on one end and a pump providing for fluid flow 84 on the other end.
Before the experiment the accumulator was filled with deformable
pouches suspended within a 0.5% guar gum solution. Then the
contents of the accumulator was displaced into the slot with water
at a pumping rate of 1 L/min. The permeability of the formed plug
resulting from the deformable pouches blocking the slot was
calculated based upon the pressure drop across the plug of about
400 psi, with the obtained value equaling about 0.8 Darcy. FIG. 6
shows the results obtained for the pressure drop across the
plug.
[0055] While the use of deformable pouches enclosing solid
particulate materials for sealing or plugging voids in a formation
behind a wellbore casing has been described with respect to a
limited number of embodiments, those skilled in the art, having
benefit of this disclosure, will appreciate that other embodiments
can be devised which do not depart from the scope of the invention
as disclosed herein. Accordingly, the scope of the invention should
be limited only by the attached claims.
* * * * *