Note: Descriptions are shown in the official language in which they were submitted.
CA 02908429 2015-09-29
V
WO 2015/065575 PCT/US2014/052546
WELLBORE SERVICING METHODS AND COMPOSITIONS COMPRISING
DEGRADABLE POLYMERS
BACKGROUND
Field
100011 This disclosure relates to methods and compositions for
servicing a wellbore. More
specifically, it relates to methods and compositions for use in a wellbore
penetrating a subterranean
formations.
Background
100021 Natural resources such as gas, oil, and water residing in a
subterranean formation or
zone are usually recovered by drilling a wellbore down to the subterranean
formation while
circulating a drilling fluid in the wellbore. After terminating the
circulation of the drilling fluid, a
string of pipe, e.g., casing, is run in the wellbore. The drilling fluid is
then usually circulated
downward through the interior of the pipe and upward through the annulus,
which is located
between the exterior of the pipe and the walls of the wellbore. Next, primary
cementing is
typically performed whereby a cement slurry is placed in the annulus and
permitted to set into a
hard mass (i.e., sheath) to thereby attach the string of pipe to the walls of
the wellbore and seal the
annulus. Subsequent secondary cementing operations may also be performed.
[00031 Degradable polymers are increasingly becoming of interest in
various subterranean
applications based, at least in part, on their ability to degrade and leave
voids, act as a temporary
restriction to the flow of a fluid, or produce desirable degradation products
(e.g., acids). One
particular degradable polymer that has received recent attention is
poly(lactic acid) because it is a
material that will degrade downhole in aqueous media after it has performed a
desired function or
because its degradation products will perform a desired function (e.g.,
degrade an acid soluble
component, or lower fluid pH to breakdown borate crosslinked fluids).
100041 Degradable polymers may be used to leave voids behind upon
degradation to improve
or restore the permeability of a given structure. For instance, a proppant
pack may be created that
comprises proppant particulates and degradable polymers so that, when the
degradable polymer
degrades, voids are formed in the proppant pack. Similarly, voids also may be
created in a set
cement in a subterranean environment. Moreover, degradable polymers may be
used as a coating
to temporarily protect a coated object or chemical from exposure to the
subterranean environment.
- 1 -
CA 02908429 2015-09-29
V
WO 2015/065575 PCT/US2014/052546
For example, a breaker or some other treatment chemical may be coated,
encapsulated, or encaged
in poly(lactic acid) and used in a subterranean operation such that the
breaker may not be
substantially exposed to the subterranean environment until the poly(lactic
acid) coating
substantially degrades. Still another use for degradable polymers in
subterranean operations
involves creating downhole tools or parts of downhole tools out of solid
masses of a degradable
polymer. In such operations, the degradable polymer may be designed such that
it does not
substantially degrade until the tool has completed its desired function. In
some operations, a tool
function may be temporarily delayed by coating with polylactic acid. Still
other uses for
degradable polymers in subterranean operations include their use as diverting
agents, bridging
agents, and fluid loss control agents.
100051 Generally, degradation of a water-degradable polymer with
suitable chemical
composition and physical properties, for example PLA, may be most likely
achieved over a time
period ranging from about few days to about few weeks at bottom hole
temperatures (BHT) of
above about 60 C (140 17). Unfortunately, many well bores have a BHT that may
be lower than
60 C. In these lower temperature environments, a relatively longer time
(e.g., weeks or even
months) may be necessary for the degradable polymer to hydrolyze and
breakdown, which may be
undesirable. In other situations, degradable polymers which will be stable for
desired durations at
high temperatures under downhole conditions may be needed. Such materials will
be required to be
more resistant to hydrolytic degradation (i.e., polymer chain scission due to
reactions with water).
In such cases, methods to accelerate the reactions with water to break the
polymer down at the end
of an operation in a controlled and predictable manner will be of use. In
general, irrespective of
BHT, it is desirable to be able to control and/or design a fluid composition
with prespecified rates
and durations for degradation and removal of the degradable polymer-based
materials employed to
accomplish timed events or functions in order to minimize waiting-on-
degradation time. It is
understood that in order to flowback out or remove the degradable material
from the location of its
placement, it may not be necessary to break it totally down to the monomer
level. For effective
removal of the material at the end of an intended operation, the percentage of
polymer degradation
needed may be as low as 20%. The polymer plug or filter cake should degrade to
an extent
sufficient to loosen its packed particle density so that a flowing fluid can
break up and flow out the
remaining undegraded particulate material.
- 2 -
CA 02908429 2015-09-29
WO 2015/065575 PCT/US2014/052546
[0006] The quantities of the degradable polymer required to accomplish a
desired objective
depend on the type of application. For example, in a diversion operation
during multistage
fracturing, the amounts of degradable polymer needed may be as high as 250 to
500 lbs/1000 gal.
It would be beneficial to reduce the amount of polymer utilized to accomplish
a particular
operation without sacrificing the intended performance objectives. This would
reduce the cost of
the operation as well as reduce the amount of breakers needed. Additionally,
in some situations it
would be beneficial to incorporate breakers into the degradable material
compositions in amounts
sufficient to achieve a predefined degradation rate and duration at the time
of introducing
degradable material into the formation. Accordingly, an ongoing needs exists
for wellbore
servicing fluids comprising degradable polymers and methods of making and
using same.
SUMMARY
100071 Disclosed herein is a method of servicing a wellbore comprising
providing a degradable
polymer and a delayed action construct within a portion of a wellbore, a
subterranean formation or
both; wherein the delayed action construct comprises (i) a degradation
accelerator comprising an
alkanolamine, an oligomer of aziridine, a polymer of azridine, a diamine, or
combinations thereof,
(ii) a solid support, and (iii) an encapsulating material; and placing the
wellbore servicing fluid
comprising the degradable polymer and delayed action construct into the
wellbore, the
subterranean formation or both.
[0008] The foregoing has outlined rather broadly the features and technical
advantages of the
present invention in order that the detailed description of the invention that
follows may be better
understood. Additional features and advantages of the invention will be
described hereinafter that
form the subject of the claims of the invention. It should be appreciated by
those skilled in the art
that the conception and the specific embodiments disclosed may be readily
utilized as a basis for
modifying or designing other structures for carrying out the same purposes of
the present
invention. It should also be realized by those skilled in the art that such
equivalent constructions
do not depart from the spirit and scope of the invention as set forth in the
appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] For a more complete understanding of the present disclosure and the
advantages
thereof, reference is now made to the following brief description, taken in
connection with the
accompanying drawings and detailed description, wherein like reference
numerals represent like
parts.
-3.
CA 02908429 2015-09-29
WO 2015/065575 PCT/US2014/052546
10010] Figure 1 is a picture of polymer swelling in the presence of water
and materials of the
present disclosure at 140 F over a 2-day period.
[0011] Figures 2A-2C depict various embodiments of the compositions and
methods of this
disclosure.
DETAILED DESCRIPTION
[0012] It should be understood at the outset that although an illustrative
implementation of one
or more embodiments are provided below, the disclosed systems and/or methods
may be
implemented using any number of techniques, whether currently known or in
existence. The
disclosure should in no way be limited to the illustrative implementations,
drawings, and
techniques below, including the exemplary designs and implementations
illustrated and described
herein, but may be modified within the scope of the appended claims along with
their full scope of
equivalents.
[0013] The methods of the present disclosure generally comprise providing a
degradable
aliphatic polymer, comprising carboxy functional groups in the polymer
backbone derived from
hydroxyalkanoic acid monomers, within a portion of a wellbore and/or
subterranean formation,
introducing a degradation accelerator (DA) to the portion of the wellbore
and/or subterranean
formation, and allowing the DA to degrade or accelerate the degradation of the
degradable
polymer. The DA may be in the form of a pumpable fluid (e.g., present in an
aqueous carrier fluid,
a liquid additive, component of a wellbore servicing fluid, etc...). In some
embodiments, the DA
is a component of a solution. As used herein, the term ''solution" does not
connote any particular
degree of dissolution or order of mixing of the substances present in the
solution. In an
embodiment, the DA is a component of an assembly of materials which functions
to accelerate the
degradation of one or more of the degradable polymers disclosed herein.
[0014] In some embodiments, the DA material may increase the volume of the
degradable
polymer by in situ swelling prior to degradation. In some embodiments, the
portion of the wellbore
and/or subterranean formation where the degradable polymer is located may have
a temperature of
about 140 F (60 C) or less. In some embodiments, the portion of the wellbore
and/or
subterranean formation where the degradable polymer is located may have a
temperature of greater
than about 140 F (60 C). In some exemplary embodiments, at least 20% of the
degradation of the
degradable polymer may take place within a time frame of less than about three
days after the
introduction of the DA solution.
- 4 -
CA 02908429 2015-09-29
WO 2015/065575 PCT/US2014/052546
100151 In an embodiment, the DA comprises an alkanolamine, an oligomer of
aziridines (e.g.,
ethyleneimine), a polymer of aziridine, a diamine, derivatives or combinations
thereof. The term
"derivative" is defined herein to include any compound that is made from one
or more of the DAs,
for example, by replacing one atom in the DA with another atom or group of
atoms, rearranging
two or more atoms in the DA, ionizing one of the DAs. or creating a salt of
one of the DAs. When
describing derivatives herein those materials are contemplated as being
"derived by," "derived
from," "formed by," or "formed from," other materials described herein and
such terms are used in
an informal sense and are not intended to reflect any specific synthetic
methods or procedure,
unless specified otherwise.
[0016] In an embodiment, the DA comprises an alkanolamine. Alkanolamines
are chemical
compounds that contain a hydroxyl group (i.e., -OH) and an amine group, which
may be a primary
amine group, a secondary amine group or a tertiary amine group. An
alkanolamine suitable for use
in the present disclosure is a compound characterized by general Formula I:
HONR1
R2
Formula I
where R1 and R2 may each independently be hydrogen, an unsubstituted alkyl
chain comprising
from about 1 to about 6 carbon atoms, or a substituted alkyl chain comprising
from about 3 to
about 6 carbon atoms. In an embodiment, X comprises a substituted or
unsubstituted alkylene
chain having from about 1 to about 4 carbon atoms. The term "alkyl group" is
used herein in
accordance with the definition specified by IUPAC: a univalent group formed by
removing a
hydrogen atom from an alkane. The term "alkylene" is used herein in accordance
with the
definition specified by IUPAC: the divalent groups formed from alkanes by
removal of two
hydrogen atoms from the same carbon atom. The term "substituted" when used to
describe a group
is intended to describe any non-hydrogen moiety that formally replaces a
hydrogen in that group
and is intended to be non-limiting.
[0017] In an embodiment, Ri and R2 may both be hydrogen, creating a primary
amine; either
R1 or R2 may be a hydrogen, creating a secondary amine; or R1 and R2 may be
substituent groups
other than hydrogen, creating a tertiary amine.
- 5 -
CA 02908429 2015-09-29
WO 2015/065575 PCT/US2014/052546
100181 Nonlimiting examples of alkanolamines suitable for use in the
present disclosure
include monoethanolamine, triethanolamine, diethartolamine,
triisopropanolamine, diglycolamine,
di-2-propanolamine, N-methyldiethanolamine, 2-amino-2-methyl-l-propanol, 2-
piperidineethanol,
aminopropanediol and the like.
100191 In an embodiment, the DA comprises an alkanolamine in the form of an
aqueous
solution with a concentration of from about 10 weight percent (wt.%) to about
99 wt.%,
alternatively from about 40 wt.% to about 85 wt.%, or alternatively from about
50 wt.% to about
80 wt.% based on the total weight of the solution. In an embodiment, the
alkanolamine solution
may have a pH of less than about 11, alternatively less than about 10, or
alternatively less than
about 9.
100201 In an embodiment, the DA comprises oligomers of aziridine or of
aziridine derivatives
(e.g., ethyleneimine). Herein the disclosure may refer to an oligomer of
aziridine and/or an
oligomer of an aziridine derivative. It is to be understood that the terms
aziridine oligomer and
aziridine derivative oligomer herein are used interchangeably. The aziridine
oligomers may
comprise amines containing at least one secondary and/or at least one tertiary
nitrogen, i.e., at least
one secondary (-NH-) and/or at least one tertiary (-1\11 amine group.
Additionally, the aziridine
oligomers may also contain primary nitrogens, i.e., primary amine groups (-
NH2). In an
embodiment, the number of monomers in the aziridine oligomer is less than
about 100,
alternatively less than about 10, or alternatively less than about 5.
100211 In an embodiment, the aziridine oligomer comprises a linear
aziridine oligomer
characterized by general Formula II:
NH
R3 n H
Formula II
where the value of n ranges from about 2 to about 100, alternatively from
about 2 to about 10,
alternatively from about 2 to about 5, or alternatively from about 2 to about
4. In an embodiment,
R3 comprises a primary amine group (-NH2). Alternatively, R3 comprises the
aziridine ring
connected to the repeating oligomer unit through the aziridine ring nitrogen.
In an embodiment,
the aziridine oligomer comprises diethylenetriatnine (i.e., n=2). In an
embodiment, the aziridine
oligomer comprises triethylenetetramine (i.e., n=3). In another embodiment,
the aziridine
oligomer comprises tetraethylenepentamine (i.e., n=4).
- 6 -
CA 02908429 2015-09-29
WO 2015/065575 PCT/US2014/052546
100221 In an embodiment, the aziridine oligomer comprises an aziridine
oligomer
characterized by general Formula III:
R4
NH
R4
Formula III
where the value of m ranges from about 2 to about 100, alternatively from
about 2 to about 10,
alternatively from about 2 to about 5, or alternatively from about 2 to about
4. While the structure
depicted by Formula III only shows one of the hydrogens from the methylene
groups of the
aziridine ring being substituted with a R4 group, both of the aziridine
methylene groups may be
substituted. In an embodiment. R4 and any of the other aziridine methylene
group substituents
comprise methyl groups.
10023] In an embodiment, the aziridine oligomer comprises a branched
aziridine oligomer. In
an embodiment, the branched aziridine oligomer comprises a branched oligo-
ethyleneimine
characterized by general Formula IV:
x
."7".
NH2
Formula IV
where the repeating units may occur in a total amount of about (x+y) with the
total value of (x+y)
ranging from about 2 to about 50, alternatively from about 2 to about 30,
alternatively from about 2
to about 10, or alternatively from about 2 to about 5. In all cases, x or y is
greater than or equal to
1.
100241 In an embodiment, the DA comprises an aziridine oligomer in the form
of an aqueous
solution with a concentration of from about 10 wt.% to about 99 wt.%,
alternatively from about
40 wt.% to about 85 wt.%, or alternatively from about 50 wt.% to about 80 wt.%
based on the total
weight of the solution. In an embodiment, the aziridine oligomer solution may
have a pH of less
than about 11, alternatively less than about 10, or alternatively less than
about 9.
- 7 -
CA 2908929 2017-03-28
[00251 In an embodiment, the DA comprises an aziridine polymer, wherein the
n and m values
in Formula II and Formula III respectively or (x+y) value in Formula IV are
greater than 100,
alternately greater than 1000, or alternately greater than 10000. In an
embodiment, the DA
comprises an aziridine polymer in the form of an aqueous solution with a
concentration of from
about 10 wt.% to about 99 wt.%, alternatively from about 40 wt.% to about 85
wt.%, or
alternatively from about 50 wt.% to about 80 wt.% based on the total weight of
the solution. In an
embodiment, the aziridine polymer solution may have a pH of less than about
11, alternatively less
than about 10, or alternatively less than about 9. An example of an aziridine
polymer suitable for
use in the present disclosure is HZ-20Im crosslinker which is commercially
available from
Halliburton Energy Services, Inc.
[0026] In an embodiment, the DA comprises a diamine. Diamines are chemical
compounds
that contain two amine groups. A diamine suitable for use in the present
disclosure is a compound
characterized by general Foimula V:
R
R7 5NN
R8 R6
Formula V
where R5, R6, R7, and R8 may each independently be hydrogen, an unsubstituted
alkyl chain having
from about 1 to about 3 carbon atoms, or a substituted alkyl chain having from
about 3 to about 4
carbon atoms and Z comprises an unsubstituted alkylene chain having from about
2 to about 6
carbon atoms, or a substituted alkylene chain having from about 2 to about 6
carbon atoms. In an
embodiment, Z comprises 2 carbon atoms resulting in an unsubstituted alkylene
chain (i.e.,
ethylene group). In such an embodiment, at least one of R5, R6, R7, or R8 is
not a hydrogen. In an
embodiment, the diamine DA does not comprise ethylenediamine.
[0027] In an embodiment, the DA comprises a di amine in the form of an
aqueous solution with
a concentration of from about 10 wt.% to about 99 wt.%, alternatively from
about 40 wt.% to about
85 wt.%, or alternatively from about 50 wt.% to about 80 wt.% based on the
total weight of the
solution. In an embodiment, the diaminc solution comprises an aqueous fluid
(e.g., water) and
may have a pH of less than about 11, alternatively less than about 10, or
alternatively less than
about 9.
- 8 -
CA 02908429 2015-09-29
WO 2015/065575 PCT/US2014/052546
100281 In an embodiment, the DA comprises amine nitrogens and/or groups
which are
chemically derivatized to contain an operable functionality or substituent.
The operable
functionality or substituent may be acted upon in any fashion (e.g.,
chemically, physically,
thermally, etc.) and under any conditions compatible with the process in order
to release the DA at
a desired time and/or under desired conditions such as in situ wellbore
conditions (e.g.,
temperature, pH induced hydrolysis). Upon removal of the operable
functionality or substituent,
the active form of the DA can be released and made available for polymer
degradation. In an
embodiment, a DA of the type disclosed herein is utilized in high temperature
applications (e.g., at
temperatures greater than about 90 C, alternatively greater than about 120
C, or alternatively
greater than about 150 C). Any suitable operable functionality or substituent
or methods for
preparing DAs containing operable functionalities or substituents may be
employed. A
nonlimiting example of such methodologies include acylation of primary or
secondary nitrogen
atoms or the alcohol groups of the DA molecules utilizing any suitable
acylating agent such as acid
anhydrides, esters, anhydrides and acid chlorides. An example of a chemically
derivatized DA
comprising amine nitrogens is tetracetyl ethylene diamine, which upon in situ
hydrolysis in a well
bore or formation can generate a mixture of amines which function as DAs of
the type disclosed
herein. In an embodiment, a chemically derivatized DA is insoluble in the
aqueous fluid.
100291 Degradable aliphatic polymers suitable for use in the methods of the
present disclosure
are those capable of being degraded by water in an aqueous solution through a
mechanism
described herein or any other suitable mechanism, and comprise carboxy (-000-)
functional
groups in the polymer backbone. Examples of functional groups that comprise
¨000- groups
include esters (C-COO-C), carbonates (C-O-COO-C), and carbamates (C-N-COO-C).
This
degradation may be the result of a chemical reaction with water under neutral
pH conditions, acid
or base- catalyzed conditions, under thermally-activated conditions, or a
combination thereof, and
the degradation may occur over time as opposed to immediately. In some
embodiments,
degradation of the degradable polymers may be the result of hydrolytic and/or
aminolytic
degradation in the presence of DA materials of the type disclosed herein. The
terms "degrading,"
"degradation," and "degradable" refer to both the relatively extreme cases of
hydrolytic or
aminolytic degradation that the degradable polymer may undergo, i.e.,
heterogeneous (or bulk
erosion) and homogeneous (or surface erosion) down to the monomer level, and
any stage of
degradation in between. The terms "polymer" or "polymers" as used herein do
not imply any
- 9 -
= CA 02908429 2015-09-29
WO 2015/065575 PCT/US2014/052546
particular degree of polymerization; for instance, oligomers are encompassed
within this definition
provided that such materials are solid particulates, and remain substantially
insoluble in an aqueous
medium for at least 3 to 8 hours at BHT.
100301 In some instances, the degradable polymer may be capable of
releasing a desirable
degradation product, e.g., an acid or a base or a neutral molecule, during its
degradation. Among
other things, the degradable polymers capable of releasing an acid may degrade
after a desired time
to release an acid, for example, to degrade a filter cake, to lower pH or to
reduce the viscosity of a
treatment fluid. Alternately, the degradable polymers capable of releasing
acidic, neutral or basic
materials may degrade after a desired time to release such materials, for
example, to chelate metal
ions capable of forming soluble materials to prevent scale depositions in the
permeable portions of
the formation.
100311 In an embodiment, the degradable polymer comprises carboxylic
acid-derived (i.e.,
-000-) functional groups on the polymer backbone. Examples of suitable
degradable polymers
that may be used in conjunction with the methods of this disclosure include,
but are not limited to,
aliphatic polyesters, poly(lactides), poly(glycolides), poly(c-caprolactones),
poly(hydroxy ester
ethers), poly(hydroxybutyrates), poly(anhydrides), poly(carbonates),
poly(ether esters), poly(ester
amides), poly(carbamates) and copolymers, blends, derivatives, or combinations
of any of these
degradable polymers. The term "derivative" is defined herein to include any
compound that is
made from one of the listed compounds, for example, by replacing one atom in
the listed
compound with another atom or group of atoms, rearranging two or more atoms in
the listed
compound, ionizing one of the listed compounds, or creating a salt of one of
the listed compounds.
The term "copolymer" as used herein is not limited to copolymerization of a
combination of two
monomers, but includes any combination of any number of monomers, e.g., graft
polymers,
terpolymers and the like. For example, suitable copolymers may include an
aliphatic polyester that
is grafted with polyethylene oxide or polyacrylamide, or block polymers
containing one or more
blocks containing a carboxy (-000-) group and another block containing a non-
carboxy
containing polymer segment such as polyamide, poly(alkylene oxide),
poly(anhydride)
polyacrylamide or poly(AMPS).
[0032] Degradable polymers comprising an anhydride bond may be the
most reactive of the
degradable polymers, e.g., they may have faster degradation rates, even at low
temperatures.
Suitable DA solutions may enhance the rate of a degradation reaction. In
embodiments wherein
- 10 -
CA 02908429 2015-09-29
WO 2015/065575 PCT/US2014/052546
the temperature of the surrounding subterranean formation is low, (e.g.
temperatures in the range
of from about 50 F (10 C) to about 140 F (60 C)), the degradable polymer
used may be an
anhydride, as such degradable polymers are thought to hydrolyze more readily.
According to some
embodiments in which the degradable polymer comprises a polyanhydride, the
degradable polymer
may be made to hydrolyze at a higher temperature by increasing the
hydrophobicity of the
degradable polymer so that water does not reach the hydrolyzable group as
readily. In general, the
hydrophobicity of a polyanhydride may be increased by increasing the size or
carbon number of
hydrocarbon groups in these polymers. Degradable polymers that contain an
ester bond (e.g.
polylactide, polyglycolide, etc.) may degrade more slowly, and when
copolymerized with a
reactive monomer such as an anhydride, the degradation reactivity may be
adjusted to meet some
user and/or process need. Simple melt blends of degradable polymers of
different degradation rates
and/or physical properties may be utilized (e.g., glass transition
temperatures, melting temperature,
crystallization temperatures, and crystalline content) provided at least one
component of such
blends comprises an aliphatic degradable polymer comprising carboxy (-000)
groups in the
polymer backbone. In exemplary embodiments, aliphatic polyesters such as
poly(lactic acid),
poly(anhydrides), and poly(lactide)-co-poly(glycolide) copolymers may be used.
100331 The choice of degradable polymers may depend on the particular
application and the
conditions involved. For example, degradable polymers may include those
degradable materials
that release useful or desirable degradation products, e.g., an acid, base or
neutral compound(s).
Such degradation products may be useful in a downhole application, e.g., to
break a viscosified
treatment fluid or an acid soluble component present therein (such as in a
filter cake), to lower the
pH or to act as scale inhibitors. Other guidelines to consider in selecting a
degradable polymer
include the time required for the requisite degree of degradation and the
desired result of the
degradation (e.g., voids).
100341 In an embodiment, the degradable polymer is an aliphatic polyester,
such as poly(lactic
acid) (PLA). Other degradable polymers comprising carboxy groups (-000-) that
are subject to
hydrolytic and/or aminolytic degradation may also be suitable for use in the
present disclosure. In
embodiments in which the degradable polymer is poly(lactic acid), the
poly(lactic acid) may have
been synthesized 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
a polymer made from
- 11 -
CA 02908429 2015-09-29
WO 20151065575 PCT/US2014/052546
lactides, lactic acid, or oligomers, without reference to the degree of
polymerization. The lactide
monomer exists generally in three different forms: two stereoisomers L- and D-
lactide and racemic
D,L-lactide (meso-lactide).
[0035] The
chirality of the lactide units provides a means to adjust, among other things,
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 disclosure where a slower degradation of the
degradable polymers 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 disclosure. Additionally, they may be
copolymerized with, for
example, glycolide or other monomers like E-caprolactone, 1,5-dioxepan-2-one,
trimethylene
carbonate, or other suitable monomers to obtain polymers with different
properties or degradation
times. The lactic acid stereoisomers can be modified to be used in the present
disclosure by,
among other things, blending, copolymerizing or otherwise mixing the
stereoisomers, by blending,
copolymerizing or otherwise mixing high and low molecular weight poly(lactic
acid), or by
blending, copolymerizing or otherwise mixing a poly(lactic acid) with another
polyester or
polyesters.
[0036]
Plasticizers may be included in the degradable polymers used in the methods of
the
present disclosure. The plasticizers may be present in an amount sufficient to
provide
characteristics that may be desired, for example, to provide tackiness of the
generated degradable
polymers or to provide improved melt processability. In addition, the
plasticizers may enhance the
degradation rate of the degradable polymers. The plasticizers, if used, are at
least intimately
incorporated within the degradable polymers. An example of a suitable
plasticizer for poly(lactic
acid) would include oligomeric lactic acid. Examples of plasticizers that may
be useful in some
embodiments of the present disclosure include, but are not limited to,
polyethylene glycol (PEG);
polyethylene oxide; oligomeric lactic acid; citrate esters (such as tributyl
citrate oligomers, triethyl
citrate, acetyltributyl citrate, and acetyltriethyl citrate); glucose
monoesters; partially hydrolyzed
fatty acid esters; PEG monolaurate; triacetin; poly(c-caprolactone);
poly(hydroxybutyrate);
glycerin- 1-benzoate-2,3-dilaurate; glycerin-2-benzoate- 1,3
-dilaurate; bis(butyl di ethylene
glycol)adipate; ethylphthalylethyl glycolate; glycerin diacetate
monocaprylate; diacetyl monoacyl
- 12 -
CA 02908429 2015-09-29
WO 2015/065575 PCT/US2014/052546
glycerol; polypropylene glycol (and epoxy derivatives thereof); poly(propylene
glycoOdibenzoate;
dipropylene glycol dibenzoate; glycerol; ethyl phthalyl ethyl glycolate;
poly(ethylene
adipate)distearate; di-iso-butyl adipate; or any combinations thereof The
choice of an appropriate
plasticizer will depend on the particular degradable polymer utilized. It
should be noted that, in
certain embodiments, when initially formed, the degradable polymer may be
somewhat pliable.
But once substantially all of the solvent has been removed, the particulates
may harden. More
pliable degradable polymers may be beneficial in certain chosen applications.
The addition of a
plasticizer can affect the relative degree of pliability. Also, the relative
degree of crystallinity and
amorphousness of the degradable polymer can affect the relative hardness of
the degradable
polymers. In turn, the relative hardness of the degradable polymers may affect
the ability of the
DA solutions to degrade the degradable polymer at low temperatures.
100371 In some embodiments in which a degradable polymer is degraded
through a DA
catalyzed, or mediated pathway and/or through a pathway that involves a DA as
the reactant, the
DA solution provides a nucleophile capable of participating in the degradation
of a degradable
polymer in low temperature subterranean environments, for example, at a BHT of
less than about
180 F (82.2 C), alternatively less than about 160 F (71.1 C), or
alternatively less than about 140
F (60 C). Alternatively the degradable polymer is designed for high
temperature applications by
suitably modifying the structure of the polymer.
[0038] The DA solution may provide a nucleophile to accelerate the
degradation rate that
would be possible when the polymer is allowed to degrade in the presence of an
aqueous fluid not
containing the DA solution. Alternatively, a derivatized DA can be used to
delay the release of
active form DA at high temperatures. For example, such high temperatures may
be greater than
about 180 F (82.2 C), alternatively greater than about 250 F (121.1 C) or
alternatively greater
than about 300 '17 (148.9 C).
[0039] In some exemplary embodiments, the degradation of the degradable
polymer in the
presence of the DA solution may take place within a time frame of less than
about 1 month,
alternatively less than about 2 weeks, alternatively less than about 1 week,
or alternatively less than
about 3 days.
[0040] The amount of DA solution that may be used to degrade a degradable
polymer in the
present disclosure will depend on several factors including, but not limited
to, the pH of the DA
solution, the nucleophilicity of nucleophiles present in the solution, the
degradable polymer, the
- 13 -
CA 02908429 2015-09-29
WO 2015/065575 PCT/US2014/052546
temperature of the subterranean formation, the nature of the subterranean
formation, and the
desired time and/or rate of degradation. In some embodiments, the molar ratio
of the DA solution
to the degradable polymer is equivalent (calculated based on the molar
quantities of ¨COO- units
in the polymer, and the molar quantities of nucleophilic centers in the DA
molecules) or slightly
greater than (e.g., about 10%) the stoichiometric ratio. In some embodiments,
the amount of DA
solution is an amount sufficient to degrade equal to or greater than about 20%
of the degradable
polymer, alternatively equal to or greater than about 50% of the degradable
polymer, or
alternatively equal to or greater than about 70% of the degradable polymer
wherein polymer
degradation is measured by degradable polymer weight loss under wellbore
conditions over a
specified duration.
10041 In some embodiments, the degradable polymer may swell and absorb
water in an
aqueous media comprising the DA to a greater extent than the swelling of the
degradable polymer
observed in the aqueous media without the DA solution. In an embodiment, the
DA functions
initially to swell the degradable polymer and later to degrade the degradable
polymer. In another
embodiment, both swelling and degradation of the degradable polymer in the
presence of the DA
solution take place simultaneously. In yet another embodiment, the DA may
swell but not degrade
the degradable polymer, and vice versa.
[0042] In an embodiment, the degradable polymer swells to at least about 2
times its volume,
alternatively at least about 5 times, or alternatively at least about 10 times
in the presence of the
DA solution. In an embodiment, the degradable polymer increases in weight, in
the presence of
DA solution, by at least about 2 times its mass, alternatively at least about
3 times or alternatively
at least about 10 times its mass prior to the reduction in weight as a result
of degradation of the
degradable polymer.
I31 According to certain embodiments of the present disclosure, while not
wanting to be
limited by any particular theory, it is believed that the DA solutions
disclosed herein may degrade
a degradable polymer by way of, inter alia, a nucleophilic substitution
reaction at the carbonyl
carbon of the ¨000- group. Nucleophilic substitution reactions at the carbonyl
carbon of a
carboxy group are generally thought to follow a nucleophilic addition-
elimination mechanism. In
general, a nucleophilic substitution reaction occurs when a nucleophile
becomes attracted to a full
or partial positive charge on an electrophile. During the reaction, the
nucleophile forms a chemical
bond to the electrophile by donating both bonding electrons and displacing
another functional
- 14 -
CA 02908429 2015-09-29
WO 2015/065575 PCT/US2014/052546
group that was previously bonded to the electrophile. Generally, all molecules
or ions with a free
pair of electrons can act as nucleophiles, however, negative ions (anions) may
be more potent than
neutral molecules. A neutral nitrogen atom in a molecule (for example, an
amine) is more
nucleophilic than a neutral oxygen atom in a neutral molecule (for example, in
water, alcohol or
ether). The nucleophiles of the present disclosure may be neutral or
negatively charged Lewis
bases. In general, the more basic the ion (the higher the pKa of the conjugate
acid), the more
reactive the ion may be as a nucleophile. In the degradable polymers of the
current disclosure, the
electrophile is the carbon of a carbonyl group of the ¨000- functional group
in the polymer
backbone.
100441 According to certain embodiments of the present disclosure, while
not wanting to be
limited by any particular theory, it is believed that the DA solutions may
degrade the degradable
polymer through a hydrolytic or arninolytic pathway. The lone electron pair of
any of the amine
groups or any of the lone electron pairs of any hydroxyl or otherwise oxygen-
containing groups in
the DA may act as a nucleophile.
100451 By way of explanation and not of limitation, it is believed that
according to some
embodiments the hydrolysis of a degradable polymer may be expressed by the
following
exemplary pathway in Scheme I:
e
+ H20 -IP' NH- + e0H
-OH
CH3) 0
Hydrolysis
.71..s.T.,0y1Lo
0 CH3
- o
CH3 0
4
0
0 CH3
Degradation
Scheme I
- 15 -
CA 02908429 2015-09-29
WO 2015/065575 PCT/US2014/052546
In the above mechanism, the DA may serve to provide a more reactive hydroxide
ion nucleophile
that increases the rate of polymer degradation compared to when the
degradation is dependent on
reaction with a neutral water molecule.
100461 Similarly, it is believed that according to some embodiments the
aminolysis of a
degradable polymer in an aqueous environment may be expressed by the following
exemplary
pathway in Scheme II:
I-12N ¨R
_ o
CH3 -
R
Aminolysis NH + H
* ____._ Degradation
=
0 CH3 _ 0 CH3
Aquezysderonvirois Hydrolysis ly
-o
CH3
-- .2N R,
Degradation
0
_ 0
Scheme II
where R may be any of the DAs that contain a primary amine group. While Scheme
IT only
depicts the nucleophilic attack by a primary amine group, the same aminolysis
pathway may occur
via a nucleophilic attack by any secondary amine group of the degradation
accelerators described
herein.
100471 In general, the rate of degradation of the degradable polymers
suitable for use in the
present disclosure may be influenced by several factors including temperature,
the type of chemical
bond in the polymer backbone, hydrophilicity or hydrophobicity of the
degradable polymer, the
molecular weight of the degradable polymer, particle size and shape, porosity,
crystallinity, and the
presence of low molecular weight compounds (e.g., MW lower than about 500) in
the degradable
polymer.
[0048] In some embodiments, it is believed that the degradation of the
degradable polymer
may be caused by the reaction of water (i.e., hydrolysis) with a labile -COO-
bond of the
degradable polymer, such as an ester or anhydride bond in a polylactide chain.
The reaction rate
may be closely related to the ability of the degradable polymer to absorb
water. Typically,
hydrophilic polymers are capable of absorbing a larger quantity of water than
a hydrophobic
matrix, and therefore, hydrophilic polymers usually degrade more quickly than
hydrophobic
- 16 -
CA 02908429 2015-09-29
WO 2015/065575 PCPUS2014/052546
matrices. In general, a degradable polymer with a greater amorphous content
may be attacked
more readily by the DA solutions of the present disclosure, and therefore may
hydrolyze more
readily than crystalline materials. Without being limited by theory, it is
believed that hydrolytic
polymer degradation reactions by hydrolysis with water or hydroxide ion (as
shown in Scheme I),
and aminolytic polymer degradation reactions by amine containing groups (as
shown in Scheme II)
may be taking place simultaneously at different rates of which aminolytic
reactions are expected to
be fastest followed by hydrolytic reactions with hydroxide ion. Hydrolytic
reaction rates with
neutral water are expected to be slowest. DA molecules are presumed to
increase the rates of
polymer degradation by providing the faster degradation pathways. Addition of
inorganic bases
such as alkali metal hydroxides or other pH-increasing inorganic material may
increase the rates of
degradation by the hydroxide ion pathway described in Scheme I, but the amine
DA materials
provide faster aminolytic pathways as described in Scheme II, as well as by
the hydrolytic pathway
described in Scheme 1 due to increased levels of hydroxide ion in the aqueous
fluid in the presence
of amines.
[0049] In an embodiment, the degradable polymer comprises amorphous PLA. In
such
embodiments, PLA is degraded by contact with an aqueous solution of
propylenediamine at
temperatures ranging from about 60 F (15.6 C) to about 120 F (48.9 C).
[0050] In an embodiment, the degradable polymer comprises semi-crystalline
PLA. In such
embodiments, PLA is swollen first by contact with an aqueous solution of
triethanolamine and then
degraded with another DA solution at temperatures ranging from about 120 F
(48.9 C) to about
250 F(121.1 C).
[0051] In an embodiment, the degradable polymer comprises poly(glycolic
acid). In such
embodiments. poly(glycolic acid) is degraded by contact with an aqueous
solution of
propylenediamine at temperatures ranging from about 80 I' (26.7 C) to about
150 F (65.6 C).
[0052] In an embodiment, the degradable polymer comprises semi-crystalline
PLA with a
melting point of about 140 F (60 C). In such embodiments, PLA is degraded by
contact with an
aqueous solution of propylenediamine at temperatures ranging from about 100 F
(37.8 C) to
about 200 F (93.3 C).
100531 In an embodiment, the degradable polymer comprises a degradable semi-
crystalline
copolymer with a melting point of about 300 F (148.9 C) having lactic acid
as one of the
monomers. In such embodiments, the PLA copolymer is degraded by contact with
an aqueous
- 17 -
CA 02908429 2015-09-29
WO 2015/065575 PCT/US2014/052546
solution of ethanolamine at temperatures ranging from about 100 F (37.8 C)
to about 180 F
(82.2 C).
[0054] In an embodiment, the degradable polymer comprises a degradable semi-
crystalline
copolymer with a melting point of about 300 F (148.9 C) having lactic acid
as one of the
monomers. In such embodiments, the PLA copolymer is degraded by contact with
an aqueous
solution of triethylenetetraamine at temperatures ranging from about 140 F
(60 C) to about 300 F
(148.9 C).
[0055] In an embodiment, the degradable polymer comprises a physical blend
of degradable
semi-crystalline polymers with melting points of 140 F (60 C) and 240 F
(115.6 C) and having
PLA as one of the blend components. In such embodiments, the degradable
polymer blend is
degraded by contact with an aqueous solution of ethanolamine at temperatures
ranging from about
180 F (82.2 C) to about 320 F (160 C).
[0056] In an embodiment, the degradable polymer is used in combination with
a DA solution
that causes initial swelling of the polymer, followed by degradation of the
degradable polymer.
[0057] In an embodiment, the degradable polymer is used in the presence of
more than one
DA solution, of which one DA is added for the purpose of swelling the polymer,
and the other DA
is for the purpose of degrading the polymer. Thus, in an embodiment, a method
of servicing the
wellbore comprises introducing to the wellbore a degradable material (DM) and
at least a first and
a second DA of the type disclosed herein where the first and the second DA
differ and where the
first and second DAs may be added sequentially or simultaneously.
[0058] In an embodiment, the DA comprises an amine of the type disclosed
herein (e.g.,
alkanolamine, aziridine). The DA may be introduced to the wellbore in the form
of a delayed-
action construct (DAC) of the type depicted in Figure 2. Referring to Figure
2A, the DAC 100
comprises a DA 20 on a solid support 30 which is encapsulated by an
encapsulating material 10.
[0059] In an embodiment, the solid support comprises any material that can
associate with the
DA and is compatible with the other materials of this disclosure. The solid
support may be an
organic or an inorganic material. The solid support may be further
characterized as hydrophobic,
alternatively the solid support is hydrophilic. Examples of materials suitable
for use as the solid
support in the DAC include without limitation crushed nut shells (for example,
walnuts)
diatomaceous earth, clay, zeolite, polymeric resin, lignite, inorganic oxides
such as silica, alumina,
aluminophosphates or combinations thereof.
- 18 -
CA 02908429 2015-09-29
WO 2015/065575 PCT/US2014/052546
100601 In an embodiment, the solid support comprises a clay. Clays herein
refer to aggregates
of hydrous silicate particles either naturally-occurring or synthetically-
produced, less than 4
micrometers (.tm) in diameter and may consist of a variety of minerals rich in
silicon and
aluminum oxides and hydroxides which include variable amounts of other
components such as
alkali earth metals and water. Clays are most commonly formed by chemical
weathering of
silicate-bearing rocks, although some are formed by hydrothermal activity.
These clays can be
replicated in industrial chemical processes. Examples of clays suitable for
use in this disclosure
include without limitation clays from the following groups: kaolinite,
serpentine, illite, chlorite,
smectite or combinations thereof. Example of suitable kaolinite group clays
include without
limitation kaolinite, dickite, halloysite, nacrite, or combinations thereof.
Examples of suitable illite
groups include clay-micas and illite.
100611 In an embodiment, the solid support comprises a zeolite. Zeolites
are three-
dimensional, microporous, crystalline solids with well-defined porous
structures. Zeolites, which
can be either naturally occurring or synthesized, comprise a group of hydrated
alumina silicates
that are linked in a three dimensional framework through shared oxygen atoms.
Examples of
zeolites suitable for use in this disclosure include without limitation
analcime, chabazite,
heulandite, natrolite, phillipsite, stilbite, or combinations thereof.
100621 In an embodiment, the solid support comprises a polymeric resin such
as for example
an ion-exchange resin. Ion exchange resins are polymeric resins that contain
charged functional
groups. The base polymer is usually a crosslinked material such as polystyrene
that is crosslinked
with a vinyl polymer. Examples of polymeric resins suitable for use in this
disclosure include
without limitation diethyl aminoethyl, or quaternary aminoethyl substituted
polystyrene, Mono-Q ,
Mono-S, or combinations thereof, all of which are commercially available from
Pharmacia
Biotech.
[0063] In an embodiment, the solid support comprises a lignite. Lignite is
a brownish black
coal that has high inherent moisture content and high ash content compared to
bituminous coal. It
is a heterogenous mixture and often has a woodlike texture.
[0064] In some embodiments, the solid support may be obtained from natural
sources,
alternatively the substrate may comprise synthetic analogs of the materials
described herein. In an
embodiment, the solid support may be present in amount the DAC of from about
30 wt.% to about
- 19 -
CA 02908429 2015-09-29
WO 2015/065575 PCT/US2014/052546
80 wt.%, alternatively from about 40 wt.% to about 70 wt.%, or alternatively
from about 50 wt.%
to about 60 wt.% based on the dry weight of DAC.
[0065] In an embodiment, the DAC comprises an encapsulating material. The
encapsulating
material may function as a barrier that inhibits disassociation of the DA from
the solid support. In
an embodiment, the encapsulating material functions as a substantially
impenetrable barrier that
prevents disassociation of the DA from the solid support. In such embodiments,
disassociation of
the DA from the solid support occurs subsequent to a reduction in structural
integrity of the
encapsulating material that removes some portion of the substantially
impenetrable barrier. As will
be understood by one of ordinary skill in the art, under such circumstances,
the function of the
DAC is delayed for the time period necessary to affect the structural
integrity of the encapsulating
material. The structural integrity of the encapsulating material may be
affected by any number of
factors such as wellbore temperature and the presence of materials that
decrease the structural
integrity of the encapsulating material.
[0066] In an alternative embodiment, the encapsulating material functions
as an external
coating through which the encapsulated material (e.g., DA) diffuses. As will
be understood by one
of ordinary skill in the art, in such embodiments, the function of the DAC is
delayed for the time
period necessary for the DA to pass through the encapsulating material and
into the wellbore
and/or wellbore servicing fluids.
[0067] Examples of other encapsulating materials suitable for use in this
disclosure include
but are not limited to EDPM rubber, polyvinyldichloride, nylon, waxes,
polyurethanes, cross-
linked partially hydrolyzed acrylics, cross-linked polyurethane, a drying oil
such as tung oil and
linseed oil, or combinations thereof.
[0068] In an embodiment, the encapsulating material comprises biopolymers,
polysaccharides,
hydrocolloids, or gums. In an embodiment, the encapsulating material, upon
contact with water,
may hydrate the outer surface forming a gel layer that encloses the
encapsulated material (e.g.,
DA). For example, the encapsulating material may comprise cellulose-based
polymers, cellulose
ethers, methyl cel lulose, hydroxypropyl
methylcellulo se, ethylhydroxyethylcellulose,
methylhydroxyethylcellulose, bacterial and plant based gums, xanthan, diutan,
gellan, gum
tragacanth, pestan, and the like, or combinations thereof.
[0069] In an embodiment, a DAC of the type disclosed herein is prepared
using any suitable
methodology. For example, the DA may be associated with the solid support such
as by spray-
- 20 -
CA 02908429 2015-09-29
WO 2015/065575 PCT/US2014/052546
coating the DA onto the solid support or by impregnating the solid support
with a DA. The
resulting material is termed a DA/solid support. The DA/solid support can be
further associated
with an encapsulating material, all of the type disclosed herein.
100701 In an embodiment, the DAC/solid support can be encapsulated by spray
coating a
variety of materials thereon. In an alternative embodiment, the liquid DA may
be encapsulated in a
particulate porous solid material that remains dry and free flowing after
absorbing the liquid DA
and through which the DA slowly diffuses. Examples of such particulate porous
solid materials
include but are not limited to crushed nut shells (for example, walnuts)
diatomaceous earth,
zeolites, silica, alumina, metal salts of alumino-silicates, clays,
hydrotalcite,
styrenedivinylbenzene-based materials, cross-linked polyalkylacrylate esters,
cross-linked
modified starches, or combinations thereof. In such embodiments, an external
coating of an
encapsulating material through which a DA slowly diffuses can be placed on the
porous solid
material.
[0071] Referring to Figure 2B, a DAC 100 placed in the wellbore may have
encapsulation
material 10 whose structural integrity is comprised allowing the DA 20 to
disassociate from the
solid support 30. In an alternative embodiment and referring to Figure 2C, the
DAC comprises an
encapsulation material 10 and DA 20 associated with the solid support 30. In
such an
embodiment, the DA 20 may dissociate from the solid support 30 and migrate
through the
encapsulation material 30 into the wellbore servicing area.
[0072] The DAs and/or DMs disclosed herein may be included in or in
combination with any
suitable wellbore servicing fluid (WSF). As used herein, a "servicing fluid"
refers to a fluid used
to drill, complete, work over, fracture, repair, or in any way prepare a well
bore for the recovery of
materials residing in a subterranean formation penetrated by the wellbore.
Examples of servicing
fluids include, but are not limited to, cement slurries, drilling fluids or
muds, spacer fluids,
fracturing fluids or completion fluids. It is to be understood that
"subterranean formation"
encompasses both areas below exposed earth and areas below earth covered by
water such as
ocean or fresh water.
[0073] The aqueous fluids that may be utilized in the WSF may be fresh
water, saltwater (e.g.,
water containing one or more salts dissolved therein), brine (e.g., saturated
saltwater), or seawater.
In certain embodiments, an aqueous fluid may be present in the WSF used in the
methods of the
present disclosure in an amount in the range of from about 40 wt.% to about 99
wt.% based on the
- 21 -
CA 02908429 2015-09-29
WO 2015/065575 PCT/US2014/052546
total weight of the WSF. In certain embodiments, an aqueous fluid may be
present in the WSF
used in the methods of the present disclosure in an amount in the range of
from about 20 wt.% to
about 80 wt.% based on the total weight of the WSF. One of ordinary skill in
the art, with the
benefit of this disclosure, will recognize the appropriate amount of an
aqueous fluid for a chosen
application.
100741 In an embodiment, the WSF comprises a suspending agent. The
suspending agent in
the WSF may function to prevent the DA particulates (e.g., aziridine oligomer
derivatives) from
settling in the suspension during its storage or before reaching its downhole
target (e.g., a portion
of the wellbore and/or subterranean formation comprising degradable polymer).
In an
embodiment, the suspending agent in the WSF may function to prevent the fully
or partially
degraded or non-degraded DM from settling during placement or flow back
subsequent to
treatment with a DA. In accordance with the methods of the present disclosure,
the suspending
agent may comprise microfine particulate materials, (e.g., less than about 1
micron) hereinafter
referred to as colloidal materials, clays and/or viscosifying or gel forming
polymers.
100751 Nonlimiting examples of colloidal materials suitable for use in the
present disclosure
include carbon black, lignite, brown coal, humic acid, styrene-butadiene
rubber latexes, polyvinyl
alcohol latexes, acetate latexes, acrylate latexes, precipitated silica,
fumed/pyrogenic silica, and
viscoelastic surfactant micelles.
100761 Nonlimiting examples of clays suitable for use in the present
disclosure include
bentonite, attapulgite, kalonite, meta kalonite, laponite, hectorite and
sepiolite.
[0077] Nonlimiting examples of viscosifying or gel forming polymers
suitable for use in the
present disclosure include a copolymer of 2-acrylamido-2-methylpropane
sulfonic acid and N,N-
dimethylacrylamide, carragenan, scleroglucan, xanthan gum, guar gum,
hydroxypropylguar,
hydroxyethylcellulo se, carboxymethylhydroxyethylcellulo se, wet an gum,
succinoglycan,
copolymers or terpolymers of acrylamidomethyl propane sulfonate, N,N-
dimethylacrylamide,
acrylic acid, and vinyl acetate.
100781 In an embodiment, the suspending agent is present in the WSF in an
amount of from
about 0.01 wt.% to about 10 wt.%, alternatively from about 0.1 wt.% to about 5
wt.%, or
alternatively from about 0.25 wt.% to about 1.5 wt.% based on the total weight
of the WSF.
100791 The WSF may further comprise additional additives as deemed
appropriate by one of
ordinary skill in the art, with the benefit of this disclosure. Additives may
be used singularly or in
-22 -
CA 2908929 2017-03-28
combination. Examples of such additional additives include, but are not
limited to, pH-adjusting
agents, pH-buffers, oxidizing agents, enzymes, lost circulation materials,
scale inhibitors,
surfactants, clay stabilizers, fluid loss control additives, or combinations
thereof Nonlimiting
examples of such additives arc also described in U.S. Patent Publication No.
2010/0273685 Al.
100801 The DM (e.g., degradable polymer) may be introduced into a
subterranean formation
for any of a number of uses. In some embodiments, degradable polymers may be
used in
subterranean operations as fluid loss control particles, diverting agents,
filter cake components,
drilling fluid additives, cement additives, and the like. In certain
embodiments, the degradable
polymer may be in a mechanical form, such as in a downhole tool (e.g., plugs,
sleeves, and the
like), or as a coating on a metallic tool. In other embodiments, the
degradable polymer may be
present in a filter cake that is present in the subterranean formation. For
example, the degradable
polymer may be introduced into the formation as part of the fluid that forms
the filter cake, such
that the filter cake contains the degradable polymer. In some instances, the
degradable polymer
may be capable of releasing a desirable degradation product, e.g., an acid,
during its hydrolysis.
The acid released by certain degradable polymers may be used to facilitate a
reduction in the
viscosity of a fluid or to degrade a filter cake, as well as for numerous
other functions in
subterranean operations. Accordingly, the methods of the present disclosure
may be used in any
subterranean operation in which the degradation of a degradable polymer is
desired.
[0081] In some embodiments, a degradable polymer may be introduced into a
subterranean
formation by including the degradable polymer in the WSF (e.g., a fracturing
fluid or an acidizing
fluid). Such a WSF may comprise an aqueous fluid (e.g., an aqueous carrier
fluid) and a
degradable polymer. Depending on the application, the WSF further may comprise
one or more of
the following: a suspending agent, a crosslinking agent, bridging agents, and
a proppant.
100821 A degradable polymer may be included in the WSFs in an amount
sufficient for a
particular application. For example, in embodiments where degradable polymers
capable of
releasing an acid are used, a degradable polymer may be present in the WSF in
an amount
sufficient to release a desired amount of acid. In some embodiments, the
amount of the released
acid may be sufficient to reduce the viscosity of the treatment fluid to a
desired level. In another
embodiment, the amount of the released acid may be sufficient to facilitate
the degradation of an
acid-soluble component, for example, an acid-soluble component of a filter
cake, an acid-soluble
-23 -
CA 02908429 2015-09-29
WO 2015/065575 PCT/US2014/052546
component adjacent to a filter cake, or an acid-soluble component (e.g.,
calcium carbonate) of a
proppant pack.
[0083] In certain embodiments, a degradable polymer may be present in the
WSF in an amount
in the range of from about 1% to about 30% by weight of the WSF. In certain
embodiments, a
degradable polymer may be present in the WSF in an amount in the range of from
about 3% to
about 10% by weight of the WSF. One of ordinary skill in the art, with the
benefit of this
disclosure, will be able to determine the appropriate amount of a degradable
polymer to include in
a treatment fluid for a particular application.
[0084] WSFs, in addition to introducing degradable polymers into a wellbore
and/or
subterranean formations, may also be used to introduce a DA solution or a DAC
into a wellbore
and/or subterranean formation. For example, by placement of a WSF comprising a
DA or a DAC
proximate to or in contact with the degradable material present in the
wellbore and/or subterranean
formation. Accordingly, in some embodiments, a WSF may comprise a DA solution
or DAC in
addition to or in lieu of a DM. Such WSFs may be used to hydrolyze degradable
polymers present
in the fluid or present in the wellbore and/or subterranean formation (e.g.,
in a filter cake, in a
proppant pack, or in a downhole tool). The DA solution may be present in the
WSF in an amount
in the range of from about 0.1 wt.% to about 50 wt.% based on the total weight
of the WSF. In
some embodiments, the DA solution may be present in an amount in the range of
from about 1
wt.% to about 15 wt.% based on the total weight of the WSF. When the DAC is
used in
combination with the DM, the amount of DAC may be in the range of from about
10 wt.% to about
60 wt.% by weight of DM, and the amount of DAC will be dependent on the amount
of DA
present in DAC, the desired rate of DM degradation and the desired duration of
DM degradation.
[0085] In some embodiments, the DA solution or DAC may be placed in the
formation prior to
the placement of the degradable material. In such cases, the DA solution or
DAC may be made to
contact the degradable materials by drawing down the pressure on the wellbore,
for example by
putting the well back on production. Alternatively, the DA solution (or DAC)
and degradable
material may be pumped together along with the well treatment fluid (e.g., a
fracturing fluid).
Alternatively, the DA solution (or DAC) may be placed in the wellbore to
contact the degradable
material already placed in the wellbore. Accordingly, the DM and DA (or DAC)
may be placed
into the wellbore in any suitable order or combination necessary to meet the
objectives of a given
wellbore service, for example simultaneously (including one or more DMs
combined with one or
- 24 -
CA 02908429 2015-09-29
WO 2015/065575 PCT/US2014/052546
more DAs (or DACs) in a common WSF or a first WSF comprising one or more DMs
placed
simultaneously with a second WSF comprising one or more DAs (or DACs), such as
pumping the
first WSF down the flowbore of a tubular placed in a wellbore and pumping the
second WSF down
an annulus between the tubular and the wellbore) or sequentially (e.g., a
first WSF comprising one
or more DMs or DACs pumped ahead or behind a second WSF comprising one or more
DAs (or
DACs) , for example as one or more slugs of material that may stay constant or
vary in sequence
such as DM/DA; DM/DAC; DA/DM; DAC(DM; DM/DA/DM/DA; DA/DM/DA;
DA/DM/DA/DM/DA; DAC/DM/DAC/DM/DAC; DM/I st DA/2nd DA; 15t DA/ st DM/2nd Dm/2nd
DA; DM/1sbAC/211d DAC etc.).
[0086] According to some embodiments, a WSF comprising a degradable polymer
may be
introduced to a wellbore and/or subterranean formation simultaneously with the
introduction of a
DA solution (or DAC) that does not adversely react with or otherwise interfere
with any aspect of
the WSF. In other embodiments, a DA solution (or DAC) may be introduced to the
wellbore
and/or subterranean formation subsequent to the introduction of the degradable
polymer. In some
embodiments, a degradable polymer, which may be provided in any of a number of
forms, e.g., in
a filter cake, may be contacted with a DA solution (or DAC) subsequent to the
introduction of the
degradable polymer into the wellbore and/or subterranean formation.
[0087] For example, in certain embodiments, the present disclosure provides
a method of
treating at least a portion of a wellbore and/or subterranean formation
comprising providing a WSF
that comprises an aqueous fluid, a degradable polymer capable of releasing an
acid, and a DA
solution or DAC solid and introducing the WSF into the wellbore and/or
subterranean formation.
At a chosen time or after a desired delay period, the DA solution hydrolyzes
the degradable
polymer so as to release an acid that facilitates a reduction in the WSF's
viscosity.
100881 In an embodiment, the WSF comprises a DAC and the DA is released
from the solid
support. In such embodiments, the DA may migrate through the encapsulating
material or the
structural integrity of the encapsulating material is compromised sufficiently
to allow release of the
DA. The released DA may contact and accelerate the degradation of the
degradable polymer.
[0089] In some embodiments, a degradable polymer may be provided in a
wellbore and/or
subterranean formation by a fluid (e.g., a drill-in and servicing fluid)
capable of forming a filter
cake on the face of a portion of a wellbore and/or subterranean formation.
Such fluids are used,
- 25 -
CA 2908929 2017-03-28
among other things, to minimize damage to the permeability of the subterranean
formation. Before
desirable fluids, such as hydrocarbons, may be produced, the filter cake
should be removed.
[0090] Accordingly, in certain embodiments of the present disclosure, a DA
solution or DAC
may be introduced into a wellbore and/or subterranean formation to facilitate
the removal of a filter
cake that comprises a degradable polymer. When introduced into the wellbore
and/or subterranean
fottnation, the DA solution or DAC degrades the degradable polymer.
[0091] In an embodiment, a DA or DAC of the type disclosed herein may be
used in
conjunction with stimulation techniques designed to increase the complexity of
fractures by first
plugging the pores in existing fractures and then diverting the fracturing
fluid to initiate other
fractures. ACCESSFRAC I'm service is an example of such a stimulation service
commercially
available from I Ialliburton Energy Services, Inc. In such embodiments, the
pores may be plugged
with a diverter material such as the ones described in the present disclosure.
BIOVERT NWBTm
diverting system is an example of a temporary polyester-based diverting agent
commercially
available from Halliburton Energy Services, Inc. In such applications the
degradable polymers
may comprise a multimodal particle size distribution, for example, bimodal or
trimodal particle
size distributions. In such an embodiment, the degradable polymer comprising
multimodal
polymer particle size distribution may contain particles with sizes ranging
from about 5 mm to
about 20 microns, alternatively from about 3mm to about 50 microns, or
alternatively from about
lmm to about 100 microns.
100921 To improve efficiency of the diverting process, the particles after
placement may be
treated with a swelling DA solution which will swell the degradable polymer
particles forming a
continuous mass of diverting plug before the degradation process sets in. The
DA solution or DAC
may be advantageously used for removing the diverter plugs under wellbore
conditions where the
BHT is less than about 320 CF (160 ()C) , alternatively less than about 140
'1'; (60 'C), or
alternatively less than about 100 CF (37.8 C). By properly selecting the
diverting polymer sizes
and choosing a suitable DA or DAC of the type disclosed herein, the wait time
for putting the well
on production may be advantageously shortened to less than about 1 week,
alternatively less than
about 3 days. In the case of the DAC and DM combination in such applications,
the diverting plug
can comprise solid materials comprised of DM and DAC, and plug can be designed
to self-degrade
at predefined degradation rates, and duration by combining the two solid
materials in weight ratios
determined in the laboratory based on downhole combinations.
- 26 -
CA 2908929 2017-03-28
[0093] In an embodiment, the DA or DAC of the type disclosed herein may be
used in
conjunction with stimulation techniques which are designed to create highly
conductive fractures.
PILLAR FRACIm stimulation technique is an example of such a technique and is
commercially
available from Halliburton Energy Services, Inc. For example, the degradable
polymer may be
advantageously soaked and/or immersed in a DA solution and then pumped
downhole, thereby
removing the need to place the DA solution separately. In such embodiments the
degradable
polymer may be soaked in a DA solution for a time period of from about 6 hours
to about 72 hours,
alternatively from about 12 hours, to about 48 hours or alternatively from
about 16 hours to about
24 hours. While the degradable polymer may function as a diverter downhole,
the DA solution
will concurrently degrade the polymer in an advantageously shorter time frame
of less than about 1
week, alternatively less than about 3 days. In such an embodiment, the
degradable polymer (e.g.,
PLA) may be used at a BHT of less than about 140 F (60 C).
[0094] In an embodiment, the degradable polymer may be used for assembling
a degradable
filter cake with drill-in fluids. In such an embodiment, the degradable
polymer comprises
multimodal polymer particles with sizes ranging from about 1 mm to about 20
microns,
alternatively from about 0.5 mm to about 50 microns, or alternatively from
about 500 microns to
about 100 microns. The filter cake may perform its intended function and it
may be subsequently
advantageously removed with a DA solution or DAC of the type disclosed herein
having a ph l of
less than about 11, alternatively less than about 10, or alternatively less
than about 9.
[0095] The following are additional enumerated embodiments of the concepts
disclosed
herein.
[0096] A first embodiment which is a method of servicing a wellbore
comprising providing a
degradable polymer and a delayed action construct within a portion of a
wellbore, a subterranean
formation or both; wherein the delayed action construct comprises (i) a
degradation accelerator
comprising an alkanolamine, an oligomer of aziridine, a polymer of azridine, a
diamine, or
combinations thereof, (ii) a solid support, and (iii) an encapsulating
material; and placing the
wellbore servicing fluid comprising the degradable polymer and delayed action
construct into the
wellbore, the subterranean formation or both.
[0097] A second embodiment which is the method of the first embodiment
wherein the
alkanolamine comprises ethanolamine, triethanolamine, monoethanolamine,
diethanolamine,
-27 -
CA 02908429 2015-09-29
WO 2015/065575 PCT/US2014/052546
diglycolamine, di-2-propanolamine. N-methyldiethanolamine, 2-amino-2-methyl-l-
propanol, 2-
piperidineethanol, aminopropane diol, or combinations thereof.
[0098] A third embodiment which is the method of the second embodiment
wherein the
alkanolamine comprises a compound characterized by Formula I:
HONR1
R2
Formula I
where R1 and R2 may each independently be hydrogen, an unsubstituted alkyl
chain comprising
from about 1 to about 6 carbon atoms, or a substituted alkyl chain comprising
from about 3 to
about 6 carbon atoms and X comprises a substituted or unsubstituted alkylene
having from about 1
to about 4 carbon atoms.
100991 A fourth embodiment which is the method of any of the first through
third
embodiments wherein the oligomer of aziridine comprises a linear aziridine
oligomer, a branched
aziridine oligomer, any derivatives thereof, or any combinations thereof.
[00100] A fifth embodiment which is the method of any of the first through
fourth embodiments
wherein the oligomer of aziridine comprises a compound characterized by
Formula II:
R3 H
Formula II
where n may range from about 2 to about 100 and R3 comprises a primary amine.
[00101] A sixth embodiment which is the method of any of the first through
fourth
embodiments wherein the oligomer of aziridine comprises a compound
characterized by Formula
R4
NH
R4
Formula III
where m ranges from about 2 to about 100 and R1 comprises a methyl group.
- 28 -
CA 02908429 2015-09-29
WO 2015/065575 PCT/US2014/052546
[00102] A seventh embodiment which is the method of any of the first
through fourth
embodiments wherein the oligomer of aziridine comprises a compound
characterized by Formula
IV:
NH2
Formula IV
where the repeating units occur in a total amount or about ( x+y) wherein the
total value of ( x+y)
ranges from about 2 to about 50.
[00103] An eighth embodiment which is the method of any of the first through
seventh
embodiments wherein the diamine comprises a compound characterized by general
Formula V:
R7
R6
Formula V
where R5, R6, R7, and R8 may each independently be hydrogen, an unsubstituted
alkyl chain having
from about 1 to about 3 carbon atoms, or a substituted alkyl chain having from
about 2 to about 4
carbon atoms and Z comprises a substituted or unsubstituted alkylene chain
having from about 2 to
about 6 carbon atoms.
[00104] A ninth embodiment which is the method of any of the first through
eighth
embodiments wherein the degradation accelerator is present in the wellbore
servicing fluid in an
amount of from about 0.1 wt.% to about 50 wt.% based on the total weight of
the wellbore
servicing fluid.
[00105] A tenth embodiment which is the method of any of the first through
ninth embodiments
wherein the degradable polymer comprises an aliphatic polyester, a
poly(lactide), a
poly(glycolide), a poly(c-caprolactone), a poly(hydroxy ester ether), a
poly(hydroxybutyrate), a
poly(anhydride), a polycarbonate, a polyether ester, a polyester amide, a
copolymer thereof, or any
combinations thereof.
[00106] An eleventh embodiment which is the method of any of the first through
tenth
embodiments wherein the degradable polymer comprises a copolymer of lactic and
gycolic acid.
1001071 A twelfth embodiment which is the method of any of the first through
eleventh
embodiments wherein the degradable polymer further comprises a plasticizer.
- 29 -
CA 02908429 2015-09-29
WO 2015/065575 PCT/US2014/052546
1001081 A thirteenth embodiment which is the method of the twelfth embodiment
wherein the
plasticizer comprises a polyethylene glycol (PEG); a polyethylene oxide; an
oligomeric lactic acid;
a citrate ester; a glucose monoester; a partially hydrolyzed fatty acid ester;
a PEG monolaurate; a
triacetin; a poly(6-caprolactone); a poly(hydroxybutyrate); a glycerin-1 -
benzoate-2,3-dilaurate; a
glycerin-2-benzoate-1,3-dilaurate; a bis(butyl diethylene glycol)adipate; an
ethylphthalylethyl
glycolate; a glycerin diacetate monocaprylate; a diacetyl monoacyl glycerol; a
polypropylene
glycol; an epoxy derivative of a polypropylene glycol; a poly(propylene
glycol)dibenzoate; a
dipropylene glycol dibenzoate; a glycerol; an ethyl phthalyl ethyl glycolate;
a poly(ethylene
adipate)distearate; a di-iso-butyl adipate, or combinations thereof.
1001091 A fourteenth embodiment which is the method of any of the first
through thirteenth
embodiments wherein the solid support comprises a clay, zeolite, polymeric
resin, lignite,
inorganic oxide or combinations thereof.
[00110] A fifteenth embodiment which is the method of any of the first through
fourteenth
embodiments wherein the solid support comprises a particulate porous material.
[00111] A sixteenth embodiment which is the method of the fifteenth embodiment
wherein the
particulate porous material comprises diatomaceous earth, silica, alumina,
metal salts of alumino-
silicates, clays, hydrotalcite, styrenedivinylbenzene-based materials, cross-
linked polyalkylacrylate
esters, cross-linked modified starches, or combinations thereof.
[00112] A seventeenth embodiment which is the method of any of the first
through sixteenth
embodiments wherein the encapsulating material comprises cellulose-based
polymers, cellulose
ethers, methylcellulose, hydroxypropyl methylcellulose,
ethylhydroxyethylcellulose,
methylhydroxyethylcellulose, bacterial and plant based gums, xanthan, diutan,
gellan, gum
tragacanth, pestan, or combinations thereof.
[00113] An eighteenth embodiment which is the method of any of the first
through seventeenth
embodiments wherein the encapsulating material comprises EDPM rubber,
polyvinyldichloride,
nylon, waxes, polyurethanes, cross-linked partially hydrolyzed acrylics, cross-
linked polyurethane
or combinations thereof.
[00114] A nineteenth embodiment which is the method of any of the first
through eighteenth
embodiments wherein the encapsulating material comprises tung oil, linseed
oil, or combinations
thereof.
- 30 -
CA 02908429 2015-09-29
WO 2015/065575
PCT/US2014/052546
[00115] A twentieth embodiment which is the method of any of the first through
nineteenth
embodiments wherein the degradation accelerator is spray coated onto the solid
support.
EXAMPLES
1001161 The embodiments having been generally described, the following
examples are given
as particular embodiments of the disclosure and to demonstrate the practice
and advantages
thereof. It is understood that the examples are given by way of illustration
and are not intended to
limit the specification or the claims in any manner.
EXAMPLE 1
[00117] Five commercial samples of degradable polymers polyesters comprising
¨000- bond
in the polymer back bone were obtained. Except for two, all polymers contained
lactic acid as one
of the monomers. Based on nuclear magnetic resonance spectroscopy it was
established that,
except for two samples, all samples contained exclusively poly(lactic acid).
One polymer sample
contained an additional monomer. One sample was polyglycolic acid. The
crystallinity of the
polylactic acid containing samples was measured by Differential Scanning
Calorimeter (DSC) by
heating the sample from room temperature to 392 F (200 C), holding the
sample at 392 F (200
C) for 30 minutes, cooling it to room temperature and reheating to 392 F (200
C) at a rate of 10
C/minute. Glass transition temperatures (Tg), melting temperatures (f,n) and
crystallization
temperatures (TO observed during the second cycle are reported in Table 1.
Polyglycolic acid
(Sample 5) was not characterized by DSC. A sample for which the area of the
melting peak
increased substantially during the second heating cycle is deemed to be
originally a low
crystallinity material. All others are referred to as amorphous or semi-
crystalline materials.
Table 1
Sample Ig Comments
1-(PLA) Not observable 140 F (60 C) 120 F
(48.9 C) Low crystallinity
2-(PLA) 76 F(24.4 C) Not observable Not observable
amorphous
3-(PLA) Not observable 312 F(155.6 C) 210
F(98.9 C) Semi-crystalline
4-(PLA + a Not observable 125 F (51.7 C) 90 F
(32.2 C) Melt blend of two
polyester) and 235 F and 165 F (73.9 semi-
crystalline
(112.8 C) C) polymers
- 31 -
CA 02908429 2015-09-29
WO 2015/065575 PCT/US2014/052546
1001181 The degradation tests were performed by first grinding the materials
and sieving them.
The particles that went through a 20 mesh sieve were collected and used in the
degradation studies.
A solid sample of 1 gram of the degradable polymer was placed in 100m1 tap
water and about a
stoichiometric amount of DA was added. The stoichiometric amounts of the DA
solution required
were calculated by dividing the weight of degradable polymer sample by the
molecular weight of
monomer (lactic acid in the case of PLA based polymer and glycolic acid in the
case of
polyglycolic acid) to obtain moles of ¨000- bonds present in the polymer, and
calculating the
weight of degrading agent containing equivalent moles of nitrogen atoms. The
mixtures were kept
in a water bath heated to 140 F (60 C). Comparative samples using water and
ethylenediamine as
the degrading agents were also investigated. The amines tested included
triethylenetetramine
(TETA) as a representative aziridine oligomer (Formula II, n=3), and
polyethyleneimine (PEI) as
polymerized aziridine (Formula IV, n=>>100). PEI is commercially available
from Halliburton
Energy Services as HZ-20 crosslinker. Ethylenediamine (EDA) also served as
representative
example of higher homologues of ethylenediamine (Formula V, Z=3-6, and R5, R6,
R7 and R8 are
hydrogens). Alkanolamines used in the study included ethanolamine (EA),
triethanolamine (TEA)
and triisopropanolamine (Formula I). The progress of the polymer degradation
was measured by
determining the remaining weight of degradable polymer at periodic intervals
by filtering the
polymer mixture, drying the undissolved solid, and measuring its weight. The
results for samples
utilizing an aziridine oligomer, aziridine polymer and diatnine as the DA are
presented in Tables 2
and 3. Table 2 presents the results from measuring remaining polymer weights
at 140 F (60 C)
after 3, 6 and 9 days. Table 3 provides results for % polymer degradation of
semicrystalline PLA
and semicrystalline polymer blends Samples 3 and 4 respectively after 25 days
at 140 F (60 C).
Table 2
Degradable Polymer Amine Remaining weight Remaining Remaining
compound (g)/ 3 days weight (g)/ 6 weight (g)/ 9
days days
Sample 1 (Low
crystallinity PLA) None 1.41 1.26 1.17
TETA 1.24 0.95 0.65
- 32 -
CA 02908429 2015-09-29
WO 2015/065575
PCT/US2014/052546
Degradable Polymer Amine Remaining weight Remaining Remaining
compound (g)/ 3 days weight (g)/ 6 weight (g)/
9
days days
EDA 0.71 0.36 0.26
PEI 2.03 1.72 i 0.97
Sample 2 (amorphous
PLA) None 0.79 0.27 0.14
1 ETA 0.95 NA 0.13
EDA 0.05 0.12 0.11
PEI 0.70 Not measured 0.25
Sample 3 (semi-
crystalline PLA) None 1.13 1.19 1.21
TETA 0.83 0.73 0.59
EDA 0.62 0.29 0.20
PEI 1.22 Not measured 1.29
Sample 4
None 1.73 1.24 Not measured
"[ETA 1.22 1.21 1.53
- 33 -
CA 02908429 2015-09-29
WO 2015/065575 PCT/US2014/052546
Degradable Polymer Amine Remaining weight Remaining Remaining
compound (g)/ 3 days weight (g)/ 6 weight (g)/ 9
days days
EDA 1.28 1.27 1.22
PEI 1.89 1.19 1.12
Sample 5 (Semi-
crystal 1 ine PGA) None 1.11 1.15 0.97
TETA 0.68 0.43 0.40
EDA 0.31 0.13 0.11
PEI 1.19 1.39 1.04
[00119] The results in Table 2 demonstrate that, semi crystalline polymers
have a tendency to
increase in weight when placed in water, whereas such behavior was not
observed for the
amorphous polymer. The increased weight in water for the semicrystalline
polymer persisted even
after 9 days, indicating no polymer degradation. The amorphous polymer
degraded significantly in
water over 6 days. All DA solutions degraded the amorphous polymer rapidly
with the diamines
providing the fastest degradation rates (<4 days). Among the semicrystalline
polymers, the weight
increase was highest and polymer degradation lowest when using DA solutions
comprising an
aziridine polymer indicating that the aziridine polymers (i.e., Formula IV, n
>>100) may be more
suitable as polymer swelling agents. In general, increases in polymer weight
were accompanied by
swelling of the polymer particles. Therefore, polymers of aziridine may be
more suitable for
swellable degradable semicrystalline polymers for improved fluid diversion
efficiency, fluid loss
control and filter cake fluid loss control efficiency. Swollen particles
contain minimized
interparticle porosity; encourage particle fusion forming a continuous layer
of filter cake, or a
single fused mass of plug blocking flow of fluid more effectively. Ethylene
diamine containing
only primary amine groups was more effective as a degradation accelerator than
the azidirine
- 34 -
CA 02908429 2015-09-29
WO 2015/065575 PCT/US2014/052546
oligomer, TETA, which contained the same number of primary amine groups but
also contained
two secondary amine groups. None of the DAs were effective in accelerating
degradation of the
most crystalline polymer blend (Sample 4) and they all increased the
degradable polymer weight
due to swelling even after 9 days.
Table 3
Degradation % Degradation for % Degradation for
Accelerator Sample 3 Sample 4
None 1 13
TETA 64 20
EDA 93 9
PEI 2 0
1001201 The results after 25 days testing at 140 F (60 C) shown in Table 3
indicate that of the
two polymers which were most resistant to degradation namely Samples 3 and 4,
the former
showed the most accelerated degradation in the presence of aziridine oligomer,
TETA, and the
diamine, EDA compared to when only water was present, whereas the latter
polymer showed
reasonably accelerated degradation rates with aziridine oligomer. The
polymeric aziridine was not
effective in degrading the polymer even after such a long duration.
[00121] The results for alkanolamine-accelerated polymer degradation in 4 days
at 140 F (60
C) are shown in Table 4.
Table 4
Degradable Polymer Alkanolamine %Degradation
in 4 days
@140 I' (60
C)
Sample 1 (Low crystallinity Control 0
PLA)
EA 19
TEA 0
- 35 -
CA 02908429 2015-09-29
WO 2015/065575 PCT/US2014/052546
Degradable Polymer Alkanolamine %Degradation
in 4 days
@140 F (60
C)
Sample 2 (amorphous PLA) Control 20
EA 100
TEA 100
Sample 3 (semi-crystalline PLA) Control 5
EA 57
TEA 8
Sample 4 Control 2
EA 35
TEA 6
1001221 The 4-day results shown in Table 4, and their comparison with the 3 or
6-day results
shown for the DAs in Table 2 demonstrate that ethanolatnine is an effective
polymer degradation
accelerator for all polymers irrespective of the polymer crystallinity. The
results also indicate that
for semi-crystalline polymers, ethanolamine is a more effective DA than the
amines.
EXAMPLE 2
1001231 The effectiveness of DAs of the type disclosed herein on polymer
swelling was studied
by measuring swollen polymer weights in the presence of DA materials. Results
in Table 2
indicated that semi-crystalline polymers swell in the presence of water
itself. However, initial
swelling rates for semi-crystalline polymers are higher when using
polyethyeleneimine than water.
Swelling was not observed for the amorphous polymer with water or amine-based
DA solutions.
Amorphous polymer (Sample 2) swelled in the presence of trialkanolamines,
namely
triethanolamine and triisopropanolamine, significantly more than in water as
shown in Figure 1. In
this example, five beads (shown in Figure I) of Sample 2 polymer were
separately placed in 100m1
of water, a solution of triethanolamine (TEA) and a solution of
triisopropanolamine and the
samples were kept in a water at 140 F (60 C) for two days. The results shown
in Figure 1 for
- 36 -
CA 2908929 2017-03-28
aminoalcohols combined with the results presented in Table 4 indicate that the
swelling step by the
DAs may be preceding the degradation step or both processes may he taking
place simultaneously.
In the latter case, the swelling process may be a kinetically-controlled
process whereas the
degradation may be thermodynamically controlled. The polymer swelling by
aminoalcohol- and
amine- based DA solutions initially before the degradation rates accelerate
allow for improving the
performance of the polymers by forming a continuous mass of solid degradable
polymer which can
increase the fluid loss, plugging and diversion efficiency of the degradable
polymers.
[00124] While
embodiments of the disclosure have been shown and described, modifications
thereof can be made by one skilled in the art without departing from the
spirit and teachings of the
disclosure. The embodiments described herein are exemplary only, and are not
intended to be
limiting. Many variations and modifications of the disclosure disclosed herein
are possible and are
within the scope of the disclosure. Where numerical ranges or limitations are
expressly stated,
such express ranges Or limitations should be understood to include iterative
ranges or limitations of
like magnitude falling within the expressly stated ranges or limitations
(e.g., from about 1 to about
includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.).
For example, whenever
a numerical range with a lower limit, R1,, and an upper limit, R. is
disclosed, any number falling
within the range is specifically disclosed. In particular, the following
numbers within the range are
specifically disclosed: K=Ri, +k* (Ku-RI), wherein k is a variable ranging
from 1 percent to 100
percent with a 1 percent increment, i.e., k is 1 percent, 2 percent, 3
percent, 4 percent, 5 percent,
....., 50 percent, 51 percent, 52 percent, 95
percent, 96 percent, 97 percent, 98 percent, 99
percent, or 100 percent. Moreover, any numerical range defined by two R
numbers as defined in
the above is also specifically disclosed. Use of the term "optionally" with
respect to any element
of a claim is intended to mean that the subject element is required, or
alternatively, is not required.
Both alternatives are intended to be within the scope of the claim. Use of
broader terms such as
comprises, includes, having, etc. should be understood to provide support for
narrower terms such
as consisting of, consisting essentially of, comprised substantially of, etc.
[00125]
Accordingly, the scope of protection is not limited by the description set out
above but
is only limited by the claims which follow, that scope including all
equivalents of the subject
matter of the claims. Each and every may be viewed as an embodiment of the
present disclosure.
The discussion of a reference in the Description of Related Art is not an
admission that it is prior
art to the present disclosure, especially any reference that may have a
publication date after the
- 37 -
CA 2908929 2017-03-28
priority date of this application. The
disclosures of all patents, patent applications, and
publications cited herein may provide exemplary, procedural or other details
supplementary to
those set forth herein.
-J8 -
