Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE
CHEMICAL SEAL RING COMPOSITION AND METHOD OF USING
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR
DEVELOPMENT
[0001] Not applicable.
THE NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT
[0002] Not applicable.
INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A CD
[0003] Not applicable.
BACKGROUND
[0004] The statements in this section merely provide background
information related
to the present disclosure and may not constitute prior art.
[0005] Various methods have been used in the past to achieve gelling
including
systems triggered by pH adjustment, temperature and the like. Attempts at
using gels to
address fluid loss in highly porous underground formations include injecting
an acidic
solution following a polymer solution to produce gelation. However, gelation
typically
occurs so rapidly that a sufficient indepth plugging is not effectively
obtained in the most
permeable strata where desired. Other attempts include injecting water, a
polymer and a
crosslinking agent capable of gelling the polymer. Crosslinking agents are
typically
sequestered polyvalent metal cations, which are admixed, and, just before
injection into
an underground formation, an acid is added thereto to effect gelation.
However, when
the acid is pre-mixed with the gelable composition, the gelation can be too
fast, making it
necessary to shear the gelled polymer in order to be able to obtain adequate
injection,
which reduces effectiveness of the gel.
[0006] Indepth gelling has also been effected by the controlled gelation
of sodium
silicate. Also, polymers have previously been gelled in permeable zones by
borate ions
supplied in various ways. However, forming a gel having adequate control over
gelation,
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gel strength, and gel composition down hole remains an illusive goal.
[0007] Furthermore, it may be desirable to restrict the flow of a fluid
through an
annulus defined by the interior walls of a fluid conduit and the exterior of a
tubular
member within said fluid conduit. As used in the preceding sentence, "fluid
conduit" may
be defined as elongated voids, such as defined by pipes, or by boreholes or
mine shafts
penetrating the earth, or the like structures having a substantially (i.e.,
disregarding small
cracks, pores, and the like) closed cross sectional perimeter; excluded from
the term as
used herein are fluid conduits which do not have a completely defined cross
section, e.g.,
an open trough. Examples of situations where such flow restriction is desired
in wells
include isolating a portion of an annulus between casing and the borehole or
between
concentric strings of casing or tubing, e.g., during the injection of treating
fluids such as
water or oil based fluids, acids, cement slurries, sand consolidation slurries
and the like.
[0008] One technique for sealing off an annulus may be through the use of a
chemical
seal ring, whereby a fluid, usually a slurry, transforms into a rubberlike gel
as it is
injected into the annulus. Should there temporarily be any leak about the gel,
the gel
swells to seal or "plug" the leak. Chemical seal rings are described in
further detail in
U.S. Pat. Nos. 3,483,706, 3,504,499, 4,137,970, 4,923,829, 5,048,605 and
6,848,505, the
disclosures of which are incorporated by reference herein in their entirety.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0009] Figure 1 is a graphical representation showing the effect of
dilution on Moduli
G' and G" of gels according to embodiments of the instant disclosure;
[0010] Figure 2 is a graphical representation showing the effect of
temperature on the
Grace viscosity of gels according to embodiments of the instant disclosure;
[0011] Figure 3 is a graphical representation showing different
polyacrylamides
crosslinked with PVP at 6%;
[0012] Figure 4 is a graphical representation showing the effect of the
crosslinker
concentration on the gel strength of gels according to embodiments of the
instant
disclosure;
[0013] Figure 5 is a graphical representation showing the effects of PVP
molecular
weight on gel strength according to embodiments of the instant disclosure;
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[0014] Figure 6 is a graphical representation showing gels according to
embodiments
of the instant disclosure having a low Mw PHPA 0.5 million Mw with a 5%
hydrolysis;
and
[0015] Figure 7 is a graphical representation showing non-ionic
polyacrylamide
(PAM) (i.e., with 0% hydrolysis) gels with PVP according to embodiments of the
instant
disclosure.
[0016] Figure 8 is a graphical representation showing the effect of PVP
molecular
weight on gel strength of gels as compared to compressive distance of the
embodiments
of the instant disclosure.
[0017] Figure 9 is a graphical representation showing the effect of polymer
loading
on gel strength of the embodiments of the instant disclosure.
[0018] Figure 10 is a graphical representation showing the effect of sodium
hydroxide on the gel strength of the embodiments of the instant disclosure.
[0019] Figure 11 is a graphical representation showing the effect of water
on the gel
strength of the embodiments of the instant disclosure.
[0020] Figure 12 is a graphical representation showing the effect of
temperature on
the gel strength of the embodiments of the instant disclosure.
[0021] Figure 13 is a graphical representation showing the effects of
different types
of brines (cesium formate vs. potassium formate) on the gel strength of the
embodiments
of the instant disclosure.
[0022] Figure 14 is a graphical representation showing the effect of PVP on
the gel
strength of the embodiments of the instant disclosure.
[0023] Figure 15 is a graphical representation showing the effect of
mineral oil as
compared to cesium formate brine on the gel strength of the embodiments of the
instant
disclosure.
DETAILED DESCRIPTION
[0024] At the outset, it should be noted that in the development of any
such actual
embodiment, numerous implementation-specific decisions must be made to achieve
the
developer's specific goals, such as compliance with system related and
business related
constraints, which will vary from one implementation to another. Moreover, it
will be
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appreciated that such a development effort might be complex and time consuming
but
would nevertheless be a routine undertaking for those of ordinary skill in the
art having
the benefit of this disclosure. In addition, the composition used/disclosed
herein can also
comprise some components other than those cited. In the summary and this
detailed
description, each numerical value should be read once as modified by the term
"about"
(unless already expressly so modified), and then read again as not so modified
unless
otherwise indicated in context. Also, in the summary and this detailed
description, it
should be understood that a concentration range listed or described as being
useful,
suitable, or the like, is intended that any and every concentration within the
range,
including the end points, is to be considered as having been stated. For
example, "a range
of from 1 to 10" is to be read as indicating each and every possible number
along the
continuum between about 1 and about 10. Thus, even if specific data points
within the
range, or even no data points within the range, are explicitly identified or
refer to only a
few specific, it is to be understood that inventors appreciate and understand
that any and
all data points within the range are to be considered to have been specified,
and that
inventors possessed knowledge of the entire range and all points within the
range.
[0025] As used in the specification and claims, "near" is inclusive of
"at."
[0026] The following definitions are provided in order to aid those skilled
in the art in
understanding the detailed description.
[0027] The term "treatment", or "treating", refers to any subterranean
operation that
uses a fluid in conjunction with a desired function and/or for a desired
purpose. The term
"treatment", or "treating", does not imply any particular action by the fluid.
[0028] The term "fracturing" refers to the process and methods of breaking
down a
geological formation and creating a fracture, i.e. the rock formation around a
well bore,
by pumping fluid at very high pressures (pressure above the determined closure
pressure
of the formation), in order to increase production rates from or injection
rates into a
hydrocarbon reservoir. The fracturing methods otherwise use conventional
techniques
known in the art.
[0029] As used herein, the new numbering scheme for the Periodic Table
Groups are
used as in Chemical and Engineering News, 63(5), 27 (1985).
[0030] As used herein, the term "liquid composition" or "liquid medium"
refers to a
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material which is liquid under the conditions of use. For example, a liquid
medium may
refer to water, and/or an organic solvent which is above the freezing point
and below the
boiling point of the material at a particular pressure. A liquid medium may
also refer to a
supercritical fluid.
[00311 As used herein, the term "polymer" or "oligomer" is used
interchangeably
unless otherwise specified, and both refer to homopolymers, copolymers,
interpolymers,
terpolyrners, and the like. Likewise, a copolymer may refer to a polymer
comprising at
least two monomers, optionally with other monomers. When a polymer is referred
to as
comprising a monomer; the monomer is present in the polymer in the polymerized
form
of the monomer or in the derivative form of the monomer. However, for ease of
reference
the phrase comprising the (respective) monomer or the like is used as
shorthand.
[00321 As used herein, the term gel refers to a solid or semi-solid, jelly-
like
composition that can have properties ranging from soft and weak to hard and
tough. The
term "gel" refers to a substantially dilute crosslinked system, which exhibits
no flow
when in the steady-state, which by weight is mostly liquid, yet behaves like
solids due to
a three-dimensional crosslinked network within the liquid. It is the
crosslinks within the
fluid that give a gel its structure (hardness) and contribute to stickiness.
Accordingly,
gels are a dispersion of molecules of a liquid within a solid in which the
solid is the
continuous phase and the liquid is the discontinuous phase. In an embodiment,
a gel is
considered to be present when the Elastic Modulus G' is larger than the
Viscous Modulus
G", when measured using an oscillatory shear rheometer (such as a Bohlin CVO
50) at a
frequency of 1 Hz and at 20 C. The measurement of these moduli is well known
to one
of minimal skill in the art, and is described in An Introduction to Rheology,
by H. A.
Barnes, J. F. Hutton, and K. Walters, Elsevier, Amsterdam (1997), which is
fully
incorporated by reference herein.
[0033] As used herein, the term "dehydrating" as in "dehydrating a gel"
refers to
removing water or whatever solvent is present in the gel. Dehydrating may be
accomplished by the application of heat, reduced pressure, freeze-drying, or
any
combination thereof
[0034] As used herein, the term "freeze-drying" refers to the process also
known in
the art as lyophilisation, lyophilization or cryodesiccation, which is a
dehydration process
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in which the temperature of a material is lowered (e.g., freezing the
material) and then
surrounding pressure is reduced to allow the frozen water in the material to
sublimate
directly from the solid phase to the gas phase.
[0035] The term polyacrylamide refers to pure polyacrylamide homopolymer or
copolymer with near zero amount of acrylate groups, a partially hydrolyzed
polyacrylamide polymer or copolymer with a mixture of acrylate groups and
acrylamide
groups formed by hydrolysis and copolymers comprising acrylamide, acrylic
acid, and/or
other monomers. Hydrolysis of acrylamide to acrylic acid proceeds with
elevated
temperatures and is enhanced by acidic or basic conditions. The reaction
product is
ammonia, which will increase the pH of acidic or neutral solutions. Except for
severe
conditions, hydrolysis of polyacrylamide tends to stop near 66%, representing
the point
where each acrylamide is sandwiched between two acrylate groups and steric
hindrance
restricts further hydrolysis. Polyacrylic acid is formed from acrylate monomer
and is
equivalent to 100% hydrolyzed polyacrylamide.
[0036] In an embodiment, a gel comprises greater than 1 wt% polyacrylamide
crosslinked with a non-metallic crosslinker.
[0037] The non-metallic crosslinkers do not include metals, but are instead
organic
molecules, oligomers, polymers, and/or the like. In an embodiment, the non-
metallic
crosslinker comprises a polylactam. Accordingly, in an embodiment, a gel
comprises
greater than 1 wt% polyacrylamide crosslinked with a non-metallic crosslinker,
the non-
metallic crosslinker comprising a polylactam.
[0038] In an embodiment, the non-metallic crosslinker comprises a
polylactam.
Polylactams include any oligomer or polymer having pendent lactam (cyclic
amide)
functionality. Polylactams may be homopolymers, copolymers, block-copolymers,
grafted polymers, or any combination thereof comprising from 3 to 20 carbon
atoms in
the lactam functional group pendent to the polymer backbone. Examples include
polyalkyl-beta lactams, polyaLkyl-gamma lactams, polyalkyl-delta lactams,
polyalkyl-
epsilon lactams, polyalkylene-beta lactams, polyalkylene-gamma lactams,
polyalkylene-
delta lactams, polyalkylene-epsilon lactams, and the like. Other examples of
polylactams
include polyalkylenepyrrolidones, polyalkylenecaprolactams, polymers
comprising Vince
lactam (2-azabicyclo[2.2.1]hept-5-en-3-one), decyl lactam, undecyl lactam,
lauryl lactam,
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and the like. The alkyl or alkylene substituents in these polymers can
include, in an
embodiment, any polymerizable substituent.having,from 2 to about 20 carbon
atoms, e.g.,
vinyl, allyl, piperylenyl, cyclopentadienyl, or the like. In an embodiment,
the non-
metallic crosslinker is polyvinylpyrrolidone, polyvinylcaprolactam, or a
combination
thereof. In an embodiment, the non-metallic crosslinker comprises a
polylactam, such as
polyvinylpyrrolidone, having a weight average molecular weight of greater than
or equal
to about 10,000 g/mol and less than or equal to about 2 million g/mol. In an
embodiment,
the non-metallic crosslinker comprises polyvinylpyrrolidone having a weight
average
molecular weight of greater than or equal to about 50,000 g/mol and less than
or equal to
about 0.4 million g/mol. In an embodiment, the non-metallic crosslinker
comprises
polyvinylpyrrolidone having a molecular weight of greater than or equal to
about 10,000
g/mol and less than or equal to about 50,000 g/mol.
[0039] In an embodiment, the gel comprises polyacrylamide crosslinked with
a non-
metallic crosslinker, gel comprising, greater than 1 wt% polyacrylamide
crosslinked with
a polylactam.
[0040] In an embodiment, the polyacrylamide has a weight average molecular
weight
of greater than or equal to about 0.5 million g/mol, or the polyacrylamide has
a weight
average molecular weight from about 1 million to about 20 million g/mol, such
as from
about 1.5 million to about 10 million g/mol and from about 2 million to about
5 million
g/mol.
[0041] In an embodiment, the polyacrylamide is a partially hydrolyzed
polyacrylamide having a degree of hydrolysis of from 0 or 0.01% up to less
than or equal
to about 40%, or from 0 or 0.05% up to less than or equal to about 20%, or
from 0 or
0.1% up to less than or equal to about 10%, or from about 0 or 1% up to less
than or
equal to 5%.
[0042] In an embodiment, the gel comprises polyacrylamide crosslinked with
a non-
metallic crosslinker wherein the polyacrylamide is present in the gel at a
concentration of
greater than or equal to about 1 wt%, or greater than or equal to about 2 wt%
and less
than or equal to about 10 wt%, based on the total weight of the gel.
[0043] In an embodiment, the gel has a pH of less than or equal to about 3
or greater
than or equal to about 9, wherein the gel pH is defined as the pH of a 5%
combination of
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the gel in water. In an alternative embodiment, the gel pH is defined as the
pH as
determined using a moistened pH probe in contact with the gel, e.g., moistened
pH
indicator paper.
[0044] In an embodiment, the gel according to the present disclosure has a
complex
viscosity of greater than or equal to about 100 Pa's at less than or equal to
about 0.01 Hz.
[0045] In an embodiment, the gel has a G' - G" of greater than or equal to
about 0.10,
when determined using an oscillatory shear rheometer at a frequency of 1 Hz
and at 20
C.
[0046] In an embodiment, a method to produce a gel comprises contacting a
composition comprising greater than or equal to about 3 wt% polyacrylamide as
described herein with a non-metallic crosslinker as described herein
comprising a
polylactam at a pH of greater than or equal to about 9, or less than or equal
to about 3, at
a temperature and for a period of time sufficient to produce the gel, wherein
the
polyacrylamide concentration in the gel is greater than about 1 wt%, and
wherein the
amount of the non-metallic crosslinker contacted with the polyacrylamide is
sufficient to
produce a gel having a concentration of the non-metallic crosslinker in the
gel of greater
than or equal to about 1 wt%, based on the total weight of the gel.
[0047] In an embodiment, the composition comprising greater than or equal
to about
3 wt% polyacrylamide is a solution, dispersion, emulsion, or slurry, or an
aqueous
solution, an aqueous emulsion, an aqueous dispersion or an aqueous slurry. In
an
embodiment, the non-metallic crosslinker is a solid or a solution, an
emulsion, a
dispersion, or a slurry, or an aqueous solution, an aqueous dispersion, an
aqueous
emulsion, or an aqueous slurry when contacted with the polyacrylamide
composition.
[0048] In an embodiment, a composition comprising greater than or equal to
about 3
wt% polyacrylamide is contacted with the non-metallic crosslinker while
mixing, stirring,
under shear, while being agitated, and/or the like to produce the gel. In an
embodiment,
the composition comprising greater than or equal to about 3 wt% polyacrylamide
is
contacted with the non-metallic crosslinker at a temperature of greater than
or equal to
about 20 C, for a period of time of about 1 minute to about 30 days. In an
embodiment,
the composition comprising greater than or equal to about 3 wt% polyacrylamide
is
contacted with the non-metallic crosslinker at a temperature of greater than
or equal to
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about 30 C, greater than or equal to about 40 C, greater than or equal to
about 50 C,
greater than or equal to about 60 C, for a period of time of about 1 minute to
about 10
days, about 5 minutes to about 24 hours, or any combination thereof.
[0049] In an embodiment, the amount of polyacrylamide present in the
aqueous
composition is sufficient to produce a gel having a polyacrylamide
concentration of
greater than or equal to about 2 wt% and less than or equal to about 10 wt%,
based on the
total weight of the gel. In an embodiment, the amount of the non-metallic
crosslinker
contacted with the polyacrylamide is sufficient to produce a gel having a
concentration of
the non-metallic crosslinker in the gel of greater than or equal to about 2
wt% and less
than or equal to about 10 wt%, based on the total weight of the gel.
[0050] In an embodiment, a method to produce a gel concentrate comprises
contacting an aqueous composition comprising greater than or equal to about 3
wt%
polyacrylamide with a non-metallic crosslinker comprising a polylactam at a pH
of
greater than or equal to about 9, at a temperature and for a period of time
sufficient to
produce a gel, wherein the polyacrylamide has a weight average molecular
weight of
greater than or equal to about 0.5 million g/mol, wherein the polyacrylamide
concentration in the gel is greater than or equal to about 1 wt%, and wherein
the
concentration of the non-metallic crosslinker in the gel is greater than or
equal to about 1
wt%, based on the total weight of the gel; and dehydrating the gel to produce
the gel
concentrate.
[0051] In an embodiment, dehydrating the gel comprises heating, freeze
drying, or
otherwise dehydrating the gel to produce the gel concentrate. In an
embodiment, the
particle size of the gel concentrate may be reduced to facilitate subsequent
rehydration
and thus reconstitution of the gel concentration to produce the reconstituted
gel.
[0052] In an embodiment, a method to produce a reconstituted gel comprises
contacting an aqueous composition comprising greater than or equal to about 3
wt%
polyacrylamide with a non-metallic crosslinker comprising a polylactam at a
first pH of
greater than or equal to about 9, at a first temperature and for a first
period of time
sufficient to produce a first gel, wherein the polyacrylamide has a weight
average
molecular weight of greater than or equal to about 0.5 million g/mol, wherein
the
polyacrylamide concentration in the first gel is greater than or equal to
about 1 wt%, and
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wherein the concentration of the non-metallic crosslinker in the first gel is
greater than or
equal to about 1 wt%, based on the total weight of the first gel; dehydrating
the first gel
to produce a gel concentrate; and contacting the gel concentrate with an
aqueous solution
at a second pH, at a second temperature and for a second period of time
sufficient to
produce the reconstituted gel. In an embodiment, the gel concentrate is
reconstituted at a
second pH of greater than or equal to about 8, or less than or equal to about
5.
[0053] In an embodiment, the gel produced according to the instant
disclosure
absorbs water when placed in contact with an aqueous solution. In an
embodiment, the
gel in contact with water uptakes greater than or equal to about 100% by
weight of water,
or greater than or equal to about 200% by weight of water, based on the weight
of the gel
present.
[0054] In an embodiment, the gel is formed at a pH of greater than or equal
to about 9
and remains as a gel when the pH of the gel is lowered below 9, or when the pH
of the
gel is lowered below about 7, below about 5, and/or below about 3.
Accordingly, in an
embodiment, the gels according to the instant disclosure are non-reversible
once formed,
pH stable once formed, or a combination thereof.
[0055] In an embodiment, the gel is formed at a concentration of
polyacrylamide
suitable to produce a gel having a polyacrylamide concentration which is
greater than or
equal to about 1 wt%, based on the total weight of the gel, and then the gel
is diluted with
a solvent, e.g., an aqueous solvent, and the diluted gel retains a G' which is
higher than a
G" indicating a gel is present. Accordingly, in an embodiment, the gels
according to the
instant disclosure are non-reversible once formed and are stable upon dilution
from 1
wt% dilution up to , and in excess of 1000 wt% dilution, based on the total
amount of gel
present. Accordingly, a 1:1 dilution of the gel up to a 10:1 dilution and
above of the gel
to produce a diluted composition, results in a diluted composition comprising
the gel.
[0056] In an embodiment, the gels are formed and/or reconstituted at a
temperature
greater than or equal to about 20 C, or greater than or equal to about 30 C,
or greater
than or equal to about 40 C, or greater than or equal to about 50 C. In an
embodiment,
the gels retain essentially all of the same physical properties (i.e., are
stable) at a
temperature of greater than or equal to about 20 C, and less than or equal to
about 150 C,
or less than or equal to about 120 C, or less than or equal to about 110 C, or
less than or
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equal to about 100 C, or less than or equal to about 90 C.
[0057] In an embodiment, a method of treating a wellbore comprises
injecting a
composition comprising polyacrylamide crosslinked with a non-metallic
crosslinker
comprising a polylactam into a wellbore. Accordingly, in an embodiment the gel
is pre-
formed and subsequently injected into the wellbore.
[0058] In an embodiment, a method of treating a wellbore comprises
injecting a
composition comprising greater than or equal to about 3 wt% polyacrylamide
into a
wellbore; injecting a composition comprising a non-metallic crosslinker
comprising a
polylactam into the wellbore, and injecting a pH adjusting fluid into the
wellbore in an
amount sufficient (or calculated to be sufficient) to produce a downhole
solution pH of
greater than or equal to about 9 or less than or equal to about 3, to produce
an in-situ gel
comprising greater than or equal to about 1 wt% polyacrylamide and greater
than or equal
to about 1 wt% of the non-metallic crosslinker, based on the amount of the
gel. As is
obvious to one of skill in the art, it may be impossible to obtain
measurements downhole.
Accordingly, the amounts sufficient may be determined based on calculations
which
include assumptions about the downhole conditions. The presence of a gel down
hole
may be determined by other indicators other than rheological measurements.
[0059] In an embodiment, the amount of polyacrylamide present in the
polyacrylamide composition injected into the wellbore is sufficient to produce
a gel
having a polyacrylamide concentration of greater than or equal to about 2 wt%
and less
than or equal to about 10 wt%, based on the total weight of the gel. In an
embodiment,
the amount of the non-metallic crosslinker injected into the wellbore is
sufficient to
produce a gel having a concentration of the non-metallic crosslinker in the
gel of greater
than or equal to about 2 wt% and less than or equal to about 10 wt%, based on
the total
weight of the gel.
[0060] In and embodiment, the composition comprising greater than or equal
to about
3 wt% polyacrylamide, the composition comprising the non-metallic crosslinker,
and the
pH adjustment fluid are injected into the wellbore separately, simultaneously,
or any
combination thereof. Accordingly, in an embodiment, the composition comprising
the
polyacrylamide and the composition comprising the non-metallic crosslinker may
be
combined and then injected into the well bore either prior to or after the
injection of the
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pH adjustment fluid into the wellbore. In an embodiment, the composition
comprising
the polyacrylamide and the pH adjustment fluid may be combined and then
injected into
the well bore either prior to or after the injection of the composition
comprising the non-
metallic crosslinker into the wellbore. In an embodiment, the composition
comprising
the non-metallic crosslinker and the pH adjustment fluid may be combined and
then
injected into the well bore either prior to or after the injection of the
composition
comprising the polyacrylamide into the wellbore.
[0061] In an embodiment, the pH adjusting fluid is an aqueous solution
comprising a
base, an acid, a pH buffer, or any combination thereof. In an embodiment, the
pH
adjusting fluid comprises sodium hydroxide, sodium carbonate, sulfuric acid,
hydrochloric acid, an organic acid, carbon dioxide or any combination thereof.
Furthermore, the composition may also comprise a pH adjusting solid material
comprising a base, an acid, a pH buffer, or any combination thereof. Specific
examples
of the pH adjusting fluid include sodium hydroxide, sodium carbonate, sulfuric
acid,
hydrochloric acid, an organic acid, carbon dioxide or any combination thereof.
The pH
adjusting solid material may be present in the composition in an amount of
from about
0.0001 weight percent to about 50 weight percent, such as from about 0.001
weight
percent to about 5 weight percent, from about 0.01 weight percent to about 2
weight
percent and from about 0.1 weight percent to about 1 weight percent.
[0062] In an embodiment, a method of treating a wellbore comprises
injecting a
composition comprising a gel concentrate into a wellbore, the gel concentrate
comprising
polyacrylaraide crosslinked with a non-metallic crosslinker comprising a
polylactam,
wherein the polyacrylamide has a weight average molecular weight of greater
than or
equal to about 0.5 million g/mol, to produce a reconstituted gel in-situ, the
reconstituted
gel comprising greater than or equal to about 1 wt% polyacrylamide and greater
than or
equal to about 1 wt% of the non-metallic crosslinker, based on the amount of
the gel
calculated to be present. In an embodiment, the gel concentrate is the gel
disclosed
herein which has been freeze dried or otherwise dehydrated or had at least a
portion of
the solvent removed to produce the gel concentrate.
[0063] In an embodiment, a wellbore treatment fluid comprises a gel
comprising,
greater than 1 wt% polyacrylamide crosslinked with a non-metallic crosslinker,
the non-
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metallic crosslinker comprising a polylactam.
[0064] In an embodiment, a wellbore treatment fluid comprises a first
composition
comprising greater than or equal to about 3 wt% polyacrylamide; and a second
composition comprising a non-metallic crosslinker comprising a polylactam.
[0065] In an embodiment, a wellbore treatment fluid comprises a gel
concentrate
comprising polyacrylamide crosslinked with a non-metallic crosslinker
comprising a
polylactam.
[0066] In an embodiment, the compositions and/or the gels may comprise
water, i.e.,
an aqueous gel, and/or an organic solvent. The organic solvent may be selected
from the
group consisting of diesel oil, kerosene, paraffinic oil, crude oil, LPG,
toluene, xylene,
ether, ester, mineral oil, biodiesel, vegetable oil, animal oil, and mixtures
thereof.
Specific examples of suitable organic solvents include acetone, acetonitrile,
benzene, 1-
butanol, 2-butanol, 2-butanone, t-butyl alcohol, carbon tetrachloride,
chlorobenzene,
chloroform, cyclohexane, 1,2-dichloroethane, diethyl ether, diethylene glycol,
polyethylene glycol, diglyme (diethylene glycol dimethyl ether), 1,2-dimethoxy-
ethane
(glyme, DME), dimethylether, dibutylether, dimethyl-formamide (DMF), dimethyl
sulfoxide (DMSO), dioxane, ethanol, ethyl acetate, ethylene glycol, glycerin,
heptanes,
Hexamethylphosphoramide (HMPA), Hexamethylphosphorous triamide (HMPT),
hexane, methanol, methyl t-butyl ether (MTBE), methylene chloride, N-methy1-2-
pyrrolidinone (NMP), nitromethane, pentane , Petroleum ether (ligroine), 1-
propanol, 2-
propanol, pyridine, tetrahydrofuran (THF), toluene, triethyl amine, o-xylene,
m-xylene,
p-xylene, combinations thereof, and/or the like.
[0067] Further solvents include aromatic petroleum cuts, terpenes, mono-,
di- and tri-
glycerides of saturated or unsaturated fatty acids including natural and
synthetic
triglycerides, aliphatic esters such as methyl esters of a mixture of acetic,
succinic and
glutaric acids, aliphatic ethers of glycols such as ethylene glycol monobutyl
ether,
minerals oils such as vaseline oil, chlorinated solvents like 1,1,1 -
trichloroethane,
perchloroethylene and methylene chloride, deodorized kerosene, solvent
naphtha,
paraffins (including linear paraffins), isoparaffins, olefins (especially
linear olefins) and
aliphatic or aromatic hydrocarbons (such as toluene). Terpenes are suitable,
including d-
limonene, 1-limonene, dipentene (also known as 1-methyl-4-(1-methyletheny1)-
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cyclohexene), myrcene, alpha-pinene, linalool and mixtures thereof.
[0068] Further exemplary organic liquids include long chain alcohols
(monoalcohols
and glycols), esters, ketones (including diketones and polyketones), nitrites,
amides,
amines, cyclic ethers, linear and branched ethers, glycol ethers (such as
ethylene glycol
monobutyl ether), polyglycol ethers, pyrrolidones like N-(alkyl or cycloalkyl)-
2-
pyrrolidones, N-alkyl piperidones, N, N-dialkyl alkanolamides, N,N,N',N'-tetra
alkyl
ureas, dialkylsulfmddes, pyridines, hexaalkylphosphoric triamides, 1,3-
dimethy1-2-
imidazolidinone, nitroalkanes, nitro-compounds of aromatic hydrocarbons,
sulfolanes,
butyrolactones, and alkylene or alkyl carbonates. These include polyalkylene
glycols,
polyalkylene glycol ethers like mono (alkyl or aryl) ethers of glycols, mono
(alkyl or
aryl) ethers of polyalkylene glycols and poly (alkyl and/or aryl) ethers of
polyalkylene
glycols, monoalkanoate esters of glycols, monoalkanoate esters of polyalkylene
glycols,
polyalkylene glycol esters like poly (alkyl and/or aryl) esters of
polyalkylene glycols,
dialkyl ethers of polyalkylene glycols, dialkanoate esters of polyalkylene
glycols, N-
(alkyl or cycloalkyl)-2-pyrrolidones, pyridine and alkylpyridines,
diethylether,
dimethoxyethane, methyl formate, ethyl formate, methyl propionate,
acetonitrile,
benzonitrile, dimethylformamide, N-methylpyrrolidone, ethylene carbonate,
dimethyl
carbonate, propylene carbonate, diethyl carbonate, ethylmethyl carbonate, and
dibutyl
carbonate, lactones, nitromethane, and nitrobenzene sulfones. The organic
liquid may
also be selected from the group consisting of tetrahydrofuran, dioxane,
dioxolane,
methyltetrahydrofuran, dimethylsulfone, tetramethylene sulfone and thiophen.
[0069] In an embodiment, the well treatment fluid, also referred to as the
carrier fluid,
may include any base fracturing fluid understood in the art. Some non-limiting
examples
of carrier fluids include hydratable gels (e.g. guars, poly-saccharides,
xanthan, hydroxy-
ethyl-cellulose, etc.), a crosslinked hydratable gel, a viscosified acid (e.g.
gel-based), an
emulsified acid (e.g. oil outer phase), an energized fluid (e.g. an N2 or CO2
based foam),
and an oil-based fluid including a gelled, foamed, or otherwise viscosified
oil.
[0070] Additionally, the carrier fluid or solvent may be a brine, and/or
may include a
brine, such as a heavy brine. As used herein, the phrase "heavy brine" refers
to salts that
contain from about 1 wt% up to the saturated concentrations to give a range of
densities.
For example, the range of densities for specific materials may be the
following: from
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1.01 g/mL to 1.392g/mL for calcium chloride, 1.01 g/mL to 1.812g/mL for
calcium
bromide, 1.01 WmL to 2.305 g/mL for zinc bromide, 1.01 g/mL to 1.2 g/mL for
sodium
chloride, 1.01 g/mL to 1.164 g/mL for potassium chloride, 1.01 g/mL to 1.164
g/mL for
ammonium chloride, 1.01 g/mL to 1.537 g/mL for sodium bromide, 1.01 g/mL to
1.330
g/mL for sodium formate, 1.01 g/mL to 1.571 g/mL for potassium formate, 1.01
g/mL to
2.4 g/mL for cesium formate. Specific examples of heavy brines may include
alkali
metal and alkali earth metal formates, such potassium formate, sodium formate
and
cesium formate; alkali metal and alkali earth metal halides such assoditun
chloride,
potassium chloride and calcium bromide; and transition metal halides, such as
zinc
halide.
[0071] In an embodiment, the well treatment fluid may include a
viscosifying agent,
which may include a viscoelastic surfactant (VES). The VES may be selected
from the
group consisting of cationic, anionic, zwitterionic, amphoteric, nonionic and
combinations thereof. Some non-limiting examples are those cited in U.S.
Patents
6,435,277 (Qu et al.) and 6,703,352 (Dahayanake et al.), each of which are
incorporated
herein by reference. The viscoelastic surfactants, when used alone or in
combination, are
capable of forming micelles that form a structure in an aqueous environment
that
contribute to the increased viscosity of the fluid (also referred to as
"viscosifying
micelles"). These fluids are normally prepared by mixing in appropriate
amounts of VES
suitable to achieve the desired viscosity. The viscosity of VES fluids may be
attributed to
the three dimensional structure formed by the components in the fluids. When
the
concentration of surfactants in a viscoelastic fluid significantly exceeds a
critical
concentration, and in most cases in the presence of an electrolyte, surfactant
molecules
aggregate into species such as micelles, which can interact to form a network
exhibiting
viscous and elastic behavior.
[0072] In general, particularly suitable zwitterionic surfactants
have the formula:
RCONH-(CH2)a(CH2CH20)4CH2)b-N+(CH3)2-(CH2)a.(CH2CH20),n,(CH2)b,C00"
in which R is an alkyl group that contains from about 11 to about 23 carbon
atoms which
may be branched or straight chained and which may be saturated or unsaturated;
a, b, a',
and b' are each from 0 to 10 and m and m' are each from 0 to 13; a and b are
each 1 or 2
if m is not 0 and (a + b) is from 2 to 10 if m is 0; a' and b' are each 1 or 2
when m' is not
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0 and (a' + b') is from 1 to 5 if m is 0; (m + m') is from 0 to 14; and
CH2CH20 may also
be OCH2CH2. In some embodiments, a zwitterionic surfactant of the family of
betaine is
used.
[0073] Exemplary cationic viscoelastic surfactants include the amine
salts and
quaternary amine salts disclosed in U.S. Patent Nos. 5,979,557, and 6,435,277
which are
hereby incorporated by reference. Examples of suitable cationic viscoelastic
surfactants
include cationic surfactants having the structure:
RIN+(R2)(R3)(R4)
in which R1 has from about 14 to about 26 carbon atoms and may be branched or
straight
chained, aromatic, saturated or unsaturated, and may contain a carbonyl, an
amide, a
retroamide, an imide, a urea, or an amine; R2, R3, and R4 are each
independently
hydrogen or a C1 to about C6 aliphatic group which may be the same or
different,
branched or straight chained, saturated or unsaturated and one or more than
one of which
may be substituted with a group that renders the R2, R3, and R4 group more
hydrophilic;
the R2 , R3, and R4 groups may be incorporated into a heterocyclic 5- or 6-
member ring
structure which includes the nitrogen atom; the R2, R3, and R4 groups may be
the same or
different; RI, R2, R3, and/or R4 may contain one or more ethylene oxide and/or
propylene
oxide units; and X- is an anion. Mixtures of such compounds are also suitable.
As a
further example, R1 is from about 18 to about 22 carbon atoms and may contain
a
carbonyl, an amide, or an amine, and R2, R3, and R4 are the same as one
another and
contain from 1 to about 3 carbon atoms.
[0074] Amphoteric viscoelastic surfactants are also suitable. Exemplary
amphoteric
viscoelastic surfactant systems include those described in U.S. Patent No.
6,703,352, for
example amine oxides. Other exemplary viscoelastic surfactant systems include
those
described in U.S. Patents Nos. 6,239,183; 6,506,710; 7,060,661; 7,303,018; and
7,510,009 for example amidoamine oxides. These references are hereby
incorporated in
their entirety. Mixtures of zwitterionic surfactants and amphoteric
surfactants are
suitable. An example is a mixture of about 13% isopropanol, about 5% 1-
butanol, about
15% ethylene glycol monobutyl ether, about 4% sodium chloride, about 30%
water,
about 30% cocoamidopropyl betaine, and about 2% cocoamidopropylamine oxide.
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[0075] The viscoelastic surfactant system may also be based upon any
suitable
anionic surfactant. In some embodiments, the anionic surfactant is an alkyl
sarcosinate.
The alkyl sarcosinate can generally have any number of carbon atoms. Alkyl
sarcosinates
can have about 12 to about 24 carbon atoms. The alkyl sarcosinate can have
about 14 to
about 18 carbon atoms. Specific examples of the number of carbon atoms include
12, 14,
16, 18, 20, 22, and 24 carbon atoms. The anionic surfactant is represented by
the
chemical formula:
R1CON(R2)CH2X
wherein R1 is a hydrophobic chain having about 12 to about 24 carbon atoms, R2
is
hydrogen, methyl, ethyl, propyl, or butyl, and X is carboxyl or sulfonyl. The
hydrophobic
chain can be an alkyl group, an alkenyl group, an alkylarylalkyl group, or an
alkoxyalkyl
group. Specific examples of the hydrophobic chain include a tetradecyl group,
a
hexadecyl group, an octadecentyl group, an octadecyl group, and a docosenoic
group.
Examples include hydrophobic chains derived from a carboxylic acid moiety
having from
to 30 carbon atoms, or from 12 to 22 carbon atoms. In an embodiment, the
carboxylic
acid moieties are derived from carboxylic acids selected from the group
consisting of
capric acid, undecylic acid, lauric acid, tridecylic acid, myristic acid,
pentadecylic acid,
palmitic acid, margaric acid, stearic acid, nonadecylic acid, arachidic acid,
heneicosylic
acid, behenic acid, tricosylic acid, lignoceric acid, pentacosylic acid,
cerotic acid,
heptacosylic acid, montanic acid, nonacosylic acid, melissic acid, myristoleic
acid,
pahnitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid,
linoleic acid,
linoelaidic acid, a-linolenic acid, arachidonic acid, eicosapentaenoic acid,
erucic acid,
docosahexaenoic acid, resinolic acid, and a combination thereof.
[0076] In an embodiment, the carrier fluid includes an acid, a
chelant, or both. The
fracture may be a traditional hydraulic bi-wing fracture, but in certain
embodiments may
be an etched fracture and/or wormholes such as developed by an acid treatment.
The
carrier fluid may include hydrochloric acid, hydrofluoric acid, ammonium
bifluoride,
formic acid, acetic acid, lactic acid, glycolic acid, maleic acid, tartaric
acid, sulfamic acid,
malic acid, citric acid, methyl-sulfamic acid, chloro-acetic acid, an amino-
poly-
carboxylic acid, 3-hydroxypropionic acid, a poly-amino-poly-carboxylic acid,
and/or a
salt of any acid. In certain embodiments, the carrier fluid includes a poly-
amino-poly-
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carboxylic acid, trisodium hydroxyl-ethyl-ethylene-diamine triacetate, mono-
ammonium
salts of hydroxyl-ethyl-ethylene-diamine triacetate, and/or mono-sodium salts
of
hydroxyl-ethyl-ethylene-diamine tetra-acetate. The selection of any acid as a
carrier fluid
depends upon the purpose of the acid ¨ for example formation etching, damage
cleanup,
removal of acid-reactive particles, etc., and further upon compatibility with
the
formation, compatibility with fluids in the formation, and compatibility with
other
components of the fracturing slurry and with spacer fluids or other fluids
that may be
present in the wellbore. The selection of an acid for the carrier fluid is
understood in the
art based upon the characteristics of particular embodiments and the
disclosures herein.
[00771 The
composition may include a particulate blend made of proppant. Proppant
selection involves many compromises imposed by economical and practical
considerations. Criteria for selecting the proppant type, size, size
distribution in
multimodal proppant selection, and concentration is based on the needed
dimensionless
conductivity, and can be selected by a skilled artisan. Such proppants can be
natural or
synthetic (including but not limited to glass beads, ceramic beads, sand, and
bauxite),
coated, or contain chemicals; more than one can be used sequentially or in
mixtures of
different sizes or different materials. The proppant may be resin coated
(curable), or pre-
cured resin coated. Proppants and gravels in the same or different wells or
treatments can
be the same material and/or the same size as one another and the term proppant
is
intended to include gravel in this disclosure. In some embodiments, irregular
shaped
particles may be used such as unconventional proppant. In general the proppant
used will
have an average particle size of from about 0.15 mm to about 4.76 mm (about
100 to
about 4 U. S. mesh), or from about 0.15 mm to about 3.36 mm (about 100 to
about 6 U.
S. mesh), more or from about 0.15 mm to about 4.76 mm (about 100 to about 4 U.
S.
mesh), more particularly, but not limited to 0.25 to 0.42 mm (40/60 mesh),
0.42 to 0.84
mm (20/40 mesh), 0.84 to 1.19 mm (16/20), 0.84 to 1.68 mm (12/20 mesh) and
0.84 to
2.38 mm (8/20 mesh) sized materials. Normally the proppant will be present in
the slurry
in a concentration from about 0.12 to about 0.96 kg/L, or from about 0.12 to
about 0.72
kg/L, or from about 0.12 to about 0.54 kg/L. Some slurries are used where the
proppant is
at a concentration up to 16 PPA (1.92 kg/L). If the slurry is foamed the
proppant is at a
concentration up to 20 PPA (2.4 kg/L). The slurry composition is not a cement
slurry
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composition.
[0078] The composition may comprise particulate materials with
defined particles
size distribution. Examples of high solid content treatment fluid (HSCF) in
which the
degradeable latex may be employed are disclosed in US 7,789,146; US 7,784,541;
US
2010/0155371; US 2010/0155372; US 2010/0243250; and US 2010/0300688; all of
which are hereby incorporated herein by reference in their entireties.
[0079] The composition may further comprise a degradable material.
In certain
embodiments, the degradable material includes at least one of a lactide, a
glycolide, an
aliphatic polyester, a poly (lactide), a poly (glycolide), a poly (E-
caprolactone), a poly
(orthoester), a poly (hydroxybutyrate), an aliphatic polycarbonate, a poly
(phosphazene),
and a poly (anhydride). In certain embodiments, the degradable material
includes at least
one of a poly (saccharide), dextran, cellulose, chitin, chitosan, a protein, a
poly (amino
acid), a poly (ethylene oxide), and a copolymer including poly (lactic acid)
and poly
(glycolic acid). In certain embodiments, the degradable material includes a
copolymer
including a first moiety which includes at least one functional group from a
hydroxyl
group, a carboxylic acid group, and a hydrocarboxylic acid group, the
copolymer further
including a second moiety comprising at least one of glycolic acid and lactic
acid.
[0080] In some embodiments, the composition may optionally further
comprise
additional additives, including, but not limited to, acids, fluid loss control
additives, gas,
corrosion inhibitors, scale inhibitors, catalysts, clay control agents,
biocides, friction
reducers, temperature stabilizers, combinations thereof and the like. For
example, in
some embodiments, it may be desired to foam the storable composition using a
gas, such
as air, nitrogen, or carbon dioxide.
[0081] The composition may be used for carrying out a variety of
subterranean
treatments, including, but not limited to, drilling operations, fracturing
treatments, and
completion operations (e.g., gravel packing). In some embodiments, the
composition may
be used in treating a portion of a subterranean formation. In certain
embodiments, the
composition may be introduced into a well bore that penetrates the
subterranean
formation as a treatment fluid. For example, the treatment fluid may be
allowed to
contact the subterranean formation for a period of time. In some embodiments,
the
treatment fluid may be allowed to contact hydrocarbons, formations fluids,
and/or
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subsequently injected treatment fluids. After a chosen time, the treatment
fluid may be
recovered through the well bore. In certaip embodiments, the treatment fluids
may be
used in fracturing treatments. Furthermore, as described above, the
composition
described herein may also be used to form a chemical seal ring, wherein the
chemical seal
is entirely free of any chromium (trivalent (Cr3+) or hexavalent (Cr6+)).
[0082] The composition may comprise additional additives specifically
directed to
chemical seal rings. Examples of additional additives, include, but are not
limited to a
degradable material or carbon nanotubes. The degradable material may also be a
hydrolysable fiber. Examples of the hydrolysable fibers include unsubstituted
lactide,
glycolide, polylactic acid, polyglycolic acid, copolymers of polylactic acid
and
polyglycolic acid, copolymers of glycolic acid with other hydroxy-, carboxylic
acid-, or
hydroxycarboxylic acid-containing moieties, and copolymers of lactic acid with
other
hydroxy-, carboxylic acid-, or hydroxycarboxylic acid-containing moieties, and
mixtures
of those materials. The composition may also include bentonite, barite, and
calcium
carbonate. The gel may start to form within about 0.5 hours to about three
hours after the
addition of water as the reaction trigger. It may continue to increase in
strength the next
several days and transform from a soft gel to rubber-like, and then to hard
rock-like
material. For example, when the gel reaches a viscosity of about 10,000 cP, it
is
considered to be for use as a chemical seal ring. The amount of time require
for the gel to
obtain that gel is approximately 30 min to 180 min, or 60 to 90 min, depending
upon the
amount of water introduced.
[0083] The method is also suitable for gravel packing, or for fracturing
and gravel
packing in one operation (called, for example frac and pack, frac-n-pack, frac-
pack,
STIMPAC (Trade Mark from Schlumberger) treatments, or other names), which are
also
used extensively to stimulate the production of hydrocarbons, water and other
fluids from
subterranean formations. These operations involve pumping the composition and
propping agent/material in hydraulic fracturing or gravel (materials are
generally as the
proppants used in hydraulic fracturing) in gravel packing. In low permeability
formations, the goal of hydraulic fracturing is generally to form long, high
surface area
fractures that greatly increase the magnitude of the pathway of fluid flow
from the
formation to the wellbore. In high permeability formations, the goal of a
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fracturing treatment is typically to create a short, wide, highly conductive
fracture, in
order to bypass near-wellbore damage done, in drilling and/or completion, to
ensure good
fluid communication between the reservoir and the wellbore and also to
increase the
surface area available for fluids to flow into the wellbore.
Examples
[0084] The following examples show that gels according to the instant
disclosure
may be formed at ambient temperature provided the solution has an alkaline pH,
and may
be formed at an acidic pH upon heating. In all cases, the formed gels appear
to be very
elastic and sticky in nature. The gels will absorb and swell when placed in
water,
uptaking more than 200% of their weight. Unlike the low pH interpolymer
complexes
discussed in the literature, the clear gels of the instant disclosure are
irreversible to
changes in pH and have excellent high temperature stability. Gel formation can
occur at
ambient temperature or elevated temperature as long as the pH is alkaline. It
was
discovered that the gel is not formed by hydrogen bonding and thus is not a
complex as
seen at low pH, but is instead the result of a non-reversible chemical
reaction between the
polyacrylamide and the non-metallic crosslinker. When the non-metallic
crosslinker is a
polylactam, such as PVP, the crosslinking appears to result from a ring-
opening event
wherein the lactam ring is opened to produce a bond between an acrylamide or
acrylate
moiety and the lactam moiety to produce the gel.
[0085] Partially hydrolyzed polyacrylamide (PHPA) at 3% and
polyvinylpyrrolidone
(PVP) at 3-6% forms a very elastic gel when heated. It has also been
discovered that
heating was not required if the pH was alkaline, but a gel would form under
acidic
conditions if heated. It is speculated that the heating step generates
alkalinity by further
hydrolysis of the PHPA generating ammonia ions that raised the pH and
initiated the
gelation. Scanning Electron Microscopy (SEM) and phase contrast micrographs of
dried
gels according to the instant disclosure show gels having a linear, fibrous
character to
them and possibly form hollow vesicles.
[0086] A gel formed from 3% PHPA and 6% PVP absorbed sufficient water (200%
by weight) to yield a strong gel at a final concentration of 1% PHPA and 2%
PVP.
However, it was discovered that mixing 1% PHPA and 2% PVP in water under gel
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forming conditions does not produce a gel. Accordingly, it was discovered that
the gels
according to the instant disclosure are formed by a unique pathway, which
suggests that
to produce gels having a final polyacrylamide concentration of 0.5 to 1 wt%,
the
concentration of the polyacrylamide composition must be initially higher than
1 wt%,
typically at least about 2 wt% to at least about 3 wt%, and then subsequently
diluted via
addition of the non-metallic crosslinker to form the gels having a final
polyacrylamide
concentration of 0.5 to 1 wt.
[0087] Gels were also prepared with different molecular weights,
concentrations and
hydrolysis level of PHPA, and various molecular weights of PVP were evaluated.
[0088] The data further shows the gel may be freeze dried and later
reconstituted by
hydrating the gel concentrate particles to produce a reconstituted gel. A
temperature
delayed gelation for water control is possible. Other methods include the use
of the
instant gel particles as friction reducers, delayed viscosity booster in
hydraulic fracturing,
diverting agent in stimulation via viscosity and gel formation, temporary plug
creation,
water absorbing gel for water control, and a low viscosity cleanout fluid that
generates
viscosity downhole to lift sand and other solids to the surface.
[0089] In one set of examples, the method to produce the gels was to mix
solutions of
polyacrylamide with solutions of the various polylactam polymers under a
variety of
conditions and then determine if a gel formed. Ambient and elevated
temperature
conditions and several pH levels from acidic to basic were evaluated. The
solutions were
observed for days to weeks for gel formation. When a gel formed, the gel was
further
characterized by visual observation, rheological measurements, and the effects
of water
dilution or acidic solutions on the formed gel. Low pH gels were characterized
by
separating the free water that invariably formed from the gel portion and
evaluating the
gel portion.
Gel Formation
[0090] The mixing procedure to produce the gels was to fully hydrate the
PHPA in
deionized water using an overhead stirrer running at 600 RPM. Powdered
polyacrylamide
polymer was gradually added to the shoulder of the vortex over a 20 second
period to
avoid the formation of clumps or fisheyes. Stirring continued for about an
hour or until
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all of the polymer particles had fully hydrated as seen by visual observation.
Next, the
non-metallic crosslinker was added and stirring ,continuously until it had
also fully
hydrated or dissolved. The pH of the mixture was measured before splitting the
sample
into several parts. Each part was then adjusted to the various levels of pH
using 10% HC1
or 10% NaOH solutions. The final pH was measured and recorded, The presence of
gels
was evaluated by periodic visual observation. As an example, the fluid with 3%
PHPA
and 6% PVP was prepared as follows:
[0091] 3 grams of PHPA were added to 97 grams of DI water and stirred until
fully
hydrated to give a true 3 wt% solution.
[0092] 6 grams of PVP was then added to the solution and stirred until
fully
dissolved. This results in a solution that is 2.83 wt% PHPA and 5.66 wt% PVP,
although
it is referred to as 3% PHPA and 6% PVP.
[0093] The native pH of the mixture was then measured and the mixture
separated
into 4 parts. The pH of each portion of the solution was then adjusted to
nominal values
of 1, 3, and 9 using 10% HC1 or 10% NaOH. The fourth portion was at the native
pH.
Rheological characterization
[0094] Rheology was measured at low temperature (less than 80 C) using a
Bohlin
rheometer with 25 mm cup and bob operating under dynamic mode (frequency sweep
at
10% strain). The resulting moduli (G', G") when determined using an
oscillating shear
rheometer at 1 Hz at 20 C, and complex viscosity were used to evaluate gel
formation.
When G' at least 0.1, or at least 1, or at least 5, or at least 10 Pa=s larger
than G", this
suggests the existence of a gel and the magnitude of G' quantifies the gel
strength. When
G" is larger than G', this suggests a liquid is present and no gel has formed.
The complex
viscosity should be comparable to the steady state viscosity if the material
being tested
follows the Cox-Merx rule.
[0095] A Grace 5600 model 50 viscometer was used to generate rheological
data
which was beyond the capabilities of the cup and bob method. Viscosity build
of the gels
was monitored by adding 50 mL of the solution to the cup, attaching the cup
and
applying nitrogen pressure of about 400 psi before heating was begun. As
temperature
rose, the initially viscous fluid would decrease in viscosity (thermal
thinning) until a
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certain point where gelation was initiated and then the viscosity would rise.
Gelation
extent was monitored by the final attained viscosity.
Visual observations
100961 The results of the ambient screening for gel formation are shown in
Table 1.
For the listed PHPA polymers, the molecular weight and % hydrolysis are shown
in
parentheses in the first row of the heading and the concentration is noted.
The second
row of the heading shows the concentration of the non-metallic crosslinker.
The nominal
pH is shown to the left of the remaining rows of data. For each cell, the
observation is
recorded. An "N" shows no gelation while a "G" indicates gelation. A phase
separated
gel consisting of gel and free water is indicated by "P/S". The actual
measured pH of the
solution is shown in parentheses. These observations were generally recorded
after one
week of observation and represent the state at that time. Most of the gels
formed over
several days, although one cationic polyacrylamide sample gelled immediately.
[0097] For purposes herein the wt% of the PHPA is listed followed by the
weight
average molecular weight, expressed as either million Daltons (MDa) or in
grams per mol
(g/mol), followed by the % hydrolysis of the PHPA expressed as a wt%.
Accordingly,
the heading: 2% PHPA, 12.5 MDa, 30% Hyd represents a composition comprising 2
wt%
PHPA having a weight average molecular weight of 12.5 million Daltons, and a
30 wt%
hydrolysis of acrylamide to acrylate. The weight average molecular weight may
also be
abbreviated "MW", which indicates g/mol. Accordingly, 3% PVP, 300k MW
represents
a 3 wt% polyvinylpyrrolidone (PVP) composition wherein the PVP has a weight
average
molecular weight of 300,000 g/mol.
Table 1 2% PHPA 2% PHPA 2% PHPA 2% PHPA 2% PHPA
12.5 MDa 6 MDa 12 MDa 12 MDa 11 MDa
30% Hyd 30% Hyd 5% Hyd 12% Hyd 20% Hyd
pH 3% PVP 3% PVP 3% PVP 3% PVP 3% PVP
300k MW 300k MW 300k MW 300k MW 300k MW
3 N (3.0) N(2.6) N(2.5) N(2.4) N(2.4)
5.6 N(6.7) N(6.9) N(5.2) G(5.9) N(5.6)
9 N(9.1) N(8.9) N(9.1) G (9.1) N(8.9)
24
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2% PHPA 2% PHPA , 2% PHPA 2% PHPA 2% PHPA
12.5 MDa 6 MDa 30% 12 MDa 12 MDa 11 MDa
30% Hyd Hyd 5% Hyd 12% Hyd 20% Hyd
pH 6% PVP 6% PVP 6% PVP 6% PVP 6% PVP
300k MW 300k MW 300k MW 300k MW 300k MW
3 N (3.0) N (3.0) P/S (2.7) P/S (2.4) N(2.9)
5.6 N(6.4) N(6.6) N(5.1) G(5.3) N(6.1)
9 N(9.2) N(9.1) G(9.1) G(9.1) N(9.2)
3% PHPA 3% PHPA 3% PHPA 3% PHPA 3% PHPA
12.5 MDa 6 MDa 30% 12 MDa 12 MDa 11 MDa
30% Hyd Hyd 5% Hyd 12% Hyd 20% Hyd
pH 3% PVP 3% PVP 3% PVP 3% PVP 3% PVP
300k MW 300k MW 300k MW 300k MW 300k MW
3 N(2.5) PIS (2.8) G(2.8) G(2.5) N(2.7)
5.6 G(6.7) G(6.7) G(5.5) G(6.1) G(6.4)
9 G (9.0) G (9.0) G (9.0) G(9.3) G(9.1)
3% PHPA 3% PHPA 3% PHPA 3% PHPA 3% PHPA
12.5 MDa 6 MDa 30% 12 MDa 12 MDa 11 MDa
30% Hyd Hyd 5% Hyd 12% Hyd 20% Hyd
pH 6% PVP 6% PVP 6% PVP 6% PVP 6% PVP
300k MW 300k MW 300k MW 300k MW 300k MW
3 N(2.6) P/S (2.7) G(2.5) G (3.0) N(2.7)
5.6 G(6.5) N(6.5) G(5.1) G(5.3) G(6.1)
9 G(9.4) G(9.4) G(9.4) G(9.2) G (9.0)
[0098] As shown in Table 1, the PHPA was evaluated at concentrations of 2%
and
3% by weight. This series spanned molecular weights from 6 to 12.5 million
Daltons and
hydrolysis levels from 5 to 30%. The non-metallic crosslinker included 3 and
6wt% PVP
with a reported molecular weight of 300,000 Daltons.
[0099] In general, gels were formed using both 3 and 6% of PVP when 3% of
PHPA
was used, but not with 2% PHPA. However, PHPA polymers with a molecular weight
of
12 million did gel at 2%. At low pH with PVP, the lower hydrolysis PHPA gelled
while
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higher levels (20% or more) either phase separated or did not gel. In all
cases with PHPA,
phase separation was limited to the low pH regime below 4. In nearly every
case a pH of
9 or more resulted in gelation for 3% PHPA at ambient temperature.
[00100] Shown in Table 2 are results obtained with PHPA having different
molecular
weights and levels of hydrolysis than those in Table 1. With PHPA, very
similar results
to those found in Table 1 are apparent. The low molecular weight PHPA polymers
showed no reaction at 5%, suggesting the concentration and molecular weight
are
relevant factors in gel formation. The cationic PHPA initially gelled
immediately, but
later phase separated at all pH levels above 3. An observation after 3 weeks
reveals that
the pH 11.2 sample is clear and gelled. Below pH 3, the sample remained
gelled.
Table 2 3% PHPA 3% PHPA 3% PHPA 3% PHPA 2% PHPA 2% PHPA
MDa 5 MDa 5 MDa 5 MDa 5 MDa 5 MDa
10% Hyd 10% Hyd 10% Hyd 10% Hyd 10% Hyd 10% Hyd
pH 3% PVP 4% PVP 5% PVP 6% PVP 4% PVP 6% PVP
300k MW 300k MW 300k MW 300k MW 300k MW 300k MW
1 N(1.2) P/S (1.1) P/S (1.1) P/S (1.0)
N(2.85) P/S (1.4)
3 G (3.0) N(3.2) P/S (2.9) P/S (3.0) --
5.6 G(4.9) N(5.2) N(5.7) N(5.6) N(5.6) N(4.5)
9 G(9.1) N (9.0) G (9.0) G(9.2) N(9.2) N(9.1)
3% PHPA 3% PHPA 5% PHPA 5% PHPA 3% PHPA
5 MDa 5 MDa 0.5 MDa 0.5 MDa 9 MDa
10% Hyd 10% Hyd 5% Hyd 1% Hyd 30% Hyd
cationic
pH 4% PVP 6% PVP 6% PVP 6% PVP 6% PVP
2.5k MW 2.5k MW 300k MW 300k MW 300k MW
1 G(2.6)
3 N (3.0) N (3.0) N (3.0) N(2.9) P/S (5.0)
5.6 G(5.1) G(5.1) N (5.0) N(3.9) P/S (9.2)
9 G (9.0) G (9.0) N(9.0) N(8.9) P/S (11.2)
11 G(11.5) G(11.0) --
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1001011 Table 3 shows results obtaineli with, an unhydrolyzed polymer or pure
polyacrylamide. Substantial differences exist from the conclusions drawn about
PHPA.
Phase separation occurred at high pH and gelation occurred at lower pH levels.
The
gelation behavior was very sensitive to the concentration of PVP, where 3%
gelled and
6% phase separated.
Table 3 3% PA 3% PA
6 MDa 6 MDa
0% Hyd 0% Hyd
pH 3% PVP 6% PVP
300k MW 300k MW
1 N(1.1) P/S (1.15)
3 P/S (3.0) P/S (3.5)
5.6 P/S (4.0) P/S (7.5)
9 G(9.1) P/S (8.9)
SEM
1001021 Scanning electron microscope pictures of the PHPA-PVP dried gel reveal
an
interesting structure resembling tubes and a fibrous sheath in which the
fibers have
aligned. Analysis shows holes which appear to be exits of tunnels formed by
aligned gel.
Alignment of the fibrous network is apparent. The outer wall appears quite
smooth.
Rheology- Bohlin
1001031 Dynamic rheology provides further characterization of the gels.
[00104] Figure 1 demonstrates that a gel can be made at 3% PHPA but not at 1%.
The
3% gel was diluted with twice its weight of water resulting in the same
overall
composition of PHPA and PVP as the 1% PHPA sample. The G' of the diluted gel
exceeds the G" value, indicating a true gel exists, whereas the 1% PHPA
mixture
suggests a viscous liquid exists since G' is less than G". G' for the diluted
sample is
much higher than that for the 1% PHPA sample. In addition, the gel moduli are
fairly
independent of temperature but the liquid shows decreasing moduli with
temperature.
Thus, the reaction that occurred in the solution with 3% PHPA and 6% PVP
appears
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irreversible upon dilution. This also demonstrates that the gelation mechanism
is path
dependent. =
Rheology- Grace
[00105] The Grace 5600 viscometer was used to observe the onset of gelation
with
temperature. Temperature accelerates the reaction and can also increase the
hydrolysis
level of PHPA or polyacrylamide in the presence of base.
[00106] The examples in Figure 2 show a mixture of 3% PHPA and 6% PVP, which
was heated in the viscometer. The gel was tested at several temperatures from
200 to
280 F. All tests resulted in similar gels of 600 to 800 cP at temperature. The
fluids at 260
and 280 F show upturns in viscosity that indicate the onset of gelation. After
cooling, the
fluids were fully gelled.
[00107] Figure 3 shows a comparison between different base polymers with PVP
at
6%. Similar gels are formed for PHPA, unhydrolyzed polyacrylamide (PAM) and
cationic polyacrylamide (CPAM).
[00108] A series of samples were prepared with varying amounts of the non-
metallic
crosslinker and are shown in Table 4. All gels were prepared at pH 12 with
PHPA
having a wt. average molecular weight of 5 M g/mol and 10% hydrolysis, and
with PVP
with Mw 55k as the non-metallic crosslinker. As the data shows, in this
embodiment, a
minimum of 2% PHPA is needed in order to create a gel. A minimum of 2% PVP is
needed at this PHPA concentration. With increased PHPA concentration to 3%,
the
minimum of PVP required is lowered to 1%.
Table 4
1% PHPA 2% PHPA 3% PHPA
PVP (wt%) \if 6 MDa 6 MDa 6 MDa
10% Hyd 10% Hyd 10% Hyd
6 Does not gel Gel Gel
Does not gel Gel Gel
4 Does not gel Gel Gel
3 Does not gel Gel Gel
2 Does not gel Gel Gel
1 Does not gel Gel
0.5 Does not gel
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Effect of PVP concentration on PHPA-PVP Gels.
[00109] Figure 4 shows the effect of the crosslinker concentration (PVP
concentration)
on the gel strength. All the gels were prepared using PVP with Mw 55k. As the
data
shows, with 1% PVP, a gel already forms. Increasing PVP concentration gives a
stronger
gel. When PVP reaches 5%, further increasing PVP concentration does not
further
increase the gel strength.
Effect of PVP Mw on PHPA-PVP systems
[00110] Figure 5 shows the effects of PVP molecular weight on gel strength.
All
examples utilized 3% PHPA and 6% PVP with PVP Mw varied. As the data shows,
the
PVP Mw has a significant impact on the gel strength. Among all Mw tested, 55k
was the
optimal. Higher or lower Mw crosslinkers all led to weaker systems, as
indicated by the
lower complex viscosities compared with the 55k gel.
Low Mw PHPA gels with PVP
[00111] As shown in Figure 6, relatively low molecular weight PHPA are
suitable for
use herein. A low Mw PHPA of 0.5 million Mw with a 5% hydrolysis gelled with
PVP.
As the data shows, the concentration of the PHPA needed to produce the gel was
higher
than with higher molecular weight PHPA.
Non-ionic polyacrylamide gels with PVP
[00112] As shown in Figure 7, non-ionic polyacrylamide (PAM) (i.e., with 0%
hydroslysis) also produced gels with PVP. A 3% PAM, Mw of 6 million g/mol and
6%
PVP 55k.
PHPA mixed with another PHPA Does not gel
[00113] A comparative composition comprising the low molecular weight PHPA
(0.5M g/mol, 5% hydrolysis) was combined with the 5M g/mol 10% hydrolysis PHPA
to
determine if any transamidation reaction would occur to form a gel among
polyacrylamide molecules themselves. As expected, experiments showed no gel
formed
at pH 12. This data suggests that the pyrrolidone ring of the polylactam is
more reactive
and is needed in order for the reaction to take place to produce the gels of
the instant
disclosure.
Order of addition of crosslinker and PHPA
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[00114] It was determined that the order of addition of the PHPA and the non-
metallic
crosslinker is not of consequence in forming the, gels of the instant
disclosure. An
experiment was performed to find out whether adjusting pH to 12 before PVP was
added
would give a gel with the PHPA, as opposed to raising the pH to 12 after PVP
is added.
It was concluded that the order did not matter. A strong gel still formed if
pH was
increased to 12 first before adding PVP and if the pH was increased to 12
after adding
PVP.
Dehydration of Gels and Reconstitution of Gels
[00115] A gel was produced according to the instant disclosure comprising 3
wt%
PHPA and 6 wt% PVP at a pH of 12. The gel was freeze dried to produce a gel
concentrate having less than 1 wt% water. The gel concentrate was then re-
hydrated by
mixing in water to produce a reconstituted gel having essentially the same
properties as
the gel prior to freeze drying.
Formation of Chemical Seal Rings
100116] A polyacrylamide-polyvinylpyrrolidone slurry was prepared by forming a
mixture containing (1) 41.2 grams of a partially hydrolyzed polyacrylamide
("PHPA" ¨
molecular weight Mw of approximately 5 million and a 10% degree of
hydrolysis), (2)
82.4 grams of polyvinylpyrrolidone (PVP ¨ Mw of approximately 55,000); (3) 8.0
grams
of sodium hydroxide (NaOH), and (4) 200 mL of mineral oil. To this mixture, a
small
amount of water (0.1 mL, 0.5 mL, 1.0 mL and 2.0 mL) was added which resulted
in the
formation of a rubber-like plug in about 1 hour. The present inventors believe
that the
water dissolved the PVP, which then reacted with the PHPA to link the
surrounding
PHPA particles together. As shown below in Table 5, only a minimal amount of
water
was required to initiate the reaction. The plug was initially soft and
gradually developed
more strength. For the 2 mL water system, it was completely solid-like after a
day and
did not deform when it was pressed with a spatula.
[00117] Table 5. Influence of water on PHPA-PVP 55k plug in mineral oil.
Slurry
Water Added Observations after 1 hr
Volume
50 mL 0.1 mL No change to the slurry
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0.5 mL Partial plug, discrete pieces
1.0 mL Rubberlike plug
2.0 mL Rubber-like plug
[00118] An additional experiment was performed to determine the influence of
PVP
molecular weight on the plug strength. The following formulations (Formulation
A and
Formulation B) were used to prepare the slurries:
Formulation A: 50 mL mineral oil, 10.3 g PHPA (Mw of about 5 million and a
10% degree of hydrolysis, 20.6 g PVP (Mw of about 10,000, 55,000, or 360,000),
2 g
NaOH and 4 mL water
Formulation B: 80 mL mineral oil, 10.3 g PHPA (same as Formulation A), 20.6 g
PVP (Mw of 1.3 million), 2 g NaOH and 4 mL water.
For Formulation B, a larger volume of mineral oil was used because the PVP
occupied a larger volume than the PVP of Formulation A (i.e., more oil had to
be added
to fully immerse all the PHPA and PVP powders). .
[00119] For all slurries, 4 mL instead of 2 mL water (see above) was added to
achieve
a more complete binding of PHPA. PVPs having a molecular weight of about
10,000 and
55,0000 k both resulted in rubbery material within 1 hr. The material then
became
stronger and stronger with the passage of time, and turned more yellow. Using
a
TA.HDplus Texture Analyzer, manufactured by Texture Technologies Corp., the
present
inventors determined gel strengths of these materials. In a typical texture
analyzer test,
the probe on the texture analyzer first compressed the material and was then
lifted up,
which result in a "loop" on a force versus compression diagram. These gel
strengths are
listed in Figure 8 of the present application.
[00120] As shown in Figure 8 (illustrating a plot of the force as a function
of
compression distance for plugs made from difference PVPs) the sample of
Formulation A
(having a Mw of about 55,000) was the strongest (see the upward part of the
plot line). .
The binding capability (i.e., gel strength) of PVP thus follows this order:
55,000> 10,000
> 360,000> 1,300,000. The 55,000 material was so strong that it reached the
instrument
31
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limit and did not result in a loop.
[00121]
[00122] The present inventors believe that although the surface of the 10,000
Mw plug
was harder, the inner part of the plug was actually weaker. Furthermore, as
shown in
Figure 8, the plug formed from the 10,000 PVP was difficult to separate it
from the
bottle. Moreover, only soft gels were formed from the 360,000 and 1.3 million
Mw PVP
slurries. So even though no solid plug was formed from the high Mw PVP
experiments
(360,000 and 1.3 million), PHPA particles were weakly bound together. Also,
the 1.3
million Mw gel was weaker than the 360,000 as both deformed when pressed with
a
spatula.
Factors That May Affect The Formation of Chemical Seal Rings with
[00123] Four different types of water (Tap water, 2% KC1 water, synthetic sea
water,
and pH 1 water) were tested to determine whether chemical seals rings could
form. A
suspension was prepared comprising 50 mL of mineral oil, 10.3 grams PHPA, 20.6
g
PVP, and 2 grams of NaOH. The four different water samples (4 mL each) were
then
introduced to the above suspension. Chemical seal rings were formed in all
cases, with
the amount of time it took for each chemical seal ring to form varying between
one hour
and 12 hours. The strength of the chemical seal ring continued to increase
with the
passage of time. For the KC1 sample, the presence of the salt in the water
made the
chemical seal ring less continuous. The chemical seal ring formed from the tap
water was
a contiguous piece, while the chemical seal rings formed from the 2% KC1 and
the sea
water formed as discrete pieces. However, the pieces of the chemical seal ring
formed
from the sea water plug pieces began to agglomerate after 2 days. One
possibility was
that the Ca2+ in sea water aided in the agglomeration of the polymers. The
chemical seal
ring formed using the pH 1 water formed at a slower rate than the chemical
seal rings
using the other three waters. This slower rate of formation may have been due
to the pH
rising more slowly.
Formation of Chemical Seal Rings Using Heavy Brines
[00124] Potassium formate (HCOOK) and cesium formate (HCOOCs) were used as
heavy brines to determine (1) the effect of polymer loading on the strength of
a chemical
seal ring (Formulations C and D), (2) the effect of a sodium hydroxide pH
adjusting fluid
32
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on the strength of a chemical seal ring (Formulations E and F) and (3) the
effect of water
on the strength of a chemical seal ring (Formulation G and H). The details
regarding the
compositions of Formulations C-H are described below in Table 6. The molecular
weight of PHPA and PVP are the same as identified above.
1001251 Table 6: Summary of Formulations C-H
Cesium Potassium
PHPA PVP Water
Formulationformate formate NaOH (g)
.
(wt.%) %
(wt) (g)
(P_Pg) (IVO
10 18.17 2
3 6 18.17 2
20 18.17 2 4
10 20 18.17 4
10 20 18.17 2 4
10 20 18.17 2
The same texture analyzer described above was used to determine the gel
strength of the
chemical seal rings formed from Formulations C-H. For the chemical seals rings
using
formulations C-D, the gel strength was determined at 30 days. The gel strength
for the
chemical seal rings prepared from formulations E-F was determined at 14 days.
The gel
strength for the chemical seal rings prepared from formulations G-H was
determined at
22 days. The gel strength results are shown in Figure 9-11. As shown in Figure
9, as the
polymer loading increased (Formulation C), the strength of the chemical seal
ring also
increased. As shown in Figure 10, the chemical seal formed from a composition
without
NaOH was stronger than a chemical seal ring formed with NaOH. The present
inventors
believed that the addition of NaOH shifted the pH away from the optimal value,
resulting
in a slower reaction. As shown in Figure 11, the chemical seal ring formed
from a
composition without water showed comparable strength to a composition
containing
water. Thus, the addition of water appears to have little effect on gel
strength.
[00126] Potassium formate and cesium formate were again used as heavy brines
to
determine (1) the effect of temperature on the strength of a chemical seal
ring
(Formulations I and J), (2) the effect of the type of heavy brine on the
strength of a
chemical seal ring (Formulations K and L), (3) the effect of PVP on the
strength of a
chemical seal ring (Formulations M and N) and (4) the effect of solvent type
on the
strength of a chemical seal ring (Formulations 0 and P) . The details
regarding the
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compositions of Formulations C-H are described below in Table 6. The molecular
weight of PHPA and PVP are the same as idpntified, above.
[00127] Table 6: Summary of Formulations C-H
Cesium Potassium
PHPA PVP NaOH
Mineral Water Temp.
Formulation formate formate
(wt.%) (wt.%) (g) Oil (g) (1)
(PPO (13Pg)
20 18.17 4 150
10 20 18.17 4 70
5 10 18.17 2
5 10 13.08 2
10 20 18.17 2 4
30 18.17 2 4
O 10 20 2 50m1 4
10 20 18.17 2 4
[00128] A texture analyzer was used to determine the gel strength of the
chemical seal
rings formed from Formulations I-P. For the chemical seals rings using
formulations I-J,
the gel strength was determined at 7 and 14 days, respectively. The gel
strength for the
chemical seal rings prepared from formulations K-L was determined at 30 days.
The gel
strength for the chemical seal rings prepared from formulations M-N was
determined at
14 and 22 days, respectively. The gel strength for the chemical seal rings
prepared from
formulations O-P was determined at 22 and 28 days, respectively. The gel
strength
results are shown in Figure 12-15. As shown in Figure 12, as the temperature
was
increased (Formulation I), the strength of the chemical seal ring also
increased. As
shown in Figure 13, the chemical seal ring formed from a composition
containing cesium
formate (Formulation K) was stronger than a chemical seal ring formed with
potassium
formate (Formulation L). As shown in Figure 14, the chemical seal ring formed
from a
composition without PVP had less strength as to a chemical seal ring formed
with PVP.
As shown in Figure 15, the chemical seal ring formed in mineral oil was much
stronger
than a chemical seal ring formed using cesium formate.
[00129] The foregoing disclosure and description is illustrative and
explanatory
thereof and it can be readily appreciated by those skilled in the art that
various changes in
the size, shape and materials, as well as in the details of the illustrated
construction or
combinations of the elements described herein can be made without departing
from the
spirit of the disclosure.
34
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[00130] While the invention has been illustrated and described in detail in
the
drawings and foregoing description, the same is to ,be considered as
illustrative and not
restrictive in character, it being understood that only some embodiments have
been
shown and described and that all changes and modifications that come within
the spirit of
the inventions are desired to be protected. It should be understood that while
the use of
words such as preferable, preferably, preferred, more preferred or exemplary
utilized in
the description above indicate that the feature so described may be more
desirable or
characteristic, nonetheless may not be necessary and embodiments lacking the
same may
be contemplated as within the scope of the invention, the scope being defined
by the
claims that follow. In reading the claims, it is intended that when words such
as "a," "an,"
"at least one," or "at least one portion" are used there is no intention to
limit the claim to
only one item unless specifically stated to the contrary in the claim. When
the language
"at least a portion" and/or "a portion" is used the item can include a portion
and/or the
entire item unless specifically stated to the contrary.
[00131] Although only a few example embodiments have been described in detail
above, those skilled in the art will readily appreciate that many
modifications are possible
in the example embodiments without materially departing from this invention.
Accordingly, all such modifications are intended to be included within the
scope of this
disclosure as defined in the following claims. In the claims, means-plus-
function clauses
are intended to cover the structures described herein as performing the
recited function
and not only structural equivalents, but also equivalent structures. Thus,
although a nail
and a screw may not be structural equivalents in that a nail employs a
cylindrical surface
to secure wooden parts together, whereas a screw employs a helical surface, in
the
environment of fastening wooden parts, a nail and a screw may be equivalent
structures.
It is the express intention of the applicant not to invoke 35 U.S.C. 112,
paragraph 6 for
any limitations of any of the claims herein, except for those in which the
claim expressly
uses the words 'means for' together with an associated function.
