U.S. patent application number 16/895752 was filed with the patent office on 2021-12-09 for methods and compositions of using viscoelastic surfactants as diversion agents.
This patent application is currently assigned to SAUDI ARABIAN OIL COMPANY. The applicant listed for this patent is KING FAHD UNIVERSITY OF PETROLEUM & MINERALS, SAUDI ARABIAN OIL COMPANY. Invention is credited to Khalid Alnoaimi, Nour Baqader, Rajendra Arunkumar Kalgaonkar, Muhammed Mansha, Nisar Ullah.
Application Number | 20210380873 16/895752 |
Document ID | / |
Family ID | 1000004941130 |
Filed Date | 2021-12-09 |
United States Patent
Application |
20210380873 |
Kind Code |
A1 |
Kalgaonkar; Rajendra Arunkumar ;
et al. |
December 9, 2021 |
METHODS AND COMPOSITIONS OF USING VISCOELASTIC SURFACTANTS AS
DIVERSION AGENTS
Abstract
A wellbore fluid may include a gemini surfactant, a zwitterionic
surfactant, an activator, and an aqueous base fluid. The gemini
surfactant may have a structure represented by formula (I):
##STR00001## where R.sup.1 is a C.sub.1-C.sub.10 hydrocarbon group,
m and o are each, independently, an integer ranging from 1 to 4,
and n is an integer ranging from 8 to 12.
Inventors: |
Kalgaonkar; Rajendra Arunkumar;
(Dhahran, SA) ; Alnoaimi; Khalid; (Aberdeen,
GB) ; Baqader; Nour; (Khobar, SA) ; Ullah;
Nisar; (Dhahran, SA) ; Mansha; Muhammed;
(Dhahran, SA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SAUDI ARABIAN OIL COMPANY
KING FAHD UNIVERSITY OF PETROLEUM & MINERALS |
Dhahran
Dhahran |
|
SA
SA |
|
|
Assignee: |
SAUDI ARABIAN OIL COMPANY
Dhahran
SA
KING FAHD UNIVERSITY OF PETROLEUM & MINERALS
Dhahran
SA
|
Family ID: |
1000004941130 |
Appl. No.: |
16/895752 |
Filed: |
June 8, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C07C 33/04 20130101;
E21B 43/162 20130101; C09K 2208/06 20130101; C09K 8/604 20130101;
C09K 2208/30 20130101; C09K 8/584 20130101; C09K 8/74 20130101 |
International
Class: |
C09K 8/60 20060101
C09K008/60; C09K 8/74 20060101 C09K008/74; C09K 8/584 20060101
C09K008/584 |
Claims
1. A wellbore fluid, comprising: a gemini surfactant having a
structure represented by formula (I): ##STR00005## where R.sup.1 is
a C.sub.1-C.sub.10 hydrocarbon group, m and o are each,
independently, an integer ranging from 1 to 4, and n is an integer
ranging from 8 to 12; a zwitterionic surfactant; an activator; and
an aqueous base fluid.
2. The wellbore fluid according to claim 1, wherein the wellbore
fluid contains the gemini surfactant in an amount of 1 to 15 wt.
%.
3. The wellbore fluid according to claim 1, wherein the wellbore
fluid contains the zwitterionic surfactant in an amount of 1 to 15
wt. %.
4. The wellbore fluid according to claim 1, wherein the wellbore
fluid contains the activator in an amount of 10 to 30 wt. %.
5. The wellbore fluid according to claim 1, wherein the wellbore
fluid further comprises an acid.
6. The wellbore fluid according to claim 1, wherein R.sup.1 is a
C.sub.1 hydrocarbon group, o is 1 or 2, m is 1, and n is 8.
7. The wellbore fluid according to claim 1, wherein the
zwitterionic surfactant has a structure represented by formula
(II): ##STR00006## where R.sup.2 is a C.sub.15-C.sub.27 hydrocarbon
group or a C.sub.15-C.sub.29 substituted hydrocarbon group, R.sup.3
is a C.sub.1-C.sub.10 hydrocarbon group, and p and q are each,
independently, an integer ranging from 1 to 4.
8. A method for treating a hydrocarbon-containing formation,
comprising: injecting a wellbore fluid into a high permeability
zone of a hydrocarbon-containing formation, wherein the high
permeability zone increases the temperature of the wellbore fluid,
resulting in the wellbore fluid having an increased viscosity;
wherein the wellbore fluid comprises: a gemini surfactant having a
structure represented by formula (I): ##STR00007## where R.sup.1 is
a C.sub.1-C.sub.10 hydrocarbon group, m and o are each,
independently, an integer ranging from 1 to 4, and n is an integer
ranging from 8 to 12; a zwitterionic surfactant; an activator; and
an aqueous base fluid.
9. The method according to claim 8, wherein the wellbore fluid
contains the gemini surfactant in an amount of 1 to 15 wt. %.
10. The method according to claim 8, wherein the wellbore fluid
contains the zwitterionic surfactant in an amount of 1 to 15 wt.
%.
11. The method according to claim 8, wherein the wellbore fluid
contains the activator in an amount of 10 to 30 wt. %.
12. The method according to claim 8, wherein the wellbore fluid
further comprises an acid.
13. The method according to claim 8, wherein R.sup.1 is a C.sub.1
hydrocarbon group, o is 1 or 2, m is 1, and n is 8.
14. The method according to claim 8, wherein the zwitterionic
surfactant has a structure represented by formula (II):
##STR00008## where R.sup.2 is a C.sub.15-C.sub.27 hydrocarbon group
or a C.sub.15-C.sub.29 substituted hydrocarbon group, R.sup.3 is a
C.sub.1-C.sub.10 hydrocarbon group, and p and q are each,
independently, an integer ranging from 1 to 4.
15. A method for stimulating the recovery of hydrocarbons from a
hydrocarbon-containing formation, the method comprising: injecting
a wellbore fluid into a high permeability zone of a
hydrocarbon-containing formation, wherein the high permeability
zone increases the temperature of the wellbore fluid, resulting in
the wellbore fluid having an increased viscosity; stimulating the
hydrocarbon-containing formation using the wellbore fluid thereby
creating pathways for hydrocarbon production; and recovering the
hydrocarbons, wherein the wellbore fluid comprises: a gemini
surfactant having a structure represented by formula (I):
##STR00009## where R.sup.1 is a C.sub.1-C.sub.10 hydrocarbon group,
m and o are each, independently, an integer ranging from 1 to 4,
and n is an integer ranging from 8 to 12; a zwitterionic
surfactant; an activator; and an aqueous base fluid.
16. The method according to claim 15, wherein the wellbore fluid
contains the gemini surfactant in an amount of 1 to 15 wt. %.
17. The method according to claim 15, wherein the wellbore fluid
contains the zwitterionic surfactant in an amount of 1 to 15 wt.
%.
18. The method according to claim 15, wherein the wellbore fluid
contains the activator in an amount of 10 to 30 wt. %.
19. The method according to claim 15, wherein the wellbore fluid
further comprises an acid.
20. The method according to claim 15, wherein R.sup.1 is a C.sub.1
hydrocarbon group, o is 1 or 2, m is 1, and n is 8.
21. The method according to claim 15, wherein the zwitterionic
surfactant has a structure represented by formula (II):
##STR00010## where R.sup.2 is a C.sub.15-C.sub.27 hydrocarbon group
or a C.sub.15-C.sub.29 substituted hydrocarbon group, R.sup.3 is a
C.sub.1-C.sub.10 hydrocarbon group, and p and q are each,
independently, an integer ranging from 1 to 4.
22. A method of preparing a wellbore fluid, comprising: mixing a
gemini surfactant, a zwitterionic surfactant, an activator, and an
aqueous base fluid, wherein the gemini surfactant has a structure
represented by formula (I): ##STR00011## where R.sup.1 is a
C.sub.1-C.sub.10 hydrocarbon group, m and o are each,
independently, an integer ranging from 1 to 4, and n is an integer
ranging from 8 to 12.
23. The method according to claim 22, wherein the wellbore fluid
contains the gemini surfactant in an amount of 1 to 15 wt. %.
24. The method according to claim 22, wherein the wellbore fluid
contains the zwitterionic surfactant in an amount of 1 to 15 wt.
%.
25. The method according to claim 22, wherein the wellbore fluid
contains the activator in an amount of 10 to 30 wt. %.
26. The method according to claim 22 wherein the method further
comprises mixing an acid with the gemini surfactant, the
zwitterionic surfactant, the activator, and the aqueous base
fluid.
27. The method according to claim 22, wherein R.sup.1 is a C.sub.1
hydrocarbon group, o is 1 or 2, m is 1, and n is 8.
28. The method according to claim 22, wherein the zwitterionic
surfactant has a structure represented by formula (II):
##STR00012## where R.sup.2 is a C.sub.15-C.sub.27 hydrocarbon group
or a C.sub.15-C.sub.29 substituted hydrocarbon group, R.sup.3 is a
C.sub.1-C.sub.10 hydrocarbon group, and p and q are each,
independently, an integer ranging from 1 to 4.
29. A gemini surfactant having a structure as represented by
formula (I): ##STR00013## where R.sup.1 is a C.sub.1-C.sub.10
hydrocarbon group, m and o are each, independently, an integer
ranging from 1 to 4, and n is an integer ranging from 8 to 12n.
30. The surfactant according to claim 29, wherein R.sup.1 is a
C.sub.1 hydrocarbon group, o is 1 or 2, m is 1, and n is 8.
Description
[0001] Well stimulation enables the improved extraction of
hydrocarbon reserves that conventional recovery processes, such as
gas or water displacement, cannot access. One well stimulation
technique is matrix stimulation, which may also be referred to as
matrix acidizing treatment. In matrix stimulation, an acidic fluid
is injected into a formation at a pressure below the fracture
pressure and is used to stimulate a reservoir by reacting with the
reservoir rock, thereby dissolving the rock to create a pathway for
hydrocarbon production.
[0002] However, when the acidic fluid has a low viscosity, the acid
may have limited penetration into the formation and only react at
the face of the rock. This is not an effective method for
stimulating the reservoir as a conductive pathway for hydrocarbon
production is not created. Further, most of the reservoirs have
heterogeneous permeabilities which result in the low viscosity acid
primarily penetrating the high permeable zones in the reservoir and
leaving most of the low permeability zones untreated.
SUMMARY
[0003] This summary is provided to introduce a selection of
concepts that are further described below in the detailed
description. This summary is not intended to identify key or
essential features of the claimed subject matter, nor is it
intended to be used as an aid in limiting the scope of the claimed
subject matter.
[0004] In one aspect, embodiments disclosed herein relate to
wellbore fluids that include a gemini surfactant, a zwitterionic
surfactant, an activator, and an aqueous base fluid. The gemini
surfactant may have a structure represented by formula (I):
##STR00002##
where R.sup.1 is a C.sub.1-C.sub.10 hydrocarbon group, m and o are
each, independently, an integer ranging from 1 to 4, and n is an
integer ranging from 8 to 12.
[0005] In another aspect, embodiments disclosed herein relate to
methods for treating a hydrocarbon-containing formation, the
methods including injecting a wellbore fluid into a high
permeability zone of a hydrocarbon-containing formation. The high
permeability zone may increase the temperature of the wellbore
fluid, resulting in the wellbore fluid having an increased
viscosity. The wellbore fluids may include a gemini surfactant, a
zwitterionic surfactant, an activator, and an aqueous base fluid.
The gemini surfactant may have a structure represented by the above
formula (I).
[0006] In another aspect, embodiments disclosed herein relate to
methods for stimulating the recovery of hydrocarbons from a
hydrocarbon-containing formation, the methods including injecting a
wellbore fluid into a high permeability zone of a
hydrocarbon-containing formation, stimulating the
hydrocarbon-containing formation using the wellbore fluid thereby
creating pathways for hydrocarbon production, and recovering the
hydrocarbons. The high permeability zone may increase the
temperature of the wellbore fluid, resulting in the wellbore fluid
having an increased viscosity. The wellbore fluids may include a
gemini surfactant, a zwitterionic surfactant, an activator, and an
aqueous base fluid. The gemini surfactant may have a structure
represented by the above formula (I).
[0007] In another aspect, embodiments disclosed herein relate to
methods of preparing a wellbore fluid, the methods including mixing
a gemini surfactant, a zwitterionic surfactant, an activator, and
an aqueous base fluid. The gemini surfactant may have a structure
represented by the above formula (I).
[0008] In a further aspect, embodiments disclosed herein relate to
a gemini surfactant having a structure represented by the above
formula (I).
[0009] Other aspects and advantages of the claimed subject matter
will be apparent from the following description and the appended
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0010] FIG. 1 is schematic representation of the synthesis of a
surfactant of one or more embodiments.
[0011] FIG. 2 is a flowchart depicting a well stimulation process
in accordance with one or more embodiments of the present
disclosure.
[0012] FIG. 3 is a schematic representation of the synthesis of an
exemplary zwitterionic surfactant.
[0013] FIG. 4 is a schematic representation of the synthesis of an
exemplary gemini surfactant.
DETAILED DESCRIPTION
[0014] Embodiments in accordance with the present disclosure
generally relate to a gemini surfactant, wellbore fluids that
contain one or more surfactants and an activator, and methods of
using the fluids in processes such as acid stimulation, enhanced
oil recovery (EOR) and fracturing. The surfactants may be
viscoelastic. Methods of one or more embodiments may involve
injecting the wellbore fluids into a formation, exposing the fluid
to an increased temperature and resulting in the wellbore fluid
having an increased viscosity. Such methods may modify the
injection profile of the formation a well stimulation treatment by
diverting stimulation fluid to lower permeability zones of the
reservoir.
[0015] The wellbore fluids may be low-viscosity aqueous solutions
that increase in viscosity under downhole conditions. The wellbore
fluids may demonstrate increased stability under high temperature
and pressure conditions, making them highly suitable for use in
downhole environments. When the wellbore fluid contacts a produced
hydrocarbon its viscosity may drastically reduce, enabling easy
flowback of the fluid post treatment. As the viscosifying material
used in the present disclosure does not contain any solid
particulates, it will be potentially non-damaging to the formation
due to effective flowback and no residual deposition inside the
formation.
[0016] One or more embodiments of the present disclosure are
directed to a gemini surfactant. As used herein, the term "gemini
surfactant" generally refers to surfactant that comprises two
surfactant moieties that are chemically bonded via a spacer group.
The surfactant moieties may contain a hydrophilic head group and a
hydrophobic tail. The two surfactant moieties may be the same as,
or different from, one another. In one or more embodiments, the
gemini surfactant may include surfactant moieties having a cationic
head group. In particular embodiments, the surfactant moieties may
include a quaternary ammonium group. The gemini surfactant of one
or more embodiments may further comprise one or more amide groups
and one or more sulfonate groups.
[0017] In one or more embodiments, the gemini surfactant may have a
structure represented by formula (I):
##STR00003##
where R.sup.1 is a C.sub.1-C.sub.10 hydrocarbon group, m and o are
each, independently, an integer ranging from 1 to 4, and n is an
integer ranging from 8 to 12.
[0018] As used herein with regard to group R.sup.1, the term
"hydrocarbon group" refers to branched, straight chain, and
ring-containing hydrocarbon groups, any of which may be saturated
or unsaturated. The hydrocarbon groups may be primary, secondary,
and/or tertiary hydrocarbons.
[0019] In one or more embodiments, the gemini surfactant may be
highly soluble in aqueous solutions, such as in deionized water,
seawater, brines, calcium chloride solutions, and the like. In some
embodiments, the gemini surfactant may be soluble in aqueous
solutions in an amount of 10% by weight (wt. %) or more, 20 wt. %
or more, 30 wt. % or more, or 40 wt. % or more at ambient
temperature. In some embodiments, the solubility of the gemini
surfactant may increase with increasing temperature, until gelation
occurs.
[0020] In one or more embodiments, the gemini surfactant may be
thermally stable at a temperature of 200.degree. C. or more,
250.degree. C. or more, 300.degree. C. or more, or 350.degree. C.
or more, as measured by thermogravimetric analysis (TGA).
[0021] One or more embodiments of the present disclosure are
directed to wellbore fluids.
[0022] The wellbore fluids of one or more embodiments may include,
for example, water-based wellbore fluids. The wellbore fluids may
be acid stimulation fluids, EOR fluids or fracturing fluids, among
others.
[0023] In one or more embodiments, the water-based wellbore fluids
may comprise an aqueous fluid. The aqueous fluid may include at
least one of fresh water, seawater, brine, water-soluble organic
compounds, and mixtures thereof. The aqueous fluid may contain
fresh water formulated to contain various salts in addition to the
first or second salt, to the extent that such salts do not impede
the desired nitrogen-generating reaction. The salts may include,
but are not limited to, alkali metal halides and hydroxides. In one
or more embodiments, brine may be any of seawater, aqueous
solutions wherein the salt concentration is less than that of
seawater, or aqueous solutions wherein the salt concentration is
greater than that of seawater. Salts that are found in seawater may
include sodium, calcium, aluminum, magnesium, potassium, strontium,
and lithium salts of halides, carbonates, chlorates, bromates,
nitrates, oxides, phosphates, among others. Any of the
aforementioned salts may be included in brine. In one or more
embodiments, the density of the aqueous fluid may be controlled by
increasing the salt concentration in the brine, though the maximum
concentration is determined by the solubility of the salt. In
particular embodiments, brine may include an alkali metal halide or
carboxylate salt and/or alkaline earth metal carboxylate salts.
[0024] The wellbore fluids include one or more surfactants. In one
or more embodiments, the surfactants may include a gemini
surfactant as discussed above. In particular embodiments, the
gemini surfactant may have a structure represented by formula (I)
above.
[0025] The wellbore fluids of one or more embodiments may comprise
the gemini surfactant in an amount of the range of about 1 to 15%
by weight (wt. %). For example, the wellbore fluid may contain the
gemini surfactant in an amount ranging from a lower limit of any of
1, 1.5, 2, 2.5, 3, 4, 5, 7, 10, and 12 wt. % to an upper limit of
any of 1.5, 2, 3, 4, 5, 6, 8, 10, 12, 14, and 15 wt. %, where any
lower limit can be used in combination with any
mathematically-compatible upper limit.
[0026] In one or more embodiments, the wellbore fluids may contain
a gemini surfactant in combination with one or more additional
surfactants. In particular embodiments, the wellbore fluids may
contain a gemini surfactant and a zwitterionic surfactant. The
zwitterionic surfactant may be any of those known to one of
ordinary skill in the art and may be, for instance, derived from a
betaine in particular embodiments. In some embodiments, the
zwitterionic surfactant may include a quaternary ammonium group and
a sulfonate group. The zwitterionic surfactant of one or more
embodiments may further comprise an amide group.
[0027] In one or more embodiments, a zwitterionic surfactant may
have a structure represented by formula (II):
##STR00004##
where R.sup.2 is a C.sub.15-C.sub.27 hydrocarbon group or a
C.sub.15-C.sub.29 substituted hydrocarbon group, R.sup.3 is a
C.sub.1-C.sub.10 hydrocarbon group, and p and q are each,
independently, an integer ranging from 1 to 4.
[0028] In reference to R.sup.2 and R.sup.3, the term "hydrocarbon
group" has the same meaning as discussed above with regard to
R.sup.1. As used with regard to R.sup.2, the term "substituted
hydrocarbon group" refers to a hydrocarbon group (as defined above)
where at least one hydrogen atom is substituted with a non-hydrogen
group that results in a stable compound. Such substituents may be
groups selected from, but not limited to, halo, hydroxyl, alkoxy,
oxo, alkanoyl, aryloxy, alkanoyloxy, amino, alkylamino, arylamino,
arylalkylamino, disubstituted amines, alkanylamino, aroylamino,
aralkanoylamino, substituted alkanoylamino, substituted arylamino,
substituted aralkanoylamino, thiol, alkylthio, arylthio,
arylalkylthio, alkylthiono, arylthiono, aryalkylthiono,
alkylsulfonyl, arylsulfonyl, arylalkylsulfonyl, sulfonamide,
substituted sulfonamide, nitro, cyano, carboxy, carbamyl,
alkoxycarbonyl, aryl, substituted aryl, guanidine, and
heterocyclyl, and mixtures thereof. In some embodiments, the
substituted hydrocarbon group may comprise one or more alkylene
oxide units. The alkylene oxide may be ethylene oxide.
[0029] In one or more embodiments, the zwitterionic surfactant may
be soluble in aqueous solutions, such as in deionized water,
seawater, brines, calcium chloride solutions, and the like. In some
embodiments, the zwitterionic surfactant may be soluble in aqueous
solutions in an amount of 10% by weight (wt. %) or more, 20 wt. %
or more, or 30 wt. % or more at ambient temperature. In some
embodiments, the zwitterionic surfactant may have a lower aqueous
solubility than the gemini surfactant. In some embodiments, the
solubility of the zwitterionic surfactant may increase with
increasing temperature, until gelation occurs.
[0030] The wellbore fluids of one or more embodiments may comprise
the zwitterionic surfactant in an amount of the range of about 1 to
15% by weight (wt. %). For example, the wellbore fluid may contain
the zwitterionic surfactant in an amount ranging from a lower limit
of any of 1, 1.5, 2, 2.5, 3, 4, 5, 7, 10, and 12 wt. % to an upper
limit of any of 1.5, 2, 3, 4, 5, 6, 8, 10, 12, 14, and 15 wt. %,
where any lower limit can be used in combination with any
mathematically-compatible upper limit.
[0031] In one or more embodiments, the wellbore fluid may comprise
the gemini surfactant and the zwitterionic surfactant in a weight
ratio of 1:5 to 5:1 by weight, where the weight ratio is given as
the weight of the gemini surfactant to the weight of the
zwitterionic surfactant. For example, the wellbore fluid may
contain the gemini surfactant and the zwitterionic surfactant in a
weight ratio ranging from a lower limit of any of 1:5, 1:4, 1:3,
1:2, 1:1, and 2:1, to an upper limit of any of 1:2, 1:1, 2:1, 3:1,
4:1, and 5:1, where any lower limit can be used in combination with
any mathematically-compatible upper limit.
[0032] The wellbore fluids of one or more embodiments may have a
total surfactant content, including both a gemini and zwitterionic
surfactant, in an amount of the range of about 1 to 30% by weight
(wt. %). For example, the wellbore fluid may have a total
surfactant content in an amount ranging from a lower limit of any
of 1, 2, 2.5, 3, 4, 5, 7, 10, 12, 15, 20, and 25 wt. % to an upper
limit of any of 1.5, 2, 3, 4, 5, 6, 8, 10, 12, 15, 20, 25, and 30
wt. %, where any lower limit can be used in combination with any
mathematically-compatible upper limit.
[0033] The wellbore fluids may include an activator. The activator
is an additive that, upon an increase in temperature, enables the
surfactant to exhibit viscoelastic behavior and cause the wellbore
fluid to increase in viscosity. Without being bound by any theory,
the activators disclosed herein may enable the surfactant micelles
to form a rod-shaped structure that entangle as the temperature of
the fluid increases. This entanglement is the cause of the
viscoelastic behavior and the increase in viscosity.
[0034] In one or more embodiments, the activator may be a salt. The
salt may, for instance comprise a monovalent cation, such as an
alkali metal or a Group 11 transition metal, or a divalent cation,
such as an alkaline earth metal or a transition metal. In some
embodiments, the salt may comprise a cation selected from the group
consisting of lithium, sodium, potassium, magnesium, calcium,
nickel, iron, tin, aluminum, and zinc. In some embodiments, the
salt may comprise an anion selected from the group consisting of
fluoride, chloride, bromide, carbonate, bicarbonate, sulfate,
nitrate, nitrite, chromate, sulfite, oxalate, phosphate, and
phosphite. In particular embodiments, the activator may be an
alkaline earth metal halide, such as calcium chloride.
[0035] The wellbore fluids of one or more embodiments may comprise
the activator in an amount of the range of about 5 to 30% by weight
(wt. %). For example, the wellbore fluid may contain the activator
in an amount ranging from a lower limit of any of 5, 6, 7, 8, 10,
12, 15, 17, 20, and 22 wt. % to an upper limit of any of 10, 12,
15, 17, 20, 22, 25, 27, and 30 wt. %, where any lower limit can be
used in combination with any mathematically-compatible upper
limit.
[0036] In one or more embodiments, the wellbore fluid may comprise
the activator and the surfactants in a weight ratio of 30:1 to 1:3,
by weight, where the weight ratio is given as the weight of the
activator to the total weight of the surfactants. For example, the
wellbore fluid may contain the activator and the surfactants in a
weight ratio ranging from a lower limit of any of 1:3, 1:2, 1:1,
2:1, 4:1, 6:1, 8:1, 10:1 and 12:1 to an upper limit of any of 1:1,
2:1, 4:1, 6:1, 8:1, 10:1, 12:1, 15:1, 20:1, 25:1, and 30:1, where
any lower limit can be used in combination with any
mathematically-compatible upper limit.
[0037] The wellbore fluids of one or more embodiments may include
one or more acids. Acids may be particularly included when the
wellbore fluid is to be used in a matrix stimulation process, as
described below. The acid may be any suitable acid known to a
person of ordinary skill in the art, and its selection may be
determined by the intended application of the fluid. In some
embodiments, the acid may be one or more selected from the group
consisting of hydrochloric acid, sulfuric acid, carboxylic acids
such as acetic acid, and hydrofluoric acid. In some embodiments,
the hydrofluoric acid may be included as a hydrogen fluoride
source, such as ammonium fluoride, ammonium bifluoride, fluoroboric
acid, hexafluorophosphoric acid, and the like.
[0038] The wellbore fluid of one or more embodiments may comprise
the one or more acids in a total amount of the range of about 0.01
to 30.0 wt. %. For example, the wellbore fluid may contain the
acids in an amount ranging from a lower limit of any of 0.01, 0.05,
0.1, 0.5, 1.0, 5.0, 10, 15, 20, and 25 wt. % to an upper limit of
any of 0.5, 1.0, 5.0, 10, 15, 20, 25, and 30 wt. %, where any lower
limit can be used in combination with any mathematically-compatible
upper limit.
[0039] The wellbore fluids of one or more embodiments may include
one or more additives. The additives may be any conventionally
known and one of ordinary skill in the art will, with the benefit
of this disclosure, appreciate that the selection of said additives
will be dependent upon the intended application of the wellbore
fluid. For instance, if the wellbore fluid is to be used as a
fracturing fluid, it may comprise a proppant such as sand. In some
embodiments, the additives may be one or more selected from clay
stabilizers, scale inhibitors, corrosion inhibitors, biocides,
friction reducers, thickeners, and the like.
[0040] The wellbore fluid of one or more embodiments may comprise
the one or more additives in a total amount of the range of about
0.01 to 15.0 wt. %. For example, the wellbore fluid may contain the
additives in an amount ranging from a lower limit of any of 0.01,
0.05, 0.1, 0.5, 1.0, 2.5, 5.0, 1.5, 10.0 and 12.5 wt. % to an upper
limit of any of 0.1, 0.5, 1.0, 2.5, 5.0, 7.5, 10.0, 12.5, and 15.0
wt. %, where any lower limit can be used in combination with any
mathematically-compatible upper limit.
[0041] In one or more embodiments, the wellbore fluid may contain
little to no solid material. For example, the wellbore fluids of
some embodiments may contain solid material in an amount of 2 wt. %
or less, 1 wt. % or less, 0.5 wt. % or less, 0.1 wt. % or less,
0.05 wt. % or less, 0.01 wt. % or less, or 0.001 wt. % or less.
[0042] In one or more embodiments, the wellbore fluid may have a
density that is greater than 0.90 g/cm.sup.3. For example, the
wellbore fluid may have a density that is of an amount ranging from
a lower limit of any of 0.90, 0.95, 1.00, 1.05, 1.10, 1.15, and
1.20 g/cm.sup.3 to an upper limit of any of 1.00, 1.05, 1.10, 1.15,
1.20, and 1.25 g/cm.sup.3, where any lower limit can be used in
combination with any mathematically-compatible upper limit.
[0043] In one or more embodiments, the wellbore fluid may have a
viscosity at 40.degree. C. that is of the range of about 1 to 20
cP. For example, the wellbore fluid may have a viscosity at
40.degree. C. that is of an amount ranging from a lower limit of
any of 1, 2, 3, 4, 5, 6, 7, 8, 10, and 12 cP to an upper limit of
any of 4, 5, 6, 8, 10, 12, 14, 16, 18, and 20 cP, where any lower
limit can be used in combination with any mathematically-compatible
upper limit. In some embodiments, the wellbore fluids may have a
viscosity at 40.degree. C. of 20 cP or less, 15 cP or less, or 10
cP or less.
[0044] In one or more embodiments, the wellbore fluid may have a
viscosity at 90.degree. C. that is of the range of about 8 to 100
cP. For example, the wellbore fluid may have a viscosity at
90.degree. C. that is of an amount ranging from a lower limit of
any of 8, 9, 10, 12, 15, 20, 30, 40, 50, 60, and 80 cP to an upper
limit of any of 10, 12, 15, 20, 30, 40, 50, 60, 70, 90, and 100 cP,
where any lower limit can be used in combination with any
mathematically-compatible upper limit. In some embodiments, the
wellbore fluids may have a viscosity at 90.degree. C. of 10 cP or
more, 20 cP or more, 30 cP or more, or 40 cP or more.
[0045] The wellbore fluid of one or more embodiments may have a
viscosity that is higher at 90.degree. C. than at 40.degree. C. In
one or more embodiments, the wellbore fluid may have a ratio of a
viscosity at 90.degree. C. to a viscosity at 40.degree. C. that is
of the range of about 3:1 to 25:1. For example, the wellbore fluids
may have a ratio of a viscosity at 90.degree. C. to a viscosity at
40.degree. C. that is of the range having a lower limit of any of
3:1, 4:1, 5:1, 6:1, 8:1, 10:1, and 12:1 to an upper limit of any of
10:1, 12:1, 15:1, 20:1, and 25:1, where any lower limit can be used
in combination with any mathematically-compatible upper limit.
[0046] In one or more embodiments, the viscosity of the wellbore
fluid may decrease after contacting with a hydrocarbon. For
example, after contacting with a hydrocarbon such as diesel, the
wellbore fluid may have a viscosity at 90.degree. C. that is of an
amount ranging from a lower limit of any of 1, 2, 3, 4, 5, 6, 7, 8,
and 10, cP to an upper limit of any of 2, 4, 6, 8, 10, 12, and 15
cP, where any lower limit can be used in combination with any
mathematically-compatible upper limit. In some embodiments, after
contacting with a hydrocarbon such as diesel, the wellbore fluid
may have a viscosity at 90.degree. C. of 15 cP or less, 12 cP or
less, 10 cP or less, 8 cP or less, or 5 cP or less.
[0047] In one or more embodiments, the wellbore fluid may have a pH
that is neutral or acidic. For example, the wellbore fluid may have
a pH ranging from a lower limit of any of 2, 3, 4, 4.5, 5, 5.5, and
6, to an upper limit of any of 3, 4, 4.5, 5, 5.5, 6, 6.5, and 7,
where any lower limit can be used in combination with any
mathematically-compatible upper limit. In some embodiments, the
wellbore fluid may have a pH of 7 or less, of 6 or less, of 5 or
less, of 4 or less, or of 3 or less.
[0048] One or more embodiments of the present disclosure are
directed to a synthesis of the surfactants represented by the
aforementioned formula (I). A synthesis of one or more embodiments
is depicted in FIG. 1, wherein R.sup.1, m, n, and o represent the
same groups as discussed above with regard to formula (I).
[0049] As shown by FIG. 1, a dicarboxylic acid 1 and an amine 2 may
undergo an amidation reaction to yield intermediate amide 3. In one
or more embodiments, an excess amount of amine 2 is used. In some
embodiments, a molar ratio of amine 2 to dicarboxylic acid 1 is in
a range of 2:1 to 5:1, or 5:2 to 4:1.
[0050] In one or more embodiments, the dicarboxylic acid 1 is
converted in situ to an acyl chloride before reaction with the
amide 2. In such embodiments, a conventional chlorinating reagent,
such as thionyl chloride, may be used. The dicarboxylic acid 1 may
be added to the chlorinating reagent at a temperature below room
temperature, such as at a temperature in the range of about -10 to
10.degree. C., or about 0.degree. C. The temperature may then be
increased to room temperature while the reaction occurs. The
chlorinating reagent and the dicarboxylic acid 1 may be allowed to
react for 6-20 hours, 8-16 hours, or about 12 hours. The mixture
may be agitated throughout the duration of the reaction by any
method known to a person of ordinary skill in the art, such as by
employing a rotary shaker, a magnetic stirrer, or an overhead
stirrer. Excess chlorinating reagent may be removed by bubbling of
inert gas, such as N.sub.2. The acyl chloride of acid 1 may be
generated in an approximately quantitative yield. The amine 2 may
be dissolved in a solvent, such as dichloromethane, chloroform, or
dichloroethane, and added slowly to the acyl chloride of acid 1. In
some embodiments, the amine solution may be added dropwise. In some
embodiments, the acyl chloride of acid 1 may be at a temperature
below room temperature, such as at a temperature in the range of
about -10 to 10.degree. C., or about 0.degree. C., when the amine 2
solution is added. The temperature may then be increased to room
temperature while the reaction occurs. The acid chloride of acid 1
and the amine 2 may be allowed to react for 6-20 hours, 8-16 hours,
or about 12 hours. The mixture may be agitated throughout the
duration of the reaction by any method discussed above. The
amidation reaction may be conducted under an inert atmosphere, such
as under one or more of nitrogen, argon, and helium gas. After the
reaction, the residue may be extracted from one or more of the
group consisting of chloroform, dichloromethane, ethyl acetate, and
iso-propanol and subsequently dried under vacuum to yield
intermediate amide 3. The intermediate amide 3 may be produced in a
yield of 75% or more, 80% or more, 85% or more, 90% or more, 95% or
more, or 97% or more.
[0051] In one or more embodiments, the reaction between the acyl
chloride of acid 1 and amine 2 may further include the use of an
amine to facilitate the amidation. The amine catalyst may be
triethylamine. A molar ratio of the amine to the acyl chloride of
acid 1 may be in a range of 1:1 to 10:1, or about 4:1 to 8:1.
[0052] In alternative embodiments, the fatty acid 1 may not be
converted to the acid chloride first, but instead directly reacted
with the amine 2. In such instances, the amidation reaction may be
performed at reflux. In some embodiments, the reaction is performed
at a temperature that is of the range of 100 to 200.degree. C., 140
to 180.degree. C., or about 160.degree. C. An external heat source,
such as an oil bath, an oven, microwave, or a heating mantle, may
be employed to heat the mixture to the aforementioned temperature.
The mixture may be agitated throughout the duration of the reaction
by any method known to a person of ordinary skill in the art, such
as by employing a rotary shaker, a magnetic stirrer, or an overhead
stirrer. In one or more embodiments, the amine 2 may be added in a
two-stage or multi-stage fashion. For example, a first portion of
the amine 2 of 50-70%, 55-65%, or about 57% of the total moles of
the amine 2 used herein, may be added to the mixture and allowed to
react with the dicarboxylic acid 1 for 4-12 hours, 6-10 hours, or
about 8 hours, and subsequently a second portion of the amine which
is 30-50%, 35-45%, or about 43% of the total moles of the amine
used herein may be added to the same mixture and allowed to react
with the dicarboxylic acid for a duration of 3-9 hours, 5-7 hours,
or about 6 hours. Alternatively, the amine may be introduced to the
mixture in one batch and allowed to react with the carboxylic acid
for 6-20 hours, 8-16 hours, or about 12 hours. In one or more
embodiments, the reaction between dicarboxylic acid 1 and amine 2
may further include the use of a fluoride catalyst to facilitate
the amidation. The fluoride catalyst may be one or more selected
from the group consisting of sodium fluoride, potassium fluoride,
silver fluoride, cesium fluoride, and tetrabutylammonium fluoride.
A molar ratio of the fluoride catalyst to dicarboxylic acid 1 may
be in a range of 1:5 to 1:20, 1:8 to 1:12, or about 1:10.
[0053] Subsequently, as shown in FIG. 1, amide 3 may be reacted
with a sultone 4 to yield a surfactant 5 having a structure
consistent with formula (I). In one or more embodiments, a molar
ratio of the sultone 4 to the amide 3 is in a range of 4:1 to 1:2,
3:1 to 1:1, or about 3:2. In some embodiments, the reaction may be
performed with a molar excess of sultone 4. In one or more
embodiments, this reaction is conducted in a polar aprotic solvent,
such as one or more selected from the group consisting of ethyl
acetate, dimethylformamide, tetrahydrofuran, acetone, acetonitrile,
and dimethyl sulfoxide. In some embodiments, the reaction may be
adapted to be performed in polar protic solvents such as one or
more selected from the group consisting of methanol, ethanol,
propanol, isopropyl alcohol, and butanol. In one or more
embodiments, reacting the intermediate amide 3 with the sultone 4
is conducted without a solvent. In one or more embodiments, the
reaction may be performed at reflux. In some embodiments, the
reaction is performed at a temperature that is of the range of 50
to 100.degree. C., 60 to 90.degree. C., or about 80.degree. C. In
one or more embodiments, the reaction may have a duration of and
has a reaction time of 2 to 36 hours, 2 to 24 hours, 4 to 16 hours,
10 to 14 hours, or about 12 hours. After the reaction, the solid
residue may be collected and washed with a solvent selected from
one or more of the group consisting of ethyl acetate and diethyl
ether and subsequently dried under vacuum to yield surfactant 5 as
a white solid. The surfactant 5 may be produced in a yield of 75%
or more, 80% or more, 85% or more, 90% or more, 95% or more, or 97%
or more.
[0054] Methods in accordance with the present disclosure may
comprise the injection of a wellbore fluid into a formation. In one
or more embodiments, the wellbore fluid may be a single treatment
fluid that is injected into the wellbore in one pumping stage. In
other embodiments, methods in accordance with one or more
embodiments may involve the injection of the wellbore fluid and one
or more additional stimulation fluids. The additional stimulation
fluids may, in some embodiments, be co-injected with the wellbore
fluid. In some embodiments, the stimulation fluids may be injected
after the wellbore fluid.
[0055] The wellbore fluid of one or more embodiments has a low
viscosity at low temperatures and, therefore, good injectivity,
while being thermally stable enough for use downhole. Upon exposure
to increased temperatures in the wellbore, the wellbore fluid may
increase in viscosity. This phenomenon has the effect of reducing
fluid mobility, resulting in diverting the flow from high
permeability zones to lower ones and, ultimately, providing
improved oil recovery.
[0056] The methods of one or more embodiments of the present
disclosure may further comprise a pre-flushing step before the
injection of the wellbore fluid. The pre-flushing step may comprise
flushing the formation with a flushing solution that comprises one
or more surfactants. The flushing solution may be an aqueous
solution, and the surfactant may be the same surfactants as
included in the wellbore fluid. The pre-flushing may limit the
adsorption of the surfactants on the rock surface of the formation
during the injection process. The suitability of the use of a
pre-flushing step may depend on the type of surfactant and
rock.
[0057] The hydrocarbon-containing formation of one or more
embodiments may be a formation containing multiple zones of varying
permeability. For instance, the formation may contain at least a
zone having a relatively higher permeability and a zone having a
relatively lower permeability. During conventional injection,
fluids preferentially sweep the higher permeability zone, leaving
the lower permeability zone incompletely swept. In one or more
embodiments, the increased viscosity of the wellbore fluid may
"plug" the higher permeability zone, allowing subsequent fluid to
sweep the low permeability zone and improving sweep efficiency.
[0058] In one or more embodiments, the formation may have a
temperature ranging from about 60 to 250.degree. C. For example,
the formation may have a temperature that is of an amount ranging
from a lower limit of any of 60, 70, 80, 90, 100, 120, 140, 160,
180, and 200.degree. C. to an upper limit of any of 100, 120, 140,
160, 180, 200, 225, and 250.degree. C., where any lower limit can
be used in combination with any mathematically-compatible upper
limit.
[0059] The methods of one or more embodiments may be used for well
stimulation. A well stimulation process in accordance with one or
more embodiments of the present disclosure is depicted by, and
discussed with reference to, FIG. 2. Specifically, in step 200, the
wellbore fluid may be injected into a hydrocarbon-bearing formation
at an injection well. In some embodiments, the injection of the
wellbore fluid may be performed at a pressure that is below the
fracturing pressure of the formation. In step 210, a zone within
the formation may be at a high temperature and increase the
viscosity of the wellbore fluid. In step 220, after the increase in
viscosity, the tail-end of the fluid is diverted to
lower-permeability zones of the formation, displacing hydrocarbons.
This results from the increase in viscosity that may "plug" the
more permeable zones of the formation. In step 230, the formation
is stimulated by the wellbore fluid, creating pathways for
hydrocarbon production. In step 240, the displaced hydrocarbons may
be recovered through the stimulated reservoir. In one or more
embodiments, the hydrocarbons may be recovered at a production
well.
[0060] The well stimulation process of one or more embodiments may
be a matrix stimulation process. In the matrix stimulation process
of one or more embodiments, the wellbore fluid, or one of the
stimulation fluids, contains an acid. The acid fluid may react with
the formation, dissolving rock, and creating wormholes that create
a pathway for hydrocarbons to be displaced from deeper within the
rock. In one or more embodiments, the wellbore fluid may increase
in viscosity in the formation, enabling the fluid to better
penetrate lower-permeability zones of the formation and allowing
the acid to more uniformly react with the entire formation. This
may provide for the formation of deeper wormholes and enhancing the
overall permeability of the near-wellbore region. In the absence of
this viscosity increase, the fluid will primarily penetrate the
high permeability zones.
[0061] In one or more embodiments, the well stimulation process may
be repeated one or more times to increase the amount of
hydrocarbons recovered. In some embodiments, subsequent well
stimulation processes may involve the use of different amounts of
the surfactant and/or different surfactants than the first. The
methods of one or more embodiments may advantageously provide
improved sweep efficiency.
[0062] The methods of one or more embodiments may be used for
fracturing a formation. In these embodiments, the wellbore fluid
may be injected into a hydrocarbon-bearing formation at an
injection well. The fluid may be driven through the formation at a
pressure higher than the formation, opening pores and cracks
present in the formation. The wellbore fluid of one or more
embodiments may contain a proppant, such as sand, that can keep the
pores and cracks of the formation open. These processes may,
therefore, increase the permeability and hydrocarbon flow of the
formation.
Examples
[0063] The following examples are merely illustrative and should
not be interpreted as limiting the scope of the present
disclosure.
[0064] A zwitterionic surfactant 10 was prepared by the synthetic
route illustrated in FIG. 3. Specifically, the zwitterionic
surfactant 10 was synthesized by initially preparing the
intermediate 8, and then then reacting 8 with 1,3-propanesultone
9.
Synthesis of N-(3-(dimethylamino)propyl)nonadecanamide (8)
[0065] A two-necked round bottom flask, fixed with a reflux
condenser and a bent tube, was charged with stearic acid 6 (5.00 g,
20.63 mmol), 3-(dimethylamino)-1-propylamine 7 (4.22 g, 41.25
mmol), and NaF (0.09 g, 2.06 mmol). The bent tube was filled with
well dried alumina, which absorbs any water generated by the
reaction. The flask was heated at a temperature of 160.degree. C.
for eight hours under a N.sub.2 atmosphere. A second aliquot of
3-(dimethylamino)-1-propylamine 7 (30.94 mmol) was added and the
conditions were maintained for a further six hours. After cooling
to room temperature, the solid residue was collected, washed with
cold acetone: water (93:7 mL), and dried under vacuum to yield a
white solid 8. .sup.1H-NMR [CD.sub.3OD]=0.869 (t, 3H), 1.451-1.521
(m, 27H), 1.240-1.657 (m, 4H), 2.133 (t, 2H), 2.224 (s, 6H), 2.334
(t, 2H), 3.332 (t, 2H); .sup.13C-NMR [CD.sub.3OD]=18.95, 22.14,
25.22, 28.11, 33.32, 35.68, 35.88, 44.02, 50.66, 61.57, 63.46,
177.53, 180.53.
Synthesis of
3-(metheyliumyl(methyl)(3-stearamidopropyl)-14-azaneyl)propane-1-sulfonat-
e (SDAS, 10)
[0066] A 250-mL two-necked flask fixed with a reflux condenser was
charged with 8 (5.00 g, 15.31 mmol), 1,3-propanesultone 9 (2.81 g,
22.97 mmol), and ethyl acetate (100 mL). The flask was heated at
80.degree. C. for 12 h. After cooling to room temperature, the
solid was collected, washed successively using ethyl acetate (100
mL) and diethyl ether (50 mL), and dried under vacuum to yield SDAS
10 as a white solid (6.14 g, 89% yield). .sup.1H-NMR
[CDCl.sub.3]=1.101 (t, 3H), 1.451-1.521 (m, 27H), 1.805 (m, 2H),
2.185 (t, 2H), 2.324-2.425 (m, 4H), 3.075 (t, 2H), 3.473 (t, 2H),
3.54 (s, 6H), 3.726 (t, 2H); .sup.13C-NMR [CD.sub.3OD]=14.0, 19.3,
22.6, 23.0, 25.9, 29.3, 29.6, 29.7, 31.9, 36.3, 36.4, 48.1, 50.9,
62.6, 63.2, 174.6; FTIR (cm.sup.-1)=3265.42, 2915.00, 2884.61,
1666.49, 1552.64, 1467.54, 1174.26, 1035.13, 723.06.
[0067] Two gemini surfactants 15.1 (r=1) and 15.2 (r=2) were
prepared by the synthetic route illustrated in FIG. 4.
Specifically, the surfactants 15 whereas synthesized by initially
preparing the intermediate 13, and reacting 13 with either
1,3-propane sultone or 1,4-propane sultone 13.
Synthesis of N.sup.1,
N.sup.10-bis(3-(dimethylamino)propyl)decanediamide (13)
[0068] Thionyl chloride (10 mL) was taken in the round bottom flask
and cold to 0.degree. C. in an ice bath. Then, sebacic acid 11
(24.72 mmol) was added slowly with continuous stirring in the
reaction flask. The temperature was slowly raised to room
temperature and the stirring was continued overnight. Upon
completion of the reaction, N.sub.2 was bubbled through the
reaction mixture to eliminate the excessive thionyl chloride
keeping the reaction flask in fume hood followed by vacuum drying
on rotavapor. The acid chloride product was received in a
quantitative yield. N.sup.1, N.sup.1-dimethylpropane-1,3-diamine 12
(2.5 eq) was taken in another round bottom flask and cold to
0.degree. C. in an ice bath. Dichloromethane was added to the flask
followed by addition of triethylamine (6.0 eq). The acid chloride
was dissolved in dichloromethane and the resulting solution was
added dropwise to the reaction flask at 0.degree. C. and the
reaction allowed to reach room temperature where it was stirred
overnight. N.sup.1,
N.sup.10-bis(3-(dimethylamino)propyl)decanediamide 13 was isolated
from the mixture. .sup.1H-NMR [CDCl.sub.3]=1.255-1.302 (m, 8H),
1.577 (m, 4H), 1.637 (t, 4H), 2.121 (t, 4H), 2.280 (s, 12H), 2.367
(t, 4H), 3.319 (t, 4H), 6.948 (b, NH). .sup.13C-NMR
[CDCl.sub.3]=25.68, 26.14, 29.19, 36.89, 39.20, 45.38, 58.60,
173.04. FTIR (cm.sup.-1)=3303.67, 2921.83, 2852.83, 2811.75,
1635.01, 1538.76, 1468.29, 1379.05, 1238.83, 1100.88, 1041.46,
830.65, 714.41.
Synthesis of
4,4,16,16-tetramethyl-9,11-dioxo-4,8,12,16-tetraazanonadecane-4,16-diium--
1,19-disulfonate (15.1)
[0069] The intermediate 13 (1.165 mmol) was taken in a clean and
dried round bottom flask and dissolved in the 15 mL of ethyl
acetate. Then, 1,3-propane sultone 14 (3.495 mmol) was added in
reaction flask and the reaction was refluxed overnight. The
precipitate formed during the reaction was filtered, washed with
plenty of ethyl acetate and diethyl ether and then dried in vacuum
using rotavapor. .sup.1H-NMR [D.sub.2O]=1.155-1.252 (m, 8H), 1.442
(m, 4H), 1.867 (t, 4H), 2.067 (t, 4H), 2.109 (t, 4H), 2.822 (t,
4H), 2.970 (s, 12H), 3.136 (t, 4H), 3.204 (t, 4H), 3.347 (t, 4H).
13C-NMR [CDCl.sub.3]=18.11, 22.23, 225.24, 35.87, 47.15, 50.70,
61.85, 62, 18, 177.56. FTIR (cm.sup.-1)=3303.34, 2927.54, 2844.68,
1669.76, 1555.30, 1486.92, 1479.07, 1156.97, 1024.45, 929.32,
794.55, 682.02.
Synthesis of
5,5,17,17-tetramethyl-10,12-dioxo-5,9,13,17-tetraazahenicosane-5,17-diium-
-1,21-disulfonate (15.2)
[0070] The same method as discuss above with regard to 15.1 was
adopted for the synthesis of 15.2, except that 1,4-butane sultone
was used instead of 1,3-propane sultone. .sup.1H-NMR
[D.sub.2O]=1.166-1.252 (m, 8H), 1.448 (m, 4H), 1.671 (t, 4H), 1.784
(t, 4H), 1.858 (t, 4H), 2.114 (t, 4H), 2.179 (t, 4H), 2.834 (t,
4H), 2.942 (s, 12H), 3.136-3.23 (m, 12H). .sup.13C-NMR
[CDCl.sub.3]=20.82, 21.07, 22.23, 25.29, 28.18, 35.73, 35.91,
43.59, 49.94, 50.74, 61.70, 63.42, 177.55. FTIR
(cm.sup.-1)=3300.66, 2919.72, 2854.78, 1666.74, 1550.05, 1496.05,
1469.57, 1176.17, 1038.42, 956.74, 795.33, 686.20.
[0071] Viscosification Experiments
[0072] The zwitterionic surfactant 10 was mixed with either the
gemini surfactant 15.1 or the gemini surfactant 15.2 in a weight
ratio of 1:1. Each surfactant mixture was then added to two
different concentrations of CaCl.sub.2) in distilled water. The
CaCl.sub.2) was used at concentrations of 20% (Examples 1 and 3)
and 30% (Examples 2 and 4) by weight. Thereafter, 10 wt. % of the
total surfactant mixture (5 wt. % SDAS 10 and 5 wt. % of gemini
15.1 or 15.2) was added to 90 wt. % of the 20 or 30% CaCl.sub.2)
solutions. The viscosity of the surfactant solutions was measured
at 40.degree. C. and at 90.degree. C. under different shear rates.
The results are provided in Tables 1 and 2.
TABLE-US-00001 TABLE 1 Viscosity results with 15.1 Conc. of Conc.
of CaCl.sub.2 CaCl.sub.2 Viscosity Viscosity SDAS 10 Gemini 15.1
(20%) (30%) (cPs; 40.degree. C.) (cPs; 90.degree. C.) Example 1 5%
5% 90% -- 3.35 14.60 Example 2 5% 5% -- 90% 3.18 9.77
TABLE-US-00002 TABLE 2 Viscosity results with 15.2 Conc. of Conc.
of CaCl.sub.2 CaCl.sub.2 Viscosity Viscosity SDAS 10 Gemini 15.2
(20%) (30%) (cPs; 40.degree. C.) (cPs; 90.degree. C.) Example 3 5%
5% 90% -- 10.99 37.60 Example 4 5% 5% -- 90% 7.45 31.96
[0073] As is shown above, under all conditions that were studied,
the viscosity of the solution greatly increased upon heating to
90.degree. C. Viscosity of the treatment fluid dropped to <10 cP
after mixing with 10% by volume diesel at a temperature of
90.degree. C.
[0074] The properties of Examples 1-4 indicate the suitability of
gemini and zwitterionic surfactants for use in wellbore fluids.
These surfactants provide low-viscosity aqueous solutions that
increase in viscosity under downhole conditions. When the wellbore
fluid contacts a produced hydrocarbon its viscosity may drastically
reduce, enabling easy flowback of the fluid post treatment.
[0075] Although the preceding description has been described herein
with reference to particular means, materials and embodiments, it
is not intended to be limited to the particulars disclosed herein;
rather, it extends to all functionally equivalent structures,
methods and uses, such as are within the scope of the appended
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. .sctn. 112(f) 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.
* * * * *