U.S. patent application number 13/502489 was filed with the patent office on 2012-08-09 for water flooding method for secondary hydrocarbon recovery.
This patent application is currently assigned to ALBERTA INNOVATES - TECHNOLOGY FUTURES. Invention is credited to Jiang Bai, Mehmet Yaman Boluk, Blaine Francis Hawkins, Robert Jost, Fred Wassmuth, Liyan Zhao.
Application Number | 20120199355 13/502489 |
Document ID | / |
Family ID | 43921189 |
Filed Date | 2012-08-09 |
United States Patent
Application |
20120199355 |
Kind Code |
A1 |
Boluk; Mehmet Yaman ; et
al. |
August 9, 2012 |
WATER FLOODING METHOD FOR SECONDARY HYDROCARBON RECOVERY
Abstract
A water flooding composition in a method of secondary
hydrocarbon recovery. The water flooding composition includes water
and a thickening polymer. The thickening polymer includes a
hydroxyethyl cellulose backbone polymer having a molecular weight
of between about 1,000,000 and about 2,000,000 and a hydrophobic
modifier. The hydrophobic modifier has a substitution level in the
thickening polymer of between about 0.1 percent and about 2 percent
by weight of the thickening polymer. The hydrophobic modifier is an
alkyl hydrocarbon based material containing between about 10 and
about 24 unsubstituted carbon atoms per group. The thickening
polymer has a concentration in the water flooding composition of
between about 0.01 percent and about 1 percent by weight of the
water flooding composition. The water flooding composition is
formulated within these ranges so that the water flooding
composition has a suitable viscosity/mobility and so that the water
flooding composition is injectable.
Inventors: |
Boluk; Mehmet Yaman;
(Edmonton, CA) ; Bai; Jiang; (Calgary, CA)
; Hawkins; Blaine Francis; (Calgary, CA) ; Jost;
Robert; (St. Albert, CA) ; Wassmuth; Fred;
(Calgary, CA) ; Zhao; Liyan; (Edmonton,
CA) |
Assignee: |
ALBERTA INNOVATES - TECHNOLOGY
FUTURES
Edmonton
AB
|
Family ID: |
43921189 |
Appl. No.: |
13/502489 |
Filed: |
September 27, 2010 |
PCT Filed: |
September 27, 2010 |
PCT NO: |
PCT/CA2010/001522 |
371 Date: |
April 17, 2012 |
Current U.S.
Class: |
166/305.1 |
Current CPC
Class: |
C09K 8/588 20130101;
E21B 43/20 20130101 |
Class at
Publication: |
166/305.1 |
International
Class: |
E21B 43/16 20060101
E21B043/16 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 30, 2009 |
CA |
2684230 |
Claims
1. In a method of secondary hydrocarbon recovery of a type which
comprises passing a water flooding composition through a
subterranean formation containing a hydrocarbon deposit, the method
characterized by the water flooding composition being comprised of
water and a thickening polymer, the thickening polymer having a
concentration of between 0.01 percent and 1 percent by weight of
the water flooding composition, the thickening polymer comprising:
(a) a hydroxyethyl cellulose backbone polymer having a molecular
weight of between 1,000,000 and 2,000,000; and (b) a hydrophobic
modifier in a substitution level in the thickening polymer of
between 0.1 percent and 2 percent by weight of the thickening
polymer, wherein the hydrophobic modifier is comprised of an alkyl
hydrocarbon based material containing between 10 and 24
unsubstituted carbon atoms per group; wherein the water flooding
composition is formulated to have a viscosity of between 2 mPas and
100 mPas and to be injectable into the subterranean formation.
2. The method as claimed in claim 1 wherein the concentration of
the thickening polymer in the water flooding composition is between
0.05 percent and 0.25 percent by weight of the water flooding
composition.
3. The method as claimed in claim 2 wherein the alkyl hydrocarbon
based material of the hydrophobic modifier contains between 12 and
18 unsubstituted carbon atoms per group.
4. The method as claimed in claim 3 wherein the substitution level
of the hydrophobic modifier in the thickening polymer is between
0.1 percent and 1.5 percent by weight of the thickening
polymer.
5. The method as claimed in claim 4 wherein the hydrocarbon deposit
has a mobility, wherein the water flooding composition has a
mobility, and wherein a ratio of the mobility of the water flooding
composition to the mobility of the hydrocarbon deposit is no
greater than 100:1.
6. The method as claimed in claim 5 wherein the water flooding
composition is adapted to be capable of being passed through a
permeable test medium from an upstream end of the permeable test
medium to a downstream end of the permeable test medium, wherein
the permeable test medium has an initial permeability of less than
10 darcies, such that the thickening polymer has an initial
concentration in the water flooding composition at the upstream end
of the permeable test medium and a final concentration in the water
flooding composition at the downstream end of the permeable test
medium, and such that the final concentration of the thickening
polymer in the water flooding composition is greater than ninety
percent of the initial concentration of the thickening polymer in
the water flooding composition.
7. The method as claimed in claim 6 wherein the ratio of the
mobility of the water flooding composition to the mobility of the
hydrocarbon deposit is no greater than 50:1.
8. The method as claimed in claim 7 wherein the ratio of the
mobility of the water flooding composition to the mobility of the
hydrocarbon deposit is no greater than 10:1.
9. The method as claimed in claim 8 wherein the ratio of the
mobility of the water flooding composition to the mobility of the
hydrocarbon deposit is no greater than 2:1.
10. The method as claimed in claim 5 wherein the water flooding
composition is adapted to be capable of being passed through a
permeable test medium from an upstream end of the permeable test
medium to a downstream end of the permeable test medium, wherein
the permeable test medium has an initial permeability of less than
10 darcies, such that the water flooding composition has an initial
viscosity at the upstream end of the permeable test medium and a
final viscosity at the downstream end of the permeable test medium,
and such that the final viscosity of the water flooding composition
is greater than ninety percent of the initial viscosity of the
water flooding composition.
11. The method as claimed in claim 10 wherein the ratio of the
mobility of the water flooding composition to the mobility of the
hydrocarbon deposit is no greater than 50:1.
12. The method as claimed in claim 11 wherein the ratio of the
mobility of the water flooding composition to the mobility of the
hydrocarbon deposit is no greater than 10:1.
13. The method as claimed in claim 12 wherein the ratio of the
mobility of the water flooding composition to the mobility of the
hydrocarbon deposit is no greater than 2:1.
14. The method as claimed in claim 4 wherein the water flooding
composition is adapted to be capable of being passed through a
permeable test medium from an upstream end of the permeable test
medium to a downstream end of the permeable test medium, wherein
the permeable test medium has an initial permeability of less than
10 darcies, such that the thickening polymer has an initial
concentration in the water flooding composition at the upstream end
of the permeable test medium and a final concentration in the water
flooding composition at the downstream end of the permeable test
medium, and such that the final concentration of the thickening
polymer in the water flooding composition is greater than ninety
percent of the initial concentration of the thickening polymer in
the water flooding composition.
15. The method as claimed in claim 14 wherein the water flooding
composition has a viscosity of between 2 mPas and 50 mPas.
16. The method as claimed in claim 4 wherein the water flooding
composition is adapted to be capable of being passed through a
permeable test medium from an upstream end of the permeable test
medium to a downstream end of the permeable test medium, wherein
the permeable test medium has an initial permeability of less than
10 darcies, such that the water flooding composition has an initial
viscosity at the upstream end of the permeable test medium and a
final viscosity at the downstream end of the permeable test medium,
and such that the final viscosity of the water flooding composition
is greater than ninety percent of the initial viscosity of the
water flooding composition.
17. The method as claimed in claim 16 wherein the water flooding
composition has a viscosity of between 2 mPas and 50 mPas.
18. The method as claimed in claim 4 wherein the hydroxyethyl
cellulose backbone polymer of the water flooding composition has a
molecular weight of 1,300,000.
19. The method as claimed in claim 18 wherein the hydrocarbon
deposit has a mobility, wherein the water flooding composition has
a mobility, and wherein a ratio of the mobility of the water
flooding composition to the mobility of the hydrocarbon deposit is
no greater than 100:1.
20. The method as claimed in claim 19 wherein the ratio of the
mobility of the water flooding composition to the mobility of the
hydrocarbon deposit is no greater than 50:1.
21. The method as claimed in claim 20 wherein the ratio of the
mobility of the water flooding composition to the mobility of the
hydrocarbon deposit is no greater than 10:1.
22. The method as claimed in claim 21 wherein the ratio of the
mobility of the water flooding composition to the mobility of the
hydrocarbon deposit is no greater than 2:1.
23. The method as claimed in claim 18 wherein the water flooding
composition has a viscosity of between 2 mPas and 50 mPas.
24. The method as claimed in claim 4 wherein the alkyl hydrocarbon
based material of the hydrophobic modifier is comprised of dodecyl
tetradecyl glycidyl ether.
25. The method as claimed in claim 24 wherein the hydrocarbon
deposit has a mobility, wherein the water flooding composition has
a mobility, and wherein a ratio of the mobility of the water
flooding composition to the mobility of the hydrocarbon deposit is
no greater than 100:1.
26. The method as claimed in claim 25 wherein the ratio of the
mobility of the water flooding composition to the mobility of the
hydrocarbon deposit is no greater than 50:1.
27. The method as claimed in claim 26 wherein the ratio of the
mobility of the water flooding composition to the mobility of the
hydrocarbon deposit is no greater than 10:1.
28. The method as claimed in claim 27 wherein the ratio of the
mobility of the water flooding composition to the mobility of the
hydrocarbon deposit is no greater than 2:1.
29. The method as claimed in claim 24 wherein the water flooding
composition has a viscosity of between 2 mPas and 50 mPas.
30. The method as claimed in claim 4 wherein the substitution level
of the hydrophobic modifier in the thickening polymer is between
0.7 percent and 1 percent by weight of the thickening polymer.
31. The method as claimed in claim 30 wherein the hydrocarbon
deposit has a mobility, wherein the water flooding composition has
a mobility, and wherein a ratio of the mobility of the water
flooding composition to the mobility of the hydrocarbon deposit is
no greater than 100:1.
32. The method as claimed in claim 31 wherein the ratio of the
mobility of the water flooding composition to the mobility of the
hydrocarbon deposit is no greater than 50:1.
33. The method as claimed in claim 32 wherein the ratio of the
mobility of the water flooding composition to the mobility of the
hydrocarbon deposit is no greater than 10:1.
34. The method as claimed in claim 33 wherein the ratio of the
mobility of the water flooding composition to the mobility of the
hydrocarbon deposit is no greater than 2:1.
35. The method as claimed in claim 30 wherein the water flooding
composition has a viscosity of between 2 mPas and 50 mPas.
36. The method as claimed in claim 4 wherein the concentration of
the thickening polymer in the water flooding composition is 0.2
percent by weight of the water flooding composition.
37. The method as claimed in claim 36 wherein the hydrocarbon
deposit has a mobility, wherein the water flooding composition has
a mobility, and wherein a ratio of the mobility of the water
flooding composition to the mobility of the hydrocarbon deposit is
no greater than 100:1.
38. The method as claimed in claim 37 wherein the ratio of the
mobility of the water flooding composition to the mobility of the
hydrocarbon deposit is no greater than 50:1.
39. The method as claimed in claim 38 wherein the ratio of the
mobility of the water flooding composition to the mobility of the
hydrocarbon deposit is no greater than 10:1.
40. The method as claimed in claim 39 wherein the ratio of the
mobility of the water flooding composition to the mobility of the
hydrocarbon deposit is no greater than 2:1.
41. The method as claimed in claim 36 wherein the water flooding
composition has a viscosity of between 2 mPas and 50 mPas.
42. The method as claimed in claim 4 wherein the hydroxyethyl
cellulose backbone polymer of the water flooding composition has a
molecular weight of 1,300,000, wherein the alkyl hydrocarbon based
material of the hydrophobic modifier is comprised of dodecyl
tetradecyl glycidyl ether, wherein the substitution level of the
hydrophobic modifier in the thickening polymer is between 0.7
percent and 1 percent by weight of the thickening polymer, and
wherein the concentration of the thickening polymer in the water
flooding composition is 0.2 percent by weight of the water flooding
composition.
43. The method as claimed in claim 42 wherein the water of the
water flooding composition is comprised of a brine solution.
44. The method as claimed in claim 43 wherein the brine solution is
comprised of one percent sodium chloride by weight of the brine
solution.
45. A method of preparing a water flooding composition for use in a
method of secondary hydrocarbon recovery of a type which comprises
passing the water flooding composition through a subterranean
formation containing a hydrocarbon deposit, the method comprising:
(a) selecting a hydroxyethyl cellulose backbone polymer having a
molecular weight of between 1,000,000 and 2,000,000; (b) selecting
a hydrophobic modifier comprised of an alkyl hydrocarbon based
material containing between 10 and 24 unsubstituted carbon atoms
per group; (c) providing a thickening polymer comprising the
hydroxyethyl cellulose backbone polymer and the hydrophobic
modifier in a substitution level in the thickening polymer of
between 0.1 percent and 2 percent by weight of the thickening
polymer; and (d) combining the thickening polymer with water to
provide the water flooding composition, wherein the thickening
polymer has a concentration of between 0.1 percent and 1 percent by
weight of the water flooding composition; wherein the water
flooding composition has a viscosity of between 2 mPas and 100 mPas
and is injectable into the subterranean formation.
Description
TECHNICAL FIELD
[0001] A method of secondary hydrocarbon recovery of the type which
comprises passing a water flooding composition through a
subterranean formation containing a hydrocarbon deposit.
BACKGROUND OF THE INVENTION
[0002] The first stage of hydrocarbon production is known as
primary hydrocarbon recovery. In primary hydrocarbon recovery,
energy (eg., pressure or potential energy) within the subterranean
formation is utilized to displace hydrocarbons from the
subterranean formation, into a production wellbore, and ultimately
to the earth's surface. Primary hydrocarbon recovery may be
assisted by artificial lift systems such as pumps or gas lift
installations.
[0003] The second stage of hydrocarbon production is known as
secondary hydrocarbon recovery. In secondary hydrocarbon recovery,
an external fluid in gas or liquid form is injected into the
subterranean formation through one or more injection wells. The
external fluid typically functions to displace hydrocarbons through
the subterranean formation toward one or more production wellbores
through which the hydrocarbons may be produced to the earth's
surface. The external fluid may also assist in maintaining or
increasing the pressure in the subterranean formation.
[0004] One form of secondary hydrocarbon recovery is water
flooding. In water flooding, a water flooding composition is
injected into the subterranean formation as the external fluid. The
water flooding composition is typically comprised of water and one
or more other materials which function to provide desirable
properties to the water flooding composition. Such other materials
may include a thickener to increase the viscosity of the water
flooding composition and thereby decrease the mobility of the water
flooding composition through the subterranean formation. Suitable
thickeners for use in water flooding compositions are often
polymers, with the result that water flooding using a water
flooding composition containing a thickener is sometimes referred
to as polymer flooding.
[0005] Mobility of a fluid is defined as the ratio of permeability
(of the medium through which the fluid is passed) to viscosity (of
the fluid). Mobility is therefore a function of both the properties
of the fluid and the properties of the environment in which the
fluid is located.
[0006] A hydrocarbon deposit in a subterranean formation may
exhibit a relatively high viscosity and a relatively low mobility.
If a water flooding composition has a relatively lower viscosity
and a relatively higher mobility than the hydrocarbon deposit, the
water flooding composition may tend to move through the hydrocarbon
deposit or to bypass the hydrocarbon deposit so that the
hydrocarbon deposit is not effectively displaced toward the
production wellbore or wellbores by the water flooding
composition.
[0007] This phenomenon is described as "fingering", and results in
a reduction in the "sweep efficiency" of the water flooding
procedure. Sweep efficiency is defined as the ratio of the volume
of the subterranean formation which is actually contacted by the
water flooding composition during a water flooding procedure to the
volume of the subterranean formation which is available to be
contacted by the water flooding composition during the water
flooding procedure.
[0008] Fingering can be reduced and sweep efficiency can be
increased by including a thickener in the water flooding
composition in order to increase its viscosity and thus reduce its
mobility through the subterranean formation.
[0009] U.S. Pat. No. 4,529,523 (Landoll) describes a water flooding
method for enhanced recovery of oil from a subterranean
oil-containing formation using a water flooding medium which
includes a thickener and which may also include a compatible
surfactant.
[0010] In Landoll, it is suggested that the problems which may
limit the effectiveness of water flooding procedures include high
mobility of the water flooding medium, immiscibility of the water
flooding medium with oil, and lack of durability of the water
flooding medium when exposed to salts/brine, shear forces, heat,
and/or biological activity. These problems are stated in Landoll to
be overcome by the use of a water flooding medium which contains a
hydrophobically modified, water-soluble polymer as the
thickener.
[0011] In Landoll, the thickening polymer includes a polymer
backbone which may be any nonionic, water soluble polymer including
poly(acrylamide), a cellulose ether, poly(ethylene oxide), a
natural polysaccharide gum, and poly(vinyl alcohol). The nonionic
character of the backbone is stated to be important in promoting
salt tolerance. Operable polymers in Landoll have molecular weights
of about 50,000 to 1,000,000. Preferable molecular weights in
Landoll are from about 150,000 to about 800,000.
[0012] The polymer backbone in Landoll is modified by the
incorporation of small amounts of long chain alkyl groups. It is
stated in Landoll that in general, the alkyl modifier contains from
about 8 to about 25 carbons, preferably from about 16 to about 25
carbons. The alkyl modifier is stated to be present in an amount
from about 0.2 percent by weight to the amount which makes the
polymer less than 1 percent soluble in water, or from about 0.2 to
about 2.0 percent by weight of the polymer.
[0013] The concentration of the polymer in the water flooding
medium is stated in Landoll to be from about 0.01 to 2.0 percent by
weight, preferably from about 0.1 to 0.5 percent by weight.
[0014] In Landoll, the preferred polymer is hydrophobically
modified hydroxyethyl cellulose where the alkyl chain modifier is
from about 8 to about 25 carbon atoms in length.
[0015] The nonionic, hydrophobically modified, water-soluble
polymers in Landoll are described in Landoll as being especially
well suited for use in polymer-water flooding media because they
possess surface activity which may reduce or eliminate the use of a
separate surfactant in water flooding procedures.
[0016] However, in addition to providing a water flooding
composition which exhibits a suitable viscosity and mobility,
another goal in formulating a water flooding composition is to
provide a water flooding composition which is injectable through
the subterranean formation. A water flooding composition is
injectable if it can pass through the subterranean formation
without causing significant plugging of the subterranean
formation.
[0017] A water flooding composition which exhibits a suitable
viscosity and mobility may be unsuitable for use as a water
flooding composition if it does not exhibit sufficient
injectability. Injectability of the water flooding compositions is
not a consideration which appears to be addressed in Landoll.
SUMMARY OF THE INVENTION
[0018] References in this document to dimensions, to orientations,
to operating parameters, to ranges, to lower limits of ranges, and
to upper limits of ranges are not intended to provide strict
boundaries for the scope of the invention, but should be construed
to mean "approximately" or "about" or "substantially", within the
scope of the teachings of this document, unless expressly stated
otherwise.
[0019] The present invention is directed at methods of secondary
hydrocarbon recovery of a type which comprises passing a water
flooding composition through a subterranean formation containing a
hydrocarbon deposit. The present invention is more specifically
directed at improvements in the composition of the water flooding
composition.
[0020] The water flooding compositions of the invention are
comprised of water and a thickening polymer, wherein the thickening
polymer is comprised of a hydroxyethyl cellulose backbone polymer
having a molecular weight of between about 1,000,000 and about
2,000,000 and a hydrophobic modifier comprised of an alkyl
hydrocarbon based material.
[0021] The hydroxyethyl cellulose backbone polymer may be described
as "HEC". The thickening polymer may be described as
hydrophobically modified HEC or as "HMHEC".
[0022] The hydroxyethyl cellulose backbone polymer has a
hydroxyethyl molar substitution or "MS", which is the average
number of moles of hydroxyethyl which are incorporated in the
polymer per anhydroglucose unit of the cellulose. In some
embodiments, the MS of the hydroxyethyl cellulose backbone polymer
is at least about 0.5. In some embodiments, the MS of the
hydroxyethyl cellulose backbone polymer is at least about 1. In
some embodiments, the MS of the hydroxyethyl cellulose backbone
polymer is at least about 2. In some embodiments, the MS of the
hydroxyethyl cellulose backbone polymer is between about 2 and
about 2.5. In some embodiments, the MS of the hydroxyethyl
cellulose backbone polymer is about 2.5.
[0023] In some embodiments, the hydroxyethyl cellulose backbone
polymer may be comprised of a combination of different hydroxyethyl
cellulose (HEC) polymers.
[0024] The alkyl hydrocarbon based material of the hydrophobic
modifier may be comprised of any alkyl group and/or substituted
alkyl group or any combination of alkyl groups and/or substituted
alkyl groups. In some embodiments, the alkyl hydrocarbon based
material of the hydrophobic modifier may be comprised of one or
more alkyl groups and/or substituted alkyl groups which contain
between about 10 and about 24 unsubstituted carbon atoms per group.
In some embodiments, the alkyl hydrocarbon based material of the
hydrophobic modifier may be comprised of one or more alkyl groups
and/or substituted alkyl groups which contain between about 12 and
about 18 unsubstituted carbon atoms per group.
[0025] As used herein, "unsubstituted carbon atom" means a carbon
atom which is directly bonded only with hydrogen and/or carbon.
[0026] The water flooding compositions of the invention may be
further comprised of other substances in addition to water and the
thickening polymer. As non-limiting examples, the water in the
water flooding composition may be present in brine form (i.e.,
containing up to about 10 percent sodium chloride and/or other
equivalent monovalent metal salts), as hard brine (i.e., brine
containing up to about 0.4 percent divalent and/or polyvalent metal
ions such as calcium or magnesium), and/or may contain other
substances and/or impurities. The water flooding composition may
also be further comprised of other materials for enhancing the
properties of the water flooding composition or the effectiveness
of the water flooding procedure.
[0027] The water flooding compositions of the invention are
formulated to have a viscosity and/or mobility which is compatible
with the viscosity and/or mobility of the hydrocarbon deposit which
is intended to be produced using the water flooding method.
[0028] As used herein, "viscosity" means dynamic viscosity and is
expressed in pascal-second (Pas) units at a shear of between about
7/s and about 10/s. As used herein, permeability is expressed in
darcy (D) units. As used herein, mobility is the ratio of
permeability to viscosity, where permeability is expressed in darcy
(D) units and viscosity is expressed in pascal-second (Pas) units
at a shear of between about 7/s and about 10/s.
[0029] In some embodiments, the viscosity of a water flooding
composition may be considered to be compatible with the viscosity
of a hydrocarbon deposit if the viscosity of the water flooding
composition is between about 2 mPas and about 100 mPas. In some
embodiments, the viscosity of a water flooding composition may be
considered to be compatible with the viscosity of a hydrocarbon
deposit if the viscosity of the water flooding composition is
between about 5 mPas and about 50 mPas. In some embodiments, the
viscosity of a water flooding composition may be considered to be
compatible with the viscosity of a hydrocarbon deposit if the
viscosity of the water flooding composition is between about 5 mPas
and about 40 mPas.
[0030] In some embodiments, the mobility of a water flooding
composition may be considered to be compatible with the mobility of
a hydrocarbon deposit if a ratio of the mobility of the water
flooding composition to the mobility of the hydrocarbon deposit is
no greater than about 100:1. In some embodiments, the mobility of a
water flooding composition may be considered to be compatible with
the mobility of a hydrocarbon deposit if a ratio of the mobility of
the water flooding composition to the mobility of the hydrocarbon
deposit is no greater than about 50:1. In some embodiments, the
mobility of a water flooding composition may be considered to be
compatible with the mobility of a hydrocarbon deposit if a ratio of
the mobility of the water flooding composition to the mobility of
the hydrocarbon deposit is no greater than about 10:1. In some
embodiments, the mobility of a water flooding composition may be
considered to be compatible with the mobility of a hydrocarbon
deposit if the ratio of the mobility of the water flooding
composition to the mobility of the hydrocarbon deposit is no
greater than about 2:1.
[0031] The water flooding compositions of the invention are also
formulated to be injectable into the subterranean formation in
which the water flooding method is to be performed. Generally, a
water flooding composition may be considered to be injectable into
the subterranean formation if it can pass through the subterranean
formation without causing significant plugging of the subterranean
formation. Plugging of the subterranean formation may result when
one or more constituents of the water flooding composition become
separated from the water flooding composition during the water
flooding procedure and remain in the subterranean formation after
the water flooding composition has passed through the subterranean
formation.
[0032] Plugging of the subterranean formation may be indicated by a
decrease in the viscosity of the water flooding composition as it
passes through the subterranean formation and/or by a decrease in
the concentration of the thickening polymer in the water flooding
composition as the water flooding composition passes through the
subterranean formation. Plugging of the subterranean formation may
also be indicated by a decrease in the permeability of the
subterranean formation as the water flooding composition passes
through the subterranean formation.
[0033] In some embodiments, the injectability of a water flooding
composition may be evaluated by passing the water flooding
composition through a permeable test medium. In some embodiments,
the injectability of a water flooding composition may be evaluated
by considering the properties of the water flooding composition
before and after the water flooding composition has been passed
through the permeable test medium. In some embodiments, the
injectability of a water flooding composition may be evaluated by
considering the properties of the water flooding composition at an
upstream end of the permeable test medium and a downstream end of
the permeable test medium. In some embodiments, the injectability
of a water flooding composition may be evaluated by considering the
permeability of the permeable test medium before, during and/or
after the water flooding composition has been passed through the
permeable test medium.
[0034] The water flooding composition may have an initial viscosity
at an upstream end of the permeable test medium and a final
viscosity at a downstream end of the permeable test medium. In some
embodiments, the injectability of the water flooding composition
may be evaluated having regard to the initial viscosity of the
water flooding composition and the final viscosity of the water
flooding composition. In some embodiments, the water flooding
composition may be considered to be injectable if the final
viscosity of the water flooding composition is greater than ninety
percent of the initial viscosity of the water flooding
composition.
[0035] The thickening polymer may have an initial concentration in
the water flooding composition at the upstream end of the permeable
test medium and a final concentration in the water flooding
composition at the downstream end of the permeable test medium. In
some embodiments, the injectability of the water flooding
composition may be evaluated having regard to the initial
concentration of the thickening polymer and the final concentration
of the thickening polymer. In some embodiments, the water flooding
composition may be considered to be injectable if the final
concentration of the thickening polymer in the water flooding
composition is greater than ninety percent of the initial
concentration of the thickening polymer in the water flooding
composition.
[0036] In some embodiments, the properties of the permeable test
medium may be selected to provide a reasonable simulation of the
properties of the subterranean formation in which the water
flooding composition may be used and/or may be selected so that
they may be correlated with the properties of the subterranean
formation empirically or in some other manner.
[0037] In some embodiments, the permeable test medium may have
specific dimensions and/or properties. For example, in some
embodiments, the permeable test medium may have an initial
permeability of less than 10 darcies. For example, in some
embodiments, the permeable test medium may have a length between
the upstream end and the downstream end of about ten
centimeters.
[0038] As indicated, the water flooding compositions of the
invention are formulated to have a viscosity and/or mobility which
is compatible with the viscosity and/or mobility of the hydrocarbon
deposit which is intended to be produced using the water flooding
method, and are formulated to be injectable into the subterranean
formation in which the water flooding method is to be
performed.
[0039] The formulation of the water flooding compositions to
achieve compatibility with the hydrocarbon deposit and
injectability into the subterranean formation has been determined
to be dependent upon one or more of the molecular weight of the
hydroxyethyl cellulose backbone polymer, the composition of the
hydrophobic modifier, the substitution level of the hydrophobic
modifier in the thickening polymer, and the concentration of the
thickening polymer in the water flooding composition.
[0040] It has been observed that the viscosity of a water flooding
composition according to the invention tends to increase and the
mobility of a water flooding composition tends to decrease as the
molecular weight of the hydroxyethyl cellulose backbone polymer
increases. It has also been observed that the injectability of a
water flooding composition according to the invention does not
appear to depend significantly upon the molecular weight of the
hydroxyethyl cellulose backbone polymer.
[0041] It has been observed that the viscosity of a water flooding
composition according to the invention tends to increase and the
mobility of a water flooding composition tends to decrease as the
number of unsubstituted carbon atoms in the hydrophobic modifier
increases. It has also been observed that the injectability of a
water flooding composition according to the invention tends to
decrease as the number of unsubstituted carbon atoms in the
hydrophobic modifier increases.
[0042] It has been observed that the viscosity of a water flooding
composition according to the invention tends to increase and the
mobility of a water flooding composition tends to decrease as the
substitution level of the hydrophobic modifier in the thickening
polymer increases. It has also been observed that the injectability
of a water flooding composition according to the invention tends to
decrease as the substitution level of the hydrophobic modifier in
the thickening polymer increases.
[0043] It has been observed that the viscosity of a water flooding
composition according to the invention tends to increase and the
mobility of a water flooding composition tends to decrease as the
concentration of the thickening polymer in the water flooding
composition increases. It has also been observed that the
injectability of a water flooding composition according to the
invention tends to decrease as the concentration of the thickening
polymer in the water flooding composition increases.
[0044] The presence of substances other than water and the
thickening polymer in the water flooding compositions of the
invention may also affect the mobility of the water flooding
compositions and their injectability. By way of non-limiting
examples, the water in the water flooding compositions of the
invention may be present in brine form and/or as hard brine.
[0045] It has been observed that the viscosity of a water flooding
composition according to the invention tends to be higher and the
mobility of a water flooding composition according to the invention
tends to be lower if the water in the water flooding composition is
present in brine form and/or as hard brine than if the water in the
water flooding composition is relatively pure. This phenomenon is
believed to be attributable to the enhancement of intramolecular
and intermolecular association of the thickening polymers of the
invention (as described below), due to the presence of ions in the
water of the water flooding composition.
[0046] The thickening polymers of the invention may be described
generally as cellulosic associating polymers. In such polymers,
viscosity/mobility and injectability are believed to be dependent
upon at least two different mechanisms of action. A first mechanism
of action is "entanglement", which is believed to be attributable
primarily to the molecular weight of the backbone polymer and which
increases as the molecular weight (and thus the length) of the
backbone polymer increases.
[0047] A second mechanism of action is "association", which is
attributable to the presence and hydrophobicity of the hydrophobic
modifier. Without intending to be bound by theory, it is believed
that the hydrophobic modifier groups interact or "associate", both
within a single molecule of a thickening polymer and between
adjacent molecules of a thickening polymer.
[0048] The degree of association of a water flooding composition
according to the invention increases as the number of unsubstituted
carbon atoms provided by the hydrophobic modifier increases.
Increasing the number of unsubstituted carbon atoms may be achieved
by increasing the "size" of the hydrophobic modifier, by increasing
the substitution level of the hydrophobic modifier in the
thickening polymer, and/or by increasing the concentration of the
thickening polymer in the water flooding composition. As the degree
of association increases, the viscosity of a water flooding
composition increases, the mobility of the water flooding
composition decreases, and the injectability of the water flooding
composition decreases.
[0049] As noted above, the molecular weight of the hydroxyethyl
cellulose backbone polymer does not appear to significantly affect
the injectability of the water flooding composition.
[0050] As a result, it would appear that while the viscosity and
mobility of a water flooding composition according to the invention
is dependent upon both the molecular weight of the hydroxyethyl
cellulose backbone polymer and upon the degree of association of
the water flooding composition, the injectability of a water
flooding composition according to the invention is dependent
primarily upon the degree of association of the water flooding
composition.
[0051] These phenomena facilitate the formulation of the water
flooding compositions of the invention which provide an appropriate
viscosity and/or mobility of the water flooding compositions while
maintaining injectability of the water flooding compositions.
[0052] For example, in comparison with the teachings of U.S. Pat.
No. 4,529,523 (Landoll), the water flooding compositions of the
invention utilize relatively higher molecular weight backbone
polymers having a molecular weight of between 1,000,000 and
2,000,000 (in stark contrast with the molecular weight range of
50,000 to 1,000,000 specified in Landoll) to increase the viscosity
and reduce the mobility of the water flooding composition, while
utilizing a modest degree of association derived from the
hydrophobic modifier to provide the beneficial effects of the
presence of the hydrophobic modifier without unduly compromising
the injectability of the water flooding composition.
[0053] As a result of the above, in some embodiments, the invention
relates to a method of secondary hydrocarbon recovery of a type
which comprises passing a water flooding composition through a
subterranean formation containing a hydrocarbon deposit, in which
the method is characterized by the water flooding composition being
comprised of water and a thickening polymer, the thickening polymer
having a concentration of between about 0.01 percent and about 1
percent by weight of the water flooding composition, the thickening
polymer comprising: [0054] (a) a hydroxyethyl cellulose backbone
polymer having a molecular weight of between about 1,000,000 and
about 2,000,000; and [0055] (b) a hydrophobic modifier in a
substitution level in the thickening polymer of between about 0.1
percent and about 2 percent by weight of the thickening polymer,
wherein the hydrophobic modifier is comprised of an alkyl
hydrocarbon based material containing between about 10 and about 24
unsubstituted carbon atoms per group; wherein the water flooding
composition is formulated to have a viscosity of between 2 mPas and
100 mPas and to be injectable into the subterranean formation.
[0056] As a result of the above, in some embodiments, the invention
relates to a method of preparing a water flooding composition for
use in a method of secondary hydrocarbon recovery of a type which
comprises passing the water flooding composition through a
subterranean formation containing a hydrocarbon deposit, the method
comprising: [0057] (a) selecting a hydroxyethyl cellulose backbone
polymer having a molecular weight of between 1,000,000 and
2,000,000; [0058] (b) selecting a hydrophobic modifier comprised of
an alkyl hydrocarbon based material containing between 10 and 24
unsubstituted carbon atoms per group; [0059] (c) providing a
thickening polymer comprising the hydroxyethyl cellulose backbone
polymer and the hydrophobic modifier in a substitution level in the
thickening polymer of between 0.1 percent and 2 percent by weight
of the thickening polymer; and [0060] (d) combining the thickening
polymer with water to provide the water flooding composition,
wherein the thickening polymer has a concentration of between 0.1
percent and 1 percent by weight of the water flooding composition;
wherein the water flooding composition has a viscosity of between 2
mPas and 100 mPas and is injectable into the subterranean
formation.
[0061] In some embodiments, the molecular weight of the
hydroxyethyl cellulose backbone polymer may be about 1,300,000.
[0062] In some embodiments, the concentration of the thickening
polymer in the water flooding composition may be between about 0.05
percent and 0.25 percent by weight of the water flooding
composition. In some embodiments, the concentration of the
thickening polymer in the water flooding composition may be between
about 0.05 percent and about 0.2 percent by weight. In some
embodiments, the concentration of the thickening polymer in the
water flooding composition may be about 0.2 percent.
[0063] In some embodiments, the alkyl hydrocarbon based material of
the hydrophobic modifier may contain between about 12 and about 18
unsubstituted carbon atoms per group. In some embodiments, the
alkyl hydrocarbon based material of the hydrophobic modifier may be
comprised of a plurality of materials. In some embodiments, the
alkyl hydrocarbon based material of the hydrophobic modifier may be
comprised of dodecyl tetradecyl glycidyl ether.
[0064] As used herein, the substitution level of the hydrophobic
modifier in the thickening polymer may be calculated by acetylating
hydroxyl groups in the thickening polymer with acetic anhydride,
analyzing the reaction products using proton nuclear magnetic
resonance (proton NMR or H NMR) techniques, and integrating the
acetyl CH.sub.3 and hydrophobic modifier CH.sub.2 peaks from the
NMR spectra. The ratio of these two peaks indicates the level of
substitution of the hydrophobic modifier in the thickening polymer.
Higher molecular weight thickening polymers may be partially
hydrolyzed by sonication prior to acetylation in order to reduce
their molecular weights and their ultimate viscosity in deuterated
chloroform (CDCl.sub.3) for the NMR analysis.
[0065] In some embodiments, the substitution level of the
hydrophobic modifier in the thickening polymer may be between about
0.1 percent and about 1.5 percent by weight of the thickening
polymer. In some embodiments, the substitution level of the
hydrophobic modifier in the thickening polymer may be between about
0.4 percent and about 1.2 percent by weight of the thickening
polymer. In some embodiments, the substitution level of the
hydrophobic modifier in the thickening polymer may be between about
0.7 percent and about 1.2 percent by weight of the thickening
polymer.
[0066] In some embodiments, the water of the water flooding
composition may be comprised of a brine solution. In some
embodiments, the brine solution may be comprised of sodium
chloride. In some particular embodiments, the concentration of the
brine solution may be about 1% by weight of the brine solution.
[0067] In a particular embodiment, the molecular weight of the
hydroxyethyl cellulose backbone polymer may be about 1,3000,000,
the alkyl hydrocarbon based material of the hydrophobic modifier
may be comprised of dodecyl tetradecyl glycidyl ether, the
substitution level of the hydrophobic modifier may be between about
0.7 percent and about 1 percent by weight of the thickening
polymer, and the concentration of the thickening polymer in the
water flooding composition may be about 0.2 percent by weight of
the water flooding composition. In the particular embodiment, the
water of the water flooding composition may be comprised of a brine
solution. In the particular embodiment, the brine solution may be
comprised of 1% sodium chloride by weight of the brine
solution.
BRIEF DESCRIPTION OF DRAWINGS
[0068] Embodiments of the invention will now be described with
reference to the accompanying drawings, in which:
[0069] FIG. 1 is a table summarizing the compositions and
properties of various thickening polymers and water flooding
compositions.
[0070] FIG. 2 is a table summarizing filtration test results for
the water flooding compositions in FIG. 1, for filtration through
both a Whatman #1 filter and a sandpack.
[0071] FIG. 3 is a table summarizing the properties of sandpack
cores which were used to conduct coreflood tests for selected water
flooding compositions from FIG. 1.
[0072] FIG. 4 is a table summarizing the properties of the oil
which was used to perform coreflood tests for selected water
flooding compositions from FIG. 1.
[0073] FIG. 5 is a table summarizing results of coreflood tests
conducted using selected water flooding compositions from FIG.
1.
[0074] FIG. 6 is a schematic drawing of the apparatus used to
conduct the sandpack filtration tests which are summarized in FIG.
2.
[0075] FIG. 7 is a schematic drawing of the apparatus used to
conduct the coreflood tests which are summarized in FIG. 5.
[0076] FIG. 8 is a graph depicting data obtained from coreflood
tests comparing injection pressure in kPa as a function of
throughput in pore volumes (PV) for the HPAM and HMHEC 1206 water
flooding compositions from FIG. 1.
[0077] FIG. 9 is a graph depicting data obtained from coreflood
tests comparing injection pressure in kPa as a function of
throughput in pore volumes (PV) for the HPAM and HMHEC 0603 water
flooding compositions from FIG. 1.
[0078] FIG. 10 is a graph depicting data obtained from coreflood
tests comparing oil recovery as a percentage of original oil in
place (OOIP) as a function of throughput in pore volumes (PV) for
the HPAM, HMHEC 1206 and HMHEC 0603 water flooding compositions
from FIG. 1.
[0079] FIG. 11 is a graph depicting data obtained from sandpack
filtration tests comparing effective viscosity in the sandpack in
mPas as a function of linear velocity in feet per day for selected
water flooding compositions from FIG. 1, in which the aqueous
component of the water flooding compositions is comprised of 1%
NaCl.
[0080] FIG. 12 is a graph depicting data obtained from sandpack
filtration tests comparing effective viscosity in the sandpack in
mPas as a function of linear velocity in feet per day for selected
water flooding compositions from FIG. 1, in which the aqueous
component of the water flooding compositions is comprised of either
1% NaCl or hard brine.
DETAILED DESCRIPTION
[0081] The present invention is directed at a method of secondary
hydrocarbon recovery of a type which comprises passing a water
flooding composition through a subterranean formation containing a
hydrocarbon deposit. One purpose of passing the water flooding
composition through the subterranean formation is to displace the
hydrocarbon deposit toward one or more production wellbores which
are in fluid communication with the subterranean formation.
[0082] As a result, the method typically involves injecting the
water flooding composition into one or more injection wellbores
which are in fluid communication with the subterranean formation
and which are separated from the production wellbores so that the
water flooding composition can displace the hydrocarbon deposit
toward the production wellbores as it passes through the
subterranean formation.
[0083] The method may further comprise additional steps or
procedures which are performed before and/or after the water
flooding composition is passed through the subterranean
formation.
[0084] The invention is particularly directed at formulations for
the water flooding composition which result in the water flooding
composition having a viscosity and/or mobility which is compatible
with the viscosity and/or mobility of the hydrocarbon deposit which
is intended to be produced from the subterranean formation, and
which result in the water flooding composition being injectable
into the subterranean formation.
[0085] The water flooding compositions of the invention are
comprised of water and a thickening polymer. The thickening polymer
is comprised of a hydroxyethyl cellulose backbone polymer and a
hydrophobic modifier. The hydrophobic modifier is comprised of an
alkyl hydrocarbon based material. The water flooding compositions
of the invention may be further comprised of other materials and/or
substances.
[0086] The formulations for water flooding compositions of the
invention are based upon a number of considerations.
[0087] First, the formulations for water flooding compositions of
the invention are based upon a consideration of the hydrocarbon
deposit which is intended to be produced from the subterranean
formation and upon the mobility of a water flooding composition
which must be achieved in order for the mobility of the water
flooding composition to be compatible with the mobility of the
hydrocarbon deposit.
[0088] Generally, the ratio of the mobility of the water flooding
composition to the mobility of the hydrocarbon deposit is
preferably no greater than about 100:1, more preferably no greater
than about 50:1, more preferably no greater than about 10:1, or
even more preferably no greater than about 2:1.
[0089] For many typical hydrocarbon deposits comprising oil, the
viscosity of the water flooding composition is preferably between
about 2 mPas and about 100 mPas, more preferably between about 5
mPas and about 50 mPas, or even more preferably between about 5
mPas and about 40 mPas.
[0090] Second, the formulations for water flooding compositions of
the invention are based upon a consideration of the properties of
the subterranean formation and upon ensuring that a water flooding
composition will be injectable into the subterranean formation.
[0091] Generally, a water flooding composition may be considered to
be injectable if it can pass through the subterranean formation
without causing significant plugging of the subterranean
formation.
[0092] A water flooding composition may be assessed for
injectability either during performance of the water flooding
method or by testing the water flooding composition before it is
used in the performance of the water flooding method. In either
case, indicia of injectability or lack of injectability may relate
to changes in the composition or properties of the water flooding
composition and/or the subterranean formation as the water flooding
composition is passed therethrough.
[0093] One method for testing a water flooding composition before
it is used in the performance of the water flooding method
comprises passing the water flooding composition through a
permeable test medium.
[0094] One suitable permeable test medium is a sandpack having an
upstream end and a downstream end. One suitable test method is a
sandpack filtration technique. A sandpack used for the sandpack
filtration technique preferably has an initial permeability of less
than about 10 darcies so that it is reasonably representative of a
subterranean formation. In one test configuration, a sandpack has
had an initial permeability of about 3 darcies. In one test
configuration, a sandpack has had a length from the upstream end to
the downstream end of about ten centimeters.
[0095] The procedure for testing a water flooding composition in a
sandpack comprises passing the water flooding composition through
the sandpack under constant or varying conditions of pressure
and/or flowrate.
[0096] The water flooding composition will exhibit an initial
concentration of the thickening polymer at the upstream end of the
sandpack and will exhibit a final concentration of the thickening
polymer at the downstream end of the sandpack. If the final
concentration of the thickening polymer is less than the initial
concentration of the thickening polymer, retention of the
thickening polymer in the sandpack, potential plugging of the
sandpack, and a lack of injectability of the water flooding
composition may be indicated.
[0097] Generally, in order for a water flooding composition to be
considered injectable in the sandpack test, the final concentration
of the thickening polymer in the water flooding composition should
be greater than ninety percent of the initial concentration of the
thickening polymer in the water flooding composition.
[0098] The water flooding composition will exhibit an initial
viscosity at the upstream end of the sandpack and will exhibit a
final viscosity at the downstream end of the sandpack. If the final
viscosity is less than the initial viscosity, retention of the
thickening polymer in the sandpack, potential plugging of the
sandpack, and a lack of injectability of the water flooding
composition may be indicated.
[0099] Generally, in order for a water flooding composition to be
considered injectable in the sandpack test, the final viscosity of
the water flooding composition should be greater than ninety
percent of the initial viscosity of the water flooding
composition.
[0100] Third, the formulations for water flooding compositions of
the invention are based upon a consideration of the effects of the
following variables upon the viscosity/mobility and the
injectability of a water flooding composition: [0101] 1. the
molecular weight of the hydroxyethyl cellulose backbone polymer;
[0102] 2. the composition of the hydrophobic modifier; [0103] 3.
the substitution level of the hydrophobic modifier in the
thickening polymer; and [0104] 4. the concentration of the
thickening polymer in the water flooding composition.
[0105] Fourth, the formulations for water flooding compositions of
the invention are based upon a consideration of the salt and/or
brine conditions which the water flooding compositions may be
exposed to, resulting either from the water from which the water
flooding compositions are prepared or from the environment to which
the water flooding compositions may be exposed.
[0106] The thickening polymers of the invention may be described
generally as cellulosic associating polymers. The formulations for
water flooding compositions according to the invention are based
upon a consideration of theories relating to the mechanisms of
action upon which the viscosity/mobility and injectability of a
water flooding composition may be dependent.
[0107] In particular these properties of water flooding
compositions are believed to be dependent upon "entanglement" as a
first mechanism of action and "association" as a second mechanism
of action.
[0108] Entanglement is believed to be attributable primarily to the
molecular weight of the hydroxyethyl cellulose backbone polymer and
appears to affect only the viscosity/mobility of a water flooding
composition. The degree of entanglement increases as the molecular
weight of the hydroxyethyl cellulose backbone polymer increases,
thereby resulting in an increase in the viscosity and a decrease in
the mobility of a water flooding composition.
[0109] Association is believed to be attributable to the presence
and hydrophobicity of the hydrophobic modifier and appears to
affect both the viscosity/mobility of a water flooding composition
and the injectability of a water flooding composition. The degree
of association increases as the number of unsubstituted carbon
atoms provided by the hydrophobic modifier increases. The number of
unsubstituted carbon atoms provided by the hydrophobic modifier may
be increased by increasing the "size" of the hydrophobic modifier,
by increasing the substitution level of the hydrophobic modifier in
the thickening polymer, and/or by increasing the concentration of
the thickening polymer in the water flooding composition.
[0110] The goal in formulating the water flooding compositions of
the invention is to increase the viscosity and thus reduce the
mobility of the water flooding composition so that the
viscosity/mobility is compatible with the hydrocarbon deposit,
while simultaneously maintaining an acceptable injectability of the
water flooding composition in the subterranean formation.
[0111] As noted above, an increase in viscosity/reduction in
mobility of a water flooding composition can be achieved by
increasing entanglement of the thickening polymer and/or by
increasing the degree of association of the water flooding
composition. However, increasing viscosity/reducing mobility of the
water flooding composition by increasing the degree of association
of the water flooding composition will simultaneously result in a
decrease in the injectability of the water flooding composition.
Increasing the viscosity/reducing mobility of the water flooding
composition by increasing the entanglement of the thickening
polymer appears to have no significant effect upon the
injectability of the water flooding composition.
[0112] As a result, a target viscosity/mobility of a water flooding
composition can be achieved by a combination of the effects of
entanglement and association. As the degree of entanglement
increases, the degree of association may decrease in order to
achieve the target viscosity/mobility. Conversely, as the degree of
entanglement decreases, the degree of association must increase in
order to achieve the target viscosity/mobility.
[0113] However, each particular hydrophobic modifier will exhibit a
maximum degree of association, above which the water flooding
composition will not be injectable. More particularly, for any
particular hydrophobic modifier, increasing the substitution level
of the hydrophobic modifier in the thickening polymer and/or
increasing the concentration of the thickening polymer in the water
flooding composition beyond an association limit will result in the
water flooding composition not being injectable.
[0114] As a result, the association limit of each particular
hydrophobic modifier will determine the minimum amount of
entanglement (i.e., the minimum molecular weight of the
hydroxyethyl cellulose backbone polymer) which is required for
achieving the target viscosity/mobility for the water flooding
composition while simultaneously maintaining the injectability of
the water flooding composition.
[0115] Fifth, the formulations for water flooding compositions of
the invention are based upon considerations of cost and
availability for different hydroxyethyl cellulose backbone polymer
candidates and different hydrophobic modifier candidates.
[0116] Other or additional considerations may apply in particular
circumstances involving the practice of the invention.
[0117] Having regard to the considerations outlined above, it has
been determined that the range of molecular weights for
hydroxyethyl cellulose backbone polymers which are suitable for use
in the invention is between about 1,000,000 and about
2,000,000.
[0118] If the molecular weight of the hydroxyethyl cellulose
backbone polymer is less than about 1,000,000, the degree of
association for the hydrophobic modifier which is required to
achieve a viscosity/mobility which is compatible with the
hydrocarbon deposit may result in a water flooding composition
which is not injectable.
[0119] As the molecular weight of the hydroxyethyl cellulose
backbone polymer increases from 1,000,000 and approaches 2,000,000,
the backbone polymer may become more difficult to obtain and the
cost of the backbone polymer may become prohibitive. As a result,
the practical upper limit of the molecular weight of the
hydroxyethyl cellulose backbone polymer may be less than 2,000,000.
In some embodiments, depending upon availability and cost, the
preferred upper limit of the molecular weight of the hydroxyethyl
cellulose backbone polymer may be about 1,500,000.
[0120] The following general guidelines have therefore been
established for the formulation of water flooding compositions
which may have a viscosity/mobility which is compatible with a
hydrocarbon deposit and which may be injectable into a subterranean
formation: [0121] (a) the hydroxyethyl cellulose backbone polymer
has a molecular weight of between about 1,000,000 and about
2,000,000; [0122] (b) the hydrophobic modifier is comprised of an
alkyl hydrocarbon based material containing between about 10 and
about 24 unsubstituted carbon atoms per group, or more preferably
between about 12 and about 18 unsubstituted carbon atoms per group;
[0123] (c) the substitution level of the hydrophobic modifier in
the thickening polymer is between about 0.1 percent and about 2
percent by weight of the thickening polymer, or preferably between
about 0.1 percent and about 1.5 percent by weight of the thickening
polymer, or even more preferably between about 0.4 percent and
about 1.2 percent by weight of the thickening polymer, or even more
preferably between about 0.7 percent and about 1.2 percent by
weight of the thickening polymer; and [0124] (d) the concentration
of the thickening polymer in the water flooding composition is
between about 0.01 percent and about 1 percent by weight of the
water flooding composition, or more preferably between about 0.05
percent and about 0.25 percent by weight of the water flooding
composition.
[0125] The water flooding compositions are preferably formulated
within the ranges set out above to achieve a target viscosity of
between about 2 mPas and about 100 mPas, more preferably between
about 5 mPas and about 50 mPas, or even more preferably between
about 5 mPas and about 40 mPas and/or to achieve a ratio of the
mobility of the water flooding compositions to the mobility of the
hydrocarbon deposit of no greater than about 100:1, more preferably
no greater than about 50:1, more preferably no greater than about
10:1, or even more preferably no greater than about 2:1.
[0126] The water flooding compositions are formulated within the
ranges set out above to achieve injectable water flooding
compositions, as assessed during performance of the water flooding
method or by testing the water flooding compositions before they
are used in the water flooding method.
[0127] In many applications of the invention, achieving
injectability of the water flooding compositions may follow from
formulating the water flooding compositions in accordance with the
above ranges and target viscosities. In some applications of the
invention, achieving injectability of the water flooding
compositions may require some modification of the formulations of
the water flooding compositions within the above ranges and target
viscosities.
[0128] The thickening polymers of the invention may be prepared by
using any suitable method, including the specific methods described
in U.S. Pat. No. 4,228,277 (Landoll), in U.S. Pat. No. 4,529,523,
and other methods known in the art.
[0129] The water flooding compositions of the invention may be
prepared by mixing the thickening polymer with water and with any
other suitable materials and/or substances. The water may be
present in relatively pure form, in brine form, as hard brine,
and/or may contain other substances and/or impurities.
Example 1
Preparation of Thickening Polymers (HMHEC) from Hydroxyethyl
Cellulose (HEC)
[0130] A 500 mL round bottom flask was charged with 10 grams of
hydroxyethyl cellulose (HEC) having a molecular weight of
1,300,000, followed by 1.25 grams of dodecyl tetradecyl glycidyl
ether and 87.5 grams of isopropanol. The flask was then purged with
nitrogen gas.
[0131] The flask was fitted with a mechanical stirrer, and 87.5
grams of 1 percent sodium hydroxide (NaOH), pre purged with
nitrogen gas was added to the flask while stirring the flask.
[0132] The resulting viscous slurry was purged briefly with
nitrogen gas and then stirred for five hours at 60 degrees Celsius.
After five hours, 2 grams of acetic acid and 100 milliliters of
acetone were added to the flask.
[0133] After 10-15 minutes, the contents of the flask was
transferred to a one liter beaker and about 400 milliliters of
acetone was added for precipitation with stirring.
[0134] The resulting material was centrifuged and washed twice with
100 milliliter acetone washings. After air drying, 180 milliliters
of water was added with stirring, yielding a gel. An additional 40
milliliters of water was added and mixed with a spatula immediately
prior to transfer of the material to a dialysis tube. The removal
of the sodium acetate salt was confirmed using Fourier transform
infrared spectroscopy (FTIR).
[0135] The material was then freeze-dried and ground to yield 9
grams of a thickening polymer, consisting of hydrophobically
modified hydroxyethyl cellulose (HMHEC) as a fluffy white powder,
which thickening polymer was designated as HMHEC 0603.
[0136] A similar synthesis process was used to prepare other HMHEC
thickening polymers from HEC having molecular weights of 720,000 or
1,000,000, also using dodecyl tetradecyl glycidyl ether as the
hydrophobic modifier. These other HMHEC thickening polymers were
designated as indicated in FIG. 1.
Example 2
Preparation of Water Flooding Compositions
[0137] A number of different water flooding compositions were
prepared using the HMHEC thickening polymers of Example 1. An
additional water flooding composition, designated as HPAM, was
prepared using Flopaam.TM. 3630 as the thickening polymer.
Flopaam.TM. 3630 is a polyacrylamide polymer produced by SNF Group
of Andrezieux, France, which is commonly used as a thickening
polymer in secondary hydrocarbon recovery.
[0138] The water flooding compositions were prepared from the
thickening polymers by mixing the thickening polymers with water.
The water was provided as either relatively pure water, as a 1
percent brine (NaCl) solution, or as a hard brine (NaCl) solution
containing total dissolved solids of 8.5 percent and a hardness of
0.38 percent.
[0139] The compositions and properties of the HMHEC and HPAM water
flooding compositions are summarized in FIG. 1.
[0140] In FIG. 1, it is noted that two different values for
viscosity in 1% NaCl are provided for the water flooding
compositions containing HMHEC 1206 and HMHEC 0603. The first (and
lower) values for viscosity were obtained from the sandpack
filtration tests. The second (and higher) values for viscosity were
obtained from the coreflood tests. Although the reason for these
discrepancies in the data is not known, it is possible that the
HMHEC 1206 and HMHEC 0603 water flooding compositions which were
used in the sandpack filtration tests may actually have contained a
lower concentration of the thickening polymers than the water
flooding compositions which were used in the coreflood tests.
Example 3
Water Flooding Compositions--Filtration Tests
[0141] The water flooding compositions of Example 2 and FIG. 1 were
filtered using one or both of two filtering techniques, both of
which involved passing the water flooding compositions through a
permeable test medium.
[0142] The first filtering technique comprised filtering the water
flooding compositions through two Whatman #1 (11 .mu.m) filters. A
net pressure drop of 100 kPa using compressed air was placed across
the filters in order to provide a pressure gradient.
[0143] The viscosities of the water flooding compositions were
measured before and after the filtration to obtain an initial
viscosity value and a final viscosity value. A reduction in the
viscosity of the water flooding composition indicated that all of
the thickening polymer did not pass through the filters. It is
noted that a similar measurement could have been made of the
concentration of the thickening polymer in the water flooding
compositions to obtain an initial concentration value and a final
concentration value.
[0144] The filterability of the water flooding compositions was
also evaluated by the filter ratio, which compares the rate of
filtration over different time intervals:
Filter Ratio = Time to Filter 300 grams - Time to Filter 200 grams
Time to Filter 200 grams - Time to Filter 100 grams
##EQU00001##
[0145] A filter ratio greater than 1 indicated that the
permeability of the filter was decreasing over time, suggesting
that all of the thickening polymer did not pass through the filter
and thus plugged the filter.
[0146] The second filtering technique comprised filtering the water
flooding compositions through a compact sandpack filtration test
core having a permeability of less than about 10 darcies and a
length from an upstream end to a downstream end of about 10
centimeters.
[0147] A schematic drawing of the apparatus which was used to
conduct the sandpack filtration tests is provided in FIG. 6.
[0148] Referring to FIG. 6, the filtration test apparatus (20)
comprises a filtration test core (22). The filtration test core
(22) has an upstream end (24) and a downstream end (26). The
upstream end (24) of the filtration test core (22) is in fluid
communication with an injection fluid vessel (28). A compressed air
source (30) is in fluid communication with the injection fluid
vessel (28). The compressed air source (30) provides a means for
pressurizing fluid which is contained within the injection fluid
vessel (28).
[0149] The downstream end (26) of the filtration test core (22) is
in fluid communication with an effluent collection vessel (32). The
weight of the effluent collection vessel (32) is measured with a
balance scale (34) in order to determine the weight of effluent
fluid which exits the downstream end (26) of the filtration test
core (22). Data from the balance scale (34) is transferred to a
computer (36) for recordation and analysis.
[0150] In the second filtering technique, the propagation of the
water flooding compositions through the filtration test core (22)
was measured under a series of net pressure drops from 3.5 kPa to
100 kPa. The weight of the effluent water flooding composition
exiting the downstream end (26) of the filtration test core (22)
was measured by the balance scale (34) and recorded by the computer
(36) as a function of time.
[0151] The water flooding compositions were sampled at the upstream
end (24) of the filtration test core (22) and evaluated with a
rheometer in order to obtain initial viscosity values for the water
flooding compositions. The water flooding compositions were sampled
at the downstream end (26) of the filtration test core (22) and
evaluated with a rheometer in order to obtain final viscosity
values for the water flooding compositions.
[0152] As with the first filtering technique, a reduction in the
viscosity of the water flooding composition indicated that all of
the thickening polymer did not pass through the filtration test
core (22). As with the first filtering technique, a similar
measurement could have been made of the concentrations of the
thickening polymer in the water flooding compositions to obtain an
initial concentration value and a final concentration value.
[0153] Results of the filtration tests for both filtering
techniques are provided in FIG. 2.
Example 4
Water Flooding Compositions--Coreflood Tests
[0154] Coreflood tests of a selected number of the water flooding
compositions were conducted to study the incremental oil recovery
resulting from the use of the water flooding compositions over the
oil recovery obtained from an initial water flood procedure. In
general, the coreflood tests were performed by conducting a brine
water flood first to obtain a meaningful water flood recovery
value, conducting a water flood using one of the water flood
compositions, and then conducting a second brine water flood as a
chaser flood. The aqueous medium for each of the water flooding
compositions was 1% NaCl brine.
[0155] A schematic drawing of the apparatus which was used to
conduct the coreflood tests is provided in FIG. 7.
[0156] Referring to FIG. 7, the coreflood test apparatus (50)
comprises a sandpack coreflood test core (52). The coreflood test
core (52) has an upstream end (54) and a downstream end (56). The
upstream end (54) of the coreflood test core (52) is in fluid
communication with a pump (58) which is connected with a source of
brine (60) and a source of water flooding composition (62).
[0157] The downstream end (56) of the coreflood test core (52) is
in fluid communication with a backpressure regulator (64). The
backpressure regulator (64) has a liquid outlet (66).
[0158] An upstream pressure transducer (72) is connected with the
upstream end (54) of the coreflood test core (52). A midstream
pressure transducer (74) is connected with the midpoint of the
length of the coreflood test core (52).
[0159] The properties of the coreflood test cores (52) for a number
of tests are set out in FIG. 3. For the coreflood tests, the length
of the coreflood test cores (52) was about 30 centimeters.
[0160] In conducting the coreflood tests, the coreflood test core
(52) was first saturated with a 1% brine solution to obtain its
brine permeability.
[0161] Oil was then injected into the coreflood test core (52) to
displace mobile water until a constant pressure drop across the
coreflood test core (52) was obtained and water production stopped.
Properties of the oil are set out in FIG. 4.
[0162] The oil permeability of the coreflood test core (52) was
then measured. The coreflood tests were carried out under net
overburden pressure of 7000 kPa at a constant core temperature of
20 degrees Celsius.
[0163] The initial brine water flood was conducted by injecting a
1% brine (NaCl) solution into the upstream end (54) of the
coreflood test core (52) at a constant flow rate of 3.6 ml/hr. This
flow rate equates to a linear velocity of 0.6 feet per day, which
is believed to be representative of the flow rates which may be
expected in typical reservoirs far removed from a wellbore.
Effluent samples were collected at the downstream end (56) of the
coreflood test core (52) in a series of pre-weighed tubes at a time
interval of 100 minutes. Pressure drops across the coreflood test
core (52) generated by the injected brine solution were
continuously monitored by the upstream pressure transducer (72) and
the midstream pressure transducer (74). The initial brine water
flood was continued until about 1 pore volume (PV) had been
injected into the coreflood test core (52).
[0164] A water flood composition was then injected continuously
into the upstream end (54) of the coreflood test core (52) until at
least 2 pore volumes (PV) of the water flood composition had been
injected into the coreflood test core (52).
[0165] Finally, a second brine water flood was injected into the
upstream end (54) of the coreflood test core (52) as a chaser until
about 1 pore volume (PV) had been injected into the coreflood test
core (52).
[0166] The results of the coreflood tests are summarized in FIG.
5.
Analysis of Filtration Test Results and Coreflood Test Results
[0167] Referring to FIG. 1, it is observed that the viscosity of
the HPAM (polyacrylamide) water flooding composition was very
significantly higher when the water flooding composition was
prepared using water as the aqueous medium than when 1% brine
(NaCl) or hard brine was used as the aqueous medium. In contrast,
the viscosity of the HMHEC water flooding compositions was
generally higher when the water flooding compositions were prepared
using 1% brine (NaCl) or hard brine as the aqueous medium than when
water was used as the aqueous medium. This phenomenon suggests that
HMHEC water flooding compositions may exhibit superior durability
for use in secondary oil recovery in brine environments than
polyacrylamide water flooding compositions.
[0168] Also referring to FIG. 1, it is observed that HMHEC water
flooding compositions prepared using a relatively high molecular
weight HEC backbone polymer (i.e., 1,300,000) tend to exhibit
relatively high viscosity at relatively lower hydrophobe
substitution levels than do HMHEC water flooding compositions which
are prepared using a relatively low molecular weight HEC backbone
polymer (i.e., 720,000). This phenomenon demonstrates that the use
of relatively higher molecular weight HEC backbone polymers can be
effective to achieve suitably high viscosities at relatively lower
levels of substitution (and thus lower degrees of association).
[0169] Also referring to FIG. 1, it is observed that qualitatively,
the best overall results with respect to injectability and oil
recovery were achieved using either the HPAM water flooding
composition or the HMHEC 0603 water flooding composition,
suggesting that relatively higher molecular weight HEC backbone
polymers with a modest level of hydrophobe substitution can be used
to overcome injectability problems which may result from the use of
relatively lower molecular weight HEC backbone polymers with a
higher level of hydrophobe substitution.
[0170] Referring to FIG. 2, it is observed in the sandpack
filtration tests that the HMHEC 0603 water flooding compositions
exhibited a very stable and consistent viscosity pre-injection and
following injection of two pore volumes, indicating that HMHEC 0603
water flooding compositions can be considered to satisfy the
requirement of injectability.
[0171] Referring to FIG. 5, it is observed in the coreflood tests
that the HMHEC 0603 water flooding composition exhibited the
highest oil recovery (slightly higher than the HPAM water flooding
composition) while the HMHEC 1206 water flooding composition
exhibited a much lower oil recovery. Furthermore, both the HPAM
water flooding composition and the HMHEC 0603 maintained a stable
and consistent viscosity pre-injection and post-injection, while
the HMHEC 1206 water flooding composition exhibited a dramatic
decrease in viscosity from pre-injection to post-injection. This
phenomenon suggests that an HMHEC water flooding composition
containing a relatively high molecular weight backbone polymer,
such as HMHEC 0603 can provide secondary oil recovery results which
are comparable to a polyacrylamide (HPAM) water flooding
composition.
[0172] Referring to FIG. 8, it is observed that a water flooding
composition containing a relatively low molecular weight backbone
polymer, such as HMHEC 1206 may exhibit a continuous increase in
required injection pressure during a water flooding procedure,
while a polyacrylamide (HPAM) water flooding composition may
exhibit a relatively stable and consistent required injection
pressure during a water flooding procedure.
[0173] Referring to FIG. 9, it is observed that a water flooding
composition containing a relatively high molecular weight backbone
polymer, such as HMHEC 0603 may exhibit a required injection
pressure during a water flooding procedure which is comparable to
that exhibited by a polyacrylamide (HPAM) water flooding
composition.
[0174] Referring to FIG. 10, it is observed that a water flooding
composition containing a relatively high molecular weight backbone
polymer, such as HMHEC 0603 may exhibit an oil recovery during a
water flooding procedure which is comparable to that exhibited by a
polyacrylamide (HPAM) water flooding composition, while a water
flooding composition containing a relatively low molecular weight
backbone polymer, such as HMHEC 1206 may exhibit a significantly
lower oil recovery during a water flooding procedure.
[0175] Referring to FIG. 11, it is observed that for water flooding
compositions in which the aqueous medium was comprised of 1% NaCl,
a polyacrylamide (HPAM) water flooding composition exhibited
increased effective viscosity in the sandpack filtration tests as
the flow rate increased. An explanation for this result is that the
transportation of polymer solutions in porous media is affected by
both shear and elongational viscosities. In the case of the HPAM
water flooding composition, its elongational viscosity increased
greatly at high flow rates, leading to higher effective
viscosities. Referring also to FIG. 10, it is observed that for
water flooding compositions in which the aqueous medium was
comprised of 1% NaCl, HMHEC water flooding compositions tended to
exhibit a relatively stable and consistent effective viscosity in
the sandpack filtration tests within the range of flow rates that
was studied.
[0176] Referring to FIG. 12, it is observed that water flooding
compositions containing a moderately high to high molecular weight
backbone HEC polymer (HMHEC 0318 and HMHEC 0603) wherein the
aqueous medium was comprised of a hard brine solution exhibited
higher effective viscosities in the sandpack filtration tests at
relatively low concentrations of the thickening polymer (i.e., less
than 2000 ppm) than did water flooding compositions comprising
HMHEC 0318 or HMHEC 0603 at relatively higher concentrations of the
thickening polymer (i.e., 2000 ppm) wherein the aqueous medium was
comprised of 1% NaCl.
[0177] In summary, an HMHEC water flooding composition containing a
relatively high molecular weight backbone polymer (i.e., at least
about 1,000,000) and a moderate level of substitution of the
hydrophobic modifier may be capable of providing performance in
water flooding applications which is comparable to the performance
of an HPAM (polyacrylamide) water flooding composition with respect
to injectability and oil recovery, and which may be superior to the
performance of an HPAM (polyacrylamide) water flooding composition
with respect to durability in the presence of a brine
environment.
[0178] In this document, the word "comprising" is used in its
non-limiting sense to mean that items following the word are
included, but items not specifically mentioned are not excluded. A
reference to an element by the indefinite article "a" does not
exclude the possibility that more than one of the elements is
present, unless the context clearly requires that there be one and
only one of the elements.
* * * * *