Note: Descriptions are shown in the official language in which they were submitted.
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1 FIELD OF THE INVENTION
2 The present invention relates to a foam for use in a
3 subterranean oil-bearing formation. The foam functions to
4 control and reduce the mobility of a gaseous displacement fluid
injected into the formation. The foam is generated using a
6 combination of surfactants.
7 BACKGROUND OF THE INVENTION
8 In the recovery of oil from a subterranean oil-bearing
9 formation only a limited amount of the oil in place is
recoverable by use of primary and secondary recovery processes.
11 Hence, several tertiary or enhanced oil recovery processes have
12 been developed. Such processes include thermal processes,
13 exemplary of which are steam flooding and in-situ combustion,
14 chemical flooding techniques and gaseous displacement fluid
recovery methods. The gases utilized include steam, carbon
16 dioxide, nitrogen or hydrocarbons. The present invention has to
17 do with improving gaseous displacement fluid recovery methods.
18 There are problems associated with the use of gaseous
19 displacement fluid recovery methods. First, fingering of the gas
phase into the oil, with attendant degradation of the uniform
21 displacement front, may take place. This is because of the
22 adverse mobility ratio between the displacing gas and the oil.
23 The second problem is gravity override which is promoted by the
24 density difference between the gas and oil phases. Thus because
the sweep efficiency, or contact between the injected fluid and
26 the oil in the reservoir, is reduced because of these problems,
27 the incremental recovery will as a result also be reduced.
28 Reservoir heterogeneity will further compound these problems by
20~7517
1 promoting channelling, thereby further reducing the sweep
2 efficiency.
3 Foams have been emplaced in a reservolr as a means for
4 combatting fingering or gravlty override by the gaseous
dis~lacement fluid. Such foams are normally formed using a gas,
6 a surfactant and a liquid. The foam ls either generated in-situ
7 by injecting the ingredients into the formation or is formed at
8 surface and injected as a foam per se. The best process involves
9 injecting the surfactant solution and, once it is in position
within the reservoir, then injecting the gas to form the foam.
11 The use of foams for mobility control has been well
12 documented and described in the patent literature. For example,
13 such a process is described by Worton et. al. in U.S. Patent No.
14 2,623,596, utilizing carbon dioxide as a miscible solvent gas.
U.S. Patent 3,342,256 by Bernard et. al., describes a process for
16 improving sweep efficiency when injecting water and gas into a
17 reservoir wherein a variety of surfactants have been added to the
18 water. Successful field applications using foams have been
19 reported. Castanier reported the results of 16 field tests of
surfactants used in conjunction with steam, both with and without
21 inert gases. (Proc. 4th European Symposium on EOR, Oct. 27 - 30,
22 Hamburg, West Germany, 1987). Hirasaki reported the results of
23 10 field tests using steam foams, all of which were successful
24 (Journal of Petroleum Technology, May, 1989, p. 449-456). Smith
disclosed the results of 4 successful non-thermal foam floods
26 (ACS Symposium Series 373, Chapter 22, 1987).
27 The foam exhibits a viscosity which is greater than
28 either the gas or liquid phases of which it is composed. The
29 foam functions by reducing the mobility of the subsequently
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1 injected gas in the portions of the reservoir where it is found.
2 The foam accumulates preferentially in the well-swept and/or
3 higher permeability zones of the formation that would otherwise
4 expend a large quantity of the injected gas. Thus, the use of
foams will cause the injected gas to be directed to other parts
6 of the formation which had been either unswept or underswept
7 previously.
8 Recent studies have indicated that the oil phase will
9 influence the stability and performance of foams. It is accepted
that crude oils will generally act as a defoaming agent.
11 However, not every foam will be destabilized by the oil phase.
12 Indeed, in some instances exactly the opposite may occur.
13 Typically, the performance of the foam in a porous
14 medium is determined by its ability to increase the pressure drop
across the porous medium.
16 It is known that fluorocarbon surfactants will function
17 as interfacial tension reducing agents in an oil medium.
18 Additionally, it is known that such surfactants will generate
19 stabilized foams in an oil phase medium. This is exemplified in
U.S. Patent No. 4,836,281, issued to M. Robin and C. Demay. It
21 is further known that amphoteric and anionic hydrocarbon
22 surfactants are extremely oil-sensitive, demonstrating poor
23 stability in the presence of an oil phase.
24 SUMMARY OF THE INVENTION
In accordance with the present invention, we have
26 found, surprisingly, that the oil-sensitivity of amphoteric and
27 anionic hydrocarbon surfactants can be rendered less severe by
28 the addition thereto of a relatively small amount of a
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l fluorocarbon surfactant. There exists a synergistic effect
2 between these two types of surfactant when they are used in
3 combination for foam generation - they produce a surfactant-
4 stabilized foam which is much more tolerant to oil.
Advantageously, only a small amount of the more costly
6 fluorocarbon surfactant is required when combined with amphoteric
7 or anionic hydrocarbon surfactants. Fluorocarbon surfactants are
8 typically ten-fold the cost of the hydrocarbon surfactants;
9 therefore the discovery that only very small quantities of
fluorocarbon surfactants impart oil tolerance to the surfactant
11 combination greatly improves the economics of foam flooding.
12 The composition of the surfactant-stabilized foam will
13 now be elaborated upon: The amphoteric hydrocarbon surfactant
14 preferably is selected from the group consisting of betaines,
sulfobetaines and carboxylate betaines. Most preferably, the
16 amphoteric hydrocarbon surfactant is Varion CADG-HS*, Varion CAS*
17 or Empigen BT*.
18 The anionic hydrocarbon surfactant preferably is
19 selected from the group consisting of sulfates and sulfonates.
More preferably, the anionic hydrocarbon surfactant is an
21 -olefin sulfonate, an alkylated diphenyloxide sulfonate, or a
22 petroleum sulfonate, and most preferably is Sterling AOS*, Dowfax
23 2A1* or Reed Lignin D254-4*.
24 The fluorocarbon surfactant preferably is selected from
the groups set forth in U.S. Patent 4,836,281. More preferably,
26 the fluorocarbon surfactant is selected from the group consisting
27 of perfluorobetaines, perfluorosulfobetaines and
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1 perfluorocarboxylate betaines. Most preferably, the fluorocarbon
2 surfactant is Fluorad FC-751*.
3 The relative proportions of the ingredients of the
4 surfactant mixture on a weight active basis, is:
fluorocarbon surfactant - 0.1% to 20% of the mixture
6 hydrocarbon surfactant - 99.9% to 80% of the mixture
7 The preferred ratio of hydrocarbon surfactant (wt.%)
8 to fluorocarbon surfactant is 90 to 99.
9 The gas used to form the foam is conventional. It is
an inert gas such as CO2, N2, or methane.
11 Broadly stated, the invention comprises a surfactant-
12 stabilized foam for use in a subterranean oil-bearing formation,
13 said foam having been generated by admixing a fluorocarbon
14 surfactant solution and a hydrocarbon surfactant solution.
In another broad aspect, the invention is a process for
16 reducing and controlling the mobility of a gaseous displacement
17 fluid in an oil-bearing formation, which process comprises
18 emplacing foam in the formation, said foam having been generated
19 by admixing a fluorocarbon surfactant and a hydrocarbon
surfactant solution.
21 DESCRIPTION OF THE DRAWINGS
22 Figure 1 is a schematic diagram of the core-flooding
23 apparatus employed to obtain gas mobility reduction factors
24 (MRF's);
Figure 2 is a plot of mobility reduction factors versus
26 percent of perfluoro surfactant relative to total surfactant
27 employed in foam core floods; and
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1 Figure 3 is a plot of normallzed foam height versus
2 percent of added petroleum oil in the presence of various
3 substitutions of fluorocarbon ("perfluoro'l) surfactant for
4 hydrocarbon surfactant.
DESCRIPTION OF THE PREFERRED EMBODIMENT
6 The invention is illustrated and supported by the
7 following examples.
8 Example 1
9 Foaming tests were conducted in an Osterizer* blender
at 21C. A 6 x 60 cm transparent graduated column was fitted
11 with a 1/8 inch stainless steel cooling coil and a calibrated
12 thermocouple and the assembly was fitted onto the blender base.
13 Temperature was controlled by water flow to the cooling coil.
14 Two hundred and fifty ml of 0.5 wt% surfactant in a 2.1% brine
solution was added to the graduated column and the solution was
16 foamed for 5-minutes at the "liquify" setting. The foam height
17 was measured. The experiment was repeated wherein the total
18 surfactant was made up of a mixture of Varion CAS* sulfobetaine
19 amphoteric surfactant (Sherex Chemical Co. Inc.) and Fluorad FC-
751* perfluoro-surfactant supplied by the 3-M Corporation. The
21 foam height measurements were conducted both in the absence of
22 petroleum crude oil and in the presence of various amounts of
23 oil. An Alberta crude oil from the Kaybob field (40 degree API
24 gravity) was employed. The results are shown in Figure 3 where
normalized foam height is:
26 Normalized Foam Height = Foam height in the presence of crude oil
27 Foam height in the absence of crude oil
1 The addition of 2% oil reduced the foam height of
2 Varion CAS by 33%, but the surfactant mixture 95% Varion CAS/5%
3 Fluorad FC-751 showed only a 5% reduction. This result was
4 totally unexpected as the perfluor-surfactant concentration was
only 250 parts per million. A very strong synergistic benefit
6 is obtained from the combination of surfactants.
7 Example 2
8 The foaming experiments of Example 1 were conducted
9 using Dowfax 2A1*, alkyldiphenyloxide sulfonate surfactant (Dow
Chemical) alone and in a mixture of 90% Dowfax 2A1/10% Fluorad
11 FC-751. The petroleum oil was from the Cynthia field (Texaco
12 Canada, API 36 degrees) and 4 ml of oil was added. In the
13 presence of oil the Dowfax 2A1 normalized foam height was 0.20;
14 the mixture foam height was 0.75.
Example 3
16 The foaming experiments of Example 2 were conducted
17 using Varion CADG-HS* betaine amphoteric surfactant (Sherex
18 Chemical Co. Ltd.) alone and in a mixture 90% Varion CADG-HS/10%
19 Fluorad FC-751. In the presence of oil the Varion CADG-HS
normalized foam height was 0.13; the mixture foam height was
21 0.49.
22 Example 4
23 The foaming experiments of Example 2 were conducted
24 using Sterling AOS* ~ -olefin sulfonate surfactant (Canada
Packers Ltd.) alone and in a mixture 90% Sterling AOS/10% Fluorad
* Trade-mark
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1 FC-751. In the presence of oil the Sterling AOS normalized foam
2 height was 0.13; the mixture foam height was 0.49.
3 Example 5
4 The foaming experiments of Example 2 were conducted
using a Sterling AOS/Dowfax 2A1 50/50 (wt) mixture. In the
6 presence of oil the normalized foam height was 0.11; in a mixture
7 40% Sterling AOS/40% Dowfax 2A1/10% Fluorad FC-751, the
8 normalized foam height was 0.33.
9 Example 6
The foaming experiments of Example 2 were conducted
11 using Reed Lignin 254-4* petroleum sulfonate surfactant alone and
12 in a mixture 90% Reed Lignin 254-4/10% Fluorad FC-751. In the
13 presence of oil, the Reed Lignin 254-4 normalized foam height was
14 0.60; the mixture foam height was 2.95.
Example 7
16 The foaming experiments of Example 2 were conducted
17 using Varion CAS sulfobetaine amphoteric surfactant (Sherex
18 Chemical Co. Ltd.) alone and in a mixture 90% Varion CAS/10%
19 Fluorad FC-751. In the presence of oil, the Varion CAS
normalized foam height was zero; the mixture foam height was
21 0.60.
22 Example 8
23 The foaming experiments of Example 2 were conducted
24 using Empigen BT* carboxylate betaine amphoteric surfactant
(Albright & Wilson) alone and in a mixture 90% Empigen BT/10%
* Trade-mark
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1 Fluorad FC-751. In the presence of oil, the Empigen BT
2 normalized foam height was 0.18; the mixture foam height was
3 0.57.
4 Example 9
Empigen BT and Fluorad FC-751 was tested in low
6 pressure ambient temperature corefloods in oil free cores and in
7 cores containing oil from the Judy Creek field, Beaverhill Lake
8 pool having a density of 0.8296 g/ml and a viscosity of 4.6 mPa.s
9 at 23.0 +/- 0.5C. The porous medium used was a Berea sandstone
cut into 2.5 x 2.5 x 20 cm blocks that had been wrapped in
11 fiberglass tape and cast in epoxy resin. The coreflooding
12 apparatus is shown in Figure 1. The cores were flooded with oil
13 and then a 2.1% total dissolved solid brine. Residual oil
14 saturation at this point Sor = 28% of pore volume. The cores were
then flooded with a mixture of 96% nitrogen + 4% brine on a
16 volume basis and the pressure drop across the core was recorded.
17 Volumetric flow rate was 19 ml/hr. Surfactant was added at 0.5
18 wt% to the brine and the pressure drop across the core was again
19 recorded. The mobility reduction factor (MRF) was calculated as
MRF = Pressure drop in the presence of surfactant
21 Pressure drop in the absence of surfactant
22 If no foam is generated within the core, the MRF will
23 be equal to l(one). Robust foams are represented by large MRF
24 values. The results using various surfactant mixtures are shown
in Table 1.
26 The betaine hydrocarbon surfactant showed a severe
27 sensitivity to the presence of residual oil; MRF fell from 14 to
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1 2. However, the replacement of only 2% of the hydrocarbon
2 betaine with perfluoro surfactant restored the MRF to 10 in the
3 presence of 28% oil. These results are also shown graphically
4 in Figure 2.
Table I
6Mobility Reduction Factors for Average 96% Foam at
719 mL/h in Berea Sandstone Corefloods at Ambient
8Temperature and Low Pressure
Surfactant Surfactant Mobility Reduction Factors
11 Class Tested
12
13 Oil-Free Core Core at Sor
14
16 Amine Oxide Atlas CD-413 17 3
17 Betaine Empigen BT 14 2
18 Mixture of
19 Betaine with 98% Varion CAS +
Perfluorobetaine 2% Fluorad FC-751 12 10
21 Perfluorobetaine Fluorad FC-751 34 30
22
23 Example 10
24A mixture of sulfonated anionic surfactants were
evaluated in the same manner as Example 9, except that the core
26 was held within a lead sleeve inside a high pressure steel
27 coreholder. Kaybob crude oil was used (40 degree API) and
28 pressure was maintained at 6.9 MPa within the core. The base
29 hydrocarbon surfactant was a 50/50 mixture of Dowfax 2A1
alkyldiphenyloxide sulfonate and Sterling AOS alfa olefin
31 sulfonate anionic surfactants. This material will be designated
11
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1 Blend A. Core floods were conducted using Blend A and various
2 mixtures of Blend A with Fluorad FC-751 perfluoro surfactant in
3 the absence of residual oil and in the presence of residual oil.
4 The results are given in Table 2 and in Figure 2. Again a strong
and unexpected synergism is demonstrated at low levels of
6 perfluoro-surfactant addition. 10% Fluorad FC-751 produces an
7 MRF increase of almost threefold.
8TABLE II
9Mobility Reduction Factors at High Pressure (6.9 MPa)
10in the Presence of Residual Oil
11
12 Anionic 50% Dowfax 2A1 +
13 Blend A 50% Sterling AOS 12
14
Blend A 45% Dowfax 2A1 +
16 + 10% 45% Sterling AOS
17 Perfluorobetaine 10% Fluorad FC-751 33
18
19 Blend A 37.5% Dowfax 2A1 +
+ 25% 37.5% Sterling AOS
21 Perfluorobetaine 25% Fluorad FC-751 31
23 Blend A 25% Dowfax 2A1 +
24 + 50% 25% Sterling AOS
Perfluorobetaine 50% Fluorad FC-751 40
26
12
