CA1274170A - Gas flooding process for the recovery of oil from subterranean formations - Google Patents

Abstract

ABSTRACT

This invention relates to a method for recovering hydrocarbon from a subterranean formation which comprises sequentially injecting, through an injection well 7 a drive fluid or a gas or a gas/liquid mixture to drive the hydrocarbon from the formation to a producing well and a mobility control fluid of a surfactant/water mixture into the subterranean formation characterized by using an alkylated diphenyl sulfonate surfactant in the mobility control fluid.
Using an alkylated diphenyl sulfonated in combination with an anionic polyoxyalkylated surfactant improves the foamability as well as the foam stability of the foaming surfactant, thereby enhancing the performance of the mobility control fluid in improving the sweep efficiency of the drive fluid in a gas flooding operation.

Description

7~

IMPROVED &AS FLOODING PROCESS FOR _ THE RECOVERY OF OIL FROM SUBTERRANEAN FORMATIONS

Thi~ invention relates generally to a process for the recovery of oil from subterranean formation~, and more particularly ko a ga~ flooding process. ~
Petroleum or oil is generally recovered from subterranean formations by penetrating the EormatiQn with one or more wells and pumping or permitting the petroleum to flow to the surface through the well. In various recovery operations, an external driving force is not required to drive the petroleum to the produoing well and/or the surface. For example, ~ome natural driving energy ~uch as underlying active water drive or a ga~ under some minimum pressure may posse~s sufficient pressure to drive the petroleum of hydrocarbon to the well and then to the surface.
Reoovery of petroleum using natural energy is referred to as primary recovery.
.. .
In many instances, the natural driving energy is insufficient or becomes insufficient to cause the petroleum to flow to the well. For example, a ~ubstantial portion o~ the petroleum to be recovered may remain in the formation after depletion of the 35,039-F ~ -1-natural driving energy. In other cases 9 the subterranean formation, while containing sub~tantial amount~ of petroleum, may not pos~ess the necessary driving force to recover any of the petroleum. In such cases~ various techniqueq have been applied heretofore to recover the petroleum. Although such techniques are commonly referred to as ~econdary recovery9 in~fact9 they may be primary~ secondary or tertiary in sequence of employment~
One conventional method for the econdary - recovery of petroleum from a subterranean formation involves injeoting water through one or more injection wells to drive the residual petroleum or oil towards a producing well. However, water alone does not efficiently displace petroleum. Therefore, it has become a common practice to add a variety of materials to the drive water to improve the efficiency of the flooding operation~ Specifically, it is a common practice to add a surf`actant such as a petroleum ~ulfonate to the drive water. The surfactant reduces the interfacial tensions b~ètween the water and the oil, thereby making the oil more miscible with the water and inareasing oil recovery. In general, the lower the interfacial tension between the oil and water, the better the performance of the water flooding operation.
In various operations, the water ar water/3urfactant mlxture channels through the formation such that a disproportionately high amount of the water pa~ses though zones of high permeability into the producing wellbore without contacting appreciable amounts of oil in the reservoir, particularly that oil contained in zones of low permeability. This greatly reduces the efficiency of the operation. There are a 35,039 F -2-~ 7~

number of method~ to control the flow o~ drive water through the ~ubterranean formationO
An alternative method of secondary oil recovery involve~ using steam, particularly in secondar-y oil recovery method~ for heavy oil~. The steam reduces the vi~cosity and, hence, increaqes the flowability of the oilO One ~uch method is cyclic steam stimulation ( o-called "huff-n-puff" method for the ~econdary recovery of oil) wherein, in one portion of the cycle, steam is injected into a producing well and, in a second portion of the cycle, oil i9 recovered from the producing well.
A second method is a steam flooding operation wherein qteam iq injected into an injection well to drive the oil to the producing well. To improve the efficiency of these recovery method~, steam injection is often alternated with injections of a surfactant solution which is capable of foaming. The resulting foam controls the mobility of the following ~team as it pa~ses through the formation by rendering it more difficult for the ~team to flow through the path~
previously swept by the steam. In general, the ability of the surfactant to reduce the interfacial tension between the steam and the oil i~ not as important a~
the ability of the surfactant solution to form a stable foam and may be of only minor, if any, importance.
Therefore, ~urfactant~ which are useful in water flooding are not necessarily useful, and are often not 3 useful, in the secondary oil recovery methods u~ing steam. The surfactant employed in secondary oil reeovery methods involving steam i~ exposed to high temperatures (e.g., 175C to 232C) and water of relatively high purity (i.e., water having a low diqsolved solid~ content) and are cho~en accordingly.

35,039-F -3-~7 --4~

Yet another method of ~econdary oil recovery is gas flooding which involves injecting a gas such as carbon dioxide or nitrogen into the formation through one or more injection wells to drive the oil in the reservoir towards a producing well. In a gas flooding operation, the gas can be injected as a solution or disper3ion with water. Alternatively9 the gas can be injected without water and, in uch ca~e, will often form either a solution or di~persion with water which naturally exi~ts in the formation or which has been injected either previous or subsequent to the gas injection. Although gas or a gas/water mixture can be employed alone, in general, gas flooding comprises alternatively injecting gas and drive water. In theory, the gas or gas/water mixture thins or solubilizes the oil and the drive water pushes the gas or gas/water mixture and oil to a producing well.

Unfortunately, the gas or gas/water mixture i3 prone to channel through the formation such that a di~proportionately high amount of the ga~ bypasses through zones of high per~eability into the produci'~g wellbore without contacting appreciable amounts of oil in the reservoir. To prevent ohanneling of the gaq and drive water and to otherwise control the mobility of the drive fluids, thereby inoreasing oil production, it -ha~ been suggested to employ a foam prepared from a mlxture of water and a ~urfactant during the ga~
flooding operation. Suoh mixture ha~ been found to prevent ohanneling and to foroe the drive fluids into the le~ permeable zoneq, thereby increasing oil production.
Surfactants which have been found to be useful a~ a mean~ of modifying the profile in a gas flooding 35,039-F . -4- . .

. . ~ .

operation are surf'actants capable of forming a foam with an aqueou~ liquid and include alkyl polyethylene 'oxide 3ulfates (see9 for example U.S. Patent No.
491139011); polyalkoxy sulfonates (see, for example 5 U.SO Patent No. 495029538); and po]~alkoxylated alcoholic or phanolic ~urfactants (~ee, for example U~S0 Patent No. 4,380,266). The surfactant employed in a gas flooding operation i3 expo~ed to relatively low _-temperature~ (eOg., less than 95C) and water of relatively low purity (i.e., water ha1ling a relatively high dissolved solid~ content). Ther?fore, surfactants which may be useful in water and/or s;eam flooding may not necessarily be u3eful, and are of en not useful, in the secondary oil recovery methods us ng ga~ flooding , techniqueq.
However, the surfactants here~ofore taught to be effective in modifying the mobilit~ of the drive fluid~ in gas flooding operation~ hav~ not proved to be particularly effective in every opera;io~.
Specifically, in certain instances, g~eater foam skabilities are desired to achieve th~ desired increase in oil production. In'other instances, the surfactants have not been found to be particularl~ effective regardles~ of their foaming ability a3 measured in the laboratory.
In view of the deficiencies cf the prior art method~ for improving the mobility of the drive fluids in a gas Plooding operation, it remai1q highly de~irable to provide an improved meth)d'for controlling the mobility of the drive fluids in a gas flooding operation.

35,03~-F -5-~Z7~.7~

Accordingly, the present invention is an improved method for recovering hydrocarbon from a subterranean formation. The recovery method comprise~
sequentially injecting, through an injection well, a drive fluid or a gas or a gas~liquid mixture to drive the hydrocarbon from the formation to a producing well and a mobility control fluid of a surfactant~water mixture into the ~ubterranean formation, the improvement in said method compri~ing using an alkylated diphenyl ulfonate surfactant in the mobility control fluid.
A~ u~ed herein, the term "mobility control'l is employed in its broadest sense and is meant to include the term "profile modification". The term "mobility control" is meant to include any process whereby the sweep ePficiency of a reservoir is improved or whereby the injection profile oP an injection well is altered.
The term "sequentially injecting" is meant to include those operations in which the drive fluid and the mobility control Pluid are injected as separate ~equential "slugs" a~ well as operations in which the drive fluid is in~ected continuously and the mobility control Pluid is injected ~imultaneous with the drive fluid, but on a periodic basis.
The alkylated diphenyl sulfonate, preferably an alkylated diphenyl oxide sulPonate, surfactant has been Pound to be useful, either alone or in combination with anionic polyoxyalkylated surfactants, as a mobility control agent in a gas Plood operation for the recovery of hydrooarbon from subterranean formations.
SpeciPically, in various applications, particularly in the recovery of hydrocarbons from reservoirs of low or extremely low permeability (e.g., a re~ervoir having a , . .

35,039-F -6-~7~7 --7~

permeability of from 0.1 to 50 millidarcie~) and/or those environments of high temperature, e.gO 7 above 120C, or having high concentration of divalent metal anions9 ~OgO~ calcium ionsO The alkylated diphenyl sulfonate surfactant acts as an excellent mobility control agent, thereby improving the sweep efficiency of the ga~ drive and the overall hydrocarbon production, without the need for supplemental surfactants0 '~
In another aspect, the alkylated diphenyl sulfonate surfactant i~ advantageously employed in combination with an anionic polyoxyalkylated surfactant and in a preferred embodiment, the pre~ent invention is _ an improved gas flooding operation wherein the improvement comprise~ using a mobility control fluid containing a surfactant mixture of at least two surfactants with one ~urfactant being an alkylated diphenyl sulfonate and the second surfactant being an anionic polyoxyalkylated qurfactant.
U31n~ an alkylated diphenyl ~ulfonate in combination with an anionic polyoxyalkylated qurfactant, e.g. 9 polyoxyethylated alcohol ~ulfate, unexpectedly improves the foamability as well as the foam ~tability of the Eoaming surfactant, thereby enhancing the performançe of the mobility control fluid in improving the sweep efPiciency of the drive fluid in a ga~ flooding operation. The improved foamability and foam ~tability is 0vident both when the mobility ! control fluid is foamed in the absence or presence of oil. Thi~ improvement in foam stability and foamability is particularly surprising in view of the fact that the alkylated diphenyl sulfonate i~ not particularly effective as a foaming surfactant. In .

35,039-F -7-, 4~7~:3 many ca~es 9 the improved ~urfactant mixture exhibits fiPty percent or more improvement in foamability and/or stability.
The mobility control fluid employed in the practice of the pre ent invention comprises an alkylated diphenyl sul~onate. As the term i~ used herein, alkylated diphenyl sulfonates are preferably represented by the general tructural formula:
(~)m (R)n ~ ~ _ (S03 M+)y (S03 M )x wherein z i~ 0 or 1, prePerably 1; each R is independently an alkyl or substituted alkyl radical;
each m and n is independently 0, 1 or 2, provided at lea~t one of m or n i~ 1; each M is indepandently hydrogen, an alkali metal, alkaline- earth metal, or ammonium or ~ub~tituted ammonium and each x and y are individually 0 or l with the proviso that at lea~t one of x or y i~ l. Preferably, the R group(s) are independently an alkyl group having from 4 to 24, more preferably from 6 to 16 carbon atoms. The alkyl groups can be linear, branched or cyclic but linear or branohed radicals are preferred. The M~ ammonium ion radical~ are of the formula (R')3HN+ wherein each R' is 35,039-F -8-~LZ~7~7~3 ~9 ~

independently hydrogen 9 a C~-C4 alkyl or a C1 C4 hydroxyalkyl radical. Illustrative C1~G4 alkyl and hydroxyalkyl radicals include methyl 9 ethyl 9 propyl 9 isopropyl, butyl, hydroxymethyl and hydroxyethylO
Typical ammonium ion radicals include ammonium (N~H~) 9 methylammonium (CH3N+H3) 9 ethylammonium (C2H5N+H3) 9 dimethylammonium ((CH3~2N+H2), methylethylammonium (CH3N+H2C2H5), trimethylammomnium ((CH3)3N~H) 9 ,_ dimethylbutylammonium ((CH3)2N+HC4Hg), hydroxyethylammonium (HOCH2CH2N+H3) and methylhydroxyethylammonium (cH3N~H2cH2cH2oH)D ..
Preferably, each M is independently ammonium or substituted ammonium or alkali metal.
The alkylated diphenyl ~ulfonates and their method~ of preparation are well known and reference is made thereto for the purpo~es of thi~ invention.
Representative surfactants and their method~ of

2~ preparation are di~clo~ed in U.S. Patent Nos.

3,264,242; 3,634,272; and 3,945,437.
In the practice of the pre~ent inventlon, the alkylated diphenyl sulfonate i~ typically a mixture of compounds having the formula (I) wherein sufficient x and y are 1 such that the sum of x plus y for the alkylated diphenyl ~ulfonate is at lea~t 1.7, more preferably at least 1.8. In additi~on, mixtures of a mono- or di-alkylated diphenyl sulfonates can be employed.
Mo~t preferably, an alkylated diphenyl oxide ~ulfonate or mixture of two or more alkylated diphenyl oxide ~ulfonate~ are employed in the practice of the present invention.

35,039-F -9-~7~7Q

The preferred alkylated diphenyl oxide 3ulfonates include ~odium disulfonated hexyl~diphenyl oxide, sodium disulfonated decyldiphenyl oxide9 ~odium disulfonated dodecyl-diphenyl oxide and qodium disulfonated hexadecyl-diphenyl oxideO
Although the alkylated diphenyl sulfonate can be employed in the mobility control fluid without _ additional ~urfactant, in general, for most pre~erred performance, the alkylated diphenyl sulfonate is employed in combination with an anionic polyoxyalkylated urfactant. In general, anionic polyoxyalkylated surfactant can be repre3ented by the general ~tructural formula:
R''O[(cH2)do]eA
wherein R" i~ a hydrocarbon or halogen substituted hydrocarbon radical containing from 4 to 24, advantageously from 6 to 18, carbon atoms; d is from 2 to 6, preferably 2 or 3; e i9 at lea t 1, preferably from 2 to 20 and A is an anionc group such as sulfate, ~ulfonate, phosphate or phosphonate. R" can be a branched or straight ¢hain aliphatic or haloeen substituted aliphatio group, an alicyclic or halogen substituted alicyclic group, an alkaryl or halagen substituted aryl group, or an aryl or halogen ~ubstituted aryl group.
3 Preferably, R" is an alkyl group having from 6 to 18, more preferably from 6 to 14 carbon atom~.
Preferably, -A is a sulfate group as represented by the formula:
-S04 M~
.

35,039-F -10-.

- ~74~7~

wherein M is an alkali metal or NH4 9 preferably ~odium or NH40 MoYt preferably, R" i9 a C6-14 alkyl9 d i~ 2 e i~ from 2 to 12 and -A i9 -S04~Na+o Repre~entative examples of preferred anionic polyoxyalkylated surfactant~ include C12_130(C2H40)3 S04NH4 ~old under the tradename Neodol~ 23-3A and C~2-130(C2H40j3S04Na sold under the tradename of Neodol~ 25 3S by Shell Chemical Company, C8-10(C2H4)2_4S4NH4 901d under the tradename of Alipal~ CD-120 by GAF, CH3-(CH2)n-CH[-(CH2)~--CH3]~-0-(C2H40)3S04X] wherein X i~ NH4 or Na sold under the tradename Tergitol~ S by Union Carbide.
In preparing the mobility control fluid, the alkylated diphenyl sulfonate surfactant or mixture of alkylated diphenyl sulfonate and anionic polyoxy-alkylated surfactants are di~solved or di~persed in an aqueous fluid. The aqueous fluid can be water (including alkaline or acidic aqueous solutions) or mixture~ o~ water and one or more water miscible liquid such~a~ a lower alkanol, e.g~, ethanol or propanol; a lower ketone, e.g., acetone or methyl ethyl ketone; and a glycol such as ethylene glycol. It will often be more convenient to use the brine native to the subterranean formatlon to prepare the mobility control fluid.
The amounts of qurfactant(~) most advantageously employed in preparing the mobility control fluid are dependent on a variety of factors including the specific surfactant(s) and aqueou~ liquid employed and the specific end u~e application. In general, the mobility control fluid will advantageously comprise from 0.01 to 5, preferably from 0.1 to 1, 35,o39~F

~ ~2~

weight percent surfactant~ When a combination of alkylated diphenyl sulfonate jurfactant and anionic polyoxyalkylated surfactant are employed, the mobility control fluid is preferably comprised of from 20 to 1009 more preferably ~rom 25 to 759 moqt preferably from 40 to 60 7 weight percent of the alkylated diphenyl sulPonate surfactant and ~rom 80 to 0, more preferably from 25 to 75, most preferably from 60 to 40, weight percent of the anionic polyoxyalkylated surfactant, ba~ed on the total weight of the ~ur~actant~.
The drive or displacement fluid employed in the gaq flooding operation of the pre~ent invention is a ga~ or a ga~/liquid, generally a gas or a gas/aqueou3 liquid mixture. The ga~e~ which can be employed aq the drive fluid are quitably any ga~ at lea~t a portion of which will not all be present as a liquid at the temperature and preq~ure of the formation. Air, nitrogen, carbon dioxide, normally gaseouq paraffinic hydrocarbon~ quch a~ methane, ethane, propane or butane a~ well a~ normally ga~eous olefinic hydrocarbon~ ~uch a~ ethylene propylene or butylene and mixture~ thereof are most often advantageou~ly employed. Crude ga~e~
quch aq exhaust gaq or flue ga~, which are predominantly oarbon dioxide and nitrogen, a~ well a~
natural gas or liquefied petroleum ga~ (LPG) may also be u~ed. Mixtures of any two or more of these gaqe~
may be used although care must be exerciqed if a 3 mixture of air or other oxygen containing gaq and a combuqtible gaq are to be used. Of the foregoing, ga~e~ which are ~omewhat ~oluble in petroleum are generally preferably employed in the practice of the pre~ent invention. Carbon dioxide and the paraffinic 35,o39-F -12-~ 2 -13~

hydrocarbons such a~ methane or ethane 9 or the olefinic Ka~e~ are mo~t preferably employed.
Although the gas flooding operation can be initiated at es~entially any time during the recovery operation, in general, the~gas flooding operation is initiated following the economic recovery of the hydrocarbon from the reservoir u~ing primary and secondary (e.g., water flooding) recovery techniques on the formation~
In the practice of the present invention, the drive fluid comprising the gas or gas/liquid mixture and the mobility control fluid are sequentially _ injected into the subterranean formation using techniques known in the art. The drive fluid comprising the gas or gas/liquid mixture is injected, for a period of time, into the formation through one or more injection well(s) to drive the hydrocarbon contained by the formation to the producing well. For example, a five-spot pattqrn wherein four injection wells are located~in a square pattern and a single producing well located at or near the center of the square defined by the inje¢tion well~ is often advantageously employed. A variety of other pattern~
are al~o advantageously employed.
In general, the temperature and pressure at which the gas flooding operation is conducted and the drive and mobility control fluids are exposed varies Prom 30C to 120C and from 300 to 6000 psig (41,000 kPa gauge~. The drive fluid i~ employed in conventional amounts normally employed in gas flooding operations.
In general, injection of the drive fluid is continued until the recovery of the hydrocarbon becomes 35,039-F -13-'7 unacceptable (iOe.9 the ~weep efficiency of the flooding operation decreaseq to an unacceptable level) or until undeqirable amount~ of the drive fluid break through into the producing wellbore, which9 to a large extent, depends on the specific ~ubterranean formation being treated, and the deqired levels of hydrocarbon production. ~t such time, the injection of the drive ~luid into the formation iq interrupted and the _ mobility control f'luid i~ injected into the formation through the ~ame or different injection well.
Injection o~ the mobility control fluid is continued for the desired amount of time. Optionally, after the injection of the qurfactant solution or mobility control fluid, water is injected into the formation through the inje¢tion wells to drive the surfactant solution into the formation to promote its effectiveneq~ as a mobility control agent. 5ubsequent to the injection of the mobility control fluid and water, if employed, injection of the same or different drive fluid i~ again initiated for a period of time, after which, if further treatment i~ de~ired, the injection of the mobility control fluid i9 again initiated.
The ~pecific conditionq at which the mobility oontrol fluid (e.g., the amounts of the mobility control fluid employed and the frequency of treatment with the mobility control fluid) mo~t advantageouqly 3 employed are dependent on a: variety of factors including the specific drive and mobility control, particularly the specific surfactants, employed in the flooding operation and ~pecific formation being treated. In general, the mobility control fluid will be employed in an amount of from 0.05 to 15 volume - 35,039-F

~15~

percent based on the total volume o~ the reservoir being treated. More preferably9 the mobility control fluid iq employed in an amount of ~rom 001 to 10 volume percent based on the total volume of the reservoir being treatedu The method of the present invention can be employed in formation~ having relatively low salt concentration or high concentrations o~ salt, e~g. 9 above three percent salt. Good re~ults can be obtained even when the salt concentration of the formation i~
above ten percent. In addition, the method of the present invention can be employed to formations having varying pH from about 2 to about 9 or higher and is relatively insensitive to formation constituents suoh as clay, silica and the like, i~e., adsorption losses to the formation are relatively low.
The following examples illustrate the present invention but are not to be construed to limit its scope. All part~ and percentages are by weight unless otherwise indicated.
Example 1 To simulate the hard water aommonly found in subterranean formation~ o~ lntere3t, a salt 301ution comprisin~ 0.5 percent calcium chloride and 0.5 percent ~odium chlaride in deionized water wa~ prepared. To the resulting hard water was added equal parts of sodium disulfonated hexyl-diphenyl oxide and an ammonium ~alt of polyoxyethylated alcohol sulfate sold under the tradename of Alipal CD-128 by GAF in amounts to prepare a 1 percent solution of the surfactant. One hundred milliliters (ml) o~ the surfactant solution waq 35,o39-F -15-.:

gently poured into a one quart Waring~ Blendor Jar.
Twenty-five ml of i~o-octane were then gently poured into the blenderO The solution was then sheared for 25 seconds with the blade being maintained at the highest setting. After shearing, the Poamed samples were immediately poured into a 1000 ml graduated cylinder.
- Foam adhering to the sides of the blender jar was scraped off with a patula and also poured into the graduated cylinder. One hundred secondq after the beginning of the shearing operation, the foam volume wa~ recorded and this reading was taken as the initial foam height. The liuqid volume half-life was also recorded. For the purposes of the Example~, the liquid volume half life is that time it takes for 50 ml of the aqueou~ surfactant solution to drain out of the foam structure. The initial foam height and the liquid volume half-life forth in the aocompanying Table I.

ExamPle 2 Te~ting was conducted in an identical manner to Example 1 except that the ~urfactant solution waq prepared u~ing equal parts of an amine salt of the di~ulfonated hexyl-diphenyl oxide and the ammonium ~alt of the polyoxyethylated a1cohol ~ulfate. The initial foam height and the liquid volume half~life was again mea~ured and set forth in the accompanying Table I.
ExamPle ~ ~
Testing wa~ oonducted in an identical manner to Example 1 except that the one percent surfactant ~olution was prepared u~ing the sodium salt of the disulfonated hexyl-diphenyl oxide only. The initial 35,039-F -16-7~7~D
--17~

Poam height and the liquid volume half~life was measured and set ~orth in the accompanyin~ Table I.
Comparative Example A
Te~ting was conducted in an identical manner to Example 1 except that the one percent surPactant solution wa~ prepared uqing the ammonium qalt of the polyoxyethylated alcohol sulfate onlyO The initial ~oam height and the liuqid volume hal~life was measured and set forth in the accompanying Table Io Comparative Exam~le 8 Testing was conducted in an identical manner to Example except that the one percent surfactant solution was prepared u~ing equal parts of an amine salt of the di~ulfonated hexyl-diphenyl oxide and an a-olefin ~ul~onate ~old under the tradename Witconate~ AOS-10 by Witco Chemical Co. The inital ~oam height and the li~uld volume half-life was measured and set forth in the accompanying Table I.
Com~arative Example C ' Testing was conducted in an identical manner to Example 1 except that the one percent ~urfactant solution was prepared using the a-olefin ~ulfonate only. The initial foam height and the liquid volume half-life was. mea~ured and set forth in the accompanying Table I.

.~ 35 , 35,039-F -17-~18`

Table I
Liquid Initial Volume Foam Half L1fe, Example Surfactant~ YC~ min.~

1 C6DPO(Na)/CD128 680 2 layers 2 C6DPO(N)/CDl28 610 2 layer~
3 C6DPO(Na) 140 1.75 A CD128 600 2 layers B C6DPOtN)/AOS10 240 6058 C AOS10 370 10.9 ~ ~
lTh~ surfactant typ~ is s~t forth in abbreviated form with:
C6DPO(Na) being the sodium s~lt of disulfDnated hexyl-diphenyl o~ide;
C6DPO(N) being the diethylamin~ salt of the disulfonated hexyl-diphenyl oxide;
CD128 being the ammonium salt of tha polyoxyethylatQd alcohol sulf~t~; and AOS10 being an a-olefin sul~onate.
2Wh~n recording recording the liquid volume half-li~e, a r~ading of 2 lly~ss indicates that th~ sampl~ separat~s as an oil/wat~
~mulslon with a 50 ml hal~ e o~ greater than 5 minut~ which indicatos that th~ foam i9 mor~ 3tabl~ than the individuAl compon~nt.

As evidenced by the data ~et forth in Tabla I, the blend of the alkylated diphenyl sul~onates with an anionic polyoxyalkylated ~urfaotant imparted increased foam heights and equivalent liquid volume half-lifes as compared to the use of the anionic polyoxyalkylated surfactant alone. The increased foam heights are surprising in view of the low initial Poam heights achieved with the alkylated diphenyl sulfonate alone and the fact that the foam height oP an -olefln ~ulfonate ~urfactant was reduced when mixed with the alkylated diphenyl sulfonate. Therefore, the 359039-F . -18-.

~ 2 -19~

oombination of the alkylated diphenyl sulfonate and an anionic polyoxyalkylated surfactant9 can be effectively employed in treating formations which require good foaming of the mobility control fluid. Although neither the initial foam height nor the liquid volume half-life using the alkylated diphenyl sulfonate alone wa~ particularly good, due to the relatively low adsorption re~i~tance and brine tolerance of the ~urfactant, it can be employed as an effective mobility control agent in formationY which do not require ~igni~icant foaming for mobility control.
Example 4 To evaluate the effect of the presence of C02 and oil on the mobility control fluids u~eful in the practice of the present invention, to a 100 ml cell capable of ~ithstanding up to at lea~t 2700 psig (19000 kPa gauge) and equipped with an inlet and outlet for C02t the outlet being connected to a back pressure regulator was added 25 ml of a 1 percent solution of equal part~ of the sodium salt~of dodecyl diphenyl ether disulfonate sold as Pusher~ XUS 40l90.00 by The Dow Chemical Company and the ammonium salt of polyoxyethylated alcohol suLfate in a brine of calcium chloride having 3 percent total di~olved ~olids. The pres~ure cell was tran~parent so that foaming ln the oell can be measured, The pressure cell wa~
transparent 90 that foaming in the cell can be measured. The ~urfaotant solution was heated to 85~C
and maintained at that temperature throughout testing.
Carbon dioxide wa~ pa~sed through the oell at a pres~ure of 300 p~ig (2100 kPa gauge) and the back regulator maintained at 200 p~ig (1400 kPa gauge).
Thi~ wa~ sufficient pre~ure to agitate the contents of 35,039-F -19-7~3 -20~

the cellO The equilibrium foam height wa~ recordedO
The flow of C02 was stopped and the cell held in equilibrium at 100 psig (690 kPa gauge)~ The time for the column to drain from its equilibrium foam height to one half its equilibrium foam height was recorded.
This value i~ referred to a~ the equilibrium foam half-life.
The above te~ting was repeated except that 1 ml of oil (We~t Texaq STD) waq placed in the cell with the ~urfactant 301ution and the temperature was lowered to 41C. The equilibrium foam half-life was measured using the same techniques. The equilibrium foam half~life is set forth in Table II for both testing with and without oil pre~ent in the cell.
Example 5 Testing was conducted in an identical manner to 20 Example 4 except that the surfactant ~olution wa~ ~
prepared u~ing equal parts of a sodium ~alt of the disulfonated hexadecyl diphenyl oxide and the ammonium salt of the polyoxyethylated alcohol sulfate. the equilibrium foam half-life is set forkh in Table II for both ts~ting with and without oil pre~ent in the cell.
Comparative Example D
Testing wa~ conducted in an identical manner to Example 4 except that the one percent surfactant ~olution wa~ prepared using the ammonium salt of the polyoxyethylated alcohol ~ulfate only. The equilibrium foam half-life is ~et forth in Table II for both te~ting with and without oil pre~ent in the cell.

35,039-F -20-.

~L%7~

Comparative Example E
Testing was conducted in an identical manner to Example 4 except that the one percent surfactant ~olution was prepared uqing the sodium salt of the disulfonated dodecyldiphenyl oxide only~ The equilibrium foam half~life is set forth in Table II for both testing with and without oil pre3ent in the cell.
Comparative Example F
Testing wa~ conducted in an identical manner to Example 4 except that the one percent surfactant solution was prepared using the sodium ~alt o~ the di~ulfonated hexadecyldiphenyl oxide only. The equilibrium foam half life i5 set ~orth in Table II for both testing with and without oil present in the cell.

.: .

35,039-F -21-~;27~7~

~A~L~ II
Equilibrium Foa~ Hal~ e, . seconds 5ExampLe Surfactantl Without Oil With Oil

4 NaC12DPO/CD128 93 49 ._ S NaC16DPO/CD128 172 23 NaC12DP 6 F Na~16DP
1Th~ sur~actant i~ set forth in abbteviated ~orm with: -NaC12DPO being th~ sodium salt o~ tha disulfonated dodecyl diphenyl oxide;
N~C16DPO is the ~odium salt of the disul~onated hexadecyl diphenyl oxid~; a~d CD128 is the ammonium salt of the polyoxyethylated alcohol ~ulfate.

A3 evidenced by the data set forth in Table II, a combination of the alkylated diphenyl oxide sulfonate with an anionic polyoxyalkylated surfactant imparted much hiBher equillbrium half-lifes than either the alkylated diphenyl oxide sulfonate or the anionic polyoxyalkylated sur~actant. The~e increa3ed half-life time~ are particularly notlceable when the foaming test is conduoted in the presenoe of oil, which more closely approximate~ conditions existing in the oil field.

ExamPle 6 In an oil recovery operation, a re~ervoir which had been depleted to economically unde~irable level~
u~ing conventional primary recovery and ~econdary recovery water flooding technique~ can be improved uslng the method of the pre~ent invention.

35,039-F -22~

~Z7 ~7~

. ~3-Specifically, a conventional five ~pot pattern wa~
- employed with four injection wells located in a qquare pattern and a single producing well located at the center of the four injection well~. A miscible C02 flood wherein eqsentially pure C02 was injected into all four injection well~ at pre3sures sufficient to obtain multiple contact oil miscibility wa~ initiated and conducked until evidence of C02 channelling to the producing well was realized.
At that time, a volume equal to 5 percent of the reservoir pore volume of an aqueous solution containing 1 percent by weight of equal parts of an alkali metal 3alt of an alkylated diphenyl oxide -sulfonate and an alkali metal ~alt of an anionic polyoxyalkylated sulfate was added to the formation through the injection wells. Sufficient water was injected after the surfactant solution to displace the ~urPactant solution outwardly into the well a di~tance oP about 20 feet. Subsequently, injection of C02 was again initiated and continued until C02 channelling wa~
again realized~ At that time, injection of ~urfactant solution, followed by water, was reinitiated. The injection of the surfactant solution (i.e., the mobility control fluid) and C02 wa~ continued in this way during the economic lifetime of the reservoir under these flooding conditions.

35,039-F -23-

Claims (16)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS
FOLLOWS:

1. An improved method for recovering hydrocarbon from a subterranean formation, the recovery method comprising sequentially injecting, through an injection well, a drive fluid of a gas or a gas/liquid mixture to drive the hydrocarbon from the formation to a producing well and a mobility control fluid of a surfactant/aqueous fluid mixture into the subterranean formation, the improvement in said method comprising using one or more alkylated diphenyl sulfonates as the surfactant in the mobility control fluid.

2. The improved method of Claim 1 wherein the surfactant in the mobility control fluid consists essentially of an alkylated diphenyl sulfonate or mixture of alkylated diphenyl sulfonates, each represented by the general structural formula:

wherein z is 0 or 1; each R is independently an alkyl or substituted alkyl radical; each m and n is independently 0, 1 or 2, provided at least one of m or n is 1; each M is independently hydrogen, an alkali metal, alkaline earth metal 9 or ammonium and each x and y is individually 0 or 1 with the proviso that at least one of x or y is 1.

3. The method of Claim 2 wherein z is l, the R group(s) are independently hydrogen or a linear or branched alkyl group having from 4 to 24 carbon atoms and each M is independently hydrogen or an alkali metal.

4. The method of Claim 2 wherein z is 1, the R group(s) are independently hydrogen or a linear or branched alkyl group having from 4 to 24 carbon atoms and M+ represents an ammonium ion radical of the formula (R')3HN+ wherein each R' is independently hydrogen, a C1-C4 alkyl or a C1-C4 hydroxyalkyl radical.

5. The method of Claim 4 wherein the C1-C4 alkyl and hydroxyalkyl radicals include methyl, ethyly, propyl, isopropyl, butyl, hydroxymethyl and 35,039-F -25-26- .

hydroxyethyl and the ammonium ion radicals is ammonium (N+H4), methylammonium (CH3N+H3), ethylammonium (C2H5N+H3), dimethylammonium ((CH3)2N+H2), methylethylammonium (CH3N+H2C2H5), trimethylammonium ((CH3)3N+H), dimethylbutylammonium ((CH3)2N+HC4H9), hydroxyethylammonium (HOCH2CH2N+H3) and methylhydroxyethylammonium (CH3N+H2CH2CH20H).

6. An improved gas flooding operation for recovering hydrocarbon from a subterranean formation, the recovery method comprising sequentially injecting, through an injection well, a drive fluid of a gas or a gas/liquid mixture to drive the hydrocarbon from the formation to a producing well and a mobility control fluid of a surfactant/aqueous fluid mixture into the subterranean formation, the improvement in said method comprising using a mobility control fluid containing a two component surfactant mixture with one component of the surfactant mixture being an alkylated diphenyl sulfonate or mixture of alkylated diphenyl sulfonates and the second component of the surfactant mixture being an anionic polyoxyalkylated surfactant or mixture of anionic polyoxyalkylated surfactants.

7. The improved method of Claim 6 wherein the two component surfactant mixture in the mobility control fluid consists essentially of an alkylated diphenyl sulfonate or mixture of alkylated diphenyl sulfonates, each represented by the general structural formula:

35,039-F -26- wherein 2 is 0 or 1; each R is independently an alkyl or substituted alkyl radical; each m and n is independently 0, 1 or 2, provided at least one of m or n is 1; each M is independently hydrogen, an alkali metal, alkaline earth metal, or ammonium and each x and y is individually 0 or 1 with the proviso that at least one of x or y is 1; and an anionic polyoxyalkylated sulfate or mixture of polyoxyalkylated sulfates of the general structural formula:
R"O[(CH2)dO]eA
wherein R" is a hydrocarbon or halogen substituted hydrocarbon radical containing from about 4 to about 24 carbon atoms; d is from about 2 to about 6, e is at least l, and A is an anionic group.

8. The method of Claim 7 wherein the n group(s) are independently a linear or branched alkyl group having from 4 to 24 carbon atoms, provided at least one R group is an alkyl group and each M is hydrogen or an alkali metal and R" is a hydrocarbon or halogen substituted hydrocarbon radical containing from about 6 to about 18 carbon atoms, d is from about 2 to 35,039-F -27-about 6, e is from about 2 to about 20 and A is a sulfate.

9. The method of Claim a wherein R" is an alkyl group having from 6 to 18 carbon atoms and -A is a sulfate group as represented by the formula:
-S04-M+
wherein M is an alkali metal or NH4.

10. The method of Ciaim 9 wherein R" is an alkyl group having from 6 to 14 carbon atoms and M+ is sodium or NH4.

11. The method of Claim 10 wherein R" is a C6-14 alkyl, d is 2, e is from 2 to 12 and _A is _SO4-Na+ .

12. The method of Claim 7 wherein the R
group(s) are independently a linear or branched alkyl group having from 4 to 24 carbon atoms, and M+
represents an ammonium ion radical of the formula (R')3HN+ wherein each R' is independently hydrogen, a C1-C4 alkyl or a C1-C4 hydroxyalkyl radical and R" is a hydrocarbon or halogen substituted hydrocarbon radical containing from 6 to 18 carbon atoms, d is from 2 to 6, e is from 2 to 20 and A is a sulfate.

13. The method of Claim 12 wherein the C1-C4 alkyl and hydroxyalkyl radicals include methyl, ethyl, propyl, isopropyl, butyl, hydroxymethyl and hydroxyethyl and the ammonium ion radical is ammonium (N+H4), methylammonium (CH3N+H3), ethylammonium (C2H5N+H3), dimethylammonium ((CH3)2N+H2), methylethylammonium (CH3N+H2C2H5), trimethylammonium 35,039-F -28-((CH3)3N+H), dimethylbutylammonium ((CH3)2N+HC4Hg), hydroxyethylammonium (HOCH2CH2N+H3) and methylhydroxyethylammonium (CH3N+H2CH2CH2OH).

14. The method of Claim 6 wherein the mobility control fluid comprises from 25 to 75 weight percent of the alkylated diphenyl sulfonate surfactant or mixture of alkylated diphenyl sulfonate surfactants and from 75 to 25 weight percent of the anionic polyoxyalkylated surfactant or mixture of anionic polyoxyalkylated surfactants, based on the total weight of the two component surfactant mixture.

15. The method of Claim 6 wherein the gas employed as the drive fluid is air, nitrogen, carbon dioxide, a normally gaseous paraffinic hydrocarbons, crude gases, natural gas, liquefied petroleum gas, a normally gaseous olefinic hydrocarbons or mixture thereof.

16. The method of Claim 14 wherein the gas is carbon dioxide or a paraffinic or olefinic hydrocarbon.

35,039-F -29-