GAS FLOODING PROCESS FOR THE RECOVERY OF OIL FROM SUBTERRANEAN FORMATIONS

PROCEDE DE CHASSE AU GAZ POUR L'EXTRACTION DU PETROLE D'UN GISEMENT

English 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.

Claims

-24-
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:
-24-

-25-
<IMG>
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-

-27-
<IMG>
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-

-28-
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-

-29-
((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-

Description

7~
--1--
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-

--2
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
--8--
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
-10
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~
1 1 -
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
-14-
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-
.:

-16-
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~
-21
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~
-22-
~A~L~ II
Equilibrium Foa~ Hal~ e,
. seconds
5ExampLe Surfactantl
Without Oil With Oil
4 NaC12DPO/CD128 93 49 ._
S NaC16DPO/CD128 172 23
D CD128 64 4
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-