Note: Descriptions are shown in the official language in which they were submitted.
L7~35~
K 9625
STEAM FO~M PROCESS
The invention relates to a steam foam process for producing
oil from, or displacing oil wlthin, a subterranean reservoir.
In certain respects, ~his invention is an improvement in the
steam-channel-expanding steam foam drive process described in
U.S.A. patent specifica~ion 4,086,964 (inventors: R.E. Dilgren,
G.J. Hlrasaki, H.J. Hill, D.G. Whitten; filed 27th May, 1977;
published 2nd May, 1978).
The inventlon is particularly useful in an oll producing
process of the type described in the above patent speciflcation.
In this process steam is injected lnto, and fluid is produced
from, horizontally spaced locations within a portion of an oil
reservolr in which the disposition of a steam flow path is de-
termined by gravity and/or oil distribution. After a steam
channel has been formed the composition of the fluid being
lS injected ls changed fro~ steam to a steam-foam-forming mix~ure.
The composition of the mixture is correlated with the properties
of the rocks and the fluids in the reservoir so that the pressure
required to inject the mixture and to move it through the steam
channel exceeds that required for s~eam alone but is less than
the reservoir fracturing pressure. The composition and rate of
in~ecting the mixture i8 ~ubsequently adjusted to the extent
required to maintain a flow of steam foam within the channel at a
relatively high pressure gradient at which the oil-displacing and
channel-e~panding effects are significantly greater than those
provided by the steam alone. Oil is recovered from the fluid
produced from the reservoir.
The present invention also relates to an improvement in an
oil recovery process in which steam is cyclically in~ected into
and fluid i9 backflowed from a heavy oil reservoir which is
s~
- 2 -
susceptible eo a gravity override that causes an oil layer to
become adjacent to a gas or vapour-containing substantially
oil-desaturated zone in which there is an undesirable intake and
retention of the injected fluid within the desaturated zone. In
such a process, the steam to be injected is premixed with
surfactant components arranged to form a steam foam within the
reservoir having physical and chemical properties such that it
(a) is capable of being injected into the reservoir without
plugging a~y portion of the reservoir at a pressure which exceeds
thae required for injecting steam but is less than ehe reservoir
fracturing pressure and (b) is chemically weakened by cantact
with the reservoir oil so that it is more ~obile in sand
containing that oil ~han in sand which is substantially free of
that oil. The surfactant-containing steam is injected into the
reservoir at a rate slow enough to be conducive to displacing a
front of the stea~ foam along the oil-containing edge portions
of the oil-desaturated zone than along the cantral portion of
~hat ~one. And, fluid is backflowed from the reservoir at a time
at which part or all of the steam is condensed withln the steam
foam in the reservoir.
As used herein the following terms have the following
meanings: "steam oam" refers to a foam i.e. gas-liquid dis-
persion which (a) is capable of both reducing the effective
mobility, or ease with which such a foam or dispersion will flow
wiehin a permeable porou~ medium and ~b) has steam in the gas
phase thereof. "~obility'l or "permeability" refers to an effective
mobility or eas~ of flow of a foam within a per~eable porous
medium. ~ "permeability reduction" or "mobility reduction" refers
to reducing t~.e ease of such a foam flow due to an increase in
the effective viscosity of the fluid and/or a decrease-in the
effective permeability of the porous medium. A reduction ln such
a mobility or permeability can be detected and/or determined by
measuring dlfferences ln internal pressures within a colu~n of
permeable porous material during a R~eady state flow of fluid
through a column of such material. "Steam quality" as used
~ ~4~5C3
-3- Z32g3-~97
regar~ing any steam-containiny fluid re~ers to the weight percent
of the water in that fluid which is in the vapour phase of the
fluid at the boiling temperature of that water at the pressure of
the fluid. For example: in a monocomponent steam-containing fluid
which consists entirely of water and has a steam quality of 50%,
one-half of the weight of the water iæ in the vapour phase; and,
in a multicomponent steam-containing fluid which contains nitrogen
in the vapour phase and dissolved or dispersed surfactant and
electrolyte in the liquid phase and has a steam quality of 50~,
one-half the weight of the weight of the water in the multi-
component steam-containing fluid is in the vapour phaæe. Thus,
the steam quality of a steam-containing fluid can be calculated
as, for example, 100 times the mass (or mass flow rate~ of the
water vapour in that fluid divided by the sum of the mass (or mass
flow rate) of both the water vapour and the liquid water in that
fluid. "Steam-foam-formin~ mixture" tor composition~ refers to a
mixture of steam and a~uaous liquid solution (or dispersion) of
surfactant, with some or all, of the steam being present in the
gas phase of a steam foam. The gas phase may include non-
condensable gas~es) such as nitroqen.
The invention provides a process for displacing oilwithin an oil-containing subterranean reservoir by flowing a
steam-containing fluid in con~unction with a surfactant component
through a relatively steam permeable zone within said reservoir
characterized in that a sur$actant component is employed which
comprises in substantial par~ at least one sulphonate of the
formula RS03X in which R is alkylaryl including benzene~ toluene or
,'~'`;l. :1
71~50
-3a- 63293-2497
xylene having atached thereto a linear alkyl group containlng 18-
30 carbon a~oms in the alkyl chain and X ls sodium, potassium,
lithium or ammonium.
The alkylaryl sulphonate-containing steam-foam-formlng
mixture suitably includes an aqueous solution of electrolyte and
advantageously further also includes a substantially
noncondensable gast with each of the surfatant, electrolyte and
yas components being present in proportions effective for s~eam-
foam-
7~5~
-- 4
formation in the presence of the reservoir oil. The inventionalso relates to the alkylaryl sulphonate-containing steam-foam-
forming mixtures which are described herein.
The invention is useful where it is desirable to remove oil
from, or displace oil within, a subterranean :reservoir. ~or
exa~ple, the invention can be used to move oil or an emulsion of
oil and water away from a well borehole in a ~ell cleanlng type
of operation, and/or to displace oil into a producing location in
an oll-reco~ery operation.
In particular, the present inventlon relaees to a process
for recovering oil from a subterranean reservoir, comprising:
in~ecting steam and producing fluid at horizontally spaced
location~ within a portion of an oil reservoir in which the
disposition of a steam flow path is determined by the effect of
gra~ity and/or oil distribution, rather than being substantially
confined within at least the one most permeable layer of reservoir
rocks;
advantageously maintaining rates of steam in~ecting and
fluid productlon such that a steam channel has been extended from
the injection location;
changing the composition of the fluid being in~ected from
steam tD a steam-foam-forming mixture including steam and an
aqueous, electrolyte-containing solution or dispersion of an
alkylaryl sulphonate-containing sur~actant, whilst continuing to
produce fluid from the reservoir;
correlating the composition of the steam-foam-forming
mixture wlth the properties of the rocks and fluids in the
reservoir s~ that the p~essure required to inject the mixture
and the foam it forms or comprises into and through the steam
channel exceeds that required for steam alone but is less than
the reservoir fracturing pressure; and
ad~usting the co~position cf the fluid being injected into
the steam channel to the extent required to maintain a flow of
bo~h steam and foam within the channel in response to a relative-
ly hlgh pressuré gratlent at which the oil-dlsplacing and channel-
5~
-- 5 --
expanding effects are signif~cantly greater than those providedby steam alone, without plugging the channel.
The inventlon also relates to an oil recovery process in
which steam is cyclically in~ected into and fluid is backflowed
from a subterranean heavy oil reservoir which is susceptible to
gravity override and tends to intake and retain undesirably large
proport$ons of the in~ec~ed fluid. This process comprise9: tl)
ln~ecting steam mixed ~ith a linear C10-C30-alkylaryl sulphonate-
contalning steam-foam-forming compound which is arranged for
forming a steam foam whieh (a) can be displace~ through the pores
of the reservoir, witho~t plugging any portion of the reservoir,
in response to a pressure ~hlch exceeds that required for dis-
placing steam through the reservoir but is less than the fractur-
ing pressure of the reservoir, and (b) can be weakened by contact
with the reservoir oil to an extent such that the weakened foam
is significantly more mobile ~n reservoir oil-containing pores of
a porous medium than in oil-free pores of that med~um; (2)
in~ecting the steam-foam-for~ing mixture at a rate equivalene to
one whlch is slow enough to cause th~ foam formed by that mixture
to advance more rapidly through the pores of a reservoir o~l-
containing permeable medium than through the pores of a substant-
ially oil-free permeable medium; ant
(3) backflowing fluid from the reservoir after a steam soak time
sufficient to condense part or all of the steam in the injected
steam-foam-forming mixture. The steam foam-forming mixture
preferably comprises steam, a noncondensable gas, a linear
C18-C30-alkylaryl sulphonate surfactant and an electrolyte.
The invention provides unobvious and beneficial advantages
in oil displacement procedures by the use of the alkylaryl
sulphonate surfactant in the steam-foam-forming compositions.
For example, where a steam-foam forming mixture contains such a
surfactant and an electrolyte in proportions near optimum for
foa~ formation, the present surfactant components provide ex-
ceptionally strong steam foams havlng mobilities many times less
than those of steam foams using other surfactants. In addition,
5~
significant reductions are reached in the mobilities of the steam
foams at concentrations which are much less than those required
for equal mobility reduc~ions by the surfactants which were
previously considered to be the best available for such a purpose.
The use of the present alXylaryl sulphonate surfactant components
involves no problems with respect to thermal and hydrolytic
stability. No chemical or physical deterioration has been detect-
able in the present alkylaryl sulphonate surfactants that were
recovered along with the fluids produced during product~ons of
oil from subterranean reservoirs. In each of ~:hose t-~pes of
sulphonate surfactants the sulphur ato~s of the sulphonate groups
are bonded directly to carbon atoms. The surfactants which were
recovered and tested during the production of oil had travelled
through the reservoirs at steam temperatures for ~ignificant
eimes and distances.
The present C18-C30-alkylaryl sulphonate-containing steam
foams have been found to represent a substantial i~provement in
mobility reduction over foams based on the C12-C15-alkylaryl
sulphonates e.g., dodecylbenzene sulphonates. The foams to be
used according to the present invention represent also sub-
stantial improvement over the C16-C1O alpha-olefinsulphonate-
containing foams.
The present invention further relates to compositions
; containing at lea~t one C18-C30-alkylaryl sulphonate, and steam,
optionally electrolyte, and optionally noncondensable gas, that
are suitable for use in oil-displacing and/or producing processes.
Of particular interest in this respect are steam-foam-forming
compoRitions consi~ting essentially of (a) water, which is
pre~nt in the composition, at a temperature substantially
equalling its boillng temperature, at the pressure of the com-
position, in both a llquid phase and a vapour phase; (b) a sur-
factant component present in the liquid phase of the co~position
in an amount between 0.01 and 10 percent by weight, calculated
on the weight of the liquid phase, said surfactant component
comprising in substantial part at lea~t one C18-C30-alkylaryl
~ 7 -
sulphonat2; (c) an electrolyte present in the liquid phase of the
composition in an amount between 0,001 percent by weight (calcu~
lated on the weight of the liquid phase) and an amount tending to
partition the surfactant into a separate liquid phase; and (d) a
noncondensable gas present in the vapour phase in an amount
between about 0.0001 and 0O3 percent by mol, calculated on total
mol~ in the vapour phase.
Illustrative of the alkylaryl sulphonate ~urfacta~ts suitably
employed in steam-foam drive processes of e~ha~ced performance,
according to the invention, are the alkylaryl sulphona~es obtained
by reaceing a linear C18~C30-alkylbenzene linear C18-C3~-alkyl-
toluene and/or C18-C30-alkylxylene with sulphurtrioxide followed
by neutralizatlon of the sulphonic acid. Particularly suitable
for purposes of the invention is a sulphonate derived from
substa~tially linear C18-C30-alkyltoluene.
Different reservoir materials have different debilitating
effects on the serength of a steam foam. Tests should there-
fore be carriet oue to determine the sulphonates or sulphonate-
containing steam-foam-forming composi~ions that perfor~ optimally
in a given reservoir. This is preferably done by testing the
influence of specific sulphonates on the mobility of a steam-
containing fluid having the steam quality selected for use in the
reservoir in the presence of the reservoir ma~erial.
Such tests are preferably conducted by flowing steam-contain-
ing fluids through a sand pack. The permeability of the sand packand foam-debilitating properties of the oil in the ~and pack
should be at least substantially equivalent to those of the
reservoir eo be ~reated. Comparisons are made of ~he mobility of
the steam-containing fluid with and without the surfactant
component. The mobility is indica~ed by the substantially steady-
state pressure drop between a palr of points located between the
inlet and ou~let portions of the sand pack in positlons which are
substantlally free of end effects on the pressures.
Some laboraeory tests to determine steam mobility will now
be described with reference to Figures 1 and 2.
~4~ 5iO
-- 8 --
Figure l shows schematically a sand pack test apparatus
which can be made of currently available apparatus components.
Th~ apparatus consists of a cylindrical tube l that is 400 mm
long and has a cross-sectional area of 8 cm2. Such a tube is
preferably arranged for a horizontal flow of fluid from an inlet
2 to an outlet 3. The tube is preferably provided ~ith 5 pressure
~aps 49 5, 6, 7 and 8. The locatlon of the first pressure tap 4
is at a distance of 150 mm from the inlet 2. The locations of the
other taps are chosen 50 as to divide the part of the tube 1
sltuated behind tap 4 into equal parts of 50 mm. The tube 1
contains a permeable and porou~ column of suitable material, such
as a sand pack, which is capable of providing an adequately
realistic laboratory model of a subterranean reservoir.
At the inlet end 2, the sand pack or equivalent column of
permeable m~ter~al is arranged to recelve separate streams of
steam, noncondensable gas such as nitrogen, and one or more
aqueous llquid solutions or dispersions containing a surfactant
to be tested and/or a dissolved or dispersed electrolyte. So~e or
all of those components are in~ected at constant mass flow rates
proportioned so that steam of a selected quality, or a selected
seeam-cOntaining fluid or composition, or a steam-foam-forming
mlxture of a selected steam quality can be injected and will be
substantially homogeneous substantially as soon as it enters the
face of the sand pack.
In the tes~s9 steam-foam-forming mixtures are compared with
and without surfactant components added thereto, by measurlng
pressure gradients formed within a sand pack during flows through
the pack at the same substantially constant mass flow rate.
Numerous te~ts have been made of different steam-foam-
for~ing mixture~ using sand pa ks composed of a reservoir sand
and havlng a high permeability, such as lO darcys. The pressures
were measured wieh pressure detectors (not shown) (such as piezo-
electric devices) installed at the ~nlet 2 and at the taps 4, 5,
6, 7 and 8 of the tube 1. rhe results of such te~ts have proven
to be generally comparable with the results obtained in the fleld.
71~Q
g
In the laboratory tests, the steam-foam-forming components
were in~ected at constant mass rates until substantially steady-
state pressures were obtained at the inlet and at ehe taps. The
ratio between the steady-state pressures at the taps during flow
of steam mixed with the foam-forming surfactant component and the
steady-state pressure at the taps during flow of the steam by
itself are indicative for the mobility reduction. The higher this
ratio, the stronger the steam foam and the higher the mobility
reduction caused by the steam-foam-forming mix~ure.
Figure 2 illustrates the results of co~parative tests with
steam and various steam-foam-forming mixtures in sand pack~
containing Oude Pekela Reservoir sand having a permeability of
8 darcys. The backpressure was 21 bar, corresponding with a tem-
perature of 215 C. The steam in~ection rate was 600 cm3/min. The
lS figure shows the variation of the pressurP in bar (Y-axis) with
distance in centimetres (X-a~is) from the pack inlet 2. The
pressures were measured at the inlet 2, at the taps 4, 5, 6, 7
and 8, and at the outlet 3 of the pipe 1 of Figure 1. Curve A
relates to the displacement wherein a mixture of 90% quality
steam was used as a displacing composition.
Curve B relates to using a steam-contalning fluid having a
steam quality of 90~ and a water phase which contains 0.25% by
weight of a surfactant. In the Curv~ B test, the surfactant was a
branched side-chain C15-C18-alkyltoluene sodium sulphonate
available from Sun Refining Company under the trademark SUNTECH
IV-1015.
Curve C relates to using ~he mixture used for Curve B e~cept
that the surfactant was a linear side-chain C20-C24-alkyltoluene
sodium sulphonate.
The greatly Improved steam per~eability reduction performance
of the presently described C20-C24-al~ylaryl sulphonate-containing
surfactant component is clear from the Curve C as compared to the
Curves A and B in Figure 2.
S~
-- 10 --
Figure 3 illustrates the results of comparative tests with
steam and various steam-foam-forming mixtures in sand packs
containing Venezuelan Reservoir sand having a permeability of
10 darcys. The backpress~re was 21 bar, corresponding with a
temperature of 215 C. The injection rate was 900 cm3/min. The
figure shows the variation of the pressure in bar (Y-axis) wlth
dis~ance in centimetres (X-axis) from the pack inlet 2. The
pressures were measured at the inlet 2, at the taps ~, 5, 6, 7
and 8, and at the outlet 3 of the pipe 1 of Figure 1. Curve A
relates to the displacement wherein a mixture of 90% quality
steam was used as a displacing composition.
Curve B relates to using a steam-containing fluid having a
steam quality of 90% and a water phase which contains 1% by
weight sodium chloride and 0.25~ by weight of a surfactant. In
the Curve B test, the surfactant was a branched side-chain
C15-C18-alkyltoluene sodium sulphonate available from Sun
Refining Company under the trademark SUNTECH IV-1015.
Curve C rclates to using the mixture used for Curve B except
that the surfactant was a linear side-chain octadecylbenzene
sodium sulphonate.
In the tests represented by Curve D the formulation was the
same as those used in the tests represented by Curves B and C
except that the sulphonate component was linear side-chain
octadecyltoluene sulphonate.
The greatly improved steam permeability reduction
performance of the presently described C18-alkylaryl
sulphonate-containing surfactant component is clear from the
Curves C and D as compared to the Curves A and B in Figure 3.
Com ositions and rocedures suitable for use in the resent
P P P
invention
For purposes of the present invention, the surfactant
component of the ste~-foam-forming mixture is necessarily
comprised in substantial part of linear C18-C30-alkylaryl
sulphonate. Materials of this class but with a much shorter alkyl
chain have heretofore found commercial utility, for example, in
~ ~z9;~5~
detergent formulations for industrial, household and personal
care application.
A class of alkylaryl sulphonates very suitable for use in
the present invention is that derived from a particular class of
olefins, which may be defined for present purposes in terms of
the configuration and number of carbon atoms in their molecular
structure. These olefins have a carbon number of 18.
In terms of molecular structure, these olefins are aliphatic
and linear. Either alpha- or internal olefins are considered
suitable for the alky~ation route chosen to produce the products
to be used according to the invention. For purposes of derivation
of the alkylaryl sulphonates for use ln the process according to
the invention, olefins are advantageously applied in which at
least 90% of the molecules are alpha-olefins.
Particularly attractive are sulphonates derived from the
~eodene alpha-olefins (trademark) sold by Shell Chemical Company,
in part for their llnear structure and high alpha-olefin con~ent,
i.e., greater than 95% in each case. The Neodene alpha-olefins
are prepared by ethylene oligomerization. Products having a high
content of internal C18-C30 olefins are also commercially
manufactured, for instance, by the chlorination-dehydro-
chlorination of paraffins or by paraffin dehydrogenation, and can
also be prepared by isomerization of alpha-olefins. Internal-
olefin-rich products are manufactured and sold, for example, by
Shell Chemical ~ompany.
For preparation of alkylaryl sulphonates, the olefins as
described above are subjected to reaction with benzene, toluene
or xylene. ~eaction conditions and catalyst type are chosen in
such a way that preferably para alkyltoluene is for~ed. The
alkylbenzene, alkylxylene or alkyltoluene isomers are reacted
with sulphur trioxide. The term "sulphur trioxide" as used in the
present specification and claims is intended to include any
compounds or complexes which contain or yield S03 for a sul-
phonation reaction as well as S03 per se. This reaction may be
conducted according to methods well kno~n in the chemical arts,
785~
- 12 -
typically by contact of a flow of dilute S03 vapour with a thin
film of liquid alkylate at a temperature in the range of about 5
to 50C~ The r~activn between the S03 and the alkylate yields a
sulphonic acid which is neutralized by reaction with a base,
preferably an alkali metal hydroxide, oxide, or carbonate.
The specific composition of alkylaryl sulphonates prepared
as described above (and also, for instance, the methods used for
sulphonation, hydrolysis, and neutralization of the specified
olefins) have not been found to be a critical factor to the
performance of the surfactant in the steam foam process according
to this invention. In this regard, it is observed that factors
which have conventionally governed the choice of sulphonation
conditions, e.g., product colour, clarity, odour, etc., do not
carry the same weight in the preparation of alkylaryl sulphonates
for purposes of use in the process according to the invention
that they have been accorded in detergent manufacture.
Consequently, reactlon condltions outside of those heretofore
considered desirable for alkylate sulphonation are still suitably
applied in the preparation of surfactant components suitable for
use in the steam-foam-forming mixture.
For purposes related to maintaining product stability,
conventional manufacture typically yields a dilute solution or
dispersion of the alkylaryl sulphonates, f or instance, products
with a 15-30 %wt active matter content in water. Such products
may be directly applied to the preparation of steam-foam-forming
mixtures for purposes of this invention.
Suitable alkylaryl sulphonates, generally prepared by
methods such as described above, are themselves commerclally
available products.
The strength of the foam formed by the steam-foam-forming
composition including alkylaryl sulphonate tends to increase with
increases in the proportion of the surfactant andlor electrclyte
components of the composition. Also, there tends to be an optimum
ratio of surfactant and electrolyte components at which the
surface activity of the composition is maximized.
S~
13 -
The steam-foam-forming composition according to the present
invention can form a steam-foam capable of reducing the effective
mobility of the steam to less than about l/lOth and even to
1/50th-1/llOth of the mobility it would have within a permeable
porous medium in the absence of the surfactant.
The steam used in the present process and/or compositions
can be generated and supplied in the form of substantially any
dry, wet, superheated, or low grade steam in which the steam
condensate and/or liquid components are compatible with, and do
not inhibit, the foam-forming properties of the foam-forming
components of a steam-foam-forming mixture according to the
present invention. The steam quality of the steam as generated
and/or amount of aqueous liquid with which it is mixed be such
that the steam quality of the resulting mixture is preferably
from 10 to 90%. The desired steam-foam is advantageously prepared
by mixing the steam with aqueous solutionts) of the sur~actant
component and optionally, an electrolyte. The water content of
these aqueous solutions must, of course, be taken ineo account in
determining the steam quality of the mixture being formed.
Su~tably, the noncondensable gas advantageously used in a
steam-foam-forming mixture according to the present invention can
comprise substantially any gas which (a) undergoes little or no
condensation at the temperatures ~100-350 C) and pressures
(1-100 bar) at which the steam-foam-forming mixture is preferably
in~ected into and displaced through the reservoir to be treated
and (b) i9 substantially inert to and compatible with the foam-
forming surfactant and other components of that mixture. Such a
gas is preferably ni~rogen but can comprise other substantially
inert gases, such as air, ethane, methane, flue gas, fuel gas, or
the like. Suitable concentrations of noncondensable gas in the
steam-foam mixture fall in the range of from 0.0001 to 0.3 mole
percent such as 0.001 and 0.2 mole percent, or between 0.003 and
0.1 mole percent of the gas phase of the mixture.
Suitably, the electrolyte used should have a composition
similar to and should be used in a proportion similar to those
29~7135~
described as suitable alkali metal salt electrolytes in the
above-mentioned USA patent speciflcatlon 4,086,964. An aqueous
solution may be applied that contains an amount of electrolyte
substantially equivalent in salting-out effect eo a sodium
chloride concentration of from 0.001 to 10% (but less than enough
to cause significant salting out) of the liquid-phase of the
steam. Some or all of the electrolyte can comprise an inorganic
salt, such as an alkali metal salt, an alkali metal halide, and
sodium chloride. Other inorganic salts, for example, halides,
sulphonates, carbonates, nitrates and phosphates, in the form of
salts of alkaline earth metals, can be used.
Generally stated, an electrolyte concentration may b~
applied which has approximately the same effect on mobility
reduction of the foam as does a sodium chloride concentration of
between 0.001 and 5 percent by weight (but less than a salting
out-inducing proportion) of the llquid phase of the steam-foam-
forming mixture. The electrolyte concentration may be between
0.001 and 10 percent calculated on the same basis.
In compounding a steam-foam-forming mixture or composition
in accordance with the present invention, the steam can be
generated by means of substantially any of the commercially
available devices and techniques for steam generation. A stream
of the steam being injected into a reservoir is preferably
generated and mixed~ in substantially any surface or downhole
location, with selected proportions of substantially noncondens-
able gas, aqueous electrolyte solution, and foam-forming sur-
factant. For exampleJ in such a mixture, the quality of the steam
which is generated and the cor.centration of the electrolyte and
surfactant-containing aqueous liquid with which it is mixed are
preferably arranged so that (1) the proportion of àqueous liquid
mixad with the dry steam which is injected into the reservoir is
sufficient to provide a steam-containing fluid having a steam
quality of from 10-90% (prsferably from 30-~0%); ~2) the weight
proportion of surfactant dissolved or dispersed in the aqueous
liquid is from 0.01 to 10.0 (preferably from 1.0 to 4.0); and (3)
3L.rl~ 9L'7 ~
the amount of noncondensable gas is from 0.0003 to 0.3 ~ole
fraction of ~he gas phase of the mixture.
