Note: Descriptions are shown in the official language in which they were submitted.
K 9631
STEAM FOAM PE~OCESS
The invention rela~es eo a steam foam process for producing
oil from, or displacing oil within, a subterranean reservoir.
In this process steam is in~ected into, and fluid ls produced
from, horizontally spaced locations within a portion of an oil
reservoir in which the disposition of a steam flow path i6 de-
termined by gravity and/or oil distribution. After a steam channel
has been formed the composition of the fluid being injected is
changed from seeam to a steam-foam-forming mixturs by addition of
surfactant components. The composition of the mixture is
correlated with the properties oE the rocks and the fluids in the
reservoir so that the pressure required to in~ect the mlxture and
to move it through the steam channel exceeds that required for
steam alone but is less than the reservoir fracturing pressureO
The composition and rate of in~ecting the mixture is subsequently
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-expanding 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 i8 backflowed from a heavy oil reservoir which is
susceptible to a gravity overrlde that causes an oil layer to
become ad~acent to a gas or vapour-containing sub~tantially
oil-de6aturated zone in which there is an undesirable intake and
retention oE the inJected fluid within the desaturated zone. In
such a process, the fluid being in~ected is changed from steam to
a steam-foam-forming mixture by addition of surfactant components
arranged to form a steam foam within the reservolr having physical
and chemical properties such that it (a) is capable of being
iDJected into the reservoir without plugging any portion of the
reservoir at a pressure whlch exceeds that required for in~ecting
steam but ls less than the reservolr fracturing pressure and (b)
is chemieally weakened by contact with the reservoir oil so that
i~ i6 more mobile ln sand containing that oil than in sand which
is substantially free of that oil. The surfactant-conta:lnlng steam
is in~ected into che reservoir at a rate 810w enough to be
conducive to displacing a front of the steam foam along the
oil-containing edge portions of the oil-desaturated zons than
along the central portion of that zone. And, fluid is backflo~ed
from the reservoir at a time at which part or all of the steam is
condensed within the steam foam in the reservoir.
As used herein the following terms have the following
meanings: "steam foam" refers to a foam i.e. gas-liquid dlspersion
which (a) is capable of both reducing the effective mobility, or
ease with which such a foam or dispersion will flow within a
permeable porous medium and (b) has steam in the gas phase
thereof. "Mobility" or "permeability" refers to an effective
mobility or ease of flow of a foam within a permeable porous
medium. A "permeability reductionl' or "mobility reduction" refers
to reducing the ease of such a foam flow due to an increase in the
effective viscosity of the fluid and/or a decrease in the effec
tive permeability of the porous medium. A reduction in ~uch a
mobility or permeability can be detected and/or determined by
measuring differences in internal pressures within a column of
~5 permeable porous material during a steady state flow of fluid
through a column of such material. "Steam quality" as used re-
garding any steam-containing fluid refers to the weight percent of
the water in that Eluid which is in the vapour phase of the fluid
at the boiling temperature of that water ae the pressure of the
fluid. For example: in a monocomponent steam-containing fluid
which consists entirely of water and has a steam quulity of 50~,
one-half of the weight of the water is in the vapour phase; and,
ln 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~,
~3~
one-half the welght of the weight of the water in the multi-
component steam-containing fluid ls ln the vapour phase. Thus, the
steam quality of a steam-containing fluid can be calculated as,
for example, 100 times ~he m~ss (or mass flow rate) of the wAter
vapour in that fluid div-lded by the sum of the mass (or mass Elow
rate) of both the water vapour and the liquid water in ~hat fluid.
"Steam-foam-forming mixture" (or composition) refers to a mixture
of steam and aqueous 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 ~nclude non-
condensable gas(es) such as nitrogen.
Object of the invention is an improved process for displacing
oil within 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.
According to the invention the surfactant component comprises
in substantial part at least one sulphonate of the formula RS03X
in which R is di-alkylaryl including aryl is phenyl, toluyl or
xylyl having attached thereto two linear alkyl groups with equal
or different chain length, but each containing 11-20 carbon atoms
in the alkyl chain and X is sodium, potassium, lithium or
ammonium. Such ~ulphonates will be further on denoted as
Cll-C20-dialkylarenesulphonates.
The di-alkylarenesulphonate-containing steam-foam-forming
mixture suitably includes an aqueous solution of electrolyte and
advantageously further also includes a substantially noncondens-
able gas, with each of the surfactant, electrolyte and gas com-
ponents being present in proportions effective for steam-foam-
formation in the presence of the reservoir oil. The invention also
relates to the di-alkylarenesulphonate-contalning steam-foam-
forming mi~tures which are described herein.
The invention is uaeful where it is desirable to remove oil
from, or displace oil within, a subterranean reservoir. For
example, the invention can be used to move oil or an emulsion of
oil and water away from a well borehole in a well-cleaning type of
-- 4 --
operation, and/or to dlsplace oil into a producing location in an
oil-recovery operation.
In particular, the present invention re]ates to a process for
recoverlng oil from a subterranean reservoir, comprising:
injecting steam and producing fluid at horizontally spaced
locations withln a portion of an oil reservoir in which the
disposition of a seeam flow path is determined by the effect o~
gravity and/or oil distribution, rather than b~ing substantially
confined wi~hin at least the one most permeable layer of reservoir
rocks;
advantageously malntaining raees of steam in;ecting and fluid
production such that a steam channel has been extended from the
injection location;
changing the composition of the fluid being injected from
steam to a steam-foam-forming mixture by addition of a linear
Cll-C20-di-alkylarenesulphonate-containing compound, whilst
continuing to produce fluid from the reservoir;
correlating the composition of the steam-foam-formlng mixture
with the properties of the rocks and fluids in the reservoir so
that the pressure required to in~ect 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 composition of the fluid being in~ected into
the steam channel to the extent required to maintain a flow of
both steam and foam within the channel in response to a relatively
high pressure gradlent at which the oil displacing and channel
expanding effects are slgnificantly greater ehan those provided by
steam alone, without plugging the channel.
The inventlon al~o relates to an oil recovery process in
which steam is cyclically in~ected into and fluid is backflowed
from a subterranean heavy oil reservolr which is susceptible to
gravity override and tends to intake and retain undesirably large
proportions of the in~ected fluid. This process comprises:
~5~
in~ecting steam mixed with a linear Cll-C20-di-alkylarene-
sulphonate-containing steam-foam-forming compound which is
arranged for forming a steam foam which (a) can be displaced
through the pores of the reservoir, withoue plugging any port-lon
of the reservoir 9 in response to a pressure ~hich exceeds that
required for displacing steam through the reservo~r but i8 less
than the fracturing pressure of the reservoir, and (b) can be
weakened by contact wi~h the reservoir oil to an extent such that
the weakened foam is significantly more mobile in reservoir
oil-containing pores of a porous medium than in oil-free pores of
that medium;
injecting the steam-foam-forming mixture at a rate equivalent
to one which is slow enough to cause the foam formed by that
mixture to advance more rapidly through the pores of a reservoir
lS oil-containing permeable medium than through the pores of a
substantially oil-free permeable medium; and
backflowing fluid from the reservoir after a steam soak time
sufficient to condense part or all of the steam in the in~ected
steam-foam-forming mixture. The steam-foam-forming mixture preferably
comprises steam, a noncondensable gas, a linear Cll-C20-di-
alkylarenesulphonate surfactant and an electrolyte.
The invention provides unobvious and beneficial advantages in
oil displacement procedures by the use of the di-alkylarene-
sulphonate surfactant in the steam-foam-forming composi~ions. For
example, where a steam-foam-forming mixture contains such a
surfactant and an electrolyte in proportions near optimum for foam
formation, the present surfactant components provide exceptionally
strong steam foams having mobllities many times less than those of
steam foams using other surfactants. In nddition, significant
reductions are reached in the mobilities of the steam foams at
concentrations which are much less than those required for equal
mobility reductions by the 3urfactants which were previously
considered to be the befit available for such a purpose. The use of
the present di-alkylarenesulphonate surfactant components involves
no problems with respect to thermal and hydrolytic stability. ~o
~.2~
-- 6 --
chemlcal or physical deterioration has been detectable in the
presen~ alkylarenesulphonate surfactants that were recovered along
with the fluids produced during productions of oil from
subterranean reservoirs. In each of those types of sulphonate
surfac~ants the sulphur atoms 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
r~servoirs at steam tempera~ures for
significant times and distances.
The present Cl1-C20-di-alkylarenesulphonate-containing steam
foams have been found to represent a substantial improvement in
mobility reduction over foams based on the mono-alkylaryl
sulphonates e.g., dodecylbenzene sulphonates. The foams to be used
according to the present invention represent also substantial
improvement over the C16-C18 alpha-olefinsulphonate-containing
foams.
The present invention further relates to compositions con-
taining at least one C11-C20-di-alkylarenesulphonate, 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
compositions consisting essentially of (a~ water, which ls present
in the composition, at a temperatùre substantially equalling its
boiling temperature, at the pressure of the composi~ion, in both a
liquid phase and a vapour phase; (b) a surfactant component
present in the liquid phase of the composition in an amount
between O.a1 and 10 percent by ~eight, calculated on the weight of
the liquid phase, said surfactant component comprising in 8ub-
stantial part at least one C11-C20-dl-alkylarenesulphonate; (c) an
electrolyte present in the liquid phase of the composition in an
amount between 0.001 percent by welght (calculated on the weight
of the liquid phase) and an amount tending to partition the
surfactant into a aeparate liquid phase; and (d) a noncondensable
gas present in the vapour phase in an amount between about 0.0001
and 0.3 percent by mol, calculated on total mols in the vapour
phase.
Illustrative of the di-alkylarenesulphonate surfactant~
suitably employed in steam-foam drive processes of enhanced
performance, according to the invention, are the di-alkylarene-
sulphonates obtalned by reacting a linear Cll-C20-di-alkylbenzene
linear Cll-C20-di-alkyltoluene and/or linear Cll-C20-di-alkylxylene
with sulphur trioxide followed by neutralization of the sulphonic
acid. Particularly suitable for purposes oE the invention is a
sulphonate derived from substantially linear
10 Cll-C20-di-alkyl-benzene.
Different reservoir materials have different debilitating
effects on the strength of a steam foam. Tests should there-
fore be carried out to determine the sulphonates or sulphonate-
containing steam-foam-forming compositions that perform 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 material.
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 sand pack
should be at least substantially equivalent to those of the
reservoir to be treated. Comparisons are made oE the mobility of
the steam-containing fluid with and without the surfactant component.
The mobility is indicated by the substantially steady-state
pressure drop between a pair of points located between the inlet
and outlet portions of the sand pack in positions which are sub
staneially free of end effects on ehe pressures.
Some laboratory tests to determine steam mobility will now be
described with reference to Figures 1 and 2.
Figure 1 shows schematically a sand pack test apparatus which
can be made of currently avnilable apparatus components. The
apparatus consists of a cylindrical tube 1 that is ~00 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
3~
outlet 3. The tube is preferably provided with 5 pressure taps 4,
5, 6, 7 and 8. The location of the first pressure tap 4 is at a
distance of 150 ~m from the inlet 2. The locations of the other
taps are chosen so as to divide the part of the tube 1 situated
behind tap 4 into equal parts of 50 mm. The tube l contains a
permeable and porous column of sultable material, such as a sand
pack, which is capable of providing an adequately reallstic
laboratory model of a subterranean reservoir.
At the inlet end 2, the sand pack or equivalent column of
permeable material is arranged to receive separate s$reams of
steam, noncondensable gas such as nitrogen, and one or more
aqueous liquid solutions or dispersions containing a surfactant to
be tested and/or a dissolved or dispersed electrolyte. Some or all
of those components are in~ected at constant mass flow rates
proportioned so that steam of a selected quality, or a selected
steam-containing fluid or composition, or a steam-foam-forming
mixture 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 tests, steam-foam-forming mixtures are compared with
and without surfactant components added thereto, by measuring
pressure gradients formed within a sand pack during flows through
the pack at the same substantially constant mass flow rate.
Numerous tests have been made of different steam-foam-forming
mixtures using sand packs composed of a reservoir sand and having
a high permeability, such as 10 darcys. The pressures were measured
with pressure detectors (not shown) (such as piezoelectric devices)
installed at the inlet 2 and at the taps 4, 5, 6, 7 and 8 of the
tube 1. The results of such tests have proven to be generally
comparable with the results obtained in the field.
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 lnlet and at the 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, ~he stronger ehe steam foam and the higher the mobllity
reduction caused by the steam-foam forming mixture.
Figure 2 illustrates the results of comparaeive tests with
steam and various steam-foam-forming mixtures in sand packs
containing Oude Pekela Reservoir sand having a permeability of
7 darcys. The backpressure was 21 bar, corresponding with a tem-
perature of 215 C. The steam injection rate was 600 cm9/min,
having in the water phase containing 0.5 %w sodium
C8-C10-di-alkylbenzenesulphonate. The figure shows the ~ariation
of the pressure difference in bar (~-axis) with distance in
centimetres (X-axis) 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 85% quality steam, having in the
water phase containing 0.5 %w sodium C8-C10-di-alkylbenzene-
sulphonate, was used as a displacing composition.
Curve B relates to using a steam-containing fluid having a
steam quality of 85% and a water phase which contains 0.5% by
weight of a surfactant. In the Curve B test, the surfactant was a
linear sodium Cll-C12-di-alkylbenzenesulphonate.
Curve C relates to using the mixture used for Curve B except
that the surfactant was a linear sodium C13-Cl~-di-alkylbenzene-
sulphonate.
To all surfactant solutions 0.25 /Ow sodium Cl~ C16 a-olefin
sulphonste had been added ln order to merease the solubility of
the sodlum di-alkylbenzenesulphonates.
The greatly improved steam permeability reduction performance
of the presently described C11-C20-di-alkylarenesulphonate-
containing surfactant component i9 clear from the Curves B and C
as compared to the Curve A in Figure 2.
Composition6 and procedures suitable for use in the present
invention
For purposes of the present invention, the surfactant component
-- 10 --
of the steam-foam-forming mixture is necessarily comprised in
substantial part o linear Cll-C20-di-alkylarenesulphonate.
Mat~rials of this class but with a much shorter alkyl chain have
heretofore found commercial utility, for example, in detergent
formulations for industrial, household and personal care application.
A class of di-alkylarenesulphonates very suitable for use in
the present invention is that derived from a particular class of
olefins, which may be defined for present purposeR in terms of the
configuration and number of carbon atoms in their molecular
struceure. These olefins preferably have a carbon number of 13-14.
In terms of molecular structure, these olefins are aliphatic
and mainly linear. Either alpha- or internal olefins are
considered suitable for the alkylation route chosen to produce the
products to be used according to the invention. For purposes of
derivation of the di-alkylarenesulphonates for use in 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
SHOP alpha-olefins (trademark) sold by Shell Chemical UK, in part
for their linear structure and high alpha-olefin content, i.e ,
greater than 95% in each case. The SHOP alpha-olefins are prepared
by ethylene oligomerization. Products having a high content of
internal Cll-C20-olefins are also commercially manufactured, for
instance, by the chlorination-dehydrochlorination of paraffins or
by paraffin dehydrogenation, and can also be prepared by
isomerization of alpha-olefins. Internal~olefin-rich products are
mamlfactured and sold, for example, by Shell Chemical UK.
For preparation of di-alkylarenesulphonates, the olefins as
described above are subJected to reaction wlth benzene, toluene or
xylene. The di-allcylbenzene, di-alkyltoluene or di-alkylxylene
isomers are reacted with sulphur trioxide. The term "sulphur
trioxide" as used in the present specification and clalms is
intended to include any compounds or complexes which contain or
yLeld S03 for a sulphonatlon reaction as well as S03 per se. This
reaction may be conducted according to methods well known in the
chemical arts, typically by contact of a flow of dllute S03 vapour
with a thin film of liquid alkylate at a temperature in the range
of about 5 to 50~C. The reac~ion between the S03 and the alkylate
yields a sulphonlc acid which is neutralized by reaction with a
base, preferably an alkali metal hydroxide3 oxide, or carbonate.
The specific composition of di-alkylarenesulphonates prepared
as described above (and also, for instance, the ~ethods 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 in~ention. 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 di-alkylarene-
sulphonates for purposes of use in the process according to the
invention that they have been accorded in detergent manufacture.
Consequently, reaction conditions 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 di-allcylarenesulphonates, for instance, products
with a 15-30 Y~wt actlve matter content ln water. Such products may
be directly applied to the preparation of steam-foam forming
mixtures for purposes of this invention.
Suitable alkylarenesulphonates, generally prepared by methods
such as descrlbed above, are themselves commercially available
products.
The stren8th of the foam formed by the steam-foam-forming
composltion including dl-alkylarenesulphonate tends to increase
with increases in the proportion of the surfactant and/or
electrolyte 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.
The steam-foam-forming composition according to the present
~nvention can Eorm a seeam-foam capable of reducing the effective
mobility of the steam to less than about l/lOth and even to
1150th-1175th of the mobility it would have within a permeable
porous medi~m in the absence of t~e surfactant.
The steam used in the present process andlor compositions can
be generated and supplied in the form of substantially any dry,
wet9 superheated, or low grade steam in which the steam condensate
andjor liquid components are compa~ible with, and do not inhlbit9
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 andlor 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 solution(s) of the surfactant component and optionally, an
electrolyte. The water content of these aqueous solutions muse~ of
course, be taken into account in determining the steam quality of
the mixture being formed.
Suitably, 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 injected
into and displaced through the reservoir to be treated and (b) is
substantially inert to and compatible with the foam-forming
surfactant and other components of that mixture. Such a gas is
preferably nltrogen but can comprlse other substantlally lnert
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
~uch 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 proporeion similar to those
described as suitable alkali metal salt electrolytes in the
above-mentioned US~ patent speciflcation 4,086,964. An aqueous
solution may be applied that contain~s an amount of electrolyte
substantially equivalent in salting-out effect to a sodium chloride
concentration of from O.OOl 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, sush as an
alkali metal salt, an al~ali metal halide, and sodiutn 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 be applied
which has approximately the same effecs on mobility reduction of
the foam as does a sodium chloride concentration of between O.OOl
and 5 percent by weight (but less than a salting out-inducing
proportion) of the liquid phase of the steam-foam-forming mixture.
The electrolyte concentration may be between O.OOl 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 ln~ected lnto a reservoir is preferably generated and mixed,
in substantlally any surface or downhole location, with selected
proportions of substantially noncondensable gas, aqueous electrolyte
solution, and foam-formlng surfactant. For example, in such a
mixture, the quality of the steam which is generated and the
concentration of the electrolyte and surfactant-containing aqueous
liquid wlth which it is mlxed are preferably arranged so that (l)
the proportion of aqueous liquid mixed with the dry steam which i9
in~ected into the reservoir is sufficient to provide a steam-
containing fluid having a steam quality of from 10-90% (preferably
from 30-85~); (2) the weight proportion of surfactant dissolved or
dispersed in the aqueous liquid ls from O.Ol to lO.O (preferably
from 1.0 to 4.0); and (3) the amount of noncondensable gas is from
0.0003 to 0.3 mole fraction of the gas phase o the mixture.
