GB2164978A - Steam foam process - Google Patents

Abstract

A steam foam process for diverting steam within a subterranean reservoir and improving oil displacement is carried our by injecting into the reservoir a steam-foam-forming mixture comprising steam and a linear C18-C30-alkylaryl sulphonate surfactant, and preferably a non-condensable gas.

Description

SPECIFICATION Steam foam process The invention relates to a steam foam process for producing oil from, or displacing oil within, a subterranean reservoir.

In certain respects,this invention is an improvement in the steam-channel-expanding steam foam drive process described in U.S.A. patent specification 4,086,964 (inventors: R. E. Gilgren, G. J. Hirasaki, H. J.

Hill, D. G. Whitten; filed 27th May, 1977; published 2nd May, 1978).

The invention is particularly useful in an oil producing process ofthetype described in the above patent specification. In this process steam is injected into, and fluid is produced from, horizontally spaced locations within a portion of an oil reservoir in which the disposition of a steam flow path is determined by gravity and/or oil distribution. After a steam channel hasbeenformedthecompositionofthefluid being injected is changed from steam to a steam-foamforming mixture. The composition ofthe mixture is correlated with the properties ofthe 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 steam alone but is less than the reservoirfracturing pressure.The composition and rate of injecting the mixture is subsequently adjusted to the extent required to maintain a flow of steam foam within the channel at a relatively high pressuregradientatwhichtheoil- displacing and channel-expanding effects are significantly greaterthan those provided bythe 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 injected into and fluid is backflowed from a heavy oil reservoirwhich is susceptible to 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 ofthe 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 any portion ofthe reservoirata pressure which exceeds that required for injecting steam but is less than the reservoirfracturing pressure and (b) is chemically weakened by contact with the reservoir oil so that it is more mobile in sand containing that oil than in sand which is substantiallyfree ofthat oil.The surfactant-containing steam is injected into the reser voirata rate slow enough to be conducive to displacing afrontofthesteamfoam along the oil-containing edge portions ofthe oil-desaturated zone than along the central portion of thatzone. And, fluid is backflowed from the reservoir at a time at which part or all ofthe 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 dispersion 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" referstoan effective mobility or ease of flow of a foam within a permeable porous medium. A "permeability reduction" or "mobility reduction" refersto 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 effective permeability ofthe porous medium.A reduction in such a mobility or permeability can be detected and/or determined by measuring differences in internal pressures within a column of permeable porous material during a steady state flow of fluid through a column of such material. "Steam quality" as used regarding any steam-containing fluid refers to the weight percent ofthe water in that fluid which is in thevapour phase ofthefluid atthe boiling tempera tureofthatwateratthe pressure of thefluid.For example: in a monocomponent steam-containing fluid which consists entirely of water and has a steam quality of 50%, one-half ofthe weight ofthewateris in the vapour phase; and, in a multicomponent steamcontaining 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 ofthe water in the multicomponentsteam-containing fiuid is in the vapour phase.Thus, the steam qualityofasteam- containing fluid can be calculated as, for example, 100 times the mass (or mass flow rate) of the water vapour in thatfluid divided bythe sum ofthe mass (or mass flow rate) of both the watervapour and the liquid water in that 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, ofthe steam being present in the gas phase of a steam foam. The gas phase may include 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 conjunction with a surfactant componentthrough a relatively steam permeable zone within said reservoir.

According tothe invention the surfactant component comprises in substantial part at least one sulphonate oftheformula RSO3X in which R is alkylaryl including benzene toluene orxylene having attached thereto a linear alkyl group containing 18 carbon atoms in the alkyl chain and Xis sodium, potassium, lithium orammonium.

The alkylaryl sulphonate-containing steam-foamforming mixture suitably includes an aqueous solution of electrolyte and advantageouslyfurther also includes a substantially non-condensable gas; with each ofthe surfactant, electrolyte and gas components being present in proportions effective for steam-foam-formation in the presence ofthe reservoir oil. The invention also 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. Forexample,the invention can be used to move oil oran emulsion of oil and waterawayfrom a well borehole in a well-cleaning type of operation, and/orto displace oil into a producing location in an oil-recovery operation.

In particular, the present invention relates to a process for recovering oil from a subterranean reservoir, comprising: injecting steam and producing fluid at horizontally spaced locations within a portion of an oil reservoir in which the disposition of a steam flow path is determined by the effect of gravity and/or oil distribution, ratherthan being substantially confined within at leastthe one most permeable layer of reservoir rocks; advantageously maintaining rates ofsteam injecting and fluid production such that a steam channel has been extended from the injection location;; changing the composition ofthefluid being injected from steam to a steam-foam-forming mixture including steam and an aqueous, electrolyte-containing solution or dispersion of an alkylaryl sulphonatecontaining surfactant, whilstcontinuing to produce fluid from the reservoir; correlating the composition ofthe steam-foamforming mixture with the properties ofthe rocks and fluids in the reservoirsothatthe pressure required to injectthe mixture and the foam itforms or comprises into and through the steam channel exceedsthat -requiredforsteam alone butis less than the reservoir fracturing pressure; and adjusting the composition ofthe fluid being injected into the steam channel to the extent required to maintain a flow of both steam and foam within the channel in responseto a relatively high pressure gradient at which the oil-displacing and channelexpanding effects are significantly greaterthan those provided by steam alone, without plugging the channel.

The invention also relates to an oil recovery process in which steam is cyclically injected into and fluid is baclcflowedfrom a subterranean heavy oil reservoir which is susceptible to gravity override and tends to intake and retain undesirably large proportions ofthe injected fluid.This process comprises: (1 ) injecting steam mixed with a linearC18-C30-alkylaryl sulphonate-containing steam-foam-forming compound which is arranged forforming a steam foam which (a) can be displaced through the pores ofthe reservoir, without plugging any portion ofthe reservoir, in response to a pressure which exceeds that required for displacing steam through the reservoir but is less than the fracturing pressure ofthe reservoir, and (b) can be weakened by contact with the reservoir oil to an extent such that the weakened foam is sigificantly more mobile in reservoir oil-containing pores of a porous medium than in oil-free pores of that medium;; (2) injecting the steam-foam-forming mixture at a rate equivalentto one which is slow enough to cause the foam formedby that mixture to advance more rapidly through the pores of a reservoir oil-containing permeable medium than through the pores ofa substantially oil-free permeable medium; and (3) backflowingfluidfromthe reservoir after a steam soak time sufficientto condense part or all ofthe steam in the injected steam-foam-forming mixture.

The steam-foam-forming mixture preferably comprises steam, a noncondensable gas, a linear C18-C30alkylaryl sulphonate surfactant and an electrolyte.

The invention provides unobvious and beneficial advantages in oil displacement procedures by the use ofthe alkylaryl sulphonate surfactant in the steamfoam-forming compositions. For example,where a steam-foam-forming mixture contains such as surfactantand an electrolyte in proportions near optimum forfoamformation,the present surfactant components provide exceptionally strong steam foams having mobilities manytimes lessthanthose of steam foams using othersurfactants. In addition, significant reductions are reached in the mobilities of the steam foams at concentrations which are much less than those required for equal mobility reductions bythe surfactants which were previously considered to be the best available for such a purpose.The use ofthe presentalkylaryl sulphonate surfactant components involves no problems with respect two thermal and hydrolytic stability. No chemical or physical deterioration has been detectable in the present alkylaryl sulphonate surfactants thatwere recovered along with the fluids products during productions of toil from subterranean reservoirs. In each ofthosetypes of sulphonate surfactants the sulphur atoms ofthe sulphonate groups are bonded directlyto carbon atoms. The surfactants which were recovered and tested during the production ofoil had travelled through the reservoirs at steam temperatures for significanttimes and distances.

The presentC18-C30-alkylaryl sulphonate-containing steam foams have been found to represent a substantial improvement in mobility reduction overfoams based on the C12-C15-alkylaryl sulphonates e.g., dodecylbenzene sulphonates. The foams to be used according to the present invention represent also substantial improvementoverthe C,6-Cr8 alphaolefinsulphonate-containing foams.

The present invention further relates to compositions containing at least 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 particularinterest in this respect are steam-foam-forming compositions consisting essentially of (a) water, which is present in the composition, ata temperature substantially equalling its boiling temperature, atthe pressure ofthe composition, in both a liquid phase and a vapour phase; (b) a surfactant component present in the liquid phase ofthe composition 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 least one C18-C30-alkylaryl sulphonate; (c) an electrolyte present in the liquid phase ofthe composition in an amount between 0.001 percent by weight (calculated on the weight ofthe liquid phase) and an amounttending 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 0.3 percent by mol, calculated on total mols in thevapour phase.

Illustrative of the alkylaryl sulphonate surfactants suitably employed in steam-foam drive processes of enhanced performance, according to the invention, are the alkylaryl sulphonates obtained es reacting a linear C18-C30-alkylbenzene linear C18-C30-alkyltoluene and/or C18-C30-alkylxylene with sulphurtrioxide followed by neutralization ofthesulphonicacid. Particu larlysuitablefor purposes ofthe invention is a sulphonate derived from substantially linear C,8-C30- alkyltoluene.

Different reservoir materials have different debilitating effects on the strength of a steam foam. Tests should therefore be carried outto determinethe sulphonates orsulphonate-containing steam-foamforming 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 ofthe reservoir material.

Such tests are preferably conducted byflowing steam-containing fluids through a sand pack. The permeability ofthe sand pack and foam-debilitating properties of the oil in the sand pack should be at least substantially equivalent to those ofthe reservoirto be treated. Comparisons are made ofthe 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 substantially free of end effects on the pressures.

Some laboratoryteststo determine steam mobility will now be described with reference to Figures 1 and 2.

Figure 1 shows schematically a sand packtest apparatuswhich can be made of currently available apparatus components. The apparatus consists of a cylindrical tube 1 that is 400 mm long and has a cross-sectional area of 8 c ù22. Such a tube is preferably arranged for a horizontal flow of fluid from an inlet 2to an outlet 3,Thetube is preferably provided with 5 pressure taps 4,5,6,7 and 8. The location ofthe first pressure tap 4 is at a distance of 150 mm from the inlet 2. The locations of the othertåps are chosen so as to divide the part ofthe tube 1 situated behind tap 4 into equal parts of 50 mm.The tube 1 contains a permeable and porous 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 material is arranged to receive separate streams of steam, noncondensable gas such as nitrogen, and one or more aqueous liquid solutions or dispersions containing asurfactanttobetested and/or a dissolved or dispersed electrolyte. Some or all ofthose components are injected 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 th rough 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 deviies) installed atthe inlet 2 and at the taps 4,5,6,7 and 8 ofthetube 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 injected at constant mass rates until substantially steady-state pressures were obtained at the inlet 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, the stronger the steam foam and the higherthe mobility reduction caused by the steam-foam-forming mixture.

Figure 2 illustrates the results of comparative tests with steam and various steam-foam-forming mixtures in sand packs containing Oude Pekela Reservoir sand having a permeability of 8 darcys. The backpressure was 21 bar, corresponding with a temperature of 21 5"C. The steam injection rate was 600 cm3/min. The figure shows the variation ofthe pressure in bar (Y-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 atthe outlet3 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 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 underthe Trademark SUNTECH IV-1015.

Curve C relates to using the mixture used forCurve B exceptthatthe surfactantwas a linear side-chain C20-C24-alkyltoluene sodium sulphonate.

The greatly improved steam permeability reduction performance of the presently described C20-C24alkylaryl sulphonate-containing surfactant component is clearfrom the Curve C as compared to the Curves A and B in Figure 2.

Compositions and procedures suitable for use in the present invention For purposes of the present invention, the surfactant component ofthe steam-foam-forming mixture is necessarily comprised in substantial part of linear C18-C30-alkylaryl sulphonate. Materials ofthis class but with a much shorteralkyl chain have heretofore found commercial utility, for example, in detergent formulationsforindustrial, household and personal care application.

A glass of alkylaryl sulphonatesvery suitable for use in the present invention is that derived from a particularclass of olefins,which may be defined for present purposes in terris ofthe configuration and numberofcarbon atoms in theirmolecularstructure.

These olefins have a carbon numberof 18.

In terms ofmolecular structu re, th ese olefins are aliphatic and linear. Either alpha- or internal olefins are considered suitableforthe alkylation route chosen to producethe products to be used according to the invention. For purposes ofderivation ofthe alkylaryl sulphonatesforuse in the process according to the invention, olefins are advantageously applied in which at least90% ofthe molecules are alpha-olefins.

Particularly attractive are sulphonates derived from the Neodene alpha-olefins (trademark) sold by Shell Chemical Company, in partfortheirlinearstructure and high alpha-olefin content, i.e., greaterthan 95% in each case. The Neodene alpha-olefins are prepared by ethylene oligomenzation Products having a high content of internal C,8-C30-olefins are also commer cially manufactured, for instance, bythechlorination- dehydrochlorination of paraffins or by paraffin dehydrogenation, and can also be prepared by isomerization of alpha-olefins. Internal-olefine-rich products are manufactured and sold,forexample, by Shell Chemical Company.

For preparation of alkylaryl sulphonates, the olefins as described above are subjected to reaction with benzene,toluene orxylene. Reaction conditions and catalysttype are chosen in such a way that preferably para alkyltoluene is formed. The alkylbenzene, alkylx yleneoralkyltoluene isomers are reactedwith sulphur tri oxide. The term "sul ph u rtrioxide" as used in the present specification and claims is intended to include any compounds or complexes which contain yield SO3fora sulphonation reaction as well as SO3 per se.

This reaction may be conducted according to methods well known in the chemical arts, typically by contact of a flow of dilute SO3 vapourwith a thin film of liquid alkylate at a temperature in the range of about 5to 50"C. The reaction between the SO3 and the alkylate yields a sulphonicacid 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 suiphonation, hydrolysis, and neutralization ofthe specific olefins) have not been found to be a critical factorto the performance ofthe surfactant in the steam foam process according to this invention In this regard, it is observed thatfactors which have conventionally governed the choice of sulphonation conditions, e.g., productcolour, clarity, odour, etc., do notcarrythesameweightinthe preparation ofalkylaryl sulphonatesfor purposes of use in the process according to the invention thatthey 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 surfac tant components suitable for use in the steam-foamforming mixture.

For purposes related to maintaining productstability, conventional manufacture typically yields a dilute solution or dispersion of the alkylaryl sulphonates,for instance, productswith a 15-30 %wtactive matter content in water. Such-products may be directly applied to the preparation of steam-foam-forming mixtures for purposes of thins invention.

Suitable alkylaryl sulphonates, generally prepared by methods such as described above, are themselves commercially available products.

The strength ofthefoamformed bythesteamfoam-forming composition including alkylaryl sul phonate tends to increase with increases in the proportion ofthe surfactant and/or electrolyte compo- nents ofthe 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 invention can form a steam-foam capable of reducing the effective mobility ofthe steam to less thanabout1/10th and even to 1/50th-i/i 10th ofthe mobility it would have within a permeable porous medium in the absence ofthe 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 ofthe foamforming components of a steam-foam-forming mix- - ture according tothe present invention. The steam quality ofthesteam as generated and/or amount of aqueous liquid with which it is mixed be such thatthe steam quality ofthe resulting mixture is preferably from 10to90%.Thedesiredsteam-foam isadvantageously prepared by mixing the steam with aqueous solution(s) of the surfactant component and optionally, an electrolyte.The water content of these aqueous solutions must, of course, betaken into account in determining the steam quality ofthe 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 0C) and pressures (1-100 bar) atwhich the steam-foam-forming mixture is preferably injectedinto and displaced through the reservoirto betreated and (b) is substantially inertto and compatible with thefoam-forming surfactant and other components ofthat mixture. Such a gas is preferably nitrogen but can comprise othersubstantially inert gases, such as air, ethane, methane, flue gas, fuel gas, orthe like. Suitable concentrations of noncondensable gas in the steam-foam mixture fall in the range offrom 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 ofthe gas phase ofthe mixture.

Suitably, the electrolyte used should have a composition similarto and should be used in a proportion similarto those described as suitable alkali metal salt electrolytes in the above-mentioned USA patent specification 4,086,964. An aqueous solution may be applied that contains an amountofelectrolytesub- stantially equivalent in salting out effectto a sodium chloride concentration offrom 0.001 to 10% (but less than enough to cause significant salting out) ofthe liquid-phase ofthe steam. Some or all ofthe electro lyre 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 be applied which has approximatelythe 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-inducting proportion) of the liquid phase of the steam-foamforming 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 ofthe commercially available devices and techni quesforsteam generation.Astream ofthesteam being injected into a reservoir is preferably generated and mixed, in substantially any surface or downhole location, with selected proportions of substantially noncondensable gas, aqueous electrolyte solution, and foam-forming 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 with which it is mixed are preferably arranged so that (1) the proportion of aqueous liquid mixed 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% (preferablyfrom 30-80%) (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) the amount of noncondensable gas is from 0.0003 to 0.3 mole fraction ofthe gas phase of the mixture.

Claims (8)

1. A process for displacing oil within an oilcontaining subterranean reservoir by flowing a steamcontainingfluid inconjunctionwith a surfactant componentth rough a relatively steam-permeable zone with said reservoir, characterized in that a surfactant component is employed which causes in substantial part at least one sulphonate ofthe formula RSO3X in which R is alkylaryl including benzene, toluene orxylene having attached thereto a linear alkyl group containing 18-30 carbon atoms in the alkyl chain and Xis sodium, lithium, potassium or ammonium.

2. A process according to claim 1, characterized in that an electrolyte is employed in the flow within the reservoir in conjunction with the steam-containing fluid.

3. A process according to claim 1 or2,characte- rized in that a substantially noncondensable gas is employed in theflowwithin the reservoir in conjunction with the steam-containing fluid.

4. A process according to any one or more ofthe preceding claims, characterized in thatthe surfactant component comprises in substantial part sulphonate obtained by reacting a linearC18-C30-alkylbenzene, linear C18-C30-alkyltoluene and/or linear C18-C30-alkylxylene with sulphurtrioxide followed by neutralization ofthe sulphonic acid.

5. A process according to claim 4, characterized in thatthe sulphonate is derived from linear C2028- alkyltoluene, alkylbenzene or alkylxylene.

6. A process according to any one or more of the preceding claims, characterized in that the aqueous liquid phase ofthe steam-foam-forming composition contains between about 0.01 and 10 percent by weight of alkylaryl sulphonate.

7. A process according to any one or more ofthe preceding claims, characterized in that in addition to or instead of nitrogen or another non-condensable gas electrolyte is used up to 10% in the liquid phase to enhancethe performanceofthesurfactant.

8. A process according to C!aim 1 substantially as hereinbefore described and with reference to the accompanying drawings.