WO1989012158A1

WO1989012158A1 - Miscible gas enhanced oil recovery method using ethoxylated alkylphenol sulfonate

Info

Publication number: WO1989012158A1
Application number: PCT/US1989/002418
Authority: WO
Inventors: Mitchell Danzik; Robert G. Wall
Original assignee: Chevron Research Company
Priority date: 1988-06-02
Filing date: 1989-06-02
Publication date: 1989-12-14
Also published as: CN1040651A

Abstract

Oil recovery from a petroleum reservoir (22) using a miscible gas, such as carbon dioxide, nitrogen or methane is enhanced by injecting a preformed stable foam into the reservoir to divert gas from high permeability paths (30, 32) to oil-rich portions of the formation. The foam composition is formed by a sulfonated ethoxylated alkylphenol (SEA) of general formula (I), wherein R is a linear or branched hydrocarbon carbon containing 8 to 22 atoms, N is 2 to 13, Y is Z or -H, Z is -(SO3 M), M is alkali metal, an ammonium, or an alkyl ammonium, or a polyalkyl aminium ion, X is >0 to 2, and Z + ZX 1.

Description

MISCIBLE GAS ENHANCED OIL RECOVERY METHOD USING ETHOXYLATED ALKYPHENOL SULFONATE

Field of the Invention

The present invention relates to enhanced oil recovery from a petroleum bearing formation.

More particularly, it relates to enhancing production of oil from a producing formation wherein a non- condensible, miscible gas is used to improve the mobility of oil through the producing formation and a stable foam, compatible with the formation fluids including connate gas, oil and water or brine, is injected with the gas to direct gas pressure to the less permeable oil-rich portions of the formation.

It is a particular object of the present invention to provide a pre-formed foam that is compatible with the oil and brine content of a petroleum-bearing formation into which a non- condensible miscible gas such as carbon-dioxide, nitrogen or methane, has been injected to assist oil displacement. Such gases reduce the viscosity of the native oil and re-pressure the formation to increase the flow of petroleum from at least one injection well to at least one producing well. These miscible gases are known to result in reduced viscosity of the petroleum by their mutual interaction, but, because of the in omogeneity of most earth formations for each of the three phases, gas, oil and water, additional means are required to control the gas to avoid pressure loss to high permeability channels or ^■'fingers" that form in the reservoir rock. Fingering of gas into relatively high permeability gas and water, or brine, channels interferes with the injection profile of the drive gas in the formation because substantially equal gas pressure is not available to move fluids through the low permeability oil-rich portions of the formation. Such pressure loss channels may also be generated by gravity effects of the low density gas which tends to cause the gas to rise to the top of the formation so that it overrides oil and water channels in the lower part of the formation.

To control such injection profiles, either due to fingering or gravity override, it has been proposed to use foam, in the same manner it is used to improve injection of steam to enhance oil recovery. However, in using a non-condensible, miscible gas (rather than condensible steam) , creation and maintenance of an effective foam is difficult, where either the salt concentration of water in the formation (connate or injected) and/or the residual oil in the reservoir, tend to break the foam or prevent it from forming initially. Accordingly, it is a particular object of the invention to provide a foam which is compatible with high residual oil and brine mixtures in the formation and which can be preformed before the foam is injected into the formation. Such foam is a mixture of the noncondensible gas, water or brine and an ethoxylated alkylphenol sul ate-εulfonate.

In a preferred method of carrying out enhanced oil recovery, foam is preformed by mixing a portion of noncondensible miscible gas with an injected aqueous phase, such as water or brine, which may have a salt content similar to that of the oil- bearing formation, and an ethoxylated alkylphenol sulfate-sulfonate selected in accordance with the invention. The fluids are injected into a well entering the formation and either preformed into a foam before introduction into the well or by adequate mixing of the constituents as the foam is pumped through the well and into the formation. The volume of the preformed foam is adequate to establish a stable bank of foam with the formation and particularly one which will enter the more permeable portions of the formation in sufficient quantity and with sufficient stability to maintain the foam when subsequently pressurized with the noncondensible miscible gas. The adequacy of the foam bank may be determined by production of oil through at least one producing well to which oil is driven by continued pressurization, so that reduced amounts of water and injection gas bypass oil rich portions of the formation before arriving at the producing well.

It is especially important that such foam be stable during extended contact with formation fluids, which contain 20% to 60% residual oil and brine with 1% to about 10% total dissolved solids (TDS) .

BACKGROUND OF THE INVENTION

It has been proposed heretofore to use a noncondensible miscible gas such as carbon dioxide, nitrogen, methane and the like for stimulating oil production from a petroleum-bearing formation. Such gas is injected into at least one well and petroleum is produced from at least one other well, penetrating the same formation. In general these gases have a relatively low critical point, that is, the temperature above which the gas cannot be compressed to a liquid. Such gases are at least partially soluble in the oil. Because these gases, although noncondensible, are in fact soluble, or miscible in the oil, they are absorbed by the petroleum, either to reduce the viscosity of the oil or to increase its mobility through the formation, and at the same time the increased pressure of the gas drives residual petroleum in the formation to a producing well or wells.

As with all enhanced oil-recovery processes, the reservoir formation is quite non-uniform, having been formed initially by sedimentary material and then consolidated into porous geological beds, capable of entrapping oil and gas (generally by displacing water) therein over geological time. Because of the heterogeneity of the formation, due to the inclusion of clays or shale material in the sedimentary beds or their process of compaction, permeability to flow of liquids through the formation is quite variable throughout its structure. Further, the permeability of the formation to flow of each of the components, oil, gas and water frequently differs substantially in various parts of the formation. In general, the formation permeability is substantially greater for gas than for oil or water. As a result, the injection gas tends to "finger" through the reservoir formation. Moreover, density differences through upper portions of the reservoir create gravity separation, known as "gravity override" of the gas, so that it tends to by-pass or break through the reservoir between injection and producing wells. Additionally, water may also create preferential flow-paths and similarly by-pass oil in less permeable portions of the earth formation. It is, of course, most desirable that the injected gas act on the fluids of the formation as a piston-like displacement so that all fluids move at substantially the same rate through the formation. Thus, desirably, the "injection profile" for the gas is made as nearly equal as possible at all points in the reservoir.

It has been proposed heretofore to use foam in the same manner as it has been used in steam- assisted oil recovery methods to equalize the injection profile across the formation. The injected foam tends to block more gas permeable portions of the formation so that the steam or gas pressure is diverted toward oil in the less permeable channels of the formation. However, a particular problem encountered in most earth formations is that the connate water is relatively saline, that is, the water or brine has a relatively high salt content as compared to fresh water. Furthermore, the brine content varies substantially between geological provinces (such as California vs. Gulf Coast, or mid- continent fields) as well as between fields or from formation to formation. Depending upon the geological formation, the environment in which the oil was originally generated, or captured within rocks serving as a reservoir, the salt content of the brine may vary from 1% or less by weight to water substantially saturated with salt, e.g., in excess of 20% by weight.

Because of such wide variations in the salt content, it has been found difficult both to form and maintain a foam which will remain stable in the presence of such brines. Further, the oil content of the formation may also prevent the formation of the foam or rapidly break such a foam.

As particularly distinguished from prior art methods, the present invention forms a stable foam of the noncondensible, miscible gas, such as the gas being used in an enhanced oil recovery process in a reservoir, and an ethoxylated alkylphenol sulfate- sulfonate. This foam is surprisingly stable, i.e., it maintains an effective foam, in contact with reservoir fluids, including substantial amounts of petroleum and brine.

U.S. Patent 2,106,716 - Bruson, discloses a process of sulfating and sulfonating ether alcohols to prepare sulfonates useful as detergents and emulsifying agents. In such compounds the sulfonate group is directly attached to an aromatic ring and the sulfate is attached to the ring through a polyalkylene ether radical. There is no disclosure or suggestion to use these materials for assisted oil recovery.

U.S. Patent 4,104,023 - Woo, (assigned to the assignee of this application) discloses ring polysulfonated alkyphenoxy alkylols useful as washing detergents without use of builders. -1-

U.S. Patent 4,502,538 - Wellington et al is directed to use of polyalkoxy aliphatic sulfonate surfactants with substantially liquified C0₂ and brine for assisted oil recovery from a reservoir having high salinity (dissolved solids) connate water. The sulfonate groups are not ring attached, but are attached through a polyalkylene ether group. The compounds are disclosed to be water soluble for foam-forming and resistance to partitioning in contact with C0₂ and oil. The compounds do not include sulfated components.

U.S. Patent 4,600,516 - Wester et al discloses a method of preparing sulfonated alkyl and alkylarylpolyalkoxylates, including ethoxylates for the manufacture of lime soaps and for emulsion polymerization. A method is disclosed to decrease interfacial tension between salt water and oil over wide temperature and pH ranges. The compounds are indicated to be useful in connection with oil well acid stimulation or fracturing of earth formations.

Use as foaming agents in gas enhanced oil recovery is not suggested.

U.S. patent 4,465,602 - McCoy is directed to use of alkylarylpolyoxyalkylene sulfonates alone or in combination with separate petroleum sulfonate surfactants in carrying out water flooding for enhanced oil recovery from a producing formation.

None of the prior patents discloses or suggests use of sulfonated ethoxylated alkylphenols, (also referred to herein as ethoxylated alkylphenol sulfonates) as stable foamers for non-condensible, miscible gas in a producing reservoir containing high brine (dissolved solids) water and in the presence of substantial percentages of residual reservoir oil.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, there is provided a method of enhancing recovery of petroleum from an oil-bearing formation during injection of a non-condensible gas having at least partial miscibility in the oil by at least periodically injecting a preformed foam composition into the reservoir formed of a sulfonated ethoxylated alkylphenol (SEA) surfactant and brine mixture. The pre-formed foam is a mixture of the non-condensible gas, water, including brine, and at least an effective amount of such surfactant in which the ethoxy component (-CH₂-CH2-0-) is from 2 to 13 groups and the alkyl component of the alkylphenol contains from 8 to 22 carbon atoms. Most preferably, the surfactant contains on average about 2.5 to 5 ethoxy groups and an alkyl component of from 10 to 14 carbon atoms. In a preferred form, the non-condensible miscible gas includes C0₂, N₂, flue gas, and hydrocarbon gases such as CH₄, or a mixture of CH₄ with heavier natural gas liquids, such as ethane, propane, butane, pentane, etc.

In a preferred form, the organic foaming surfactant component is injected into a producing formation, either intermittently or continuously, and either in a water solution, or as an additive to the miscible injection gas, (i.e., C0₂, N_2/ CH4, C₂Hg, etc. , flue gas, or the like) . The surfactant is preferably in the form of an ethoxylated alkylphenol sulfonate which is capable of interacting with the injected fluid, including gas, water, including brine or reservoir fluid, to form a stable foam. Particularly in single well stimulation of a petroleum reservoir, it is important that the injected foam does not interfere with petroleum production. The present invention appears to mobilize substantial amounts of oil in pore spaces of the reservoir which may have been effectively bypassed by gas flowing through high-permeability gas channels but which were apparently then blocked by the injected foam. Thus the instant invention makes the injection profile more uniform, such that residual oil in these channels may be recovered.

The exthoxylated alkylphenol sulfonate is a mixture of compounds of the general formula:

wherein: R is a linear or branched hydrocarbon containing 8 to 22 carbon atoms, N is 2 to 13, - Y is -Z or -H, Z is -(SO₃M) ,

M is an alkali metal, ammonium, alkyl ammonium or polyalkyl aminium ion X is >0 to <2 , and

Z + Z_x is >1

As indicated, X is greater than zero and equal to, or less than, 2, and Z + Z_x is equal to or greater than 1. Preferably, R is 10 to 14 carbon atoms, N is about 2.5 to 5 ethoxy groups, and Z + Z_x is greater than 1.4, and more preferably is about 2.

Further objects and advantages of the present invention will become apparent from the following detailed description of the methods of the present invention set forth below, including the drawings and examples forming an integral part of the present application.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic elevational view of an injection well penetrating a petroleum reservoir formed by a sedimentary formation. A miscible, non¬ condensible gas and a stable foam are injected through an injection well to increase the pressure on the connate fluids in low-permeability portions of the formation to enhance recovery of oil from a producing well also penetrating the formation.

Fig. 2 is a schematic flow diagram of a test arrangement for generating foam in the presence of oil and water representative of connate fluids in a reservoir in which foam is formed for flow through a permeable core so that a surfactant forming such foam may be evaluated as to its usefulness to resist foam breaking by connate oil or brine and thereby maintain its effectiveness to block gas permeable paths so as to improve the profile of miscible gas injected to move fluids through less permeable portions of a formation.

DESCRIPTION OF THE INVENTION

The present invention is, at least in part, based on the discovery that a foam may be created and maintained in a reservoir formation containing waters having significant amounts of dissolved solids and a significant volume of residual oil during miscible- gas-enhanced oil recovery and which, without addition of other surfactants, substantially improves oil mobilization from previously bypassed permeability channels. Contrary to normal expectations as to activity of known foaming agents, it has now been found that sulfonated ethoxylated alkylphenols form a hydrophilic and oleophilic foam that will persist in the environment of high residual oil and high dissolved solids water (brine) within a formation. This persistence is particularly useful in reservoirs undergoing assisted recovery using a miscible, non¬ condensible gas such as nitrogen, carbon dioxide or methane. The foam is formed to a desired foam "quality" before it is injected into the formation, thereby increasing its effectiveness as a barrier in the high gas-permeability areas. This action blocks gas from flowing through high permeability paths in the reservoir, for example, due to gravity override or fingering channels. Thus, the injected gas is able to apply more nearly, equal and higher pressure to channels, or paths having lower permeability and correspondingly higher oil content. Oil production with gas drive is accordingly enhanced from a production well penetrating the same formation.

Preferred Embodiments of Sulfonated Ethoxylated Alkylphenol Surfactants

The foam forming sulfonated ethoxylated alkylphenols of the present invention comprise a mixture of compounds of the following general structure:

whereiri: R is a linear or branched hydrocarbon containing 8 to 22 carbon atoms, N is 2 to 13,

Y is -Z or -H Z is -(S0₃M) ,

M is an alkali metal, ammonium, alkyl ammonium ion, or polyalkly ammonium ion, X is >0 to <2, and

Z + Z_x is >1.

In a preferred form R is 10 to 14 carbon atoms and N on average about 2.5 to 5. More preferably R is 12 and N is 3. M is preferably sodium, and Z+Z_x is greater than 1, preferably greater than 1.4 and, most preferably, about 2. Further, the sulfonate component X attached to the aromatic ring is from greater than zero (0) and up to, and including, 2. In a commercial form, the desired surfactants may be formed by alkylating phenol followed by ethoxylation to give alkylphenol ethoxylates, which are then reacted with S0₃ or oleum to give the desired sulfonates. In general such compounds, depending upon reaction conditions, yield sulfonated ethoxylated alkylphenols as a major component, (i.e., preferably such sulfate-sulfonate component is greater than about 50% and most preferably greater than about 70%) , of the product.

For example, using a Cι alkylphenol and 3 mole equivalents of ethylene oxide, followed by sulfonation, a sodium triethoxy alkylphenol sulfate- sulfonate such as

can be formed.

The balance of the composition may also include some triethoxy alkylphenol sodium sulfonates, such as

^c12 as well as some sodium triethoxy alkylphenol sulfates, such as

C 12 and some disodium triethoxy alkylphenol disulf onates , such as

Superior foaming results are obtained where on average about 3 ethoxy groups are present in the compounds of this mixture to form the foam.

Foams are generally formed with from more than 0.1% to about 5% of the sulfonated ethoxylated alkyphenol mixture as the active compound; more preferably from more than 0.1% to 2%, and most preferably from about 0.2% to 0.7%. The foams so formed are useful with liquid pore volume fractions of up to about 60% oil, more preferably up to about 40% oil, and most preferably up to about 20% oil. They are also useful at up to about 20% total dissolved solids in the brine, but preferably up to about 10%, and most preferably at up to about 6%. Dependent upon the constituent mono- or di-valent ions dissolved in the brine, the number of ethoxy groups may be from 2 to 13, but most preferably are, on average, about 3.

Desirably, the alkyl group, linear or branched, may vary from 8 to 22 carbon atoms, but more preferably, it has from 10 to 14 carbon atoms, and most preferably on average about 12 carbon atoms. Generally the alkyl group is formed of molecules having a range of differing numbers of carbon atoms, usually a range of from +2 to -2 carbon atoms. Further, the number of carbon atoms in the alkyl may be either an even or an odd number.

Desirably, the foam formed with the sulfonated ethoxylated alkylphenol composition as set forth herein is preformed in the well tubing or by injection into a producing formation undergoing enhanced recovery by injection of miscible gas. Such foam is preferably preformed by introducing the sulfonated ethoxylated alkylphenol and brine into a stream of the miscible gas flowing into the reservoir through the gas injection well tubing. This assures foam production before injection into the producing formation. Such preformed foam may be formed using either fresh water (little dissolved solids) br brine compatible with the reservoir brine, either using brine separated from produced fluids from such reservoir or compounded to have any desired amount of dissolved solids up to about the same total dissolved solid content as the formation connate water. Desirably, the liquid volume fraction (LVF) of such foam does not exceed about 50%. More preferably, the LVF is between about 5% to 50%. Most preferably, the LVF is between 10% and 20%.

Referring now to the drawings, Fig. 1 illustrates schematically an arrangement for injecting the preferred foam, as above specified, through an injection well into a reservoir formation. A source of miscible gas such as nitrogen, carbon dioxide, methane, flue gas, or the like is supplied at relatively high pressure (but below the fracturing pressure of the reservoir formation) to an injection well. In practice, this may be a central well producing radially outwardly to a group of producing wells surrounding the injection well. Alternatively, the injection well may be one of several in a line capable of creating a "front" for a line-drive of oil through the formation to one or a line o j. producing wells. In Figure 1 a single injection well and a single producing well are illustrative of the system. A source of gas flowing in pipeline 10 supplies a miscible, non-condensible gas to injection well 12. For illustrative purposes, a compressor 14 driven by motor 16 supplies the gas at a desirable pressure to well 12 through well head 18 and injection pipe 20. The gas is conducted to the desired reservoir rock, such as earth formation 22, through an injection pipe string 24 within casing 26. Injection string 24 may be isolated within well bore 12 in casing 26 by packers 28 above and below formation 22.

As indicated above, the permeability of nearly all sedimentary earth formations that form a petroleum reservoir, such as 2, are inherently inho ogeneous to flow of connate fluids, (i.e., water, oil, and gas) . Each of these fluids tends to flow selectively in permeability channels that have the least resistance to their flow. The resistance to flow of each primarily depends on its viscosity either alone or relative to the other fluids. Typically, the resulting permeability for flow of each fluid is different in each formation.

Since gases are more mobile than either oil or water, or their mixtures, injected gas in general tends to flow through more permeable gas channels or "fingers" 30 of formation 22 as indicated by dash lines. This gas flow tends to by-pass "tighter" or less-permeable zones wherein the oil-permeable passages are smaller or the oil is more tightly bound to the surface of the rock. In particular, the oil may be in contact with, or partially bound to, clay or shale material that over- or under-lies the reservoir or are within a generally sandy or carbonate rocks of the formation that form the permeable and entrapping oil channels of the reservoir. Thus, "fingering" as indicated by channels 30, or "gas override" as indicated by area 32 at the top of formation 22, generally develop so that large portions of the liquid oil are not adequately pressured by the injected gas. As a result, gas may flow predominantly through the lower- resistance paths, gas channels 30 and 32, even where such paths include substantial volumes of movable oil and connate water around such paths. It is accordingly important to form a stable foam in these channels without permanently blocking or decreasing the mobility of substantial volumes of such entrapped oils. Thus, it is possible with the sulfonated ethoxylated alkylphenol foams of the present invention to maintain the desired injection profile for the drive gas to produce a piston-like movement of oil through the formation, as indicated generally by dotted line 34.

To correct the distortion of the injection profile to approximate front 34, foam-forming components of this invention are added to the injected gas stream through injection line 35. For thiε purpose, surfactant and water or brine are supplied by tanks 36 and 38 through valves 40 and 42, respectively, by metering pump 37 to foam generator 44 and then to injection line 35. Foam may be supplied to the formation by forming it in generator 44 with gas before injection into well head 18. For this purpose, a portion of the injection gas flows from line 20 to generator 44 through line 46 under control of valve 48 to develop the desirable foam quality. Foam may also be formed in injection line 24 before contact with formation fluids, as by flow of surfactant solution and gas through perforations 50 in the lower end of tubing 24. Foam so generated upon injection into the reservoir preferentially flows to gas-permeable channels 30, 32. It effectively plugs them so that gas is then diverted to oil-rich portions of the formation. As indicated, the miscible gas is thus made to move in a relatively piston-like manner to displace reservoir fluids.

In the present illustration, oil is produced from an adjacent producing well such as 51, by pump 53 operating through sucker rods 52 through well head 54. The surfactant composition prepared in accordance with the present invention is preferably supplied as a concentrated liquid which is then diluted with injection brine. The solution is then pumped from tanks 36 and 38, and etered by pump 37 through line 35 at a desired rate to contact gas flowing in well head 18 or injection string 24. Mobilitv Test Apparatus

Referring now to Figure 2, there is shown a test apparatus suitable for evaluating foam forming surfactant compositions in the presence of oil and different percentages of residual oil and brines of different dissolved solids content. The apparatus simulates steady-state flow through oil depleted channels (i.e., after primary oil production) of the oil-bearing reservoir rock being subjected to miscible gas injection. The rock is simulated by a glass bead pack 56 in cylinder 60 of known permeability. Pressure is applied, preferably by nitrogen or carbon dioxide from tank, or source, 63, used as the miscible gas for primary drive in a reservoir. Temperatures are on the order of 70°F and pressures are up to 500 psi. Fluids selectively flow through cylinder 60 under suitable flow conditions. The flow arrangement includes inlet and outlet pipes 62 and 72 for passing fluids through pack 56 including (a) aqueous liquids, (b) oil and (c) a non¬ condensible gas. Differential pressure cell 59 provides means for measuring the pressure drop across the cylinder 60 during flow. In one embodiment, the main bed 56 of cylinder 60 was a hollow cylinder, six inches long by 3/4 inch diameter, packed with 70-100 mesh (250-180 micron) glass beads. The inlet end was connected to a three-inch-long cylinder 55 packed with the same glass beads which function as a foam generator. Liquid-metering pump 67 is attached to line 68 from oil-containing vessel 65 and fed into the line 62 between foam generator 55 and main bed 56. Outlet line 72 from main bed 56 pass through back pressure regulator 70 and into liquid separator vessel 74. Gas from vessel 74 passed through wet test meter 73 where its volume was measured at standard temperature and pressure. A pressure measuring device, such as recorder 72, recorded differential pressure measured by (DP) cell 59 and was indicated by meter 71. Cell 59 measured the pressure difference between inlet and outlet lines 62 and 72 across main bed 56.

A second high pressure liquid metering pump 80, whose inlet is connected to surfactant-brine solution vessel 64 forms an aqueous surfactant solution. The outlet of pump 80 is fed into a T-joint 81 where it mixes with a non-condensible gas from tank 63 through pressure let-down valve 82 and through gas-flow-measuring device 83. The combined liquid surfactant and non-condensible gas pass through line 69 into the entrance of foam generator cylinder 55. All connecting lines in the above apparatus were 1/8 inch outside diameter.

Mobility Test Procedure

The following experiments demonstrate the efficiency of the foam compositions of sulfonated ethoxylated alkylphenols of the present invention to improve miscible-gas-enhanced oil recovery. They were carried out as follows:

Oil storage vessel 65 was charged with the test oil. The surfactant-brine storage vessel 64 was charged with an aqueous solution of the test surfactant in the desired brine. Tank 63 containing the non-condensible gas of the experiment was attached to pressure-let-down valve 82 and then passed through foam cylinder 55 and main test bed 56 to establish a desired back pressure as measured by DP cell 59. Then the surfactant-brine solution was pumped into the system at a rate calculated to give the desired ratio of gas to liquid. This mixture was passed through foam generator 55 and the resulting foam was passed into the main bed 56. The pressure developed by passing this foam through the glass bead packed bed was detected by pressure cell 59, and measured and recorded by recorder 71. After passing through back-pressure valve 70, the foam was collected in liquid separator vessel 74 wherein the foam broke and the gaseous portion passed out through wet test meter 73. Measurements of total pressure, gas flow rate, surfactant flow rate, pressure drop, and outlet gas volume were taken. Next, oil metering pump 67 was started, and oil was pumped into the foam line 62 at a predetermined rate. Again, the same measurements were made and in addition, the oil flow rate was measured. The combined flow of foam, gas, and oil through bed 56 were measured under steady- state flow conditions. The value of the differential pressure with foam only flowing through test bed 56 and then oil flowing with the foam at given flow rates are then compared as an indication of the foam susceptibility to breakdown during such flow when exposed to gas, brine and oil.

EXAMPLES

Ethoxylated alkylphenol sulfonate εulfates used in the compositions of specific examples of the present invention may be prepared as follows: EXAMPLE A

Preparation of triethoxylated dodecylphenol

A pressure vessel was charged with 200 g of an alkylphenol (0.75 mol) , with an average C₁₂ chain length (prepared from a C^₂ polypropylene) , and 0.5 g sodium methoxide (0.009 mol). The mixture was stirred and heated to 160"C for 2.5 hours at less than 20 mm of Hg. Nitrogen was added to bring pressure up to ambient and 100 g ethylene oxide (2.27 mol) was added to 160"C over 5 hours, during which time the pressure increased to 25 psig. When the addition was complete, the solution was heated and stirred for an additional 1.5 hours.

The product mixture was extracted with 400 ml of chloroform and 200 ml of water. After separation, the organic layer was dried over sodium sulfate, filtered, and the solvent removed under vacuum to recover 300 g of the ethoxylated dodecylphenol.

EXAMPLE B

Preparation of triethoxylated dodecylphenol sulfate- sulfonate

To a one liter flask equipped with a condenser, thermometer, εtirrer, addition funnel, and nitrogen inlet, was added 286 g of the ethoxylated dodecylphenol from Example A (0.74 mol) and 200 ml methylene chloride. The solution was purged with nitrogen, cooled from 0°C to -24*C, and a solution of 127 g of sulfur trioxide (1.59 mol) in 100 ml methylene chloride was added within 15 minutes. The reaction solution was refluxed for 2 hour, cooled to 20^βC, and neutralized with 5 N NaOH to a pH of 11.3. An additional 200 ml of water was added, and the solution was heated to 60"C to remove the methylene chloride. The pH dropped to 5.8 and was adjusted to 11.8 by additional 5 N NaOH. The active content of the resulting slurry was about 38%.

A dried sample of the above slurry contained 2.29 meq/g of active. After the correction for the estimated sodium sulfate content, this was equivalent to about 1.5 to 1.7 active groups (i.e. , sulfate/sulfonate groups) incorporated per molecule.

EXAMPLE C

Other ethoxylated alkylphenols can be prepared in a manner similar to Example A, by adjusting the mole ratio of ethylene oxide. EXAMPLE D

Other sulfonates were prepared in a manner similar to Example B.

Surfactant Testing

As a preliminary test of selected sulfonated ethoxylated alkylphenol surfactants, a portion of each was subjected to a brine-foam test. This test comprised mixing 25 ml of a 0.5% solution of surfac¬ tant in a brine of given total dissolved solids plus 1 gm of crude oil and agitated (as by shaking) to form the foam. The foam height was then tested after a set-time of 5 minutes. Persiεtency of the foam iε thus determined. Those that performed adequately were then carried through to the mobility test. The brines used in brine-foam test were as shown in Table I.

TABLE I BRINES USED TO TEST SURFACTANTS

Approximate Composition. PPM

% TDS NaCl Other Salts 1. 1.9 19,000 100

2. 3.5 34,000 1,000

3. 5.3 41,000 12,000

4. 2.8 a 50/50 Blend of 1 and 2

The results of the brine-foam test are shown in Table II.

TABLE II

BRINE-FOAM TEST

AVERAGE NO. FOAM HEIGHT,

EXAMPLE SAMPLE OF ETHOXY BRINE ML AFTER NO. TYPE 1 GROUPS %TDS ³- 5 MINUTES²-

1 I 3 1.2 57 2 II 3 1.2 47

3 I 3 1.9 84 4 II 3 1.9 84

5 I 6 2.8 37 6 I 13 2.8 15

7 I 2 2.8 19

8 I 3 3.5 86 9 II 3 3.5 69

10 I 3 5.3 64 11 II 3 5.3 63 12 I 6 5.3 8 13 I 13 5.3 7

I Samples were: C₁ alkylphenol which had been ethoxylated to an average number of ethoxy groups as shown in this Table, followed by reaction with SO₃ to prepare sulfate sulfonates.

II Samples were: aε in I Sampleε, but refluxed at 100 "C per example A with added baεe for about 5 hours.

25 ml of 0.5% active solution (by solids weight), 1 gm oil.

Total Disεolved Solidε content of the brine.

Aε can be seen from Table II, in each example of surfactant having on average 3 ethoxy groups shows greater persistence of foam at all concentrations of total dissolved saltε in the brine than did an average of fewer or greater numberε of ethoxy groups. Further, the superiority of an average of 3 ethoxy groups in the sulfonated ethox¬ ylated alkylphenols sulfactants will be seen to be particularly effective at the highest brine concentr¬ ations, as compared to SEA surfactants having an average of 2, 6 or 13 ethoxy groups. To be particul¬ arly noted is the fact that the foam persistence was particularly superior where the total diεsolved solids is from about 2% to about 5%.

TABLE III

MOBILITY CONTROL⁴. ⁵

AVERAGE NO. OIL,LIQUID MOBILIT

EXAMPLE SAMPLE OF ETHOXY BRINE, VOLUME RATIO

NO. TYPE 1 GROUPS % TDS 3 FRACTION md/cp

14 I 3 2.8 0 257

15 I 3 2.8 0.04 308

16 I 3 2.8 0.25 364

17 I 3 5.3 0 278

18 I 3 5.3 0.04 406

19 I 3 5.3 0.25 596

20 II 3 5.3 0 274

21 II 3 5.3 0.04 602

22 II 3 5.3 0.25 644

23 No surfactant - 0 to 6 — >15,000

I Samples were: C₁₂ alkylphenol which had been ethoxylated to an average number of ethoxy groups as shown in this Table, followed by reaction with SO₃ to prepare sulfate sulfonates.

II Samples were: as in Table I Samples, but refluxed at 100 ^βC per example A with added base for about 5 hours.

25 ml of 0.5% active solution (by solids weight), 1 gm oil.

3 Total Dissolved Solids content of the brine. 4 250 psi C0₂, 6" by 3/4" column packed with 70-100 mesh glass beads.

0.5 wt% Surfactant in brine.

Table III indicates values of mobility ratio (millidarcies/centipoiεe) which were obtained with the foregoing apparatuε, and uεing the above described mobility test method, for brines at different percentages of total dissolved solids (% TDS) , and oil content of three different liquid volume fractions (fractions of total fluids) using sulfonated ethoxylated alkylphenol surfactants in the brine. The average number of ethoxy groups in the surfactant was about three.

5 The data in Table III shows that in each example the gas mobility ratio decreased significantly with use of the surfactant; further, the low mobility ratios show improved movement of oil over a range of total disεolved solids. Such results

10 indicate that in commercial use of the compositionε of the present invention, satisfactory results may be obtained in reservoirs having connate brines containing up to about 20 wt% total disεolved solids and up to about 60% liquid volume fraction of

15 residual oil in the formation pore volume. Superior reεults may be obtained where the brine contains from about 1% to 10% total dissolved solidε and the reεidual oil liquid volume fraction iε up to about 40% of the pore volume.

20 Moveover, the reεiεtance factor, RF, is low. The resistance factor, RF, compares the mobility ratio in the absence and presence of oil. RF is defined aε:

2 -5° R*F^f ~ —RF-₂ ¹ where RF! is the mobility ratio of the foam in the packed column in the presence of oil, and

where RF₂ is the mobility ratio of the foam 0 in the packed column in the absence of oil.

RF factors less than 6 are desirable; RF factors less than 3 are preferred. As can be seen by looking at the numbers in Table III, the RF factor changes with, oil and brine concentrations. Nonetheless, the RF factors for the sulfonate of this invention are less than 6, and at the concentrations tested, less than 3. For example, taking:

the ratio of Ex 16 / Ex 14 = 364/257, the RF factor is 1.42;

the ratio of Ex 19 / 17 = 596/278, the RF factor is 2.14;

the ratio of Ex 22 / Ex 20 = 644/274, the RF factor is 2.35.

From the foregoing, it will be apparent that with low ratios for RF, the foam remains effective to block high gas permeability channels over a wide range of residual oil contentε in the earth formation. This effectively maintains the deεired pressure on the miscible, non-condensable gas, acting on the oil-rich, low permeability portions of the reservoir at both high and low total disεolved solids in the reservoir connate water.

Variouε odificationε and changes in the present invention will occur to those skilled in the art from the foregoing detailed description. All such modifications or changes coming within the terms of the appended claims are intended to be included therein.

Claims

1. A method of enhancing recovery of petroleum from an oil-bearing formation during injection of a non-condensible gas having at least partial miscibility in the oil which comprises at least periodically injecting into said reservoir a foam forming composition including at least an effective amount of a sulfonated ethoxylated alkyl¬ phenol in water, including a brine compatible with the connate fluid in said formation, and said gas, said sulfonated ethoxylated alkylphenol com¬ pound having the general formula:

wherein: R is a linear or branched hydrocarbon containing 8 to 22 carbon atoms, N is 2 to 13, Y is Z or -H, Z is -(S0₃ M) , M is an alkali metal, an ammonium, or an alkyl ammonium, or a polyalkyl aminium ion, X is >0 to <2, and Z + Z_x >1.

2. A method in accordance with Claim 1 wherein R is a branched hydrocarbon containing 10 to 14 carbon atoms and N is on average about 2.5 to 6 ethoxy groups.

3. A method in accordance with Claim 1 wherein said sulfonated ethoxylated alkylphenol is a sulfonated triethoxylated dodecylphenol. 4. A method in accordance with Claim 1 wherein Z and Z is greater than 1.

4.

5. A method in accordance with Claim 1 wherein said sulfonated ethoxylated alkylphenols com¬ prises R having on average about 12 carbon atoms and said ethoxy group is on average about 3.

6. The method of Claim 1 wherein said non¬ condensible gas includes C0₂, N₂, flue gas, hydrocarbon gases and mixtures thereof.

7. The method of Claim 1 wherein the concentration of said sulfonated ethoxylated alkyl¬ phenol in said foam is at least 0.1% by weight.

8. The method of Claim 1 wherein said foam is preformed by introducing an aqueous solution of said εulfonated ethoxylated alkylphenol compound into a stream of said non-condensible gas flowing in the gas injection well tubing εo that said foam is stab¬ ilized before introduction into said formation.

9. The method of Claim 1 wherein said preformed foam is formed by simultaneous injection of an aqueous solution of said sulfonated ethoxylated alkylphenol and said gas into the gaε injection well tubing to form a εtable foam and then pumping εaid foam into εaid formation.

10. The method of Claim 1 wherein the liquid volume fraction of said preformed foam does not exceed about fifty percent.

11. The method of Claim 10 wherein the liquid volume fraction of said preformed foam is between five percent and fifty percent.

12. The method of Claim 11 wherein said liquid volume fraction of said preformed foam is between about ten percent and twenty percent.

13. A foam composition for injection into a petroleum reservoir to improve the injection profile of a non-condensible miscible gaε for enhanced recovery of petroleum therefrom said foam composition including an aqueous phase having therein an effective amount of an ethoxylated alkylphenol sulfate-sulfonate of the general formula

wherein: R is a linear or branched hydrocarbon containing 8 to 22 carbon atomε, N is 2 to 13, Y is Z or -H,

Z is -(S0₃ M) ,

M is an alkali metal, an ammonium, or an alkyl ammonium, or a polyalkyl aminium ion, X is >0 to <2, and Z + Z_χ >1.

to form a εtable foam in a mixture of the non¬ condensible, miscible gas used in a reservoir and the resistance factor RF for said foam to flow through a packed column is not greater than 6; wherein RF = —RF-i κ* *^■ and

RF^ = the mobility of said foam to flow in the presence of oil in said packed column, and RF₂ = the mobility of said foam to flow in the absence of oil in said packed column.

14. A foam composition in accordance with Claim 13 wherein said resistance factor RF is lesε than 3.

15. A foam composition in accordance with Claim 13 wherein R is a branched claim hydrocarbon containing 10 to 14 carbon atoms and N is on average 2.5 to 6 ethoxy groups.

16. A foam composition in accordance with Claim 13 wherein said εulfonated ethoxylated alkylphenol is a sulfonated triethoxylated dodecyl¬ phenol.

17. A foam composition in accordance with Claim 13 wherein Z and Z is greater than 1.4.

18. A foam composition in accordance with Claim 13 wherein said sulfonated ethoxylated alkylphenols comprises R having on average about 12 carbon atoms and said ethoxy group is on average of about 3.

19. A method of selectively blocking gas flow and mobilizing residual oil within or around high-permeability gas channels through a reservoir formation wherein a miscible, non-condensible gas is being injected to enhance recovery of oil from εaid reservoir, said reservoir containing brine having a total dissolved solids content in excess of one weight percent which comprises injecting with said miscible gas a foamable mixture which includes an aqueous phase compatible with said reservoir brine, and an ethoxylated alkylphenol sulfonate in an amount effective to form and maintain a stable foam in contact with reservoir fluids, including oil and reservoir brine, and then, producing reservoir oil from εaid reεervoir,

said ethoxylated alkylphenol sulfonate including from about 2.5 to 6 ethoxy moieties and from 8 to 22 carbon atoms in the alkyl moiety thereof, and said foam including from about 0.1 wt% to about 7 wt% thereof as the foaming agent.

20. A method in accordance with Claim 19 wherein the liquid volume fraction of residual oil of said reservoir fluids contacted by said foam is from about 5% to about 60% of the formation pore volume and the total disεolved solids of the brine therein is from about 1 wt% to about 20 wt%.

21. A method in accordance with Claim 20 wherein the liquid volume fraction of residual oil is from about 5% to about 40% and said total dissolved solidε in the reεervoir brine iε 1 wt% to 10 wt%.

22. A method in accordance with Claim 20 wherein the liquid volume fraction of residual oil is fro about 10% to about 30% and said total dissolved solids in the reservoir brine is 1 wt% to 6 wt%.