Stability enhanced water-in-oil emulsion and method for using same.

The present invention relates to a water-in-oil émulsion used for enhanced oil recovery. More specifically, the stability of a water-in-oil émulsion is enhanced by pretreating at least a portion of the oil prior to émulsification. The pretreatment step 10 can be accomplished by adding polymers to the oil, biotreating the oil, photochemically treating the oil and combinations thereof. Solid particles may also be added to the oil prior to émulsification to further stabilise the water-in-oil émulsion. The émulsion may be used as a drive fluid to displace hydrocarbons from a subterranean formation or as a banier fluid for diverting the flow of hydrocarbons in the formation.

BACKGROÜND OF THE INVENTION

It is well known that a significant percentage of oil remains in a subterranean formation after the costs of primary production rise to such an extent that further oil recovery is cost ineffective. Typically, only one-fifth to one-third of the Original oil in place is recovered during primary production. At this point, a number of enhanced oil _ 20 recovery (EOR) procedures can be used to further recover the oil in a cost-effective manner. These procedures are based on re-pressuring or maintaining oil pressure and/or mobility.

For example, waterflooding of a réservoir is a typical method used in the industiy to increase the amount of oil recovered from a subterranean formation.

Waterflooding involves simply irÿecting water into a réservoir, typically through an injection well. The water serves to displace the oil in the réservoir to a production well. However, when waterflooding is applied to displace viscous heavy oil from a

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-2fonnation, the process is inefficient because the oil mobility is much less than the water mobility. The water quickly channels through the formation to the producing well, bypassing most of the oil and leaving it unrecovered. For example, in Saskatchewan, Canada, primary production crude has been reported to be only about 2 to 8% of the 5 original oil in place, with waterflooding yielding only another 2 to 5% of that oil in place. Consequently, there is a need to either make the water more viscous, or use another drive fluid that will not channel through the oiL Because of the large volumes of drive fluid needed, it must be inexpensive and stable under formation flow conditions. Oil displacement is most efficient when the mobility of the drive fluid is 10 significantly less than the mobility of the oil, so the greatest need is for a method of generating a low-mobility drive fluid in a cost-effective manner.

Oil recovery can also be affected by extreme variations in rock permeability, such as when high-permeability “thief zones” between injection wells and production wells allow most of the injected drive fluid to channel quickly to the production wells, 15 leaving oil in other zones relatively unrecovered. A need exists for a low-cost fluid that can be injected into such thief zones (from either injection wells or production wells) to reduce fluid mobility, thus diverting pressure energy into displacing oil from adjacent lower-permeability zones.

In certain formations, oil recovery can be reduced by coning of either gas 20 downward or water upward to the interval where oil is being produced. Therefore, a need exists for a low-cost injectant that can be used to establish a horizontal “pad” of low mobility fluid to serve as a vertical barrier between thé oil producing zone and the zone where coning is originating. Such low mobility fluid would retard vertical coning of gas or water, thereby improving oil production.

For moderately viscous oils -- i.e., those having viscosities of approximately

20-100 centipoise (cP) — water-soluble polymers such as polyacrylamides or xanthan gum hâve been used to increase the viscosity of the water injected to displace oil from the formation. For example, polyacrylamide was added to water used to waterflood a 24 cP oil in the Sleepy Hollow Field, Nebraska. Polyacrylamide was also used to

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-3viscosify water used to flood a 40 cP oil in the Chateaurenard Field, France. With this process, the polymer is dissolved in the water, increasing its viscosity.

While water-soluble polymers can be used to achieve a favorable mobility waterflood for low to moderately viscous oils, usually they cannot economically be 5 applied to achieving a favorable mobility displacement of more viscous oils — i.e., those having viscosities of approximately 100 cP or higher. These oils are so viscous that the amount of polymer needed to achieve a favorable mobility ratio would usually be uneconomic. Further, as known to those skilled in the art, polymer dissolved in water often is desoibed from the drive water onto surfaces of the formation rock, 10 entrapping it and rendering it ineffective for viscosifying the water. This leads to loss of mobility control, poor oil recovery, and high polymer costs. For these reasons, use of polymer floods to recover oils having viscosities in excess of 100 cP is not usually technically or economically feasible. Also, performance of rnany polymers is adversely affected by levels of dissolved ions typically found in formations, placing limitations on 15 their use and/ or effectiveness.

Water and oil macroemulsions hâve been proposed as a method for producing viscous drive fluids that can maintain effective mobility control while displacing moderately viscous oils. For example, water-in-oil and oil-in-water macroemulsions hâve been -evaluated as drive fluids to improve oil recovery of viscous oils. Such 20 émulsions hâve been created by addition of sodium hydroxide to acidic crude oils from Canada and Venezuela. The émulsions were stàbilized by soap films created by saponification of acidic hydrocarbon components in the crude oil by sodium hydroxide. These soap films reduced the oil/water interfacial tension, acting as surfactants to stabilize the water-in-oil émulsion. It is well known, therefore, that the stabihty of 25 such émulsions substantially dépends on the use of sodium hydroxide (te., caustic) for producing a soap film to reduce the oil/water interfacial tension.

Various studies on the use of caustic for producing such émulsions hâve demonstrated technical feasibility. However, the practical application of this process for recovering oil has been limited by the high cost of the caustic, likely adsorption of

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-4the soap films onto the formation rock leading to graduai breakdown of the émulsion and the sensitivity of the émulsion viscosity to minor changes in water salinity and water content. For example, because most formations contain water with many dissolved solids, émulsions requiring fresh or distilled water often fail to achieve design 5 potential because such low-salinity conditions are difficult to achieve and maintain within the actual formation. Ionie species can be dissolved from the rock and the injected fresh water can mix with higher-salinity résident water, causing breakdown of the low-tension stâbilized émulsion.

Various methods hâve been used to selectively reduce the permeability of high10 permeability “thief’ zones in a process generally referred to as “profile modification.” Typical agents that hâve been injected into the réservoir to accomplish a réduction in permeability of contacted zones include polymer gels or cross-linked aldéhydes. Polymer gels are formed by crosslinking polymère such as polyacrylamide, xanthan, vinyl polymère, or lignosulfonates. Such gels are injected into the formation where 15 crosslinking réactions cause the gels to become relatively rigid, thus reducing permeability to flow through the treated zones.

In most applications of these processes, the région of the formation that is affected by the treatment is restricted to near the wellbore because of cost and the reaction time of the gelling agents. Once the treatments are in place, the gels are 20 relatively immobile. This can be a disadvantage because the drive fluid (for instance, water in a waterflood) eventually finds a path around the immobile gel, reducing its effectiveness. Better performance should be expected if the profile modification agent could slowly move through the formation to plug off newly created thief zones, penetrating significant distances from injection or production wells.

McKay, in U.S. Pat. No. 5,350,014, discloses a method for producing heavy oil or bitumen from a formation undergoing thermal recovery. McKay describes a method for producing oil or bitumen in the form of oil-in-water émulsions by carefully maintaining the température profile of the swept zone above a minimum température, T_c. If the température of the oil-in-water émulsion is maintained above this minimum

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- 5 température, the émulsion will b'e capable of flowing through the porous subterranean formation for collection at the production well. McKay describes another embodiment of his invention, in which an oil-in-water émulsion is inserted into a formation and maintained at a température below the minimum température. This immobile émulsion is used to form a barrier for plugging water-depleted thief zones in formations being produced by thermal methods, including control of vertical coning of water. However, the method described by McKay requires careful control of température within the formation zone and, therefore, is useful only for thermal methods of recovery. Consequently, the method disclosed by McKay could not be used for non-thermal (referred to as “cold flow”) recovery of heavy oil.

A new process has recently been disclosed that uses novel solids-stabilized émulsions for enhanced oil recovery. The added solid particles help stabilize the oil and water interface to provide enhanced stability to the émulsion. U.S. Patent 5,927,404 describes a method of using the novel solids-stabilized émulsion as a drive fluid to displace hydrocarbons for enhanced oil recovery. U.S. Patent 5,855,243 claims a similar method of using a solids-stabilized émulsion, whose viscosity is reduced by the addition of a gas, as a drive fluid. U.S. Patent 5,910,467 claims the novel solids-stabilized émulsion described in U.S. Patent 5,855,243. U.S. Patent No. 6,068,054 describes a method for using the novel solids-stabilized émulsion as a barrier for diverting the flow of fluids in the formation.

Preparing an émulsion with optimum properties is key to successfully_usmg the émulsion for enhanced oil recovery. Two important properties for using an émulsion in EOR processes are an emulsion's stability and its rheology. The émulsion should be shelf-stable, that is, the émulsion should be able to remain a stable émulsion without water or oil breakout when left undisturbed. In addition, the émulsion should be stable under flow conditions through porous media, i.e. in a subterranean formation. The emulsion's rheological characteristics are also important. For instance, EOR methods for which this émulsion may be used include injecting the émulsion as a drive or barrier fluid into a subterranean formation. Accordingly, the émulsion should hâve an

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-6optimom viscosity for injection and to serve as either a drive or barrier fluid. In practicing EOR, and particularly with using the émulsion as a drive fluid, it is useful to match the rheology of the émulsion with the rheology of subterranean oil to be produced. Oil displacement using a drive fluid is typically more efficient when the drive fluid has a greater viscosity than that of the oil to be displaced.

Because water and oil are readily available at most production sites, water-inoil émulsions are a good choice for making the émulsions for EOR. Some oils possess the chemical composition and physical properties necessary to make stable water-in-oil émulsions. Exemples of such compositions are polar and asphaltene compounds.

However, if the oil does not contain the right type and sufficient concentration of polar and asphaltene compounds, the oil may not form stable water-in-oil émulsions. The previously cited art related to solids-stabilized émulsions suggests that asphaltenes or polar hydrocarbons may be added to these oils to improve their abîlity to form stable émulsions. U.S. Patent 5,855,243, column 7, lines 6-10; U.S. Patent 5,927,404 column 6, lines 44-47; U.S. Patent 5,910,467 column 7, lines 3-6. However, this addition is not always successful because incompatibility between some oil components and the added asphaltenes and polars can resuit in phase séparation or rejection of the added compounds. These cases limit the scope of the inventions disclosed in the U.S. Patents cited above.

Accordingly, there is a need for a method to produce an émulsion that can be made economically and is capable of pérfonning under a wide range 'of formation conditions, including salinity, température and permeability. The présent invention satisfies this need.

SUMMARY OF THE INVENTION

According to the invention, there is described a method for enhancing the stability of a water-in-oil émulsion comprising pretreating at least a portion of the oil prior to émulsification.

c

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-7In one embodiment of the invention, the oil pretreatment step comprises the addition of a polymer to the oil prior to émulsification.

In another embodiment of the invention, the oil pretreatment step comprises biotreating the oil prior to émulsification.

In another embodiment of the invention, the oil pretreatment step comprises photochemically treating the oil prior to émulsification.

Combinations of these embodiments may also be used

Further disclosed is a method for producing hydrocarbons from a subterranean formation, comprising:

a) preparing a water-in-oil émulsion with pretreated oil;

b) contacting the formation with said émulsion, and

c) producing hydrocarbons from the formation using said émulsion.

Further disclosed is the water-in-oil émulsion, at least a portion of the oil being pretreated oil.

Optionally, solid particles mày be added to the oil, either before or after the pretreatment step, to further enhance the stability of the émulsion.

DETAILED DESCRIPTION OF THE INVENTION

The current invention is a method for enhancing the stability of a water-in-oil émulsion comprising pretreating at least a portion of the oil prior to émulsification. 20 The pretreatment step may comprise adding a polymer to the oil, biotreating the oil, photochemically treating the oil, or combinations thereof. Solid particles may also be added to the oil, before or after the pretreatment step, to further enhance the stability of the émulsion. The novel émulsion can be used as a drive fluid to displace hydrocarbons in a subterranean formation, or used as a barrier fluid to divert the flow 25 of hydrocarbons within a subterranean formation.

Accordingly, the présent invention describes a method of pretreating oil to increase the stability of a water-in-oil émulsion. Several embodiments of this invention will now be described. As one of ordinary skill in the art can appreciate, an r

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-8embodiment of this invention may be used in combination with one or more other embodiments of this invention, which may provide synergistic effects in stabilizing the water-in-oil émulsion.

The term oil as used in the spécification, including the claims, comprises oil of any type or composition, including but not limited to crude οΐζ refined oil, oil blends, chemically treated oils, or mixtures thereof. Crude oil is unrefîned liquid petroleum. Refined oil is crude oil that has been. purified in some manner, for example, the removal of sulfur. Crude oil is the preferred oil used to practice this invention, more preferably, the crude oil is produced from the formation where the émulsion is to be used. The produced crude oil may contain formation gas, or formation water or brine mixed with the oiL It is preferred to dehydrate the crude oil prior to treatment, however, mixtures of oil, formation gas and/or formation brine may also be used in this invention.

1. Pretreatment by Addition of a Polymer

To make a polymer stabilized water-in-oil émulsion, a polymer is added to the oil prior to émulsification. The water-in-oil émulsion is formed by adding water in and mixing for a time sufficient to disperse the water as small droplets in the continuons oil phase.

Polymers useful for this invention are preferably polymers, copolymers or tert polymers that either contain reactive and/or interactive functionalities or are capable of being functionalized. Accordingly, the term polymer as used herein includes polymers, copolymers, tert polymers and combinations thereof. Non-limiting examples of reactive and/or interactive functionalities are maleic anhydride, carboxylic acid, sulfonic acid, carboxylates, sulfonates and sulfates. Polymers that are capable of being functionalized in the oil typically, but not exclusively, contain aromatic or olefinic characteristics. The preferred concentration of polymer is from about 0.01% to about c

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-91% based on the weight of the oiL The polymers should be either oil soluble or water soluble, but are preferably oil soluble polymers.

A sulfonating agent may be used to functionalize the polymers that are capable of being functionalized, which can provide additional stability to the émulsion. Thè 5 preferred sulfonating agent is concentrated sulfuric acid. The preferred treat rate of sulfuric acid to oil is between 0.5 to 5wt%, more preferably 1 to 3wt%, based on the weight of oiL The sulfonating agent can be used alone or in combination with other sulfonating agents. Such sulfonating agents are generally described in E. E. Gilbert, Sulfonation and Relaied Réactions, Interscience, New York, (1965). Other 10 sulfonating agents that may be useful in this invention include fuming sulfuric acid, sulfur trioxide, alkali disulfates, pyrosulfates, chlorosulfonic acid and a mixture of manganèse dioxide and sulfurous acid.

As one of ordinary skill in the art can appreciate, the amount of sulfonation useful in the présent invention can be adjusted according especially to the asphaltene 15 and resin content of the oil and the sulfonating agent used. Asphaltenes are natural components in crude oil, which help stabilize the oil-water interface of water-in-oil émulsions. Accordingly, an oil containing a large amount of asphaltene may require less sulfonation than one containing a small amount of asphaltene. Typically, the concentration of the sulfonation agent will be from about 0.1% to about 15% based on 20 the weight of the oiL

The sulfonation procedure results in chemical modifications to the oil and the polymers that are capable of being functionalized:

a) the fonctionalizable components in the oil, or components containing unsaturated and/or aromatic groups, are converted to the corresponding 25 sulfonates and/or sulfonic acid salts. These salts are more surface-active than the base components themselves and thus contribute to improving the stability of the water-in-oil émulsion,

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-loti) if napthenic acids are présent in the oil, sulfonation will markedly enhance their acidity and interfacial activity through the chemically-attached sulfonate groups, and

c) the polymers will be functionalized, which will contribute to the stability of 5 the water and oil interface.

The sulfonation step can occur before or after the addition of the polymer. Because the polymer will be functionalized as a resuit of the sulfonation, and as a resuit contribute to the stability of the émulsion, it is preferred to add the polymer to the oil and then perfoim the sulfonation step.

After the oil is treated with the polymer, and is sulfonated if the sulfonation step is used, water is added in small aliquots or continuously and the mixture is subjected to shear mixing (e.g. at 1000 to 12000 revolutions/minute or rpm) for a time sufficient to disperse the water as small droplets in the continuons oil phase. Preferably, formation water is used to make the émulsion, however, fresh water can 15 also be used and the ion concentration adjusted as needed to help stabilize the émulsion under formation conditions. ît is preferred to hâve a water concentration in the waterin-oil émulsion of 40 to 80%, more preferably 50 to 65%, and most preferably 60%.

The pH of the émulsion can be adjusted by adding a calculated amount of a weak base to the émulsion and shear mixing for a time sufficient to raise the pH to the 20 desired level, preferably in the 5-7 range. The preferred base for this-pH adjustment is ammonium hydroxide. Stronger bases like sodium hydroxide, potassium hydroxide and calcium oxide may hâve a négative effect on émulsion stability. A possible explanation is that these strong bases tend to invert the émulsion from a water-in-oil to an oil-in-water émulsion, which is undesirable for the process of this invention. 25 Adjusting the pH is optional as in some, but not ail, cases it is désirable to inject an acidic émulsion and allow the réservoir formation to buffer the émulsion to the réservoir alkalinity.

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-11Optionally, solid particles can be added to further enhance the stability of the water-in-oil émulsion. Such solids-stabilized émulsions are disclosed in U.S. Patents 5,927,404, 5,910,467, 5,855,243 and 6,068,054. U.S. Patent 5,927,404 describes a method of using the novel solids-stabilized émulsion as a drive fluid to displace 5 hydrocarbons for enhanced oil recovery. U.S. Patent 5,855,243 claims a similar method of using a solids-stabilized émulsion, whose viscosity is reduced by the addition of a gas, as a drive fluid. U.S. Patent 5,910,467 claims the novel solidsstabilized émulsion described in U.S. Patent 5,855,243. U.S. Patent 6,068,054 describes a method for using the novel solids-stabilized émulsion as a barrier for 10 diverting the flow of fluids in the formation.

As disclosed in the above referenced U.S. patents, the solid particles should hâve certain physical properties. The individual particle size should be suffidently small to provide adéquate surface area coverage of the internai droplet phase. If the émulsion is to be used in a porous subterranean formation, the average particle size 15 should be smaller than the average diameter of pore throats in the porous subterranean formation. Methods for determining average particle size are discussed in the previously cited U.S. patents. The solid particles may be spherical in shape, or nonspherical in shape. If spherical in shape, the solid particles should preferably hâve an average size of about five microns or less in diameter, more preferably about two 20 microns or less, even more preferably about one micron or less and most preferably,

100 nanometers or less. If the solid particles are non-spherical in shape; they should preferably hâve an average size of about 200 square microns total surface area, more preferably about twenty square microns or less, even more preferably about ten square microns or less and most preferably, one square micron or less. The solid particles 25 must also remain undissolved in both the oil and water phase of the émulsion under the formation conditions.

The solid particulates used in conjunction with polymer pretreatment preferably possess an oleophilic nature. Typical inorganic particulates that are useful include layered silicates, clays, fumed and precipated silicas, and nonlayered particulates.

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- 12Typical organic particulates include unfùnctionalized and functionalized carbon blacks, asphalts, soot, fibers, and asphaltenes. The particulates can also be treated to obtain an oleophilic quality. Such procedures for forming oleophilic particulates are generally known in tire art and include silane coupling agent technology, and adding surfactants and lignosulfonates. Mixtures of particulates are also useful in this invention. The preferred concentration of the solid particles is from about 0.01wt% to about 10wt% based on the weight of the oil.

If the step of adding a sulfonating agent is used in conjunction with the solid particle addition, the sulfonation procedure will functionalize the surface of the solids and thus modifÿ the solids* surface to improve the interaction with the surface-active components of the oil. Accordingly, it is preferred to add the solid particles before sulfonation, although the solids may also be added after the sulfonation step.

Oleophilic particulates may be formed through functionalization of the oil itself, for instance through sulfonation. However, other functionalization chemistries are available and are known in the art, for example as described in, Advanced Organic Chemistry, J. March, Third Edition. J. Wiley & Sons (1985). These functionalized species form aggregates in the preferred size range described above. Due to their chemical nature and structure, these particulates are interfacially active and will strongly enhance stability of the émulsion.

While pretreatment of the entire quantity of crude oil necessary to make an émulsion is feasible by the method of this invention, it is also possible to treat a slipstream or master batch of oil and subsequently mix the slipstream with a main stream of oil prior to water addition and émulsification. This main stream of oil is preferably untreated crude oil, however, it may be any oil, including oil that has been treated to enhance its ability to form a stable émulsion or treated to optimizè its rheology. If the slipstream method is used, the amount of polymers, solid particles (if any) and sulfonating agent (if any) for the slipstream treatment is sealed accordingly to obtain the desired amounts in the resulting émulsion.

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-13Examples:

This invention has been demonstrated on several different crude oils that do not form stable water-in-oil émulsions. However, as shown in these examples, by nsing the inventive method disclosed herein stable water-in-oil émulsions were formed.

Emulsions prepared by the foregoing methods were subjected to the following tests:

1. Shelf stability at 25°C for 48 hours

2. Optical microscopy and NMR for détermination of water droplet size / size distribution

3. Centrifuge stability (see Appendix-1)

4. Emulsion stability: flow through a sand pack (details of the micropercolation test procedure is given in Appendix-1)

5. Emulsion rheology using a Brookfield® viscometer (cône (#51) and plate configuration) at 60°C in a shear range of 1.92 to 384 sec’¹.

Example I

Crude Oil #1 was sulfonated according to the following procedure: 12 grams (g) of the crude oil was combined with 0.36g concentrated sulfuric acid (96 wt%). This represents 3 parts of acid per 100 parts of oil. This mixture was stirred on a hot plate with a magnetic stirrer attachaient at 55°C for 24 hours.

The sulfonated crude oil (12g) was then combined with 0.1 wt% (based on the weight of the crude oil) maleated ethylene propylene copolymer (EP) (product of Exxon Chemical, Houston, Tx.)> which was added to the sulfonated'crude oil and stirred at 55°C for an additional 24 hours. The solution was cooled to room température and the pH was adjusted to 7.3 using an ammonium hydroxide solution.

A synthetic brine solution 18 g (comprised of 9.4 g sodium chloride, 3.3 g CaCl₂(calcium chloride) · 2H₂0, 0.48 MgCI₂ (magnésium chloride) · 6H₂0, and 0.16 g potassium chloride per liter of distilled water) was added to the sulfonated oil and copolymer mixture as follows: the sulfonated oil—copolymer mixture was mixed in a r 012480

-14Glas-Col 099A S3OA25 high shear mixer for 15 minutes at 5000 rpm to ensure homogenity. The synthetic brine solution was added either dropwise or continuously during mixing. The émulsion thus formed was mixed for an additional 15 minutes at 7500 rpm.

The resulting polymer stabilized water-in-crude oil émulsion had an aqueous phase droplet diameter of less than 4 microns, with a majority of particles less than 3 microns as identified by light microscopy. The émulsion was shelf-stable, and.showed no brine breakout under the microcentrifuge test. This émulsion was also stable under the micropercolation test as indicated by a 1.6% brine breakout.

Example 2

Crude Oil #2 containing 0.05 wt% of maleated EP copolymer was sulfonated according to the procedure described above. The speed of the mixer in ail stages of the émulsion préparation was increased to 7500 ipm due to the viscosity of the crude oil component. The pH of the solution was adjusted to 7.0 using a concentrated 15 ammonium hydroxide solution. The brine breakout of the 60/40 polymer stabilized water-in-crude oil émulsion, as demonstrated by the micropercolation test, was 0%. Droplet diameters were less than 3 microns. The émulsion was also stable under the microcentrifuge test showing no brine breakout and was shelf stable.

Rheological évaluation using a cône and plate viscometer demonstrated high 20 émulsion stability under shearing conditions. Example 3

Example 2 was repeated using 0.1 wt% maleated EP copolymer, instead of 0.05 wt% maleated EP copolymer. Again, the pH of the resulting émulsion was adjusted to approximate the as-received Crude Oil #2 level (~7 pH) by adding a 25 calculated amount of concentrated ammonium hydroxide. The brine breakout was found to be 0% under the micropercolation test using Berea sand. The émulsion was stable under the microcentrifuge test, and was shelf stable. Extensive light microscopy examination of the émulsion shows particle diameters less than 3 microns.

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- 15Example 4

A crude oil blend (50/50 wt% mixture of Crude Oil #2 and a low viscosity crude oil, Crude Oil #3) was prepared and sulfonated as described previously. In this example, 0.05 wt % maleated EP copolymer was used. The pH was adjusted to 7.1 using a concentrated ammonium hydroxide solution. The mixing speed used to préparé the émulsion ranged from 5000-7000 ipm. The brine breakout was evaluated and found to be 0% under the micropercolation test. The émulsion was also stable under the microcentrifuge test showing no brine breakout and was shelf stable. Extensive light microscopy was used to evaluate particle diameter, which in this case was less than 3 microns.

2. Pretreatment bv Biotreating the Oil

Another pretreatment method to enhance the stability of a water-in-oil émulsion comprises the step of biotreating at least a portion of the oil prior to émulsification. The water-in-oil em,ulsion made from the biotreated oil has enhanced stability over water-in-oil émulsions made with untreated oil. Oil degrading microbes are used in the biotreatment process.

To biotreat the oil, the oil is placed in a bioreactor or similar holding vessel. Water should be présent in the reactor, preferably at a volume of 10 to 100 times the volume of the oil. Oil-degrading microbes are added to the reactor at a preferred rate of 0.1wt% to 5wt% inoculum based upon the weight of the bioreactor water. Inoculum is a culture of microbes contained in an aqueous medium. The concentration of microbes in the inoculum is measured by colony foiming units (CFU). Typically the CFU count for microbes in the inoculum will range between 10’ to 10⁹ CFU. These CFU déterminations are known to those of ordinary skill in the art. The oil degrading microbes can be obtained from an oil waste-water treatment facility.

Nutrients can be provided to feed the microbes. The nutrients will preferably contain nitrogen and phosphorus, and which more preferably hâve a carbon to nitrogen to phosphorus (C:N:P) ratio of 100:10:1 to 100:10:0.1. Optionally, other c

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-16nutrients including, without limitation, copper métal sait, iron métal sait, magnum métal sait or cobalt métal sait may also be added to the bioreaction. Air or oxygen is purged into the bioreactor at a preferred rate of about 5 to 3000 cubic centimeters per minute. The température ofthe bioreactor should be between about 20 to 70°C.

It is believed that this biotreatment step has the following affect on the oil that promûtes enhanced stability of a water-in-oil émulsion:

a) Some of the aliphatic components of oil are oxidized and polar ketones or acid functionality are introduced on the aliphatic chain. Organo sulfur compounds are also susceptible to oxidization and can form corresponding sulfoxides. The oxygenated compounds are more surface active than the aliphatic components themselves and thus contribute to improving the stability of the water-in-oil émulsion.

b) If naphthenic acids are présent as salts of divalent cations like calcium, biooxidation is likely to couvert these salts to decaiboxylated naphthenic hydrocarbons or lower carbon number naphthenic acids and the corresponding métal oxide. These constituées serve to enhance the stability of the water-in-oil émulsion.

c) In the process of biotreating oil, the aqueous phase of the bioreaction also undergoes substantial changes. Upon completion of the bioreaction, the aqueous phase is a dispersion of biosurfactants (rhammanolipids produced by the microbes) and dead microbe cells. These-components act synergistically to enhance the stability of water-in-oil émulsions. The aqueous phase of the bioreaction may therefore be used to make the waterin-oil émulsion, and serve to further enhance the stability of the resulting 25 émulsion.

After the biotreatment step, the biotreated oil can be separated from the aqueous phase of the bioreaction prior to forming a water-in-oil émulsion with the biotreated oil. However, it is preferred to form an émulsion using both the biotreated oil and the aqueous phase of the bioreaction as the aqueous phase contains

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- 17components that will help further enhance the stability of the resulting water-in-oil émulsion, as described above.

The water-in-oil émulsion is formed by adding water to the biotreated oil, which may or may not include the aqueous phase of the bioreaction, in small aliquots or continuously and subjecting the mixture to shear mixing (e.g. at 6000 to 12000 rpm) for a time sufficient to disperse the water as small droplets in the continuous oil phase. Preferably, formation water is added to make the émulsion. However, fresh water can be used and the ion concentration adjusted as needed to help stabilize the émulsion under formation conditions. Preferably, the water droplets in the water-in-oil émulsion will be 5 microns or less in size. It is preferred to hâve a water concentration in the water-in-oil émulsion of 40 to 80%, more preferably 50 to 65%, and most preferably 60%.

Optionally, sub-micron or micron sized solid particles can be added to the oil prior to forming the émulsion, as previously discussed, to further enhance the stability of the émulsion.

For this embodiment, it is preferred to hâve solid particles that are hydrophilic or hydrophobie in nature: The solid particles can be added after the oil is biotreated, however, it is preferred to add the solid particles and then biotreat the oil-solid particle mixture. If the solid particles are present during the biotreatment process, the polar oxygenated products that resuit from the biotreatment process adsorbs on to the surface of the solids, thereby rendering them amphiphilic or enhancing their amphiphilic nature. Amphiphilic material has both hydrophobie and hydrophilic characteristics. The enhanced amphiphilic nature of the solid particles increases their effectiveness as stabiiizers at the oil and water interface. Fumed silica, sold under the trade name Aerosil® R972 or Aerosil® 130 (products of Degussa Corp.), divided bentonite clays, kaolinite clays, organophilic or carbonaceous asphaltenic solids are the preferred solids. The preferred treat rate for solids is 0.05 to 0.25wt% based on the weight of the oil.

012480

- 18The biotreatment step may be used in conjunction with acid treatment to provide additional stability to the resulting water-in-oil émulsion. The acid treatment consists of adding dilute acid to the oil prior to émulsification. The acid is preferably added to the oil after the biotreatment step as the acid content may harm the microbes 5 used for oil dégradation and diminish their effectiveness as oil degraders. The acid can be added at a preferred rate of between 8 to 30,000 ppm based on the weight of the oil, more preferably 10 to 80 ppm, and even more preferably 8 to 20 ppm. The dilute acid can be minerai or organic acid. Dilute sulfuric acid is the preferred minerai acid, however other minerai acids like hydrochloric acid, perchloric acid, and phosphoric 10 acid may also be used. The preferred organic acid is acetic acid. However, other organic acids like para-toluene sulfonic, alkyl toluene sulfonic acids, mono di and trialkyl phosphoric acids, organic mono or di caiboxilic acids, e.g. formic, C3 to Cl6 organic carboxylic acids, succinic acid and petroleum naphthenic acid are also effective in this embodiment. Mixtures of minerai acids, mixtures of organic acids or 15 combinations of minerai and organic acids may be used to produce the same effect.

Petroleum naphthenic acid or crude oils containing a high concentration of naphthenic acid can be added to provide the enhanced stability.

If this acid treatment is used, the pH of the resulting émulsion can be adjusted by adding a calculated amount of a weak base to the émulsion and shear mixing for a 20 time sufficient to raise the pH to a desired level, preferably to a pH of between 5-7.

Ammonium hydroxide is the preferred base. Stronger bases like sodium hydroxide, potassium hydroxide and calcium oxide hâve a négative effect on émulsion stability, as these strong bases tend to invert the émulsion from a water-in-oil émulsion to an oil-inwater émulsion, which is undesirable for the puiposes of the présent invention.

Adjusting the pH is optional, as in some cases it is désirable to inject an acidic émulsion and allow the réservoir formation to buffer the émulsion to the réservoir alkalinity.

One may also blend the biotreated oil vrith thennally treated oil to further stabilize and/or reduce the viscosity of the resulting water-in-oil émulsion. Thennally

012480

- 19treated oils are discussed in correspondingly filed U.S. Patent Application No. 09/819,331, related to solids-stabilized émulsions. The émulsion formed from the biotreated oil can also hâve its viscosity reduced by the addition of gas.

The preferred process is to biotreat a slipstream or master batch of oil and subsequentiy mix the slipstream with a main stream of oil. prior to water addition and émulsification. This main stream of oil is preferably untreated crude oil, however, it may be any οϊζ including oil that hàs been treated to enhance its ability to form a stable émulsion or treated to optimize its rheology.

Examples:

In a typical experiment 5grams (g) of crude oil was added to 30 milliliters (ml) of water or brine in a conical flask with a four-way baffle at the bottom. The conical flask with the four-way baffle is a spécial design to allow adéquate aération in biotreatment experiments. Urea and ammonium dihydrogen phosphate were added to the flask in an amount where the C:N.P ratio was 100:10:1. This level is optimum for 48 hour biotreatment of crude oil. Lower levels can be used with appropriate increase in reaction time. Hydrophobie solid particles like divided bentonite or hydrophobie silica, e.g. Aerosil® R 972, can be added to the flask for enhanced effectiveness. If solid particles are used, the polar oxygenated products can adsorb onto the surface of the solids and render them more hydrophobie. Thus, it is préférable to add the-solids prior to the bioreaction. N.ext, a 1 ml aliquot of an inoculum of hydrocarbon degraders, i.e. microbes, obtained from a refinery wastewater treatment plant-was added to the bioreactor. The contents of the flask were shaken on an orbital shaker at 250 rpm for 48 hours at room température.

After 48 hours of biotreatment, the entire contents of the flask were added in 5 ml aliquots to 15g of untreated crude oil and mixed using a Silverson® mixer at 12000 rpm to provide a solids-stabilized water-in-crude oil émulsion. The procedure described above generates an untreated/biotreated feed of 75/25. For higher ratios of untreated/biotreated feed (e.g., 90/10 or 95/5) the entire contents of the bioreactor

012480

-20were added to the required quantity of untreated crude oil and mixed. This step was followed by addition of more water and mixing to provide the desired émulsion.

The biotreated water-in-oil émulsions were subjected to the following tests

1. Bench stability at 25°C

2. Optical Microscopy and NMR for détermination of brine droplet size / size distribution

3. Centrifuge stability (the microcentrifuge test is described in Appendîx-1)

4. Micropercolation test (Flow stability through a sand pack as described in Appendix - 1)

5. Emulsion rheology using a Brookfield® viscometer (cône (#51) and plate configuration) at 60°C in a shear range of 1.92 to 384 sec'¹.

Illustrative Examples

The invention has been demonstrated using two crude oils referred to herein as Oil #1 and Oil #2.

As indicated in Table ,1, Iatroscan and HPLC-2 analyses of Oil #1 before and after biotreatment indicate that the primary change in the crude oil composition is a decrease in saturâtes and increase in polars due to the biotreatment. This observation is in line with expectations conceming nutrient enhanced crude oil bio-oxidation.

01248 Ο

-21 TABLE-1

Changes in Crude Oil Resulting from Biotreatment

Iatroscan Results

Mass % Components

Untreated Oil #1

Biotreated Oil #1

HPLC-2 Results

Untreated Oil #1

Biotreated Oil #1

Saturâtes Aromatics NSO’s Asphaltenes

<td> 39.22</td><td> 38.26</td><td> • 14.19</td><td> 8.34</td>

<td> 35.99</td><td> 38.59</td><td> 17.08</td><td> 8.40</td>

<td> Saturâtes</td><td> IRing</td><td> Mass %Components 2Rine 3Ring 4Ring</td><td> Polars</td><td> Mass Recoverv</td>

<td> 49.10</td><td> 7.85</td><td> 8.24 5.12 13.17</td><td> 16.52</td><td> 76.27</td>

<img file="OA12480A_D0001.tif" />

<img file="OA12480A_D0002.tif" />

<img file="OA12480A_D0003.tif" />

<img file="OA12480A_D0004.tif" />

<img file="OA12480A_D0005.tif" />

<img file="OA12480A_D0006.tif" />

<img file="OA12480A_D0007.tif" />

en

Experimental data on émulsification using blends of biotreated and untreated crude oil are compiled in Table 2.

TABLE-2

Solids Stabilized 60/40 Water-in-Oil Emulsions Containing Biotreated Oil and

<td> Oil</td><td> Solids</td><td> Wt%</td>

<td> -</td><td> -</td><td> solids</td>

<td> l.Oil#l</td><td> R 972</td><td> 0.15</td>

<td> 2.Oil#l</td><td> R 972</td><td> 0.15</td>

<td> 3.Oil#l</td><td> D-Bent^2-</td><td> o.oz,</td>

<td> 4.OiI#l</td><td> R 972³</td><td> 0.15</td>

<td> 5.Oil#l</td><td> R 972</td><td> 0.15</td>

<td> 6.0il#l</td><td> R 972</td><td> 0.15</td>

<td> 7.0il#l</td><td> D-Bent</td><td> 0.07</td>

<td> 8.0il#2</td><td> R 972</td><td> 0.15</td>

<td> 9.Oil#2</td><td> R 972</td><td> 0.15</td>

Biotreated Water

<td> %Biotreated Oil #1</td><td> %Biotreated Water</td><td> Stability % bbo</td><td> Viscosity (cP) 60°C, 9.6s’¹</td>

<td> 0</td><td> 0</td><td> 47</td><td> 3644</td>

<td> 0</td><td> o¹·</td><td> 47</td><td> 3644</td>

<td> 0</td><td> 0</td><td> 62</td><td> Unstable</td>

<td> 12</td><td> 50</td><td> 0</td><td> 4258</td>

<td> 5</td><td> 20</td><td> 0</td><td> 4750</td>

<td> 1</td><td> 22</td><td> 10</td><td> 4750</td>

<td> 5</td><td> 100</td><td> 20</td><td> 4258</td>

<td> 0</td><td> 0</td><td> 45</td><td> 1474</td>

<td> 12</td><td> 50</td><td> 0</td><td> 2457</td>

012480

-22^L Urea and ammonium dihydrogen phosphate were added to the brine in this experiment to détermine the influence of nutrients only on stability ^x D- Bent is divided bentonite clay ³· R 972 is Aerosil® R972 (product of Degussa Corp.)

The first three entries in Table 2 are controls that indicate solids-stabilized water-in-oil émulsions made from Oil #1 with no biotreatment. These émulsions show sigmficant brine breakout in the Berea micropercolation test. Note that Entry number 2 shows that the nutrients do not act as additives to influence émulsion stability.

Entries number 4, S, 6 &amp; 7 illustrate the influence of biotreatment on enhancing émulsion stability.

With 0.15 wt% Aerosil® R 972 as the solids stabilizer, addition of biotreated crude and brine imparts significant émulsion stability as evidenced by the low brine breakouts. In experiments 4, 5 &amp; 6 the hydrophobie solids, Aerosil® R 972, were added to the oil after the bioreaction step but before the addition of brine and mixing. The viscosity of the émulsions was unchanged with repeat cycles, indicative of émulsion stability to shear. Dispersed brine droplets were less than 4 microns in diameter in these émulsions.

In the experiment relating to entry number 7, divided bentonite-was added to the bioreactor and the solids were allowed to interact with the bioproducts during the biotreatment process. Improved émulsion stability is observed using divided bentonite clay as the solids stabilizer when used in conjunction with the biotreatment process, as indicated by the réduction of brine breakout from 62% without biotreatment to 20% with biotreatment.

Entry number 8 is a control émulsion made from Oil #2 and solids (with no biotreatment) showing significant brine breakout in the Berea micropercolation test.

Entry number 9 illustrâtes the influence of biotreatment of the crude oil on enhancing émulsion stability of Oil #2.

012480

-23The présent invention has been described in connection with its preferred embodiments. However, persons skilled in the art will recognize that many modifications, alterations and variations to the invention are possible without departing from the true scope of the invention. Accordingly, ail such modifications, alterations 5 and variations shall be deemed to be induded in this invention as defined by the appended claims.

3. Pretreatment bv Photochemical Treatment of Oil

Another pretreatment step for improving the stability of a water-in-oil émulsion comprises the step of photochemically treating at least a portion of the oil prior to 10 émulsification. The photochemically treated oil is mixed with water to form a waterin-oil émulsion, which has enhanced stability over a water-in-oil émulsion made with untreated oil. Optionally, solid particles can be added to make a solids-stabilized water-in-oil émulsion with enhanced stability.

The photochemical treatment process comprises exposing oil to a suitable light source for a sufficient time to cause a photochemical reaction to occur in the oil. The light source can be from UV to visible radiation, and is preferably sunlight. Increasing the surface area of the oil exposed to the light source enhances the photochemical reaction. Accordingly, the oil is preferably placed such that optimum surface area is exposed to the light source. For example, for the preferred embodiment of using sunlight as the light source, it is preferred to spread the oil in a thin layer so that a large surface area of the oil is exposed to the sunlight. Moreover, the surface area of the oil exposed to the light source can be increased by periodical mixing.

The photochemical treatment of oil can be performed either with or without the presence of air of oxygen. When the process is performed in the absence of air or 25 oxygen, radical cross-linking reactions can occur which lead to increased production of asphaltene-like compounds. These asphaltene-like compounds are surface-active and act as stabilizers at the water and oil interface, thereby promoting émulsion stability. When the process is performed in the presence of air or oxygen, these asphaltene-like

012480

-24compounds are also formed. But in addition to the radical cross-linking reactions that form these stabilizing compounds, oxidation reactions can also occur. The aromatic components of the oil that hâve benzylic carbons and those that hâve fused rings that are oxidizable including, but not limited to naphthalene and anthracene, are oxidized to the corresponding acids, ketones or quinone products. Organo sulfur and nitrogen compounds présent in the oil are oxidized to sulfoxides and nitrogen oxides. These oxygenated compounds are more surface-active than the aromatic components themselves and act as stabilizers at the oil and water interface, thereby providing enhanced émulsion stability. It is preferred to photochemically treat the oil in the presence of air or oxygen.

A dye sensitizer can be added to the oil to enhance the photochemical treatment process. The dye sensitizer will increase the quantum efficiency of the photochemical conversion of· crude oil to oxidized and cross-linked products. Oil soluble dyes are the preferred dyes, however water soluble dyes can also be used. Non-limiting examples of dye sensitizers are Rhodamine-B, Crystal Violet and Mallicite Green. Such dye sensitizers and the techniques of using such are well known in the art, and therefore will not be discussed herein. The photo-oxidation can be conducted at elevated. températures to enhance the reaction rate and achieve product selectivity, however, photo-oxidation between 25 to 50°C is preferred.

Optionally, sub-micron or micron sized solid particles can be added to the oil prror to formiflg the émulsion, as previously discussed, which particles act -to further enhance the stability of the resulting émulsion.

The solid particles useful in conjunction with photochemical pretreatment can be either hvdrophilic or hydrophobie. Bentonite clays, such as those mined in Wyoming, Ga, or other numerous locations around the world, are particularly suitëd as stabilizers for water-in-oil émulsions. As mined, these clays naturally consist of aggregates of particles that can be dispersed in water and broken up by shearing into units having average particle sizes of 2 microns or less. However, each of these particles is a laminated unit containing approximately 100 layers of fondamental silicate

012480

-25 layers of 1 nanometer (nm) thickness bonded together by inclusions of atoms such as calcium in the layers. By exchanging the atoms such as calcium by sodium or lithium (which are larger and hâve strong attractions for water molécules in fresh water), and then exposing the bentonite to fresh water, the bentonite can be broken into individual 1 nm thick layers, called fondamental particles. The chemistry of this délamination process is well known to those skilled in the art of clay chemistry. The resuit of this délamination process is a gel consisting of divided bentonite clay.

The solid particles can be added after the oil is photochemically treated, however, it is preferred to add the solid particles to the oil and then photochemically treat the oil-solid particle mixture. If the solid particles are présent during the photochemical treatment process performed in the presence of air or oxygen, the polar oxygenated products that resuit from the treatment can adsorb on to the surface of the solids, thereby rendering them amphiphilic or enhancing their amphiphilic nature. Amphiphilic material has both hydrophobie and hydrophilic characteristics. The enhanced amphiphilic nature of the solid particles increases their effectiveness as stabilizers at the oil and water interface. Fumed siiica, sold under the trade name Aerosil® R 972 or Aerosil® 130 (products of Degussa Corp.), divided bentonite clays, kaolinite clays, organophilic or carbonaceous solids like coke fines or coal dust are the preferred solids.

Preferably, formation water is used to make.the émulsion, however, fresh water can also be used and the ion concentration adjusted as needed to help stabilize the émulsion under formation conditions.

Préparation of a Solids-Stabilized Emulsion Usine Photochemically Treated Oil

To préparé an émulsion using photochemically treated oil, the oil is photochemically treated for a sufficient time to enable the physical and chemical modifications to the oil. Preferably, the oil is irradiated by sunlight, however any other light source within the UV to visible range will suffice. The treatment may occur in the absence of air or oxygen. but it is preferred to photochemically treat the oil in the presence of air or oxygen.

012480

-26If solid particles are used, the solid particles may be added before, during or after the photochemical treatment, but should be added before émulsification. The amount of solid particle added to the oil can vary in the range of about 1% to 90% based on the weight of the oil. At the higher concentrations, the mixture of solids and oil will be a high solids content slurry. The preferred treat rate for the solids is 0.05 to 2.0 wt%, based on the weight of the oil.

The preferred solid is divided or delaminated bentonite clay that is obtained as a gel from the délamination process described above. The amount of gel added to the oil before the photochemical treatment step can vary in the range of 5 to 95 % of gel 10 based on the weight of the oil, preferably 40 to 60%. The weight of bentonite clay solids in the gel can vary from 1 to 30% based on the weight of the water. When bentonite clay gel is used as the solid particle. and is added to the oil and subjected to the photochemical treatment step, water from the gel will evaporate from the oil/gel mixture. It is preferred to evaporate more than 50% of the water from the bentonite clay gel and oil mixture.

It is preferred to photochemically treat a slipstream or master batch of a mixture of oil and solids and subsequently mix the slipstream with a main stream of oil prior to water addition and mixing, i.e. prior to émulsification. This main stream of oil is preferably untreated crude οίζ however, it may be any oil, including oil that-has been 20 treated to enhance its ability to form a stable émulsion or treated to optimize its rheology. If untreated crude oil is used as the main stream, the preferred blending rate is 0.01 to 10% of photochemically treated oil in the untreated main stream, more preferably 1 to 2%.

After the photochemical treatment step and solid particle addition (if any), water is added in small aliquots or continuously and the mixture is subjected to shear mixing at 1000 to 12000 rpm for a time sufficient to disperse the water as small droplets in the continuous oil phase. It is preferred to hâve a water concentration in the water-in-oil émulsion of 40 to 80%, more preferably 50 to 65%, and most preferably 60%. The température of the émulsion will rise above ambient température

012480

-27of 25°C during mixing. Controlling the température of the émulsion during mixing is not critical, However, higher températures between 40 to 70°C are preferred.

The photochemically treated oil can be further treated with dilute minerai or organic acid to provide additional stability to the water-in-oil émulsion. The preferred 5 acid treat rate is between S and 30,000 ppm. If this acid pretreatment step is used, the pH of the resulting émulsion can be adjusted by adding a calculated amount of a weak base to the émulsion to obtain an émulsion in the preferred pH range of 5 to 7. However, adjusting pH is optional as in some cases it is désirable to inject an acidic émulsion and allow the réservoir formation to buffer the émulsion to the réservoir 10 alkalinity.

. Ammonium hydroxide is the preferred base for pH adjustment. Stronger bases like sodium hydroxide, potassium hydroride and calcium oxide hâve a négative effect on émulsion stability. One possible explanation for this effect is that strong bases tend to invert the émulsion, i.e. couvert the water-in-oil émulsion to an oil-in-water 15 émulsion. Such an inversion is undesirable for the puiposes of this invention.

In addition to increasing the stability of the water-in-oil émulsion, dilute acid treatment lowers the viscosity of the émulsion. This reduced viscosity aids in enhancing the injectivity of the émulsion, and may also be bénéficiai in other aspects in EOR processes, for example, matching the emulsion's rheology with that of the 20 subterranean oil to be recovered when using the émulsion as a drive fluid. Gas may also be added to further lower the viscosity of the émulsion.

Examples:

In a typical experiment, lgram (g) of bentonite clay gel is mixed with 0.1g of a crude oil, Crude Oil #1, providing a gel to crude oil ratio of 1:0.1. The oily gel is then 25 spread out as a thin layer on a pétri dish and photochemically treated by placing the oil under a 200 Watt (W) tungstenlamp for 48 hours.

For a dye sensitized photochemical treatment process, lg of Crude Oil #1 is first mixed with 0.01g of Rhodamine-B dye, which is a red dye that is known to incrèase the quantum efficiency of the photo-chemical conversion of oil to oxidized

012480

-28 products. The dye-sensitized oil is then mixed with bentonite clay gel at a gel to crude oil ratio of 1:0.1. The oily gel is spread out as a thin layer on a pétri dish and photochemically treated by placing under a 200W tungsten lamp for 48 hours.

Crude Oil #1 and dye sensitized Crude Oil #1 samples without added solid 5 particles were also photochemically treated under the 200W tungsten lamp for 48 hours.

Results of the IATRO scan (silica gel column chromatography) analyses on untreated Crude Oil #1 and photochemically treated Crude Oil #1 are shown in Table3. Photochemical treatment results in a decrease in the aromatic fraction and an 10 increase in the oxidized fraction and the polar asphaltene fraction of the crude oil.

012480

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012480

-30Préparation of Water-in-Crude Emulsions Usine Photochemically Treated Bentonite Solids-stabilized water-in-crude oil émulsions were prepared by first mixing the 5 photochemically treated bentonite solids with the untreated crude oil at a treat rate of 0.12 wt% of solids to the weight of crude oil. This was followed by water addition in small aliquots to the crude oil and mixing after each addition, as described above. Mixing was accomplished using a Silverson Mixer at 12000 rpm.

The water-in-oil émulsions were subjected to the following tests

1. Bench stability at 25’C

2. Optical Microscopy and NMR for détermination of brine droplet size / size distribution

3. Flow stability through a sand pack with and without ethane addition (Micropercolation test is described in Appendix-1)

4. Centrifuge stability (described in Appendix-1)

5. Emulsion rheology using a Brookfiéld viscometer (cône (#51) and plate configuration) at 60°C in a shear range of 1.92 to 384 sec*¹.

Emulsion stability results for a 60/40 Water-in-Crude Oil #1 stâbilized with

0.12wt% of photochemically treated bentonite is shown in Table-4. Addition of untreated bentonite is observed to cause destabilization of the émulsion. However when the photochemically treated bentonite is used a significant increase in stability results. Further, when ethane (400 psi) is added to the émulsion as viscosity reducing agent, rétention in émulsion stability is observed.

012480

-31TABLE-4

Micro-Percolation Test Results for Water-in-Crude Oil #1 Emulsions Stàbilized by Photochemical Treatment %Brine

Break Out

Untreated Emulsion

Bentonite Treated Emulsion

Photochemical Treatment + Bentonite Treated Emulsion

Photochemical Treatment + Bentonite + Ethane Treated Emulsion

48%

58%

21%

18%

TJsing the Pretreated Water-in-Oil Emulsion

The pretreated water-in-oil émulsion can be used in a wide range of enhanced oil recovery applications. One typical application is using such an émulsion for displacing oil from a subterranean formation, i.e. using the pretreated water-in-oil émulsion as a drive fluid. The pretreated water-in-oil émulsion is prepared and then injected into the subterranean formation, typically, but not necessarily through an injection well. The water-in-oil émulsion, which is injected under pressure, is used to displace the oil in the formation towards a well, typically a production well, for recovery.

Another application is to use the pretreated water-in-oil émulsion as a barrier fluid to divert the flow of hydrocarbons in a subterranean formation. The pretreated water-in-oil émulsion is prepared and then injected into the subterranean formation. The émulsion is used to fill thief zones or to serve as a horizontal barrier to prevent coning of water or gas. As previously noted, thief zones and coning events will reduce the efficiency of enhanced oil recovery operations.

The présent invention has been described in connection with its preferred embodiments. However persons skilled in the art will recognize that many modifications, alterations, and variations to the invention are possible without

012480

-32departing from the true scope of the invention. Accordingly, ail such modifications, alterations, and variations shall be deemed to be included in this invention, as defined by the appended claims.

0Î2480

-33Appendix-1: Micro-Percolation Test for Emulsion Stability in Flow Through Porous Media

The observation that émulsions that are unstable will form two separate macroscopie phases, an oil/emulsion phase and a water phase, is relied upon in order to 5 ascertain the stability of an émulsion on flow through porous media in a rapid, convenient assay. A volume of émulsion that passes completely through the porous media can therefore be centrifuged to form two distinct phases, whose volumes can be used as a measure of the émulsion stability—the greater the proportion of water or water originally in the émulsion, that forms a clear, distinct phase after passage and 10 centrifugation, the more unstable the émulsion. A convenient parameter to measure stability is therefore the “brine-breakout” or “bbo”, defined as the fraction of the water or brine that is in the émulsion that forms the distinct separate aqueous phase. Since it is a proportion, the bbo is dimensionless and ranges between one (maximally unstable) and zéro (maximally stable). The brine breakout is measured under a well-defined set 15 of conditions.

A commercially available spécial fritted micro-centrifuge tube that is comprised of two parts is used as the container for the experiment. The bottom part is a tube that catches any fluid flowing from the top tube. The top part is similar to the usual polypropylene microcentrifuge tube, except that the bottom is a frit that is small 20 enough to hold sand grains back, but allows the easy flow of fluidr In addition, the tubes corne supplied with Iids to each part, one of which serves also as a support that allows the top to be easily weighed and manipulated while upright. They are available from Princeton Séparations, Inc., Adelphia NJ and are sold under the name CENTRISEP COLUMNS.

A heated centrifuge is used to supply the pressure to flow the émulsion fluid through a bit of sand placed in the upper tube. It was supplied by Robinson, Inc., (Tulsa, OK) Model 620. The température is not adjustable, but stabilizes at 72°C under our conditions. The top speed is about 2400 révolutions per minute (RPM) and

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-34the radius to the sandpack is 8 centimeters (cm), which gives a centrifugal force of 520

g. Ail weights are measured to the nearest milligram.

The columns corne supplied with a small supply of silica gel already weighed into the tube. This is discarded, and the weights of both sections noted. About 0.2 5 grams (g) of sand is weighed into the top and 0.2 ± 0.01 g of oil added to the top.

Typical sands used for this experiment are Berea or Ottawa sands. The sand that is used in this test can be varied according to one's purpose. For simplicity, one may use unsieved, untreated Ottawa sand, supplied by VWR Scientific Products. This gives a convenient, forgiving system because the sand particles are rather large and free of 10 clay. Alternatively, one may use one fraction that passes through 100 Tyler mesh, but is retained by a 150 mesh, and another fraction that passes through the 150 Tyler mesh, blended in a ten to one ratio respectively. The tube is weighed again, then centrifuged for one minute at full speed on the heated centrifuge. The bottom tube is discarded and the top is weighed again, which gives the amount of sand and oil 15 remaining in the top. The sand is now in an oil wetted state, with air and oil in the pore space.

Now, 0.18 ± 0.02 g of émulsion is placed on top of the wetted sand, and the top is weighed again. A bottom tube is weighed and placed below this tube to catch the effluent during centrifugation.

A separate bottom tube is filled with 0.2 to 0.5 g of émulsion only. This serves as a control to détermine if the centrifuging of the émulsion, without it being passed through the oil-wetted sand, causes brine to break from the émulsion. This step is known as the microcentrifuge test, and is also an indicaior of émulsion stability.

Both tubes are then centrifuged for a noted time (15 to 45 minutes) depending 25 on the oil viscosity and centrifuge speed. The object in adjusting the length of time is to get to a point where at least 75% of the émulsion arrives in the bottom tube after passing through the sand. If less than that appears, the assembly is centrifuged for an additional time(s).

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-35After spinning, the weight of the top and bottom pièces are again recorded. If the émulsion is unstable, a clear water phase will be visible in the bottom of the tube, below an opaque, black emulsion/oil phase. The volume of water in the bottom réceptacle is then measured by pulling it up into a précision capillaiy disposable pipette 5 (100-200 microliters) fitted with a plunger. These are supplied by Drummond

Scientific Co. (under the name Wiretroll H). The length of the water column is measured and converted to mass of water through a suitable calibration curve for the capillary. The water breakout can be then calculated from these measurements and the knowledge of the weight fraction of water in the émulsion originally.