OA12250A - Solids-stabilized water-in-oil emulsion and methodfor using same. - Google Patents

Abstract

A method for enhancing the stability of a solids-stabilized water-in-oil emulsion by pretreating the oil prior to emulsification. The pretreatment step can be accomplished by adding dilute acid to the oil, adding a lignosulfonate additive to the oil, sulfonating the oil, thermally oxidizing the oil, thermally treating the oil in an inert environment, and combinations thereof. The emulsion can be used in enhanced oil recovery methods, including using the emulsion as a drive fluid to displace hydrocarbons in a subterranean formation, and using the emulsion as a barrier fluid for diverting flow of fluids in the formation.

Description

012250 -1-

SOLIDS-STABILIZED WATER-IN-OIL EMULSIONAND METHOD FOR USING SAME

FCELD OF THE INVENTION

The présent invention relates to a solids-stabilized water-in-oil émulsion usedfor enhanced crude oil recovery. More specifically, the stability of the solids-stabilizedwater-in-oil émulsion is enhanced by the method of pretreating the oil prior toémulsification. The pretreatment step can be accomplished by adding dilute acid to theoil, adding a lignosulfonate additive to the oil, sulfonating the oil, thermally treating theoil in an inert environment, thermally oxidizing the oil, and combinations thereof.. Theimproved émulsion may be used either as a drive fluid to displace hydrocarbons from asubterranean formation or as a barrier fluid for diverting the flow of hydrocarbons inthe formation.

BACKGROUND OF THE INVENTION lt is well known that a significant percentage of oil remains in a subterraneanformation after the costs of primary production rise to such an extent that further oilrecovery is cost ineffective. Typically, only one-fifth to one-third of the original oil inplace is recovered during primary production. At this point, a number of enhanced oilrecovery (EOR) procedures can be used to further recover the oil in a cost-effectivemanner. These procedures are based on re-pressuring or maintaining oil pressureand/or mobility.

For example, waterflooding of a réservoir is a typical method used in theindustry to increase the amount of oil recovered from a subterranean formation.Waterflooding involves simply injecting water into a réservoir, typically through aninjection well. The water serves to displace the oil in the réservoir to a productionwell. However, when waterflooding is applied to displace viscous heavy oil from a 012250 -2- formation, the process is inefficient because the oil mobility is much less than the watermobility. 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 theoriginal oil in place, with waterflooding yielding only another 2 to 5% of that oil inplace. Consequently, there is a need to either make the water more viscous, or useanother drive fluid that will not channel through the oil. Because of the large volumesof drive fluid needed, it must be inexpensive and stable under formation flowconditions. Oil displacement is most efficient when the mobility of the drive fluid issignificantly less than the mobility of the oil, so the greatest need is for a method ofgenerating 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 productionwells allow most of the injected drive fluid to channel quickly to the production wells,leaving oil in other zones relatively unrecovered. A need exists for a low-cost fluidthat can be injected into such thief zones (from either injection wells or productionwells) to reduce fluid mobility, thus diverting pressure energy into displacing oil fromadjacent lower-permeability zones.

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

For moderately viscous oils -- i.e., those having viscosities of approximately20-100 centipoise (cP) — water-soluble polymers such as polyacrylamides or xanthangum hâve been used to increase the viscosity of the water injected to displace oil fromthe formation. For example, polyacrylamide was added to water used to waterflood a24 cP oil in the Sleepy Hollow Field, Nebraska. Polyacrylamide was also used to 012250 -3- viscosify 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 mobilitywaterflood 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 viscousthat the amount of polymer needed to achieve a favorable mobility ratio would usuallybe uneconomic. Further, as known to those skilled in the art, polymer dissolved inwater often is desorbed from the drive water onto surfaces of the formation rock, 10 entrapping it and rendering it ineffective for viscosifÿing the water. This leads to lossof mobility control, poor oil recoveiy, and high polymer costs. For these reasons, useof polymer floods to recover oils having viscosities in excess of 100 cP is not usuallytechnically or economically feasible. Also, performance of many polymers is adverselyaffected 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 producingviscous drive fluids that can maintain effective mobility control while displacingmoderately viscous oils. For example, water-in-oil and oil-in-water macroemulsionshâve 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 fromCanada and Venezuela. The émulsions were stabilized by soap films created bysaponification of acidic hydrocarbon components in the crude oil by sodium hydroxide.These soap films reduced the oil/water interfacial tension, acting as surfactants tostabilize the water-in-oil émulsion. It is well known, therefore, that the stability of 25 such émulsions substantially dépends on the use of sodium hydroxide (i.e., caustic) forproducing a soap film to reduce the oil/water interfacial tension.

Various studies on the use of caustic for producing such émulsions hâvedemonstrated technical feasibility. However, the practical application of this processfor recovering oil has been limited by the high cost of the caustic, likely adsorption of 012250 -4- the 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 andwater content. For example, because most formations contain water with manydissolved solids, émulsions requiring fresh or distilled water often fai! to achieve designpotential because such low-salinity conditions are difficult to achieve and maintainwithin the actual formation. Ionie species can be dissolved from the rock and theinjected fresh water can mix with higher-salinity résident water, causing breakdown ofthe low-tension stabilized émulsion.

Various methods hâve been used to selectively reduce the permeability of high-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 inpermeability of contacted zones include polymer gels or cross-linked aldéhydes.Polymer gels are formed by crosslinking polymers such as polyacrylamide, xanthan,vinyl polymers, or lignosulfonates. Such gels are injected into the formation wherecrosslinking reactions cause the gels to become relatively rigid, thus reducingpermeability to flow through the treated zones.

In most applications of these processes, the région of the formation that isaffected by the treatment is restricted to near the wellbore because of cost and thereaction time of the gelling agents. Once the treatments are in place, the gels arerelatively 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 itseffectiveness. Better performance should be expected if the profile modification agentcould 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 oilor bitumen from a formation undergoing thermal recovery. McKay describes a methodfor producing oil or bitumen in the form of oil-in-water émulsions by carefullymaintaining the température profile of the swept zone above a minimum température,Tc. If the température of the oil-in-water émulsion is maintained above this minimum 012250 -5- temperature, the émulsion will be 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 relatively immobile 5 émulsion is used to form a barrier for plugging water-depleted thief zones informations being produced by thermal methods, including control of vertical coning ofwater. However, the method described by McKay requires careful control oftempérature within the formation zone and, therefore, is useful only for thermalmethods of recovery. Consequently, the method disclosed by McKay could not be 10 used for non-thermal (referred to as “cold flow”) recovery of heavy oil. A new process has recently been disclosed that uses novel solids-stabilizedémulsions for enhanced oil recovery. U.S. Patent 5,927,404 describes a method ofusing the novel solids-stabilized émulsion as a drive fluid to displace hydrocarbons forenhanced oil recovery. U.S. Patent 5,855,243 daims a similar method of using a 15 solids-stabilized émulsion, whose viscosity is reduced by the addition of a gas, as adrive fluid. U.S. Patent 5,910,467 daims the novel solids-stabilized émulsiondescribed in U.S. Patent 5,855,243. U.S. Patent 6,068,054 describes a method forusing the novel solids-stabilized émulsion as a barrier for diverting the flow of fluids inthe formation. 20 Preparing a solids-stabilized émulsion with optimum properties is key to successfùlly using the émulsion for enhanced oil recovery. Two important propertiesare an emulsion's stability and its rheology. The solids stabilized émulsion should beshelf-stable, that is, the émulsion should be able to remain a stable émulsion withoutwater or oil breakout when left undisturbed. In addition, the émulsion should be stable 25 under flow conditions through porous media, i.e. in a subterranean formation. Theemulsion's rheological characteristics are also important. For instance, EOR methodsfor which this émulsion may be used include injecting the émulsion as a drive or barrierfluid into a subterranean formation. Accordingly, the émulsion should hâve anoptimum viscosity for injection and to serve as either a drive or barrier fluid. In Ù12250 -6- practicing EOR, and particularly with using the émulsion as a drive fluid, it is useful tomatch the rheology of the émulsion with the rheology of subterranean oil to beproduced. Oil displacement using a drive fluid is typically more efficient when thedrive fluid has a greater viscosity than that of the oil to be displaced. In addition to 5 providing stability to the solids-stabilized émulsion, the invention described herein willallow the user to préparé solids-stabilized émulsions with a wide range of rheology tomatch that of the oil to be produced.

Because water and oil are readily available at most production sites, water-in-oil émulsions are a good choice for making the solids-stabilized émulsions for EOR. 10 Some oils possess the Chemical composition and physical properties necessaiy to makestable solids-stabilized water-in-oil émulsions with a wide range of solids. The addedsolids interact with components of oil, i.e., polars and asphaltenes, resulting in anincrease in their effectiveness as surface-active agents. This interaction is spécifie tothe type of solids and the composition of the oil to which they are added. 15 However, if the oil does not contain the right type and sufficient concentration of polar and asphaltene compounds, the addition of solids is ineffective because thesolids are not adequately and suitably modified to function as stabilizers of the oil-water interface. Accordingly, some oils do not form stable solids-stabilized water-in-oil émulsions with any solids, or, some oils may form stable émulsions with some types 20 of solids, e.g. silica, and may not form similar stable émulsions with other types ofsolids, e.g., clays and coal dust. The previously cited art suggests that asphaltenes orpolar hydrocarbons may be added to these oils to improve their ability to form stableémulsions. U.S. Patent 5,855,243, column 7, lines 6-10; U.S. Patent 5,927,404column 6, lines 44-47; U.S. Patent 5,910,467 column 7, lines 3-6. However, this 25 addition is not always successfùl because incompatibility between some oil componentsand the added asphaltenes and polars can resuit in phase séparation or rejection of theadded compounds. These cases limit the scope of the inventions disclosed in the U.S.Patents cited above. 012250 -7-

To broaden the scope and improve the solids-stabilized émulsions described in U.S. Patents 5,927,404, 5,855,243, 5,910,467, 6,068,054, an approach is needed that suitably modifies the oil composition so that it is responsive to the addition of solids for the préparation of stable water-in-oil émulsions. The présent invention satisfies this need.

SUMMARY OF THE INVENTION

According to the invention, there is provided a method for enhancîng thestability of a solids-stabilized water-in-oil émulsion, said method comprising the step ofpretreating at least a portion of the oil prior to émulsification.

In one embodiment of the invention, the oil pretreatment step comprises tbeaddition of dilute organic or minerai acid to at least a portion of the oil prior toémulsification.

In another embodiment of the invention, the oil pretreatment step comprises theaddition of a Iignosulfonate additive to at least a portion of the oil prior toémulsification.

In another embodiment of the invention, the oil pretreatment step comprisessulfonating at least a portion of the oil prior to émulsification.

In another embodiment of the invention, the oil pretreatment step comprisesthermally treating at least a portion of the oil in an inert environment prior toémulsification.

In another embodiment of the invention, the oil pretreatment step comprisesthermally oxidizing at least a portion of the oil prior to émulsification.

Combinations of these embodiments may also be used.Further disclosed is amethod for producing hydrocarbons from a subterranean formation, comprising: a) making a solids-stabilized water-in-oil émulsion with the pretreated oil; b) contacting the formation with said solids-stabilized émulsion, and c) producing hydrocarbons from the formation using said solids-stabilizedémulsion. 012250 -8-

PETAILED DESCRIPTION OF THE INVENTION

Solids-stabilized water-in-oil émulsions hâve been generally described in US5,927,404, US 5,855,243 and US 5,910,467. Such émulsions are made by the processof combining oil with submicron to micron-sized solid particles and mixing with wateruntil the solids-stabilized water-in-oil émulsion is formed.

As disclosed in the above referenced U.S. patents, the solid particles shouldhâve certain physical properties. The individual particle size should be sufficientlysmall to provide adéquate surface area coverage of the internai droplet phase. If theémulsion is to be used in a porous subterranean formation, the average particle sizeshould be smaller than the average diameter of pore throats in the porous subterraneanformation. Methods for determining average particle size are discussed in thepreviously cited U.S. patents. The solid particles may be spherical in shape, or non-spherical in shape. If spherical in shape, the solid particles should preferably hâve anaverage size of about five microns or less in diameter, more preferably about twomicrons 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 shouldpreferably hâve an average size of about 200 square microns total surface area, morepreferably about twenty square microns or less, even more preferably about ten squaremicrons or less and most preferably, one square micron or less. The solid particlesmust also remain undissolved in both the oil and water phase of the émulsion under theformation conditions.

The présent invention allows the formation of stable solids-stabilizedwater-in-oil émulsions from oil that would otherwise lack adéquate polar andasphaltene compounds to form such stable émulsions. The oil needed to make a stableémulsion using the method described by U.S. Patents 5,927,404, 5,855,243 and5,910,467, has to contain a sufficient amount of asphaltenes, polar hydrocarbons, orpolar resins to stabilize the solid-particle-oil interaction. But, as noted, some oils donot hâve the sufficient type or amounts of these compounds to allow the formation of 012250 -9- stable solids-stabilized émulsions. Pursuant to the présent invention, the oil is pretreated to promote the formation of a stable solids-stabilized water-in-oil émulsion.

The oil used to make the solids-stabilized émulsion of the current invention canbe oil of any type or composition, including but not limited to crude oil, refined oil, oilblends, chemically treated oils, or mixtures thereof. Crude oil is unrefined liquidpetroleum. Refined oil is crude oD 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 tobe used. The produced crude oil may contain formation gas, or formation water orbrine 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 thisinvention.

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

Solids-stabilized water-in-oil émulsions according to the présent invention areuseful in a variety of enhanced oil recovery applications generally known in the art,including, without limitation, using such émulsions (a) as drive fluids to displacehydrocarbons in a subterranean formation; (b) to fill high permeability formation zonesfor “profile modification” applications to improve subséquent EOR performance; and(c) to form effective horizontal barriers, for instance, to form a barrier to vertical flowof water or gas to reduce coning of the water or gas to the oil producing zone of awell.

Attached in Table 1 are detailed physical and Chemical propertycharacterization data for three different types of crude oils which are referenced asCrude Oil #1, Crude Oil #2 and Crude Oil #3. Crude Oil #1 and Crude Oil #3 possessproperties that enable formation of stable water in crude oil émulsions with theaddition of solids, as described in U.S. Patents 5,927,404, 5,855,243 and 5,910,467. Ü12250 -10-

However, Crude Oil #2 does not form a stable solids-stabilized water-in-oil émulsionwhen using the same method. 01 2250 -11- TABLE 1

PHYSICAL & CHEMICAL PROPERTEES OF CRUDE OELS PROPERTY Crude Oil #1 Crude Oil #2 Crude Oil #3 API Gravity 16.8 15.5 8.6 Viscosity (cP) 4800 2400 384,616 (25°C, 1 sec1) • Interfacial Tension (dynes/cm) •2.2 33.7 Sea Water Asphaltenes (n-heptane insolubles (wt.%)) 0.1 ±0.02 2.6 13.7 Toluene Equivalence 0.0 14 20 Sulfur (wt.%) 0.12 0.98 3.89 Nitrogen (wt.-%) 0.18 0.07 0.19 Distillation Cuts (Vol. %} IC5/175°F Lt. Naph -- 0.6 0.2 175/250°F Med. Naph — 1.3 — 250/375°F Hvy. Naph 1.80 3.22 1.0 375/530°F Kerosene 7.83 12.39. 4.8 530/650°F Lt. Gasoil 9.88 14.27 9.5 650/1049°FPGO 38.04 42.41 38.8 1049°F + Resid 42.45 25.80 45.7 HPLC Fractions (wt. %1 Mass Recovery 83.8 56.6 ££ on Saturâtes 41.7 28.51 17.67 1-Ring 7.5 11.40 10.07 2-Ring 7.0 9.85 12.89 3-Ring 7.6 7.96 10.15 4-Ring 13.0 16.06 20.93 Polars 23.2 26.23 28.29 Aromaticitv 17.1 20.27 22.37 Iatrascan data Saturâtes 27.2 19.4 6.4 Aromatics 44.7 44.7 42.5 NSO's 19.0 30.1 29.0 Asphaltenes (npentane insolubles) (wt. °/o) 8.9 5.8 22.1 Arom/Saturates 1.64 2.3 6.66 NSO's/Asph. (n-pentane insoluble) 2.13 5.19 1.31 TAN 6.2 6.2 5.13 01 2250 -12- TABLE 1 (continued)

PHYSICAL & CHEMICAL PROPERTIES OF CRUDE OELS PROPERTY Crude Oil #1 Crude Oil #2 Crude Oil #3 HPLC PeterminedDistribution of Acid Fractions (%) 250 MW 8.5 47.2 22.4 300 MW 23.9 24.5 20.7 425 MW 30.5 15.9 20.4 600 MW 20.4 7.0 14.6 750 MW 16.7 5.4 21.7 Acid Aromaticity Metals ÎDoml 8.6 17.2 19.0 Ca 30-160 4.22 1.83 Na 10.4-15.5 1.51 11.2 V 0.16-0.31 69.6 434 Ni 9.05-13.0 65.6 102

Crude Oil #2 differs from Crude Oils #1 and #3 in the following ways: 5 1. Crude Oil #2 has a higher resin/asphaltene ratio, 2. Crude Oil #2 has a higher proportion of lower molecular weight naphthenic acids,and 3. Crude Oil #2 has lower calcium and sodium as compared to the Crude Oil # 1. 10 These différences suggest.· 1. the surface-active species, i.e., asphaltenes and acids/resins, which arethe key components essential for émulsification, are not readilyavailable to stabilize the water droplets in Crude Oil #2, and 2. pretreatment of the oil to alter its physical properties and Chemical 15 composition is a potential route to enhance the stability of the émulsion.

Accordingly, the présent invention describes a method of pretreating oil toincrease the stability of the solids-stabilized émulsion. Several embodiments of thisinvention will now be described. As one of ordinary skill in the art can appreciate, anembodiment of this invention may be used in combination with one or more other 012250 -13- embodiments of this invention, which may provide synergistic effects in stabilizing the solids-stabilized émulsion.

Pretreatment of Oil with Dilute Acid

One method of pretreating oil to enhance its ability to form a stable solids-stabilized water-in-oil émulsion is to pretreat the oil with dilute minerai or organic acidprior to émulsification. This acid pretreatment results in modifications to the oil andsurface of the solids: (1) The basic nitrogen containing components of the oil areconverted to the corresponding minerai or organic acid salts. These salts are moresurface-active than the basic nitrogen containing components themselves and thuscontribute to improving the stability of the solids-stabilized water-in-oil émulsion; (2)If the oil contains napthenic acids, the stronger minerai or organic acids displace thenapthenic acids from the basic nitrogen containing compounds to which they arecomplexed thereby providing higher surface activity; (3) The protons from the acid actto protonate the anionic charged sites on the surface of the solids and thus modify thesolids’ surface to improve its interaction with the surface-active components of oil(either preexisting in the oil or generated by the acid treatment); (4) If the oil containscalcium and naphthenic acids, the minerai or organic acids can displace the calcium andfree the naphthenic acids, which are more surface-active than the calciumnaphthenates.

Making the Solids-stabilized Water-in-Oil Emulsion Usine Dilute Acid Pretreatment

To make this embodiment of the invention, dilute minerai or organic acid isadded to the oil prior to émulsification. Solid particles can be added to the oil eitherbefore or after the acid pretreatment, but it is preferred to add the solids to the oil andthen acid pretreat the oil with the solids. After the acid pretreatment and solidsaddition, the solids-stabilized émulsion is formed by adding water in small aliquots orcontinu ously and mixing, preferably at a rate of between 1000 to 12000 rpm, for a timesufficient to disperse the water as small droplets in the continuous oil phase. It is 0 î 22 5 0 -14- 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 acid is added to the oil with mixing, preferably for about 5 to 10 minutes at25 to 40°C. The preferred acid treat rate is between 8 and 30,000 ppm. The dilute 5 acid may be minerai acid, organic acid, a mixture of minerai acids, a mixture of organicacids, or a mixture of minerai and organic acids. The preferred minerai acids arehydrochloric and sulfone acid. However, other minerai acids can be used, includingbut not limited to perchloric acid, phosphoric acid and nitric acid. The preferredorganic acid is acetic acid. However, other organic acids may also be used including, 10 but not limited to para-toluene sulfonic, alkyl toluene sulfonic acids, mono di andtrialkyl phosphoric acids, organic mono or di carboxylic acids (e.g. formic), C3 to Cl 6organic carboxylic acids, succinic acid, and petroleum naphthenic acid. Petroleumnaphthenic acid can also be added to increase the surface-activity in the oil, or oilscontaining high naphthenic acid can be blended with the oils of interest to provide the 15 increased surface-activity.

The solid particles are preferably hydrophobie in nature. A hydrophobie silica,sold under the trade name Aerosil® R 972 (product of DeGussa Corp.) has been roundto be an effective solid particulate material for a number of different oils. Otherhydrophobie (or oleophilic) solids can also be used, for example, divided and oil- 20 wetted bentonite clays, kaolinite clays, organophilic clays or carbonaceous asphaltenicsolids. The preferred treat rate of solids is 0.05 to 0.25 wt% based upon the weight ofoil.

After the émulsion is prepared, its pH can be adjusted by adding a calculatedamount of weak aqueous base to the émulsion for a time sufficient to raise the pH to 25 the desired level. It is désirable to adjust émulsion pH in the 5 to 7 range. However,adjusting pH is optional as in some cases it is désirable to inject an acidic émulsion andallow the réservoir formation to buffer the émulsion to the réservoir alkalinity. 012250 -15-

Ammonium hydroxide is the prefemed base for pH adjustment. Stronger baseslike sodium hydroxide, potassium hydroxide and calcium oxide hâve a négative effecton émulsion stability. One possible explanation for this effect is that strong bases tendto invert the émulsion, i.e. convert the water-in-oil émulsion to an oil-in-waterémulsion. Such an inversion is undesirable for the purposes of this invention.

In addition to increasing the stability of the solids-stabilized water-in-oilémulsion, the acid pretreatment method results in an émulsion with lower viscositycompared to one produced without acid pretreatment. This reduced viscosity aids inenhancing the injectivity of the émulsion. Thus, one may decrease the viscosity of asolids-stabilized émulsion by suitably adjusting the amount of acid pretreatment. Thisability to manipulate the viscosity of the émulsion allows the user to optimally matchthe rheological characteristics of the émulsion to that of the oil to be recoveredspecifically for the particular type EOR method used. As noted in U. S. Patents5,855,243 and 5,910,467, gas may also be added to further lower the viscosity of theémulsion.

Another embodiment of this invention is to pretreat a slipstream or masterbatch of oil with dilute acid as described above and subsequently mix the slipstreamwith a main stream of oil prior to water addition and émulsification. This main streamof oil is preferably untreated crude oil, however, it may be any oil, including oil thathas been treated to enhance its ability to form a stable émulsion or treated to optimizeits rheology. If this slipstream method is used, the amounts of solids and dilute acidneeded for the slipstream treatment are scaled accordingly to obtain the desiredamounts in the resulting émulsion.

Examples:

The following laboratory tests were conducted to demonstrate the efîectivenessof acid pretreatment on enhancing an oil's ability to form stable solids-stabilized water-in-oil émulsions. These examples focused on Crude Oil #2 and another crude oil,Crude Oil #4. Neither of these crude oils form stable solids-stabilized émulsions by the 012250 -16- method described in U.S. Patents 5,927,404, 5,855,243 and 5,910,467. Physical properties for Crude Oil #4 are given in Table 2. The tests demonstrated that the acid pretreatment enhanced the oils1 abilities to form stable solids-stabilized émulsions.

Stable émulsions were formed in the pH range of 1.2 to 7.0, and up to 72 wt% water 5 was incorporated into these émulsions. TABLE 2

PHYSICAL & CHEMICAL PROPERTIES OF CRUDE OILS PROPERTY Crude Oil #4 API Gravity 17.2

Viscosity (cP) 8500 (25°C, 1 sec"1)

Asphaltenes (n-heptane insolubles) (wt.%) 0. 1

Asphaltene (cyclohexane insolubles) (wt.%) 3.25

Toluene Equivalence 0.0

Sulfur(wt. %) 0.12

Nitrogen (wt. %) 0.26

Distillation Cuts (Vol. %) IC5/175°FLt. Naph 175/250°F Med. Naph 250/375°F Hvy. Naph 0.03 3 75/530°F Kerosene 6.09 530/650°F Lt. Gasoil 8.67 650/1049°F PGO 36.48 1049°F + Resid 48.73 HPLC Fractions (wt. %)

Mass Recovery 84.4

Saturâtes 43.3 1- Ring 7.6 2- Ring 6.8 3- Ring 7.5 4- Ring 12.6

Polars 22.2

Aromaticity 15.6 latroscan Data

Saturâtes 35.4

Aromatics 39.8 012250 -17- NSO’s 15.4 Asphaltene 9.4 Arom./Saturates 1.13 NSO’s/Asph. 1.64 TABLE 2 (continued) PROPERTY Crude Oil #4 TAN 5.4 HPLC Detertnined

Distribution of Acid Fractions (%) ** 250 - 300MW 15.4 300 - 425 MW 14.7 425-600 MW 27.1 600 -750MW 21.5 750 +MW 21.3 Acid Aromaticity 8.6 Metals (ppm) Ca 400-900 Na 7.7-15.3 V 0.2-0.9 Ni 11.2-17.9 Mn 13.1 K 181-935 Mg 1.1-25.2

In a typical experiment, dilute aqueous minerai or organic acid (0.35 to 35%5 concentration) was added to the oil at a treat rate of 8 to 30,000 ppm and thoroughlymixed for 10 minutes using a Waring blender or a Silverson homogenizer. Solidparticles were added followed by mixing. After acid pretreatment was completed,water was added to the oil in small aliquots with mixing, which resulted in a solids- stabilized water-in-oil émulsion. 10 Emulsions prepared by oil pretreatment with dilute aqueous acid were subjected to the following tests: 012250 -18- 1. Shelf stability at 25°C for 48 hours 2. Optical microscopy and/or Nuclear Magnetic Résonance (NMR) fordétermination of water droplet size / size distribution 3. Microcentrifuge test -- émulsion stability to centrifugation (asdescribed in Appendix-1) 4. Emulsion stability -- flow through a sand pack (this micropercolationtest is described in Appendix-1) 5. Emulsion rheology using a Brookfield viscometer (cone(#51) and plateconfiguration) at 60°C in a shear range of 1.92 to 384 sec'1.

Test results for Crude Oil #2 using hydrochloric acid and sulfiiric acidpretreatment are presented in Tables 3-6. Results for Crude Oil #4 using sulfiiric acidand acetic acid pretreatment are presented in Table 7.

Example 1 : Hydrochloric Acid Pretreatment of Crude Oil #2

Crude Oil #2 was used to préparé a 60/40 water-in-oil émulsion with 0.15 wt%hydrophobie silica, Aerosil® R 972, but without acid pretreatment. As shown in Table3, the solids-stabilized émulsion was shelf stable, however, the émulsion was unstablein the microcentrifiige and micropercolation tests as evidenced by the high water(brine) breakout (%bbo). Dispersed water droplets ranged in the size from 1 to 10microns in diameter.

The effect of hydrochloric acid pretreatment on the stability of the solids-stabilized émulsion was then tested. Crude Oil #2 was used to préparé a 60/40 solids-stabilized water-in-oil émulsion. However, in this example, the oil was pretreated withhydrochloric acid at a rate of 38,000 ppm followed by addition of 0.15 wt% ofAerosil® R 972. Dispersed water droplets ranged in size from 1 to 2 microns indiameter. As shown in Table 3, the hydrochloric acid pretreatment resulted inenhanced microcentrifiige and micropercolation stability and therefore enhancedémulsion stability as indicated by the decreased amount of water breakout in both tests. 012250 -19- TABLE3

Pretreatment of Crude Oil #2 With Hydrochloric Acid

Pretreat Procedure: 38,000 ppm HCl added to crude and mixed using Waring Blenderfor 10 min. HCl Crude/ Solid particles Shelf Droplet Micro- Micro- Water (Aerosil® R972) Stability diameter centrifiige percolation ppm (wt%) (2 days) (microns) (%bbo) (%bbo) 0 40/60 0.15 stable 10 to 1 18 35 38,000 40/60 0.0 stable 10 to 1 0 20 38,000 40/60 0.15 stable 2to 1 0 5 38,000 33/66 0.15 stable 2to 1 0 4 bbo :: brine (water) breakout in microcentrifuge test using Ottawa sand

Example-2: Sulfone Acid Pretreatment of Crude Oil #2

Crude Oil #2 was used to make a 60/40 water-in-oil émulsion containing 0.15 wt% of Aerosil® R 972 with no acid pretreatment. As shown in Table 4, thisémulsion, though shelf-stable, was unstable in the microcentrifuge and 10 micropercolation tests. Dispersed water droplets ranged in size from 1 to 10 micronsin diameter. A 60/40 water-in-crude oil émulsion was made with sulfuric acid pretreatmentof Crude Oil #2, but without the addition of solids. The sulfuric acid was added at arate of 8750 ppm, based on the weight of the oil. The resulting émulsion was very 15 unstable in the microcentrifuge and micropercolation tests. A 60/40 water-in-crude oil émulsion was prepared with sulfuric acidpretreatment of Crude Oil #2 at a rate of 8750 ppm, based on the weight of the oil,with 0.15 wt% of Aerosil® R 972. As shown in Table 4, this procedure resulted in astable émulsion. Dispersed water droplets ranged in size from 1 to 2 microns in 20 diameter. The pH of the résultant émulsion was 1.2. The sulfuric acid pretreatment ofoil resulted in enhanced microcentrifuge and micropercolation stability as indicated bythe decreased amount of water or brine breakout (%bbo). 012250 -20- A 60/40 water-in-crude oil émulsion was prepared with sulfuric acid pretreatment of Crude Oil #2 at a treat rate of 8750 ppm, based on the weight of the oil, followed by addition of 0.15 wt% of a hydrophilic silica, Aerosil® 300 (product of

DeGussa Corp.). This procedure did not provide a stable water-in-oil émulsion, as the 5 émulsion had increased water breakout in the microcentrifuge and micropercoîationtests. The poor performance of the hydrophilic silica, Aerosil® 300, suggests thathydrophobie solids, in general, are required for the formation of stable émulsions usingdilute acid pretreatment. TABLE 4 10 Pretreatment of Crude Oil #2 With Sulfuric Acid

Pretreat Proc: 8750ppm H2SO4 addedto crude & mixed using Waring Blender for 10min. H2SO4 Oil/ Solid particles Shelf Droplet Micro- Micro- Water (Aerosil® R972) Stability diameter centrifuge percolation ppm (wt%) (2 days) (microns) (%bbo) (%bbo) 0 40/60 0.15 stable 10 to 1 18 35 8750 40/60 0.0 stable 10 to 1 20 91 8750 40/60 0.15 stable 2 to 1 0 0 8750 33/66 0.15 stable 2to I 1 2 8750 40/60 0.10 stable 2to 1 0 0 8750 40/60 0.075 stable 2 to 1 0 0 bbo :: brine (water) breakout in micropercolation test using Ottawa sand

Example-3 : Increasing the Water Content of Sulfuric Acid Pretreated Crude15 Oil #2

As shown in Table 5, about 70 wt% water could be incorporated into theresulting solids-stabilized water-in-oil émulsion made by pretreating Crude Oil #2 withdilute sulfuric acid. Above about 72 wt% water, an increase in water droplet size wasobserved. Above about 80 wt% water, the émulsion phase separated as an émulsion 01 2250 -21- and excess water. The rheological measurements sbow that the viscosity of theémulsions increased with an increase in the water content of the émulsion. 012250 -22- TABLE5

Effect of Increastng the Water Content ofSulfuric Acid Pretreated Crude Oil #2 Emulsion % water Shelf stability Micro- centrifuge (%bbo) Micro- percolation (%bbo) Droplet diameter (microns) Viscosity35C, 9.6 60 yes 0 0 <2 15,400 65.5 yes 0 0 <2 15,888 69.2 yes 0 0 <2 20,152 71.4 yes 0 0 <2 27,852 75 yes 0 5 <2-5 26,214 80 yes 0 10 <2-10 85 phase séparâtes as émulsion &amp; excess water

Note: 5 Solids : 0.15 wt% Aerosil® R 972 Silica bbo :: brine (water) breakout in micropercolation test using Ottawa sandSulfuric acid treat rate : 8750 ppm

Example-4: Decreasing the Solids Content of a 60/40 Water-in-Crude Oil #2

Emulsion 10 As shown in Table 6, stable émulsions were prepared with the hydrophobie silica, Aerosil® R 972, ranging in concentration from 0.025 wt% to 0.15 wt%. Theviscosity of the émulsions decreased with decreasing solids content. TABLE 6

Effect of Decreasing the Solids Content of

Sulfuric Acid Pretreated Crude Oil #2 Emulsion % Solid particles Shelf Micro- Micro- Droplet viscosity (Aerosil® R972) stability centrifuge (%bbo) percolation (%bbo) diameter (microns) 35C, 9.6 s 0.15 yes 0 0 <2 15400 0.1 yes 0 0 <2 7864 0.075 yes 0 0 <2 7536 0.05 yes 0 0 <2 8192 0.025 yes 0 0 <2-5 6389

Note:

Oil/Water ratio = 40/60 bbo :: brine (water) breakout in micropercolation test using Ottawa sandSulfuric acid treat rate : 8750 ppm 012250 -23-

Example-5: Sulfuric and Acetic Acid Pretreatment of Crude Oil #4

Similar to the results on Crude Oil #2, acid pretreatment of Crude Oil #4resulted in enhanced stability of the resulting solids-stabilized émulsions. As the data s

in Table 7 indicate, pretreatment of the Crude Oil #4 with sulfuric acid at a rate of5 8750 ppm, based on the weight of oil, followed.by addition of 0.15 wt% Aerosil® R 972 resulted in a stable émulsion.

Pretreatment of Crude Oil #4 with acetic acid at a treat rate of 24,500 ppmfollowed by addition of 0.15 wt% Aerosil® R 972 also resulted in a stable solids-stabilized 60/40 water-in-oil émulsion. The viscosity of the acetic acid treated 10 émulsion was observed to be lower than the sulfuric acid treated counterpart,suggesting the nature of the acidifÿing agent could influence émulsion viscosity. TABLE 7

Acid Pretreatment of Crude Oil #4

Acid % Solids (Aerosil® R972) Shelf stability Micro- centrifuge (%bbo) Micro-percolation(% bbo) Droplet diameter (microns) viscosity60C, 9.6 s*: None 0.15 yes 0 9 <2-10 5240 Sulfuric 0.15 yes 0 3.5 <2 2948 Acetic 0.15 yes 0 0 <2 4095

Note: 15 Viscosity of Crude Oil #4= 164cP @ 60C , 9.6 s'1 bbo :: brine (water) breakout in micropercolation test using Ottawa sandSulfuric acid treat rate : 8750 ppm

Acetic acid treat rate: 24,500 ppm

Example-6; Adiusting the pH of the Acid Treated Emulsion 20 Two approaches are described to produce water-in-oil émulsions in the preferred pH range of 5 to 7: a) Neutralization of the preformed acid treated oil émulsion with theappropriate amount of base:

Neutralization of the acid pretreated oil with ammonium hydroxide before or 25 after addition of water is the preferred method to increase the émulsion pH. In 012250 -24- contrast, neutralization of the émulsion with sodium hydroxide or calcium oxide resultsin destabilization of the émulsion. As previously noted, a possible explanation for thiseffect is that ammonium hydroxide is a weaker base than sodium hydroxide or calciumoxide. Strong bases tend to invert the émulsion, i.e. convert the water-in-oil émulsionto an oil-in-water émulsion. Such an inversion is undesirable for the process of thisinvention. b) Reducing the Acid Treat Rate to Levels Just Enough to Neutralize the BasicComponents of the Oil:

Another approach to obtaining an émulsion in the pH range of 5-7 is to reducethe acid treat rate to levels just enough to neutralize the basic components of the oil.Acids used in this experiment were hydrochloric, sulfuric and acetic acids. For CrudeOil #2 and Crude Oil #4, it was found that an acid treat rate of 8.7 ppm was adéquateto produce the required émulsions at a pH of 5.5 to 6.5. A summary of émulsionproperties for Crude Oil #4 pretreated with 8.75 ppm sulfuric acid is given in Table 8. TABLE 8

Summary of Emulsion Properties of a Water-in-Oil EmulsionPrepared by Pretreatment of Crude Oil #4 with 8.75 ppm Sulfuric Acid

Emulsion Properties:

Crude : 40wt%

Water : 60 wt%

Hydrophobie Silica (R 972) : 0.15wt%

Water Droplet Size (Mean Diameter): 6 microns

Shelf Stability : > 2 weeks

Stability to Centrifugation : 0% water breakout

Stability to Percolation through Berea sand: 16% water breakout

Viscosity : 3700 cP @ 60C, 9.6 sec’1 pH: 6.2

Example-8: Gas Addition for Viscosity Réduction of Water-in-Oil

Emulsions

Addition of CO2 to the acid pretreated oil émulsion is effective in reducing theviscosity of the émulsion. Experiments hâve been conducted on émulsions made ffomCrude Oil #2 pretreated with 8700 ppm sulfuric acid and 0.15 wt% Aerosil® R 972 012250 -25-

Results shown in Table-9 reveal that at 500 psi pressure and the corresponding réservoir température, émulsion viscosity réduction is feasible using carbon dioxide gas. Other gases like ethane and propane can also lower émulsion viscosity TABLE 9 5 Influence of CO? on an Acid Pretreated

Solids-Stabilized Water-in-Crude Oil Emulsion

Emulsion Temp (°C) VISCOSITY fcP) at 10 sec1 Viscosity (cP)Without CO2 At 10 sec'1with 500 psi CO2 Crude Oil #2 35 11213 1671

Pretreatment of Oil bv Sulfonation Chemistry

Another method for pretreating oil to enhance its ability to make a solids- 10 stabilized water-in-oil émulsion is to pretreat the oil with a sulfonating agent prior toémulsification. The sulfonation procedure can resuit in Chemical modifications to theoil and to the surface of the solids. For example, (1) the sulfonation procedure hereindescribed créâtes sulfur-functionalized components of oil, and these components aresurface active and aid the formation of the water-in-oil émulsion; (2) If naphthenic 15 acids are présent in the oil, sulfonation will markedly enhance their acidity andinterfacial activity through the chemically attached sulfonate groups; (3) The sulfonategroups from the sulfonating agent will also functionalize the surface of the solids andthus modifÿ the solids’ surface to improve its interaction with the surface-activecomponents of oil (préexistent in the oil or generated from the sulfonation reaction); 20 and (4) The basic nitrogen containing components of oil are converted to thecorresponding sulfonates and/or sulfate salts. These salts are more surface-active thanthe base nitrogen containing components themselves and thus contribute to improvingthe stability of the solids-stabilized water-in-oil émulsion. 012250 -26-

Procedure for Préparation of a Solids-Stabilized Water-in-Oil Emulsion Usine

Sulfonation Chemistry

The oil is pretreated with a sulfonating agent either before or after the additionof solid particles, and followed by the addition of water. The water is added in small 5 aliquots or continuously and the mixture subjected to shear mixing, preferably between1000 to 12000 rpm, for a time sufficient to disperse the water as small droplets in thecontinuons oil phase, typically between 0.5 to 24 hours. It is preferred to hâve a waterconcentration in the water-in-oil émulsion of 40 to 80%, more preferably 50 to 65%,and most preferably 60%. 10 The 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. Other sulfonating agents can be used alone or incombination with other agents. Such sulfonating agents are generally described in E.E. Gilbert, Sulfonation and Related Reactions, Jnlerscience, New York, (1965). 15 Other common sulfonating agents that may be useful in the présent invention includefùming sulfuric acid, sulfur trioxide, alkali disulfates, pyrosulfates, chlorosulfonic acidand a mixture of manganèse dioxide and sulfurous acid. The process températureduring sulfonation can be ffom -20°C to 300°C, preferably from 10°C to 100°C andmore preferably from 20°C to 60°C. Reaction can be accelerated by various methods, -20 including without limitation thermal, mechanical, sonie, electromagnetic, vibrational,mixing, and spraying.

As can be appreciated by one of ordinary skill in the art, the amount ofsulfonating agent useful in the présent invention can be adjusted according especially tothe nature of the sulfonating agent, and the asphaltene and resin content of the oils. An 25 oil containing a large amount of asphaltene may require less sulfonation than onecontaining a small amount of asphaltene. The amount of asphaltene in oil can bedetermined using standard techniques known in the art. The range of sulfonation canbe ffom 0.01 to 40%, preferably from 0.1 to 10% and more preferably ffom 0.1 to 2%of the mass of the solid particles. 012250 -27-

One method for practicing this embodiment of the invention is to first sulfonatethe oil, and then add the solid particles. However, addition of the solid particles to theoil and sulfonation of the mixture is preferred. The solids can be silica, clays,hydrophobie particulates, and/or unfunctionalized and functionalized asphalts and theircorresponding mixtures. The preferred treat rate of the solids to the oil is 0.05 to 2.0wt% solids based on the weight of oil.

The hydrophobie particulates for this embodiment of the invention are anyparticulate wherein the hydrophobicity is greater than 50% and less than 99.9% andhydrophilic or polar moieties are less than 40% and greater than 0.1% of theparticulate mass. The hydrophilic or polar moieties can be formed as a resuit ofsulfonation of the combination of hydrophobie particulates with oil. Examples ofhydrophobie particulates useful for this invention include, without limitation,phylosilcates, lignin, lignite, coal, gillsonite, silica, dolamite, métal oxides, layeredoxides, and quatemary onium exchanged phylosilicates.

Functionalized and unfunctionalized asphalts are also effective solids formaking the sulfonate-pretreated solids-stabilized water-in-oil émulsions. In particular,phosphonated asphalt that has been sufnciently immersed in the oil, preferably for 24hours at 55°C, is an effective solid. The asphalts can be used in their natural State ormay be functionalized or functionalized by sulfonation agents of the présent invention.Nonlimiting examples of functional moieties are -sulfonic acid, phosphoric acid,carboxylic acid, nitric acid or salts thereof, and hydrophilic groups.

After émulsion préparation, the pH of the émulsion can be adjusted aspreviously described in connection with the first embodiment of the invention relatedto pretreating oil with dilute' acid. As previously described, a calculated amount ofweak base is added to the émulsion and the émulsion is riibjected to shear mixing for atime sufficient to raise its pH to the desired level, preferably in the 5-7 range.Adjusting pH is optional, as in some cases it is désirable to inject an acidic émulsionand allow the réservoir formation to buffer the émulsion to the réservoir alkalinity. 01 2250 -28-

The viscosity of the émulsion increases with sulfonation. However, theémulsion viscosity is not a linear fonction of sulfonating agent addition. The viscosityof the émulsion increases at a reduced rate as a fonction of sulfonation. Therefore, theuser may make increasingly stable solids-stabilized émulsions via sulfonation, whilemaintaining désirable rheological properties. Further, the viscosity of the émulsionmay also be reduced by the addition of gas as discussed in U.S. Patents 5,855,243 and5,910,467.

While sulfonation of the entire quantity of oil necessary to make such anémulsion is feasible, it is also possible to sulfonate a slipstream or master batch of oiland subsequently mix the slipstream with a main stream of oil prior to water additionand 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 astable émulsion or treated to optimize its rheology. If this slipstream method is used,the amounts of solids and sulfonating agent needed for the slipstream treatment arescaled accordingly to obtain the desired amounts in the resulting émulsion.'

Examples:

This embodiment of the invention has been demonstrated using Crude Oil #2and another oil, Crude Oil #5, as these oils do not form stable solids-stabilizedémulsions using the method described in U.S. 5,927,404, 5,855,243 and 5,910,467.However, as indicated by the experiments below, pretreating the oil with sulfonationchemistry improves the oil's ability to form stable solids-stabilized water-in-oilémulsions.

In a typical experiment, the solid particles are added to oil and then sulfonated.Concentrated sulforic acid is used as the sulfonating agent, and is added at a treat rateof 3 parts of acid per 100 parts of oil. This mixture is stiaed on a hot plate with amagnetic stirrer attachment at a température of around 50°C. Water is then added tothe oil in small aliquots with mixing, which results in a solids-stabilized water-in-oilémulsion. 012250 -29-

These émulsions 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 (described in Appendix-1) 4. Emulsion stability: flow through a sand pack (the micropercolation testprocedure is grven in Appendix-1)

Example 1

Crude Oil #2 and solid particulates were co-sulfonated as foîlows: 12 grams(g) of Crude Oil #2 and the solid particles, comprised of 0.06 g of 2-methylbenzyltallow intercalated monomorillonite (Organotrol© 1665; product of Cimar Corp.) and0.12 g ASP-97-021 untreated Billings asphalt (product of Exxon), were combined in aglass jar. The mixture was stirred at 50°C for 72 hours. Sulfuric acid, was added at 3parts acid per 100 parts oil and the mixture stirred at 50° C for 24 hours.

The sulfonated oil and solids were then combined with 18 g of synthetic brinesolution (comprised of 9.4 g sodium chloride, 3.3 g CaCb (calcium chloride) · 2H2O,0.48g MgCl2 (magnésium chloride) -6H2O and 0.16g potassium chloride per liter ofdistilled water). The brine was added dropwise over 30 minutes at 5000 rpm. Theémulsion thus formed was mixed for an additional 15 minutes at 7500 rpm.

The oil extemal sclids-stabiiized émulsion thus produced was tested forstability usina the micropercolation test as described in Appendix-1. The sand used inthis test was Ottawa sand and the oil was centrifuged with the sand for one minute at50°C. Duplicate samples showed 0% and 3.2% brine breakout (%bbo) followinginjection through the sand pack. Light microscopy showed water droplet diameter lessthan 20 microns and a majority of particles having diameters less than 7 microns.

Example 2

Crude Oil £5 and oxidized asphalt (OX-97-29-180; product of Impérial Oil) were co-sulfonated according to the previously described procedure. However, in this 012250 -30- exemple the oil and asphalt were stirred together for 2.5 hours at 50°C prior to theaddition of the sulfonating agent, sulfuric acid at 3 parts sulforic acid per 100 parts oil.

The sulfonated product was mixed with the synthetic brine solution asdescribed. The résultant mixture contained 60% aqueous phase content. This oilextemal émulsion exhibited a pH of 1.6 and was then neutralized to a pH of 7.3 withthe addition of ammonium hydroxide and then remixed on an Arrow 850 mixer at 350rpm for 15 minutes. The émulsion pH approximated the pH of Crude Oil #5. Thisémulsion showed no brine breakout in the micropercolation test. Droplet diameterswere less than 10 microns with the majority of water droplets less than 5 microns.Rheological testing using a cône and plate viscometer demonstrated high émulsionstability, i.e. the viscosity remained essentially constant as a fonction of cycle number.

Example 3

The same experiment was performed using Crude Oil #5 and 2-methylbenzyltallow intercalated montmorillonite (Organotrol® 1665, a product of CimbarPerformance Minerais, Cartersville GA) as the solid particulate. The crude oil andsolid particles were combined and stirred for 4 hours at 50°C prior to the addition ofsulfone acid. Otherwise, this mixture was sulfonated according to the methodsdescribed above.

The synthetic brine solution described above was added to the oil and solidsand mixed as before. The resulting emulsion's pH level was also adjusted to 7.5 withthe addition of ammonium hydroxide and mixing with an Arrow 850® mixer at 350rpm for 15 minutes. The oil extemal émulsion exhibited an aqueous phase dropletdiameter of less than 10 microns and a majority of brine droplets were less than 5microns. No brine breakout was found under the micropercolation test described inAppendix-1, using Berea sand.

Example 4

Crude Oil #2 and untreated asphalt (ASP-97-021, a product of Impérial OilCorporation, Canada) were co-sulfonated. The oil and asphalt were stirred at 50°C for 01 2250. -31- 72 hours prior to the addition of the sulfuric acid. Otherwise, sulfonation wasperformed by the steps described above.

The solids-stabilized water-in-oil émulsion was produced with the addition ofthe synthetic brine solution described above and mixing according to the proceduresabove. However, in this example, the émulsion pH was not adjusted, but remainedacidic. Light microscopy showed an aqueous phase droplet diameter less than 10microns with a majority of droplets less than 5 microns. No brine breakout was foundby the micropercolation test described in Appendix-1, using Ottawa sand.

Example 5 12 g of Crude Oil #2 and 0.06 g of an hydrophobie particulate, Wolastafil-050-MH-0010® (methylalkoxysilane coated calcium metasilicate having a 1% coating byweight of calcium metasilicate — product of United Minerai Corp.), were co-sulfonatedas previously described. In this example, the oil and particulate were stirred at 50°Cfor 2.5 hours prior to the addition of the sulfuric acid. A solids-stabilized water-in-oil émulsion was produced by the above describedprocedures, and the émulsion pH was adjusted to 6.1 using ammonium hydroxide.Light microscopy revealed an aqueous phase droplet diameter of less than 5 microns.The resuit of the micropercolation test demonstrated no brine breakout followingémulsion injection. Rheological testing showed no significant change in viscosity withcycle number indicating high shear stability.

Example 6 A solids-stabilized water-in-oil émulsion was formed using Crude Oil #2 andphosphonated asphalt (Kew 97-149®, a product of Impérial Oil Corporation, Canada)as the solid particles. The oil and solids were added together and the mixture wasstirred at 50°C for 48 hours prior to the addition of sulfuric acid, as described above.

The resulting water-in-oil émulsion showed aqueous phase droplet diameterless than 5 microns using light microscopy. The micropercolation test revealed no 012250 -32- brine breakout. Rheological testing indicated high émulsion stability, i.e. the viscosity remained essentially constant as a fonction of the number of cycles.

Pretreatment of Oil with Lignosulfonate Additive

Another method of pretreating oil to enhance its ability to form a stabile solids-stabilized water-in-oil émulsion is to add a lignosulfonate additive to the oil prior tomaking the émulsion. The salts of lignosulfonic acid (e.g., sodium, potassium,ammonium, calcium, etc.) are surface-active in nature, and when added to an oil/watermixture they will tend to aggregate at the oil/water interface. This effect increases theinterfacial activity of the oil and enhances the stability of the émulsion.

Préparation of the Lignosulfonate Treated Solids-Stabilized Emulsion

To practice this embodiment of the invention, a lignosulfonate additive is addedto oil, before or after the addition of the solid particles, but prior to émulsification. Forthe sake of simplicity and clarity, this spécification shall reference adding one type oflignosulfonate additive to the oil. However, it should be understood that combinationsof different lignosulfonate additives may be used to practice this embodiment of theinvention. The lignosulfonate additive is added at a treat rate of between 200 to20,000 ppm based on the weight of the oil, more preferably 500 to 5000 ppm, andeven more preferably 500 to 1000 ppm, for 5 to 10 minutes at 25 to 40°C. The solidparticles are added either before or after lignosulfonate additive addition, followed bythe addition of water in small aliquots or continuously. The mixture is then subjectedto shear mixing at a rate of between 1000 to 12000 rpm for a time sufficient todisperse the water as small droplets in the continuous oil phase. It is preferred to hâvea water concentration in the water-in-oil émulsion of 40 to 80%, more preferably 50 to65%, and most preferably 60%.

The température of the émulsion will rise above ambient température (25°C)during mixing. Controlling the température of the émulsion during mixing is notcritical, however, higher températures between 40°C and 75°C are preferred. -33- 012250

Both oil soluble and water-soluble lignosulfonate additives can be used toenhance the stability of the solids-stabilized water-in-oil émulsion. Non-Iimitingexamples of water-soluble lignosulfonates are sulfonate salts of monovalent cationslike sodium, potassium, and ammonium. Non-limiting examples of oil solublelignosulfonates are sulfonate salts of divalent cations like calcium, magnésium, andiron. It is preferred to use water-soluble additives because of the ease of delivery andthe use of water as the delivery solvent. The preferred water-soluble lignosulfonateadditive is ammonium lignosulfonate. In addition, mixtures of lignosulfonate salts maybe used to produce the same or an enhanced effect. A hydrophobie silica, Aerosil® R 972, was found to be an effective solid forseveral types of oil. The invention has been demonstrated using Aerosil® R-972 at atreat rate of 0.15wt%, based on the weight of the oil. Other hydrophobie soîids likedivided and oil wetted bentonite clays, organophilic clays or carbonaceous asphaltenicsolids may also be used. Hydrophilic solid particles can also be used. The preferredtreat rate for solids is 0.05 to 0.25wt% based on the weight of the oil.

One may first pretreat the oil with the lignosulfonate additive and then add thesolid particulates. However, it is preferred to add the solid particulates to the oil andthen add the lignosulfonate additive to the mixture. Optionally, the solid particulatescan be first treated with the lignosulfonate additive and the treated solids can be addedto the oil prior to the addition of water and mixing. As aforementioned, either wateror oil soluble lignosulfonate additives can be used to pretreat the solids. The choice ofwhich type of lignosulfonate additive to use dépends upon the type of solid to betreated. Generally, a hydrophobie solid is treated with a water soluble lignosulfonateadditive and a hydrophilic solid with an oil soluble lignosulfonate additive. Such achoice would enable suitable modification of the solids' surface to render optimumhydrophilic and hydrophobie character.

While lignosulfonate pretreatment of the entire quantity of oil necessary to make a desired émulsion is feasible by this embodiment of the invention, it is also possible to pretreat a slipstream or master batch of oil and subsequently mix the 012250 -34- slipstream with a main stream of oil prior to water addition and émulsification. Thismain 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 ortreated to optimize its rheology. If this slipstream method is used, the amounts ofsolids and lignosulfonate additives needed for the slipstream treatment are scaledaccordingly to obtain thedesired amounts in the resulting émulsion.

This embodiment of the invention can be used in conjunction with the methodof pretreating oil with dilute minerai or organic acid to further enhance the surface-active properties in the oil. The dilute acid addition can occur before or afterlignosulfonate addition, as the order of addition of the acid and the lignosulfonateadditive are not critical. However, the acid addition and the lignosulfonate additionshould occur prior to émulsification. If the lignosulfonate addition is combined withacid addition, the pH of the émulsion can be adjusted by adding a calculated amount ofa weak base, as previously described, to raise the pH to the desired level, preferably toa pH of between 5-7.

Examples:

This invention has been demonstrated on Crude Oil #4 and Crude Oil #6, asthese crude oils do not form stable solids-stabilized émulsions using the methoddescribed in U.S. 5,927,404, 5,855,243 and 5,910,467. Crude Oil #6 is a low viscositycrude oil. In a typical experiment, the lignosulfonate additive was added to the oil at atreat rate of 0.05 to 0.5wt% based on the weight of the oil and mixed for 10 minutesusing a Silverson® homogenizer at from about 1000 to 12,000 rpm. Ammoniumlignosulfonate and calcium lignosulfonate were used as the lignosulfonate additives inthese examples. Solid particles, either divided bentonite or hydrophilic silica, wereadded at 0.15wt% based on the weight of the oil, followed by further mixing. Waterwas then added to the mixture in small aliquots with further mixing to provide a solids-stabilized water-in-oil émulsion. 012250 -35-

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 / 5 size distribution 3. Centrifuge stability (see Appendix-1 ) 4. Emulsion stability: flow through a sand pack (details of themicropercolation test procedure is given in Appendix-1 ) 5. Emulsion rheology using a Brookfield® viscometer (cône (#51) and 10 plate configuration) at 60°C in a shear range of 1.92 to 384 sec'1.

Exampïe-1: Crude Oil #4

Test results for Crude Oil #4 pretreated with ammonium lignosulfonate orcalcium lignosulfonate are presented in Table 10. A solids-stabilized 60/40 water-in-oil émulsion was formed using lignosulfonate pretreatment at 0.5wt% and a 15 hydrophobie silica, Aerosil® R 972, at 0.15wt%.

As indicated in Table 10, the lignosulfonate pretreatment enhanced the stabilityof the émulsions as evidenced by the decreased brine breakout (%bbo) under themicropercolation test, as compared to the untreated solids-stabilized water-in-oilémulsion. 20 TABLE 10

Influence of 0.5 wt% ammonium and calcium lignosulfonate on a solids-stabilized water-in-oil émulsion made from Crude Oil #4

Lignosulfonate Additive MicropercolationStability (%bbo) EmulsionViscosity (cP)at 60 °C None 38 2743 Ammonium Lignosulfonate 4 2620 Calcium Lignosulfonate 8 2620 012250 -36-

Example-2: Crade Oil #6 A solids-stabilized 60/40 water-in-oil émulsion was made with Crade Oil #6 and 0.15wt% hydrophobie silica, Aerosil® R 972. No lignosulfonate pretreatment was used. The émulsion was unstable with a 40% water breakout under the micropercolation test. The viscosity of the émulsion at 60°C and 9.6 sec'1 was 983 cP.

However, when the same 60/40 water-in- oil émulsion was prepared usingCrade Oil #6 pretreated with 0.5wt% ammonium lignosulfonate, the stability of theémulsion was enhanced, with the water breakout reduced to 17%. The viscosity of theémulsion at 60°C and 9.6 sec'1 increased slightly to 1064 cP.

Example-3: 50/50 Crade Oil Blend using Crade Oil #4 and Crade Oil #6

An untreated solids-stabilized 60/40 water-in-oil émulsion was prepared using a50% Crade Oil #4 and 50% Crade Oil #6 blend. The solid particles were comprised ofa hydrophobie silica, Aerosil® R 972, at 0.15wt% based upon the weight of the oilblend. The untreated solids-stabilized émulsion had a water breakout of 32%.Viscosity for this émulsion at 60°C and 9.6 sec'1 was 2129 cP.

The same émulsion was prepared with a 50/50 Crade Oil #4 / Crade Oil #6blend that was pretreated with 0.5wt% of ammonium lignosulfonate. Thelignosulfonate treated solids-stabilized émulsion showed enhanced stability asevidenced by the decrease in brine breakout to 5%. The viscosity of the treatedémulsion at 60°C and 9.6 sec'1 remained at 2129 cP. The data indicate that thetreatment enhanced émulsion stability with no change in the viscosity.

Pretreatment of Oil bv Thermal Air Oxidation

Another pretreatment embodiment that can be used to increase the stability of asolids-stabilized water-in-oil émulsion is to thermally treat the oil, either before or afterthe addition of solid particles, in the presence of air or oxygen.

Thermally treating oil or a mixture of oil and solid particles in the presence of air or oxygen causes various reactions to occur in the oil and on the surface of the 012250 -37- solid particles. (1) The aromatic components of the oil that hâve benzyllic carbons and those that hâve fosed rings that are oxidizable including, but not limited to naphthelene and anthracene, are oxidized to the corresponding acids, ketones or quinone products.

Organo sulfur and nitrogen compounds présent are oxidized to sulfoxides and nitrogen 5 oxides. The oxygenated compounds are more surface-active than the aromaticcomponents themselves and adsorb strongly on the surface of the solid particles toimprove the stability of the solids-stabilized water-in-oil émulsion. (2) If naphthenicacids are présent as salts of divalent cations like calcium, air oxidation can couvertthese salts to naphthenic acids and the corresponding métal oxide, for example calcium 10 oxide. The free napthenic acid can adsorb on the surface of the solids and alsoimprove the stability of the solids-stabilized water-in-oil émulsion. (3) Thermaltreatment with an air purge dehydrates the solid particles and thus modifies the solids'surface to improve its interaction with the surface-active components of oil(préexistent in the oil or generated fforn air oxidation). 15 Préparation of a Solids-Stabilized Emulsion Usine Thermal Air Oxidized Oil

To préparé a solids-stabilized water-in-oil émulsion using this method, the oil isthermally treated for sufficient time and température in the presence of an air oroxygen purge to enable the physical and Chemical modifications to the oil and solidparticles. Preferably, the oil is heated to températures of between 110-180°C for 15 20 minutes to 6 hours, under an air or oxygen purge at a preferred rate of 20 to 100standard cubic feet per barrel per hour (scfibbl/hr).

The solid particles may be added before, during or after the thermal airoxidation step, but should be added before émulsification. However, it is preferred toadd the solids to the oil and then thermally air oxidize the mixture. The solid particles 25 may be hydrophilic or hydrophobie in nature. Fumed silica, sold under the trade nameof Aerosil® R 972 or Aerosil® 130 (Products of DeGussa Corp.) were found to beeffective solids for a number of oils. Other solid particles like bentonite clays, dividedbentonite clays, kaolinite clays, organophilic clays or carbonaceous asphaltenic solidsmay also be used. 012250 -38-

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, preferably 0.01 to 20 wt%, and more preferably0.05 to 5.0 wt%. At the higher concentrations, the mixture of solids and oil will be ahigh solids content slurry.

Bentonite clays, such as those mined in Wyoming, Ga, or other numerouslocations around the world, are particularly suited as stabilizers for water-in-oilémulsions. As mined, these clays naturally consist of aggregates of particles that canbe dispersed in water and broken up by shearing into units having average particle sizesof 2 microns or less. However, each of these particles is a laminated unit containingapproximately 100 layers of fondamental silicate layers of 1 nm thickness bondedtogether by inclusions of atoms such as calcium in the layers. By exchanging the atomssuch as calcium by sodium or lithium (which are larger and hâve strong attractions forwater molécules in fresh water), and then exposing the bentonite to fresh water, thebentonite 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 ofclay chemistry. The resuit of this délamination process is a gel consisting of dividedbentonite clay.

The preferred solid is divided or delaminated bentonite clay that is obtained ?.sa gel from the délamination process described above. The amount of gel added to foeoil before the thermal air oxidation step can very in the range of 5 to 95% of gel basedon the weight of the oil, preferably 40 to 60%. The weight of bentonite clay solids inthe gel can very from 1 to 30% based on the weight of the water. When bentonite claygel is used as the solid particle, and is added to the oil and subjected to the thermal airoxidation step, water is expelled from the reaction vessel as steam. The reactionshould be carried out until at least 80% of the water is expelled, preferably until 95%of the water is expelled, and even more preferably until 100% of the water is expelled.

It is preferred to oxidize 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 012250 -39- untreated crude oil, however, it may be any oil, including oil that has been treated toenhance its ability to form a stable émulsion or treated to optimize its rheology. Ifuntreated crude oil is the main stream, the preferred blending rate is 0.5 to 5%oxidized oil in the untreated oil main stream, more preferably 0.1 to 2.5%. 5 After the air oxidation step and solid particle addition, water is added in small aliquots or continuously and the mixture is subjected to shear mixing at 1000 to 12000rpm for a time sufficient to disperse the water as small droplets in the continuous oilphase. The température of the émulsion will rise above ambient température of 25°Cduring mixing. Controlling the température of the émulsion during mixing is not 10 critical. However, higher températures between 40 to 70°C are preferred.

Catalysts may be used to enhance the oxidation reaction. Finely dividedcatalysts like iron, manganèse or nickel, or their oil soluble métal salts can be used tocatalyze oxidation rates and efifect selectivity in the oxidation products. Suchoxidation promoting catalysts and the techniques of using such catalysts are well 15 known in the art, and therefore will not be discussed herein. Oxidation can beconducted at elevated pressures to further catalyze the reaction rate and achieveproduct selectivity, however, oxidation at ambient pressures is preferred.

The oxidized oil can be further treated with dilute minerai or organic acid toprovide additional stability to the solids-stabilized water-in-oil émulsion. The preferred 20 acid treat rate is between 8 and 30,000 ppm. If this acid pretreatment step is used, thepH of the resulting émulsion can be adjusted to a preferred range of 5 to 7 by adding acalculated amount of weak base to the émulsion. However, adjusting pH is optional asin some cases it is désirable to inject an acidic émulsion and allow the réservoirformation to bufifer the émulsion to the réservoir alkalinity. Ammonium hydroxide is 25 the preferred base for pH adjustment. Stronger bases like sodium hydroxide,potassium hydroxide and calcium oxide hâve a négative effect on émulsion stability.One possible explanation for this efifect is that strong bases tend to invert the émulsion, i.e. convert the water-in-oil émulsion to an oil-in-water émulsion. Such an inversion isundesirable for the purposes of this invention. 012250 -40-

In addition to increasing the stability of the solids-stabilized water-in-oilémulsion, dilute acid treatment lowers the viscosity of the émulsion. This reducedviscosity aids in enhancing the injectivity of the émulsion, and may also be bénéficiai inother aspects in EOR processes, for example, matching the emulsion's rheology withthat of the 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, 200g of oil was placed in a Parr® autoclave or three-necked glass flasks and oxidized at températures of 150 to 160 °C for 2 to 6 hourswith a continuous purge of air at 80 to 100 scfZbbl/hour. The oxidized oil was thenblended to various ratios with untreated oil or other thermally air oxidized oils, asdetailed in the spécifie examples below. A hydrophobie silica, Aerosil® R 972 wasadded to the oxidized oil blend at 0.05 to 0.15 wt%, based on the weight of the oil.After the solids addition, the product was mixed using a Silverson® homogenizer.Water was then added in small aliquots with mixing to produce the solids-stabilizedwater-in-oil émulsion.

For the preferred case of thermal air oxidation of a mixture of oil and dividedbentonite gel, the oil and gel are first mixed to form a slurry. Air or oxygen gas ispurged into the reactor and the température raised to between 150°C and 170°C. Thewater is expelled as steam and can be condensed outside for recovery and reuse.

For the optional case of acid addition to the oxidized oil, 10 ppm of sulfuricacid was added to the oxidized sample and mixed for 10 minutes at 40°C. Addition ofsolids and water with mixing followed as described above.

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 01 2250 -41- 3. Centrifuge stability (described in Appendix-1) 4. Emulsion stability: flow through a sand pack (details of themicropercolation test procedure is given in Appendix-1) 5. Emulsion rheology using a Brookfîeld® viscometer (cone(#51) andplate configuration) at 60°C in a shear range of 1.92 to 384 sec'1.

Example-1 : Untreated Crude Oil #4 Blended with Air Oxidized Crude Oil #4

Aerosil® R 972 was added at a treat rate of 0.15wt% to untreated Crude Oil#4, followed by water and mixing to form a 60/40 solids-stabilized water-in-crude oilémulsion. This émulsion, though shelf-stable, was unstable in the centrifuge andmicropercolation tests. Dispersed water droplets ranged in size from 2 to 40 micronsin diameter, and a 54% water breakôut was observed in the micropercolation testdescribed in Appendix-1, using Berea sand. The viscosity of the émulsion at 60°C and9.6 sec'1 was 3644 cP.

Another batch of Crude Oil #4 was thermally air oxidized according to theprocedure described above. The thermally air oxidized Crude Oil #4 was blended withuntreated Crude Oil #4 at 2.5wt% of treated oil in the untreated oil. Delivery of thethermally air oxidized Crude Oil #4 was in toluene in a 1:2 ratio. A hydrophobie silica,Aerosil® R 972, was added to the blend at 0.15wt% based on the weight of theblended oil. Addition of water and mixing followed to make a 60/40 solids-stabilizedwater-in-crude oil solids-stabilized émulsion. NMR determined droplet sizedistribution indicates that 90% of the water droplets were less than 2 microns indiameter. The emulsion's stability improved over that of the untreated Crude Oil #4solids-stabilized émulsion, as evidenced by a réduction to 10% water breakôut in theBerea micropercolation test. The emulsion's viscosity was 2452 cP at 60°C and 10sec'1. Additionally, the viscosity profiles repeated over a 1-hour shear cycle.

Ethane gas was added to reduce the thermally air oxidized solids-stabilized water-in-oil emulsion's viscosity. The resuiting emulsion's viscosity was lowered from 2452 to 390 cP at 60°C with saturation of ethane at 400 psi. The émulsion was stable to ethane addition and shearing at 10 sec'1 for the duration of the experiment of 5 days. 012250 -42-

Example-2: Blends of Oxidized Crude Oil #4 and Low Vîscosity Crude Oil #6

In this experiment Crude Oil #4 and a low vîscosity crude oil, Crude Oil #6, were blended to various ratios. A hydrophobie solid, Aerosil® R 972, was added at0.15wt% solids to the blended oil, along with 10 ppm sulfuric acid and mixed for 30 5 minutes. Water was then added in small aliquots and mixed to provide a 60/40 water-in-blended oil émulsion. Results are shown in Table 11. As is observed from the data,increasing the proportion of the low vîscosity Crude Oil #6 decreases the vîscosity ofthe 60/40 water-in-blended oil émulsion from 3644 cP (measured at 60°C and 9.6 sec’) to 983 cP. However, the stability of the émulsions are poor as evidenced by the 30 10 to 40% water breakout in the micropercolation test using Berea sand. TABLE 11 Crude Oil #4/Crude Oil #6 Blend Ratio % bbo Viscositv, cP 60°C, 96s1 100/0 38 3644 75/25 34 2621 50/50 32 2129 25/75 41 1638 0/100 40 983

Table 12 shows the effectiveness of thermal air oxidation of the oil before15 émulsification to enhance the stability of the resulting émulsion. Crude Oil #6 wasthermaîly air oxidized by the method previously described and then blended withuntreated Crude Oil #4 to resuit in a 75% untreated Crude Oil #4 to a 25% thermaîlyair oxidized Crude Oil #6 blend. A hydrophobie solid, Aerosil® R 972, was added tothe blend along with 10 ppm sulfuric acid, and mixed for 30 minutes. Water was then 20 added in small aliquots and mixed to provide a 60/40 water-in-blended oil émulsion. 01 225 Ο -43-

Results shown in Table 12 illustrate the effectiveness of this method as indicated by themicropercolation test using Berea sand. TABLE 12

Oils Brine Breakout (%bbo) 75% Crude Oil #4 . 34 25% Crade Oil #6 75% Crade Oil #4 25% Thennally Air Oxidized 16

Crude Oil #6

Viscositv. cP 60°C, 96s'12621 - 2620 5 Upon addition of 25% of thermally air oxidized Crade Oil #6 to untreated

Crade Oil ??4, the stability of the émulsion doubles as evidenced by the decrease inpercent briné breakout from 34% to 16%.

Example-3: Solids-Stabilized Emulsion Prepared Usina Crade Oil #4 and Divided

Bentonite Gel 10 A mixture of 70 grams (g) of Crade Oil #4 and 30 g of divided bentonite gel (providing an oil to gel ratio of 70:30, and with a bentonite solids concentration of 3.5wt% in the gel) was air oxidized at a température of 160°C for 4 hours with an airpurge of 80 scf/bbl/hour. About 25 g of water was expelled from the reacror. Theproduct from the reaction was used to préparé a solids-stabilized 60/40 water-in-oil 15 émulsion. The air oxidized product was blended with untreated crude oiL with aresulting blend consisting of 2.4 wt% of the air oxidized product, to 97.6% of theuntreated crade oil.

Tne resulting 60/40 water-in-oil émulsion showed a 12% brine breakout in the micropercolation stability test. The émulsion was stable to ethane gas addition at 400 20 psi. -44- 012250 A mixture of 30 g of Crude Oil #4 and 70 g divided bentonite gel (oil to gel ratio of 30:70) was subjected to thermal air oxidation using as described above. Water was expelled from the reactor and the resulting product was an oily solid. A solids-stabilized 60/40 water-in-oil émulsion was made using the oily solidproduct. The amount of oily solid used was 0.1% based on the weight of the untreatedcrude oil.

The resulting émulsion showed a 20% brine breakout in the micropercolationstability test. The dispersed water droplets were less than 4 microns in diameter.

Pretreatment of Oil by Thermal Treatment in an Inert Environment

Another method of pretreating an oil to enhance its ability to form a stablesolids-stabilized water-in-oil émulsion is to thermally treat the oil in an inertenvironment prior to émulsification. This embodiment has the added benefit ofreducing the viscosity of the solids stabilized water-in-oil émulsion.

The thermal treatment can: a) generate asphaltenic solids which by themselves and/or in combination withexternally added solids provide improved stability to the solids-stabilizedwater-in-oil émulsions, b) reduce viscosity of the crude oil which translates to lower émulsionviscosity of the solids-stabilized water-in-oil émulsions, and c) retain or dégradé napthenic acids.

Préparation of Solids-Stabilized Water-in-Oil Emulsions with Thermally Treated ΟΪΓ

To enhance an oil's physical and Chemical properties for the formation of astable solids-stabilized émulsion, the oil may be thermally treated in an inertenvironment for a sufficient time, and at a sufficient température and pressure prior toémulsification. It is preferred to thermally treat the oil by heating to températuresbetween 250°C-450°C at 30 to 300 pounds/square inch (psi) for 0.5 to 6 hours. The 012250 -45- thermal treatment can occur in an inert atmosphère with no purge gas, or altemativelyin the continuous presence of an inert purge gas. For the preferred method ofthermally pretreating with no purge gas, the oil is initially purged with an inert gas likenitrogen for 30 minutes and the autoclave sealed and heated to the requiredtempérature. For the alternative embodiment of thermally pretreating with acontinuous purge of inert gas, an inert gas like argon is bubbled into the reactor at 200to 450 standard cubic feet/barrel/hour (scfihbl/hour) during the entire course ofthermal treatment. This process is preferred if a greater réduction in viscosity isdesired. The latter process will resuit in a greater percentage destruction of the surfaceactive napthenic acids and is less preferred for the purposes of preparing a stableémulsion. The treatment severity is suitably chosen to produce the optimum viscosityréduction and napthenic acid rétention. This treatment severity can vary from one oilto another but is within the ranges disclosed.

After the thermal treatment, solids are added followed by water and mixing toform the solids-stabilized water-in-oil émulsion. The addition of solids to the oil priorto the thermal pretreatment is also within the scope of the présent invention.However, in the latter case, the potential for fouling of the process equipment needs tobe addressed, and thermal treatment conditions optimized to minimize the equipmentfouling.

The water addition is made in small aliquots or continuously and the mixturesubjected to shear mixing, preferably at between 1000 to 12000 rpm, for a timesufficient to disperse the water as small droplets in the continuous oil phase. It ispreferred 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 theémulsion will rise above ambient température (25°C) during mixing. Controlling thetempérature of the émulsion during mixing is not critical. However, highertempératures between 40°C to 75°C are preferred.

With regards to solids, the solid particles are preferred to be hydrophobie innature^ Fumed silica, sold under the trade name Aerosil® R 972 (product of DeGussa 012250 -46-

Corp.) was found to be effective for a nuraber of different oils. Other solids likedivided and oil wetted bentonite clays, kaolinite clays, organophilic clays orcarbonaceous asphaltenic solids may also be used. The preferred concentration ofsolids to oil is in the range of 0.05 to 0.25 wt%.

It is preferred to thermally treat a slipstream of oil to a high level of severityand then mix the slipstream with a main stream of oil prior to addition of solids, waterand mixing to form the émulsion. This main stream of oil is preferably untreated crudeoil, however, it may be any oil, including oil that has been treated to enhance its abilityto form a stable émulsion or treated to optimize its rheology.

To fùrther stabilize the solids-stabilized émulsion made with thermally treatedoil, it is anticipated to be particularly useful to add 0.1 to 1.0 wt% of a lignosuîfonateadditive to the oil prior to émulsification. This method of enhancing the stability of asolids-stabilized émulsion, i.e. addition of a lignosuîfonate additive, is described above.

Dilute acid can also be added to the oil prior to émulsification, which willfùrther enhance the emulsion's stability and reduce the emulsion's viscosity. This diluteacid addition is also described herein.

The method of thermally treating oil before émulsification has the added benefitof decreasing the solids-stabilized emulsion's viscosity, as compared to a solids-stabilized émulsion made with untreated oil. This ability to manipulate the viscosity ofthe émulsion allows the user to optimally match the rheological characteristics of theémulsion to that of the oil to be recovered specifically for the particular type EORmethod used. Gas may also be added to fùrther lower the viscosity of the émulsion.

Yet another method to reduce the viscosity of a thermally treated solids-stabilized émulsion is to âge the émulsion. The thermally treated solids-stabilizedémulsion can be aged by simply allowing the émulsion to rest at room température orat an elevated température for a sufficient period of time. The viscosity of theémulsion can be reduced by more than 50% by using this method. The aging processcan be accelerated by centrifùgation, preferably repeated centrifùgation, which will 012250 -47- produce a similar réduction in viscosity of the thermally treated solids stabilized émulsion. Centrifugation is conducted preferably at températures between 35°C and 80°C for 15 minutes to 2 hours at 500 to 10,000 rpm.

Examples:

In a typical experiment, 200 g of oii was placed in a PARR autoclave andheated to températures of 150 to 450°C for 0.5 to 6 hours at pressures ranging from30 to 280 psi. The thermal pretreatment occuned either an inert atmosphère with nopurge gas, or altematively in the continuous presence of a purge gas. For thermalpretreatment with no purge gas, the oil was initially purged with an inert gas likenitrogen for 30 minutes and the autoclave sealed and heated to the requiredtempérature. For thermal pretreatment with a continuous purge of inert gas, an inertgas like argon was bubbled into the reactor at 200 to 450 scfZbbl/hour during the entirecourse of thermal treatment. A hydrophobie silica, Aerosil® R 972, was then added tothe heat treated oil. Mixing using a Silverson® homogenizer followed sôlids addition.Finally, water was added to the oil and solid particles in smali aliquots and mixed toprovide a solids-stabilized water-in-oil émulsion.

The thermal pretreatment method was demonstrated at three levels of severity,which impacted the following oil properties: (1) total acid number (TAN), (2) amountof n-heptane insolubles, (3) toluene équivalence (measure of solubility of the thermallygenerated asphaltenes), and (4) viscosity.

The émulsions prepared by thermally treated oil were subjected to thefollowing 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 (as described in Appendix-1 ) 4. Emulsion stability: flow through a sand pack (details of themicropercolation test procedure is given in Appendix-1) Ό12250 -48- 5. Emulsion rheology using a Brookfield® viscometer (cone(#51) and plate configuration) at 35 or 60°C in a shear range of 1.92 to 384 sec"1.

Example-1 A 60/40 water-in-oil émulsion was prepared using Crude Oil #2 without any 5 thermal treatment, but with addition of 0.15wt% hydrophobie silica (Aerosil® R 972).This émulsion, though shelf-stable, was unstable in the centrifuge and micropercolationtests. Dispersed water droplets ranged in size from 0.4 to 80 microns in diameter.

Example-2

Crude Oil #2 was thermally treated at 360°C for 6 hours at 280 psi in an inert 10 environment, using a nitrogen preflush. The resulting oil's viscosity at 35°C and 9.6sec'1 was lowered from 643 centipoise (cP) to 328 cP. The TAN was reduced from6.6 to 3.9. The toluene équivalence increased fforn 14 to 31 while the n-heptaneinsolubles remained unchanged at 2.7%.

Solid particles, 0.15wt% Aerosil® R 972, were added to the thermally treated 15 Crude Oil #2 followed by water and mixing to form a 60/40 water-in-oil solids-stabilized émulsion, as previously described. The resulting solids-stabilized émulsionhad a viscosity of 5734 cP at 35°C and 9.6 sec'1, which represented a 63% réduction inémulsion viscosity as compared to an untreated solids-stabilized émulsion made withuntreated Crude Oil #2 and 0.15wt% Aerosil® R 972. The NMR determined water 20 droplet size distribution of the heat treated solids-stabilized émulsion indicates anarrow distribution of water droplets in the size range of 2 to 10 microns in diameter.The émulsion was stable to flow as no water breakout was observed in themicropercolation tests described in Appendix - 1. The pH of the émulsion was about6.2. 012250 -49-

Example-3

Thermal treatment of Crude Oil #2 at 350°C for 2 hours at 90 psi in an inertenvironment resulted in a treated oil whose viscosity at 35°C and 9.6 sec"1 was loweredfrom 643 cP to 328 cP. The TAN was reduced from 6.6 to 5.1. The tolueneéquivalence increased from 14 to 25 while the n-heptane insolubles remainedunchanged at 2.7%.

Addition of 0.15wt% Aerosil® R 972 to the thermally treated oil followed bywater and mixing, as previously described, provided a stable solids-stabilized 60/40water-in-oil émulsion. NMR revealed a distribution of water droplets in the size rangeof 2 to 14 microns in diameter. A 14% water breakout in the micropercolationsandpack test and no water breakout in the microcentrifuge test were observed. ThepH of the émulsion was 6.2. The viscosity of the émulsion at 35°C and 9.6 sec'1 was7373 cP, which represents a viscosity réduction of greater than one-half whencompared to a similar solids-stabilized émulsion prepared from Crude Oil #2, that hadbeen pretreated with dilute acid using the method described above.

Example-4 A 60/40 water-in- oil émulsion was prepared with another crude oil, Crude Oil#4, without any thermal pretreatment, but with the addition of 0.15% of Aerosil® R972. Crude Oil #4 does not form stable solids-stabilized émulsions by the methoddescribed in U.S. Patents 5,927,404, 5,855,243 and 5,910,467. Physical properties forCrude Oil #4 are contained in Table 2. This émulsion, although shelf-stable, wasunstable in the centrifuge and micropercolation tests. Dispersed water droplets rangedin size from 2 to 40 microns in diameter, and a 54% water breakout was observed inthe micropercolation test, described in Appendix-1, using Berea sand. The viscosity ofthe émulsion at 60°C and 9.6 sec'1 was 3644 cP. 012250 -50-

General Test for Increase in Surface-Activîty of Oil

Increases in the surface-activity of oil due to pretreatment can be measured by detennining the decrease in interfacial tension between the oil and water. Interfacial5 tensions -were determined by the standard pendant drop technique at 25°C. Results foruntreated Crude Oil #4 and pretreated Crude Oil #4 are given below. Note thatinterfacial tension results for Crude Oil #4 treated with solid particles and sulfonation could not be measured using the standard pendant drop technique. TABLE 13 10 Measurement of Interfactal Tension

Oil Interfacial Tension dynes/cm

Untreated Crude Oil #4 32.3

Crude Oil #4+solid particles (solids) 32.6

Crude Oil #4 + acid pretreatment + solids 15.8

Crude Oil #4 + lignosulfonate + solids 12.5

Solids = 0.15wt% Aerosil® R 972Lignosulfonate = 0.1wt% ammonium lignosulfonateAcid pretreatment = 8000 ppm sulfuric acid

The présent invention has been described in connection with its preferred15 embodiments. However persons skilled in the art will recognize that many modifications, alterations, and variations to the invention are possible withoutdeparting 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 daims. -51- 012250

Appendix-l: Micro-Percolation Test for Emulsion Stabilityin Flow Through Porous Media

The observation that émulsions that are unstable will form two separatemacroscopie phases, an oil/emulsion phase and a water phase, is relied upon inorder to ascertain the stability of an émulsion on flow through porous media in arapid, convenient assay. A volume of émulsion that passes completely throughthe porous media can therefore be centrifuged to form two distinct phases,whose volumes can be used as a measure of the émulsion stability—the greaterthe proportion of water or water originally in the émulsion, that forms a clear,distinct phase after passage and 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 thatforms the distinct separate aqueous phase. Since it is a proportion, the bbo isdimensionless and ranges between one (maximally unstable) and zéro(maximally stable). The brine breakout is measured under a well-defined set ofconditions. A commercially available spécial fritted micro-centrifuge tube that iscomprised of two parts is used as the container for the experiment. The bottompart is a tube that catches any fluid flowing from the top tube. The top part issimilar to the usual polypropylene microcentrifuge tube, except that the bottomis a frit that is small enough to hold sand grains back, but allows the easy flow offluid. In addition, the tubes corne supplied with lids to each part, one of whichserves also as a support that allows the top to be easily weighed andmanipulated while upright. They are available from Princeton Séparations, Inc.,Adelphia NJ and are sold under the name "CENTRI-SEP COLUMNS." A heated centrifuge is used to supply the pressure to flow the émulsionfluid through a bit of sand placed in the upper tube. It was supplied byRobinson, Inc., (Tulsa, OK) Model 620. The température is not adjustable, butstabilizes at 72°C under our conditions. The top speed is about 2400 -52- 012250 révolutions per minute (RPM) and the radius to the sandpack is 8 centimeters(cm), which gives a centrifugal force of 520 g. Ail weights are measured to thenearest milligram.

The columns corne supplied with a small supply of silica gel alreadyweighed into the tube. This is discarded, and the weights of both sectionsnoted. About 0.2 grams (g) of sand is weighed into the top and 0.2 ±0.01 g ofoil added to the top. Typical sands used for this experiment are Berea orOttowa sands. The sand that is used in this test can be varied according to one'spurpose. For simplicity, one may use unsieved, untreated Ottawa sand, suppliedby VWR Scientific Products. This gives a convenient, "forgiving" Systembecause the sand particles are rather large and free of clay. Altematively, onemay use one fraction that passes through 100 Tyler mesh, but is retained by a150 mesh, and another fraction that passes through the 150 Tyler mesh, blendedin a ten to one ratio respectively. The tube is weighed again, then centrifugedfor one minute at full speed on the heated centrifuge. The bottom tube isdiscarded and the top is weighed again, which gives the amount of sand and oilremaining in the top. The sand is now in an oil wetted State, with air and oil inthe pore space.

Now, 0.18 ± 0.02 g of émulsion is placed on top of the wetted sand, andthe top is weighed again. A bottom tube is weighed and placed below this tubeto catch the effluent during centrifugation. A separate bottom tube is filled with 0.2 to 0.5 g of émulsion only. Thisserves as a control to détermine if the centrifuging of the émulsion, without itbeing passed through the oil-wetted sand, causes brine to break from theémulsion. This step is known as the microcentrifuge test, and is also anindicator of émulsion stability.

Both tubes are then centrifuged for a noted time (15 to 45 minutes)depending on the oil viscosity and centrifuge speed. The object in adjusting thelength of time is to get to a point where at least 75% of the émulsion arrives in -53- 01 2250 the bottom tube after passing through the sand. If less than that appears,the assembly is centrifuged for an additional time(s).

After spinning, the weight of the top and bottom pièces are againrecorded. If the émulsion is unstable, a clear water phase will be visible in thebottom of the tube, below an opaque, black emulsion/oil phase. The volume ofwater in the bottom réceptacle is then measured by pulling it up into a précisioncapillary disposable pipette (100-200 microliters) fitted with a plunger. Theseare supplied by Drummond Scientific Co. (under the name "Wiretroll II"). Thelength of the water coîumn is measured and converted to mass of water througha suitable calibration curve for the capillary. The water breakout can be thencalculated from these measurements and the knowledge of the weight fraction ofwater in the émulsion originally.

Claims (39)

1. -54- 012250 C L A I M S

   1. A method for enhancing the stability of a solids-stabilized water-in-oil émulsion,said method comprising the step of pretreating at least a portion of said oil prior toémulsification, said pretreating step comprising at least one of the steps of addingdilute acid to said oil, adding a lignosulfonate to said oil, sulfonating said oil, thermallytreating said oil in an inert environment, and thermally oxidizing said oil.
2. 2. A method for recovering hydrocarbons from a subterranean formation, saidmethod comprising the steps of: (a) preparing a solids-stabilized water-in-oil émulsion by (1) pretreating at least a. portion of said oil prior to émulsification, saidpretreating step comprising at least one of the steps of adding diluteacid to said oil, adding a lignosulfonate to said oil, sulfonating saidoil, thermally treating said oil in an inert environment, and thermallyoxidizing said oil, (2) adding solid particles to said oil prior to émulsification, and (3) adding water and mixing until said solids-stabilized water-in-oilémulsion is formed; (b) injecting said solids-stabilized water-in-oil émulsion into said subterraneanformation; and (c) recovering hydrocarbons from said subterranean formation.
3. 3. The method of daim 2, wherein said solids-stabilized water-in-oil émulsion isused as a drive fluid to displace hydrocarbons in said subterranean formation.
4. 4. The method of claim 2, wherein said solids-stabilized water-in-oil émulsion isused as a barrier fluid to divert the flow of hydrocarbons in said subterraneanformation. -55- 012250
5. 5. The method of claim 1 or claim 2, wherein said pretreating step comprises addingdilute acid to at least a portion of said oil prior to émulsification, said dilute acidselected from the group consisting of at least one minerai acid, at least one organicacid, mixtures of at least two minerai acids, mixtures of at least two organic acids, andmixtures of at least one minerai acid and at least one organic acid.
6. 6. The method of claim 5, wherein said acid is added to said oil at a rate of fromabout 8 parts per million to about 30,000 parts per million.
7. 7. The method of daim 5, wherein said method further comprises the steps ofdetermining the pH of said water-in-oil émulsion following émulsification and ifnecessary adjusting said pH so that it fàlls in the range of from about 5.0 to about 7.0.
8. 8. The method of claim 7, wherein said pH of said water-in-oil émulsion is adjustedby adding ammonium hydroxide to said émulsion.
9. 9. The method of claim 1 or claim 2, wherein said pretreating step comprisessulfonating at least a portion of said oil prior to émulsification.
10. 10. The method of claim 9, wherein said step of sulfonating at least a portion of saidoil comprises the addition of at least one sulfonating agent.
11. 11. The method of claim 10, wherein said sulfonating agent is sulfuric acid.
12. 12. The method of claim 10, wherein said sulfonating agent is added to said oil at atreat rate of from about 0.5wt% to about 5wt%.
13. 13. The method of claim 1 or claim 2, wherein said pretreating step comprises addinga lignosulfonate additive to at least a portion of said oil prior to émulsification. -56- 012250
14. 14. The method of claim 13, wherein said lignosulfonate additive is added to said oilat a rate of between about 500 parts per million to about 5000 parts per million.
15. 15. The method of claim 13, wherein said lignosulfonate additive is oil soluble.
16. 16. The method of claim 13, wherein said lignosulfonate additive is water soluble.
17. 17. The method of claim 1 or claim 2, wherein said pretreating step comprisesthermally oxidizing at Ieast a portion of said oil prior to émulsification.
18. 18. The method of claim 17, wherein said thermal oxidation step is carried out at atempérature of between about 110°C and about 180°C.
19. 19. The method of claim 17, wherein said thermal oxidation step is enhanced byaddition of a catalyst.
20. 20. The method of claim 1 or claim 2, wherein said pretreatment step comprisesthermally treating at least a portion of said oil in an inert environment prior toémulsification.
21. 21. The method of claim 20, wherein said thermal treatment step is carried out at atempérature in the range of between about 250°C and about 450°C.
22. 22. The method of claim 20, wherein said thermal treatment step is carried out at apressure in the range of between about 30 psi and about 300 psi.
23. 23. The method of claim 20, said method further comprising the step of adding adilute acid to said oil prior to émulsification, said dilute acid selected from the groupconsisting of at least one minerai acid, at least one organic acid, mixtures of at leasttwo minerai acids, mixtures of at least two organic acids, and mixtures of at least oneminerai acid and at least one organic acid. -57- 012250
24. 24. The method of claim 20, said method further comprising the step of adding alignosulfonate additive to said oil prior to émulsification.
25. 25. The method of claim 20, wherein said step of thermally treating said oil in aninert environment reduces the viscosity of said solids-stabilized water-in-oil émulsion.
26. 26. The method of claim 20, said method further comprising the step of aging saidsolids-stabilized water-in-oil émulsion following émulsification whereby the viscosityof said émulsion is reduced.
27. 27. The method of claim 26, wherein said step of aging said émulsion comprisescentrifuging said émulsion at about 500 rpm to about 10,000 rpm for about 15 minutesto about 2 hours.
28. 28. The method of claim 27, wherein said step of centrifuging said émulsion isrepeated.
29. 29. The method of claim 2, wherein said solid particles are hydrophobie solidparticles.
30. 30. The method of claim 2, wherein said step of adding solid particles to said oiloccurs after said pretreatment step.
31. 31. The method of claim 2, wherein said step of adding solid particles to said oiloccurs prior to said pretreatment step.
32. 32. The method of claim 2, wherein said solid particles comprise at least one offunctionalized asphalts, unfunctionalized asphalts, bentonite clays, bentonite clay gel,kaolinite clays, organophilic clays, carbonaceous asphaltenic solids, phylosilicates,lignin, lignite, coal, gillsontite, silica, dolamite, metaloyides, layered oxides, andquatemary onium exchanged phylosilicates. -58- 012250
33. 33. The method of daim 2, wherein said lignosulfonate additive is combined with hydrophilîc solid partides. 34 The method of daim 2, wherein said thermally oxidized oil is combined withhydrophilîc solid partides.
34. 35. The method of daim 2, wherein said solid partides are combined with alignosulfonate additive, and then said combination is added to said oil prior toémulsification.
35. 36. The method of daim 2, wherein said solid partides are added as a gel comprisedof solid partides and water.
36. 37. The method of daim 36, wherein said solid partides comprise about lwt% toabout 30wt% of said gel based on the weight of said water.
37. 38. The method of daim 36, wherein said gel is added to said oil in a treat range offrom about 5 wt% to about 95 wt% of said gel to said oil.
38. 39. The method of daim 2, wherein said solid partides are added at a treat rate ofabout .05 wt% to about 5 wt%.
39. 40. A solids-stabilized water-in-oil émulsion for use in recovering hydrocarbonsfrom a subterranean formation, said émulsion comprising (a) oil, wherein at least a portion of said oil is pretreated by at least oneof the steps of adding dilute acid to said oil, adding a lignosulfonateadditive to said oil, sulfonating said oil, thermally treating said oil inan inert environment and thermally oxidizing said oil; (b) water droplets suspended in said oil; and -59- 01 2250 (c) solid particles which are insoluble in said oil and said water at theconditions of said subterranean formation.