Fluid loss additive for well drilling

Abstract

The present invention relates to a process for the plugging of a porous formation which may be encountered during the drilling of a well. The process entails plugging of the porous formation by means of a polymeric solution containing pseudo-emulsion spheres. These particles penetrate the pore structure within a formation. Eventually, sufficient numbers of the spheres will accumulate within the pores, blocking further flow through the formation by both the pseudo-emulsion particles and any aqueous solutions. The pseudo-emulsion system is formed by a process which includes the steps of forming a solvent system of an organic liquid or oil and a polar cosolvent, the polar cosolvent being less than about 15 weight percent of the solvent system being less than about 100 cps; dissolving a neutralized sulfonated polymer in the solvent system to form a solution, a concentration of the neutralized sulfonated polymer in the solution being about 0.01 to about 0.5 weight percent, a viscosity of the solution being less than about 200 cps; and admixing or contacting said solution with about 5 to about 500 volume percent water, the water being immiscible with the organic liquid and the polar cosolvent and neutralized sulfonated polymer transferring from the organic liquid to the water phase, thereby causing the water phase to gel (i.e., thicken).

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for the plugging of a porous formation which may be encountered during the drilling of a well. The process entails plugging of the porous formation by means of a aqueous solution containing water-in-water pseudo-emulsion spheres. Preferably this aqueous solution which is a suspension of the spheres is prepared prior to injection into the well and then the aqueous solution suspension is injected into the well by suitable pump means. These particles penetrate the pore structure within a formation. Eventually, sufficient numbers of the spheres will accumulate within the pores, blocking further flow through the formation by both the pseudo-emulsion spheres and other aqueous solutions. The pseudo-emulsion system is formed by a process which includes the steps of forming a solvent system of an organic liquid or oil and a polar cosolvent, the polar cosolvent being less than about 15 weight percent of the solvent system, a viscosity of the solvent system being less than about 100 cps; dissolving a neutralized sulfonated polymer in the solvent system to form a solution, a concentration of the neutralized sulfonated polymer in the solution being about 0.01 to about 0.5 weight percent, a viscosity of the solution being less than about 200 cps; and admixing or contacting said solution with about 5 to about 500 volume percent water, the water being immiscible with the organic liquid and the polar cosolvent and neutralized sulfonated polymer transferring from the organic liquid to the water phase, thereby causing the water phase to gel (i.e. thicken).

2. Description of the Prior Art

There are many applications for very viscous or gelled solutions of polymers in water which are quite diverse. There are also a number of physical and chemical techniques for preparing such systems. The present invention is concerned with a process for plugging a porous formation encountered during the drilling of a well, wherein the porous formation has water or salt water therein. If during the drilling of a well, a porous formation or water-bearing formation is encountered, a major problem which is faced is loss of material from the drilling fluid. If the loss of material from the drilling mud or dilution of a drilling mud with excess water becomes significant, the success of the drilling operation will be jeopardized. The instant invention provides a fluid loss additive which is capable of plugging the pores in the porous formation or water-bearing formation by providing an aqueous solution containing a large number of water-in-water pseudo-emulsion spheres which are capable of penetrating the pores structure within an underground formation. Preferably this aqueous solution which is a suspension of the spheres is prepared prior to injection into the well and then the aqueous solution suspension is injected into the well by suitable pump means. These particles will accumulate within the porous media, preventing further flow of both the pseudo-emulsion spheres and aqueous solution through the formation.

The instant invention differs from a number of applications, Ser. Nos. 223,482 now U.S. Pat. No. 4,361,658; 136,837 now U.S. Pat. No. 4,322,329; and 106,027 now U.S. Pat. No. 4,282,130, filed by Robert Lundberg et al, one of the instant inventors. These previously filed applications were directed to the gelling of the organic liquid by a water insoluble, neutralized sulfonated polymer whereas the instant invention is directed to the gelling (i.e., thickening) of an aqueous phase via a water-in-water pseudo-emulsion solution in order to plug a porous formation in a well. Quite unexpectedly, it has been discovered that when the concentration of the sulfonated polymer is maintained in a critical concentration range of 0.01 to 0.5 weight percent of the total volume of solvent, which is a mixture of nonpolar organic liquid and a polar cosolvent, upon the addition of water, a transfer of the polar solvent and water insoluble neutralized sulfonated polymer from the nonpolar organic liquid phase to the water phase occurs. The water insoluble neutralized sulfonated polymer causes the water phase to gel, wherein the neutralized sulfonated polymer is insoluble in the water phase. In the previously filed patent applications, substantial viscosification of the nonpolar organic liquid phase did not occur until the concentration of the neutralized sulfonated polymer was sufficiently high enough to permit chain entanglement of adjacent polymer molecules thereby completely filling the solvent space. The gelation of the aqueous phase of the instant invention does not occur by this previously described mechanism because the resultant concentration of water insoluble, neutralized sulfonated polymer is not sufficiently high enough to permit chain entanglement. The mechanism of gelatin of the aqueous phase, as defined in the instant invention, occurs by the formation of macroscopic, spherical polymer membranes or films dispersed throughout the aqueous fluid, wherein large volumes of the water of the aqueous liquid are encapsulated within a series of minute polymer bags (termed pseudo-emulsion spheres or particles).

The instant invention describes a process which permits (1) the preparation of polymer solutions of sulfonated polymers in organic liquid having reasonably low viscosities (i.e., less than about 2,000 cps); and (2) the preparation of a large number of pseudo-emulsion spheres within an aqueous fluid from such solutions by a process of contacting and agitating water with the polymer solution; and (3) the plugging of the pores of a porous formation in a well by the means of the formed aqueous pseudo-emulsion sphere system. These operations are achieved by the use of the appropriate concentration; 0.01 to 0.5 weight percent of water insoluble, neutralized sulfonated polymers, having low concentrations of ionic groups present, prefereably metal sulfonate groups. Such polymers are described in detail in a number of U.S. Patents (U.S. Pat. Nos. 3,836,511; 3,870,841; 3,847,854; 3,642,728; and 3,921,021) which are herein incorporated by reference. These polymers possess unusual solution characteristics some of which are described in U.S. Pat. No. 3,931,021. Specifically, these polymers, such as lightly sulfonated polystyrene, containing about 2 mole percent sodium sulfonate pendant to the aromatic groups, are typically not soluble in solvents commonly employed for polystyrene itself. However, the incorporation of modest levels of polar cosolvents permit the rapid dissolution of such ionic polymers to form homogeneous solutions of moderate viscosity.

In the instant process, the role of the polar cosolvent pertains to the following observation of solvating the ionic groups while the main body of the solvent interacts with the polymer backbone. For example, xylene is an excellent solvent for the polystyrene backbone and when combined with 5 percent methanol readily and rapidly, will dissolve the previous example of lightly sulfonated polystyrene.

The discovery of the instant invention is the ability of a large number of pseudo-emulsion spheres to penetrate a porous formation, preventing the loss of material from a drilling fluid. Preferably this aqueous solution which is a suspension of the spheres is prepared prior to injection into the well and then the aqueous solution suspension is injected into the well by suitable pump means. In addition, these spheres are capable of totally inhibiting flow of unwanted aqueous solutions into the drilling fluids. Even more remarkable is that the phenomena occurs via wholly hydrocarbon soluble sulfonated polymers at quite low polymer levels. The pseudo-emulsion system is formed by a process which includes the steps of forming a solvent system of an organic liquid or oil and a polar cosolvent, the polar cosolvent being less than about 15 weight percent of the solvent system, a viscosity of the solvent system being less than about 100 cps; dissolving a neutralized sulfonated polymer in the solvent system to form a solution, a concentration of the neutralized sulfonated polymer in the solution being about 0.01 to about 0.5 weight percent, a viscosity of the solution being less than about 200 cps; and admixing or contacting said solution with about 5 to about 500 volume percent water, the water being immiscible with the organic liquid and the polar cosolvent and neutralized sulfonated polymer transferring from the organic liquid to the water phase, thereby causing the water phase to gel (i.e., thicken).

SUMMARY OF THE INVENTION

The present invention relates to a process for the plugging of a porous formation which may be encountered during the drilling of a well which comprises the plugging of the porous formation by means of an aqueous solution which contains a large number of pseudo-emulsion particles. The pseudo-emulsion system is formed by mixing a polymer solution containing low levels of polymer with an aqueous solution, wherein the mixing is preferably down outside the well and the resultant aqueous solution is injected into the well by suitable pump means. The polymeric solution is formed by dissolving the polymer in a solvent system of an organic liquid or oil and a polar cosolvent, the polar cosolvent being less than about 15 weight percent of the solvent system, a viscosity of the solvent system being less than about 100 cps. The polymer which is dissolved in the solvent system is a water insoluble, neutralized sulfonated polymer, wherein a concentration of the water insoluble, neutralized sulfonated polymer in the solution being about 0.01 to 0.5 weight percent, and a viscosity of the solution being less than about 200 cps. Preferably this aqueous solution which is a suspension of the spheres is prepared prior to injection into the well and then the aqueous solution suspension is injected into the well by suitable pump means.

Accordingly, it is a primary object of the instant invention to describe an economical process for forming a highly viscous or gelled aqueous solution having a viscosity from about 50 cps to about 1,000 cps, which can be used as a fluid loss additive capable of readily plugging the pores in a porous formulation in a well.

GENERAL DESCRIPTION

The present invention relates to a process for the plugging of a porous formation which may be encountered during the drilling of a well which comprises the plugging of a porous formation by means of an aqueous solution which contains a large number of pseudo-emulsion spheres.

The aqueous solution water-in-water pseudo-emulsion spheres after being pumped into the well enters a water-bearing zone or porous formation and subsequently increases resistance to flow in this portion of the formation due to the spheres relatively large size which act as plug means within the porous sphere. Therefore, a heavy concentration of spheres results which plugs the fracture in the water-bearing zone and prevents flow of water through the fracture to the well. The pseudo-emulsion system is formed by mixing, preferably outside the well, a polymer solution containing low levels of polymer with an aqueous solution. Agitation of the two solutions can occur at the surface of the drilling site via standard mixing equipment or alternatively through the rotational action of the drill bit in the vicinity of the water-bearing formation. In the former instance, the water-in-water pseudo-emulsion system is formed and subsequently allowed to flow to the water-bearing strata whereby plugging of the porous strata occurs. In any event, the water-in-water pseudo emulsion system can enter the porous formation admixed with the drilling mud or as a separate injected system. The polymeric solution is formed by dissolving the polymer in a solvent system of an organic liquid or oil and a polar cosolvent, the polar cosolvent being less than about 15 weight percent of the solvent system, a viscosity of the solvent system being less than about 100 cps. The polymer which is dissolved in the solvent system is a neutralized sulfonated polymer, wherein a concentration of the neutralized sulfonated polymer in the solution being about 0.01 to about 0.5 weight percent, a viscosity of the solution being less than about 200 cps.

The gelled aqueous phase (containing the pseudo-emulsion particles) having a viscosity greater than 50 cps is formed by contacting the water insoluble solution having a viscosity less than 200 cps with water wherein the water insoluble solution comprises an organic liquid, a polar cosolvent and a neutralized sulfonated polymer and a concentration of neutralized sulfonated polymer in the water insoluble solution is 0.01 to 0.5 weight percent. Upon contacting the water insoluble solution with water, the polar cosolvent and water insoluble, neutralized sulfonated polymer rapidly transfers from the organic liquid to the aqueous water which undergoes immediate gelation. The gelation (i.e., thickening) of the water to a viscosity of at least 50 cps can be quite rapid in the order of less than 1 minute to about 24 hours, more preferably less than 1 minute to about 30 minutes, and most preferably less than 1 minute to about 10 minutes, however, this depends on temperature, shear, solvent type, etc. Agitation of the two solutions can occur at the surface of the drilling site via standard mixing equipment or alternatively, through the rotational action of the drill bit in the vicinity of water-bearing formation. In the former instance, the water-in-water pseudo-emulsion system is formed and subsequently allowed to flow to the water-bearing strata whereby plugging of the porous strata occurs. In any event, the water-in-water pseudo-emulsion system can enter the porous formation admixed with the drilling mud as a separate injected system. The formed pseudo-emulsion system readily and rapidly plugs the pores of the porous formation in the well.

The component materials of the instant process generally include a water insoluble, ionomeric polymer such as a water insoluble, neutralized sulfonated polymer at a critical concentration level of 0.01 to 0.5 weight percent, a nonpolar organic liquid, polar cosolvent and water containing in specific instances, acid or salt.

Gelation of an aqueous phase does not occur, if one employs a conventional unsulfonated polymer or a water soluble, neutralized sulfonated polymer in place of the water insoluble, neutralized sulfonated polymer, but rather only classical phase separation occurs.

In the instant invention, the gelation of the aqueous phase occurs by the formation of geometrically shaped spheres of the water insoluble, neutralized sulfonated polymer within the aqueous phase, wherein the water is encapsulated within these geometrically shaped spheres. During the process, approximately 10 weight percent of the nonpolar organic liquid also transfers to the aqueous phase and is encapsulated within these geometrically shaped spheres.

The sulfonated polystyrenes which are the preferred embodiment of this invention lose their effectiveness (i.e., as a water-in-water pseudo-emulsion former) in salt water. More specifically, it has been found that a suitable nonionic surfactant must be employed with the water insoluble, sulfonated polystyrene to give formulations which are effective in producing these water-in-water pseudo-emulsion in high concentrations of salt water.

In general, the water insoluble ionomeric polymer will comprise from about 10 to about 200 meq. pendant ionomeric groups per 100 grams of polymer, more preferably from 10 to 100 meq. pendant ionomeric groups. The ionic groups may be conveniently selected from the groups consisting of carboxylate, phosphonate, and sulfonate, preferably sulfonate groups. In most instances, the ionomers utilized in the instant invention are neutralized with the basic materials selected from Groups IA, IIA, IB and IIB of the Periodic Table of Elements and lead, tin and antimony, as well as ammonium and amine counterions. Ionic polymers which are subject to the process of the instant invention are illimitable and include both plastic and elastomeric polymers. Specific polymers include sulfonated polystyrene, sulfonated t-butyl styrene, sulfonated ethylene copolymers, sulfonated propylene copolymers, sulfonated styrene/acrylonitrile copolymers, sulfonated styrene/methyl methacrylate copolymers, sulfonated block copolymers of styrene/ethylene oxide, acrylic acid copolymers with styrene, sulfonated polyisobutylene, sulfonated ethylene-propylene terpolymers, sulfonated polyisoprene and sulfonated elastomers and their copolymers. The preferred polymers of the instant invention are ethylene-propylene terpolymers and polystrene, wherein polystyrene is most preferred.

Neutralization of the cited polymers with appropriate metal hydroxides, metal acetates, metal oxides, or ammonium hydroxide etc., can be conducted by means well-known in the art. For example, the sulfonation process as with Butyl rubber containing a small 0.3 to 1.0 mole percent unsaturation can be conducted in a suitable solvent such as toluene, with acetyl sulfate as the sulfonated agent, such as described in U.S. Pat. No. 3,836,511. The resulting sulfonic acid derivative can then be neutralized with a number of different neutralization agents such as a sodium phenolate and similar metal salts. The amounts of such neutralization agents employed will normally be equal stoichiometrically to the amount of free acid in the polymer plus any unreacted reagent which is still present. It is preferred that the amount of neutralizing agent be equal to the molar amount of sulfonating agent originally employed plus 10 percent more to insure full neutraliziation. The use of more of such neutraliziation agent is not critical. Sufficient neutralization agent is necessary to effect at least 50 percent neutralization of the sulfonic acid groups present in the polymer, preferably at least 90 percent, and most preferably essentially complete neutralization of such acid groups should be effected.

The degree of neutralization of said ionomeric groups may vary from 0 (free acid) to greater than 100 mole percent, preferably 50 to 100 percent. With the utilization of neutralized ionomers in this instant invention, it is preferred that the degree of neutralization be substantially complete, that is with no substantial free acid present and without substantial excess of the base other than that needed to insure neutralization. The neutralized ionomers possess greater thermal stability compared to its acid form. Thus, it is clear that the polymers which are normally utilized in the instant invention comprise substantially neutralized pendant groups, and in fact, an excess of the neutralizing material may be utilized without defeating the objects of the instant invention.

The ionomeric polymers of the instant invention may vary in number average molecular weight from 1,000 to 10,000,000 preferably from 5,000 to 500,000, most preferably from 10,000 to 200,000. These polymers may be prepared by methods known in the art, for example, see U.S. Pat. No. 3,642,728, hereby incorporated by reference.

The preferred ionic copolymers for use in the instant invention, e.g., sulfonated polystyrene and substituted derivatives thereof, may be prepared by the procedures described in U.S. Pat. No. 3,870,841, filed Oct. 2, 1972, in the names of H. S. Makowski, R. D. Lundberg and G. H. Singhal, hereby incorporated by reference.

The ionic polymers may be incorporated into the organic liquid at a level of from 0.01 to 0.5 weight percent and more preferably from 0.01 to 0.4 weight percent, based on the organic liquid and the polar cosolvent.

Specific examples of preferred ionomeric polymers which are useful in the instant invention include sulfonated polystyrene, sulfonated poly-t-butyl styrene, sulfonated polyethylene (substantially noncrystalline), and sulfonated ethylene copolymers, sulfonated polypropylene (substantially noncrystalline), and sulfonated polypropylene copolymers, sulfonated styrenemethyl methacrylate copolymers, (styrene)-acrylic acid copolymers, sulfonated polyisobutylene, sulfonated ethylene-propylene terpolymers, sulfonated polyisoprene, sulfonated polyvinyl toluene and sulfonated polyvinyl toluene copolymers.

The ionomeric polymers of the instant invention may be preferred prior to incorporation into the organic solvent, or by neutralization of the acid in situ. For example, preferably the acid derivative is neutralized immediately after preparation. For example, if the sulfonation of polystyrene is conducted in solution, then the neutralization of that acid derivative can be conducted immediately following the sulfonation procedure. The neutralized polymer may then be isolated by means well-known to those skilled in the art, i.e., coagulation, steam stripping, or solvent evaporation, because the neutralized polymer has sufficient thermal stability to be dried for employment at a later time in the process of the instant invention. It is well-known that the unneutralized sulfonic acid derivatives do not possess good thermal stability and the above operations avoid that problem.

It is also possible to neutralize the acid form of these polymers in situ; however, this is not a preferred operation, since in situ neutralization requires preparation of the sulfonic acid in the organic liquid which is to be subjected to the instant process, or the acid form of the ionic polymer must be dissolved in said organic liquid. The latter approach may involve handling of an acid form of an ionic polymer which has limited thermal stability. Therefore, it is quite apparent that the preparation and isolation of a neutralized ionic polymer affords the maximum latitude in formulation, less problems in handling polymers of limited thermal stability and maximum control over the final mixture of ionic polymer, polar cosolvent and organic liquid.

The organic liquids, which may be utilized in the instant invention, are selected with relation to the ionic polymer and vice-versa. The organic liquid is selected from the group consisting of aromatic hydrocarbons, cyclic aliphatic ethers, aliphatic ethers, or organic aliphatic esters and mixtures thereof.

Specific examples of organic liquids to be employed with the various types of polymers are:

______________________________________Polymer Organic Liquid______________________________________Sulfonated Polystyrene benzene, toluene, ethyl benzene, methylethyl ketone, xylene, styrene, ethylene, dichloride, methylene chloride.sulfonated poly-t-butyl benezene, toluene, xylenestyrene ethyl benezene, styrene, t-butyl styrene, aliphatic oils, aromatic oils, hexane, heptane, decane, nonane.sulfonated ethylene- pentane, aliphatic andpropylene terpolymer aromatic solvents, oils such as Solvent "100 Neutral", "150 Neutral" and similar oils, benezene, diesel oil, toluene, xylene, ethyl benzene, pentane, hexane, heptane, octane, isooctane, nonane, decane, aromatic solvents, ketone solvents.sulfonated styrene- dioxane, halogenatedmethacrylate copolymer aliphatics, e.g., methylene chloride, tetrahydorfuran.sulfonated saturated aliphaticpolyisobutylene hydrocarbons, diisobutylene, triisobutylene, aromatic and alkyl substituted aromatic hydrocarbons, chlorinated hydrocarbons, n-butyl ether, n-amyl, ether, methyl oleate, aliphatic oils, oils predominantly paraffinic in nature and mixtures containing naphthenic hydrocarbons. "Solvent 100 Neutral", "Solvent 150 Neutral" and all related oils, low molecular weight polymeric oils such as squalene, white oils and process oils having 60 percent or less aromatic content.sulfonated polyvinyl toluene, benzene, xylene,toluene cyclogexane ethyl benzene, styrene, methylene chloride, ethylene dichloride.______________________________________

The method of the instant invention includes incorporating a polar cosolvent, for example, a polar cosolvent in the mixture of organic liquid and water insoluble ionomer to solubilize the pendant ionomeric groups. The polar cosolvent will have a solubility parameter of at least 10.0, more preferably at least 11.0 and is water miscible and may comprise from 0.1 to 10.0 weight percent, preferably 0.1 to 5.0 weight percent of the total mixture of organic liquid in which the neutralized sulfonated polymer is dissolved contains less than about 10.0 weight percent of the polar cosolvent, more preferably about 0.1 to about 5.0 weight percent, and most preferably about 1.0 to about 5.0 weight percent. The viscosity of the solvent system is less than about 1,000 cps, more preferably less than about 800 cps and most preferably less than about 500 cps.

Normally, the polar cosolvent will be a liquid at room temperature; however, this is not a requirement. It is preferred, but not required, that the polar cosolvent be soluble or miscible with the organic liquid at the levels employed in this invention. The polar cosolvent is selected from the group consisting of water soluble alcohols, amines, di or trifunctional alcohols, amides, acetamides, phosphates, or lactones and mixtures thereof. Especially preferred polar cosolvents are aliphatic alcohols such as methanol, ethanol, n-propanol, isopropanol, 1,2-propane diol, monethyl ether of ethylene glycol, and n-ethylformamide.

The amount of water contacted with the solution of neutralized sulfonated polymer, organic liquid and polar cosolvent having a viscosity of less than about 200 cps, is about 5 to 500 volume percent of water, more preferably about 10 to about 300 volume percent water, most preferably about 10 to about 200 volume percent water.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following example will demonstrate the performance of sulfonated polystyrene of varying sulfonate levels in several specific aqueous environments.

EXAMPLE 1

It has been observed that under certain conditions, a hydrocarbon solution containing a low concentration of a sulfonated polystyrene or sulfonated EPDM is mildly agitated with water for a short period of time, a pseudo-emulsion is formed. In the initial formation stage, the type of pseudo-emulsion produced in these systems has a continuous aqueous phase while the hydrocarbon medium is the dispersed phase. It is believed that the sulfonated polymer stabilized the hydrocarbon/water interface. Upon standing for a short period of time after mixing has occurred, it is observed that approximately 90 percent of the initial hydrocarbon solvent can be separated from the system leaving behind a pseudo-emulsion system characterized as a water-in-water pseudo-emulsion. Addition of a small amount of nonionic surfactant can be added to facilitate this process. Experimental evidence indicated that free passage of nonpolar organic solvent occurs through the sulfonated polymer membrane and the hydrocarbon solvent is replaced within each sphere by water as the nonpolar, organic solvent passes through the membrane.

As shown in Table I, the essential material needed for the formation of a pseudo-emulsion system in a hydrocarbon/water environment is the water insoluble, neutralized sulfonated polymer. Table I shows that the addition of water to a No. 2 diesel oil (or xylene) solution containing tridecyl alcohol as a cosolvent and/or unsulfonated EPDM (Socabu 55) or polystyrene (Styron 666) results in a classic phase separation of the hydrocarbon and water phases. On the other hand, spontaneous formation of a pseudo-emulsion system occurs in the presence of the sulfonated polymer. In addition, it has been observed that more stable pseudo-emulsion systems are produced with increasing sulfonation level. The nature of the counterion does not impair the interfacial activity of the polymer.

Further confirmation of the interfacial activity of these sulfonated polymers can be obtained utilizing viscosity measurements. The viscosity of several water-in-water pseudo-emulsions as a function of the polymer concentration is shown in Table II. It is readily apparent that due to the particular "macroscopic" structures formed in the aqueous phase, significant viscosification occurs as compared to the dissolution of a water soluble polymer of equivalent molecular weight and concentration. The viscosity of the pseudo-emulsion system at high polymer levels rises, while within the concentration range between approximately 1 and 5 g/l, the viscosity is essentially constant. Only when rather low polymer levels are reached does the viscosity begin to decline again. A comparison of the EPDM and polystyrene data indicates that the nature of the backbone chain may have little influence on the viscosity of the system, while the sulfonate level is of paramount importance. These results can be rationalized by assuming that the sulfonated polymer resides at the water-water interface. This latter observation is supported through the use of light microscopy. Under low magnification (approximately 100.times.) the structural details of the pseudo-emulsion system can be observed. In the first place, a large number of spheres constitutes a typical pseudo-emulsion system. Secondly, each pseudo-emulsion particle is a spherical structure in which a large volume of water is contained with the polymer film. The continuous phase outside of each particle is identical in composition to the internal aqueous phase.

EXAMPLE 2

Table III shows the relationship between the viscosity of the pseudo-emulsion phase, formed with polystyrene containing various sulfonation levels, as a function of polymer concentration. The viscosity tends to rise at very low polymer concentrations. Outside of this concentration regime, the viscosity remains constant to rather high polymer levels (approximately 0.5 g/dl.) The viscosity of the pseudo-emulsion at a particular polymer concentration does increase with higher sulfonation levels. Undoubtedly, this observation is related to both the sphere size and packing within the aqueous phase.

EXAMPLE 3

Aqueous solutions containing pseudo-emulsion spheres were tested as a fluid loss additive using Millipore.RTM. filters (Millipore Corporation--Bedford, Mass.) possessing a range of pore sizes (0.2, 1.0 and 5.0 microns). This test is based on the ability of an aqueous solution containing a large number of pseudo-emulsion spheres to completely prevent the aqueous phase from percolating through the filter. In this example, 20 ml. of a pseudo-emulsion system is placed in a funnel containing the appropriate filter. The maximum amount of fluid which can pass through (prior to any plugging) is measured. We observe only a small volume of fluid (.ltoreq.0.5 ml.) passed through the 0.2 micron and 1.0 micron filters, while less than 1 ml. of solution came through the 5 micron filter. However, complete plugging of the filter occurs in all instances.

This example shows that pseudo-emulsion spheres are capable of plugging the pores within a filter which, in turn, completely inhibits flow of the aqueous phase. The filter pore sizes are comparable to pore sizes found in a variety of underground formations.

Moreover, we observe that the aqueous solution (without pseudo-emulsion spheres) passes rapidly and uninhibitedly through the filter paper, regardless of pore size.

TABLE I______________________________________FORMATION OF WATER-IN-WATER PSEUDO-EMUL-SION 50 HYDROCARBON/50 WATER Water/WaterMaterial Pseudo-Emulsion Formed______________________________________Tridecyl Alcohol NoSocabu 55 or Styron 666 NoSocabu 55/Tridecyl Alcohol NoZinc NoNeutralized (10-30 meq.) EPDMMagnesium and Calcium Neutralized Yes(10 meq.) EPDMMagnesium and Calcium Neutralized Yes(10 meq.) EPDMTridecyl AlcoholUnneutralized Sulfonated (25 meq.) YesEPDM Tridecyl AlcoholSodium Sulfonated (1-6 mole %) YesPolystyreneZinc Sulfonated (1-3 mole %) YesPolystyrene______________________________________ TABLE II______________________________________VISCOSITY* - POLYMER CONCENTRATION DATAOF A TYPICAL PSEUDO-EMULSION SYSTEM Polymer Concentration ViscosityMaterial (g/l) (cps)______________________________________Sulfonated Polystyrene 0.25 210(Sodium Salt - 1.7 mole %) 0.5 295 1.25 315 2.5 320 5.0 340Sulfonated EPDM 0.50 160(Magnesium Salt - 10 meq.) 1.25 204 2.5 210 5.0 210______________________________________ *Viscosity measured with a Brookfield viscometer at 30 RPM. TABLE III______________________________________VISCOSITY* - POLYMER CONCENTRATION DATAOF SEVERAL PSEUDO-EMULSIONSYSTEMS FORMED WITH SEVERALSODIUM SALTS OF SULFONATED POLYSTYRENESMaterial (mole %) Polymer Level (g/l) Viscosity (cps)______________________________________3.0 0.12 280 0.5 430 1.0 480 2.0 4904.19 0.12 380 0.25 440 0.5 570 2.0 8206.05 0.12 420 0.25 540 0.5 820 2.0 950______________________________________ *Viscosity measured with a Brookfield .RTM. viscometer at 30 RPM.

Claims

1. A process for plugging the pores of a porous formation of a well with a water-in-water pseudo-emulsion solution having a viscosity of at least about 50 cps which includes the steps of:

(a) forming a solvent system of an organic liquid and a polar cosolvent, said polar cosolvent being less than about 15 weight percent of said solvent system, a viscosity of said solvent system being less than about 100 cps;

(b) dissolving a water insoluble, neutralized sulfonated polymer in said solvent system to form a solution, a concentration of said unneutralized or neutralized sulfonated polymer in said solution being about 0.01 to about 0.5 weight percent, a viscosity of said solution being less than about 200 cps;

(c) adding about 5 to about 500 volume percent water to said solution, said water being immiscible with said solution, with said polar cosolvent and said water insoluble, neutralized sulfonated polymer transferring from said organic liquid to said water causing the viscosity of said water to increase to at least 50 cps to form said water-in-water pseudo-emulsion solution;

(d) injecting said water-in-water psuedo-emulsion solution into said well having said porous formation; and

(e) penetration of said porous formation by the water-in-water pseudo-emulsion solution to plug the pores of said porous formation of said well.

2. A process according to claim 1 whereby said organic liquid is removed from said water-in-water pseudo-emulsion solution.

3. A process according to claim 1, wherein said neutralized sulfonated polymer has about 10 to about 200 meq. of pendant SO.sub.3 groups per 100 grams of polymer.

4. A process according to claim 3 wherein said SO.sub.3 H are neutralized within an ammonium or metal counterion.

5. A process according to claim 4 wherein said metal counterion is selected from the group consisting of antimony, tin, lead or Groups IA, IIA, IB or IIB of the Periodic Table of Elements.

6. A process according to claim 3 wherein said SO.sub.3 H groups are at least 90 mole percent neutralized.

7. A process according to claim 6 wherein said elastomeric polymer is selected from the group consisting of EPDM terpolymer or Butyl rubber.

8. A process according to claim 7 wherein said thermoplastic is selected from the group consisting of polystyrene, t-butyl styrene, ethylene copolymers, propylene copolymers, or styrene/acrylonitrile copolymers.

9. A process according to claim 1 wherein said neutralized sulfonated polymer is formed from an elastomeric polymer.

10. A process according to claim 1 wherein said neutralized sulfonated polymer is formed from a thermoplastic.

11. A process according to claim 1 wherein said polar cosolvent has greater polarity than said organic liquid.

12. A process according to claim 1 wherein said polar cosolvent is selected from the group consisting of aliphatic alcohols, aliphatic amines, di- or trifunctional aliphatic alcohols, water miscible amides, acetamides, phosphates, or lactones and mixtures thereof.

13. A process according to claim 1 wherein said polar cosolvent is selected from the group consisting of methanol, ethanol, propanol, isopropanol and mixtures thereof.

14. A process according to claim 1 wherein said polar cosolvent has a solubility parameter of at least about 10 and is water miscible.

15. A process according to claim 1 wherein said organic liquid is selected from the group consisting of aromatic hydrocarbons, ketones, chlorinated aliphatic hydrocarbons, aliphatic hydrocarbons, cyclic aliphatic ethers, aliphatic ethers or organic aliphatic esters and mixtures thereof.

16. A process according to claim 1 wherein said organic liquid is selected from the group consisting of aliphatic hydrocarbons or aromatic hydrocarbons.

17. A process according to claim 16 where said neutralized sulfonated polymer is formed from polystyrene.

18. A process according to claim 1 wherein said organic liqud is selected from the group consisting of benzene, toluene, ethyle benzene, xylene or styrene and mixtures thereof.