Methods of Consolidating Incompetent Subterranean Formations Using Aqueous Treating Solutions

Subterranean formations penetrated by well bores often contain loose or incompetent sands which are dislodged when fluids such as oil, gas and water are produced from the formations into the well bores. The presence of such sand particles in the produced fluid is undesirable in that the particles abrade pumping and other producing equipment, and generally reduce the fluid production capability of the formations. Incompetent subterranean formations are those in which particles making up the formation are bonded together with insufficient bond strength to withstand the forces produced by fluids flowing through the formation to the well bore. As a result, particles are dislodged and flow to the well bore with the fluids. Other subterranean formations include loose sands which are readily entrained by the fluids being produced from the formation.

Various methods of consolidating loose or incompetent sands in subterranean formations have been developed and used heretofore. One such method involves displacing a hardenable organic consolidating fluid into the formation using liquid hydrocarbon displacing solutions so that sands contained in the formation are coated with the organic consolidating fluid. The consolidating fluid is then caused to harden so that the sands are formed into a hard permeable mass. Another method developed and used heretofore involves dispersing a hardenable organic consolidating fluid into a liquid hydrocarbon carrier solution and then introducing the carrier solution into the formation so that the consolidating fluid coats loose or incompetent sands therein. The consolidating fluid is cured to form the sands into a hard permeable mass. Yet another method which has been used heretofore involves dispersing a hardenable organic consolidating fluid in a liquid hydrocarbon carrier solution and then combining a quantity of particulated solids therewith so that the particulated solids are coated with the consolidating fluid. The consolidating fluid-solids-hydrocarbon carrier mixture is introduced into the formation so that the consolidating fluid coated solids are deposited in contact with the formation adjacent the well bore. Upon the hardening of the consolidating fluid, a hard permeable mass is formed between the well bore and the formation so that loose or incompetent sands are prevented from flowing into the well bore with produced fluids. In the latter technique, additional consolidating fluid is often injected into the formation so that loose or incompetent sands contained therein are also consolidated.

While the foregoing methods and techniques have been utilized successfully, they all require the use of liquid hydrocarbon treating fluids. Generally, the formation to be treated is preconditioned using a liquid hydrocarbon treating fluid containing additives for shrinking clays, minimizing emulsions, preventing fluid blocks, etc. The consolidating fluid or consolidating fluid coated particles are then placed into the formation by displacement with liquid hydrocarbon solutions or by liquid hydrocarbon carrier solutions. Such liquid hydrocarbon treating fluids present disposal problems, particularly on off-shore locations, and are hazardous to handle. In addition, and perhaps most importantly, the use of liquid hydrocarbon fluids in treating subterranean formations is costly in that such treatments often involve the loss of portions of the treating fluids to the formation.

Attempts have been made heretofore to substitute aqueous treating fluids for the liquid hydrocarbon treating fluids in the above-described treatments. Such attempts have been unsuccessful due to the general inability of the organic consolidating fluids to coat siliceous materials in the formation being treated in the presence of water and to resist subsequent wash off. Further, attempts to combine organic consolidating fluids with aqueous carrier fluids have been largely unsuccessful due to portions of the consolidating fluid compositions being leached therefrom leaving a very thick gunky resin which is not dispersible in the carrier in a finely divided state, which cannot be pumped effectively in the carrier and which cannot be placed into the formation to be treated, particularly formations of low permeabilities. Also, in prior attempts to utilize aqueous carrier fluids, the resin portion remaining undissolved in the aqueous carrier has been tacky and when deposited on siliceous materials has agglomerated into large sticky masses which can cause damage to the formation permeability. In addition to the foregoing, problems relating to the formation of foams and emulsions have been experienced.

By the present invention, methods of consolidating loose or incompetent sands in subterranean formations using aqueous treating fluids are provided which obviate the above-described problems. Aqueous treating solutions such as readily available formation brines, fresh water, and bay and sea waters can be used. Such aqueous treating fluids are easily handled, present minimal disposal problems, and do not have fire hazard characteristics. The ready availability of aqueous treating fluids results in reduced storage tank requirements at job sites, and eliminates the need for transporting liquid hydrocarbons to off-shore locations. Further, the loss of aqueous treating fluids to the subterranean formation being treated does not materially increase the cost of carrying out the treatment.

The methods of the present invention basically comprise the steps of contacting the formation to be consolidated with an aqueous preflush solution to condition the formation for the acceptance of a hardenable organic consolidating fluid followed by contacting the formation with a hardenable organic consolidating fluid so that at least a portion of the loose or incompetent sands contained therein are coated by the consolidating fluid. The formation is next contacted with a spacer solution so that the hardenable organic consolidating fluid is distributed in the formation and excess consolidating fluid is flushed through the formation whereby permeability in the formation is retained. The consolidating fluid is then caused to harden whereby the coated sands are formed into a hard permeable mass which prohibits the movement of loose or incompetent sands with the production of fluids from the formation into the well bore.

In one aspect of the present invention, the hardenable organic consolidating fluid is displaced into the formation by an aqueous spacer solution followed by an aqueous solution containing a hardening agent.

In another aspect of the present invention, the consolidating fluid is combined with an aqueous carrier solution so that a portion of the consolidating fluid is dissolved and a portion is dispersed as an immiscible phase therein. The resultant consolidating fluid-aqueous carrier solution mixture is introduced into the formation so that the consolidating fluid coats loose or incompetent sands contained therein. Prior to introducing the consolidating fluid-aqueous carrier solution into the formation, an aqueous carrier solution containing a quantity of consolidating fluid coated solid particles can be introduced into the formation to place the coated solids into contact with the formation whereby upon hardening of the consolidating fluid, in addition to consolidating loose or incompetent sands in the formation, a hard permeable pack is formed between the formation and the well bore.

In yet another aspect of the present invention, methods of consolidating loose or incompetent sands in a subterranean formation are provided which are particularly useful in treating formations containing high percentages of acid soluble materials, such as calcium carbonate, dolomite, siderite, etc. These methods include the use of a liquid hydrocarbon spacer solution and a liquid hydrocarbon overflush solution containing a hardening agent, but allow the use of an aqueous preflush solution. Further, if it is desired to form a hard permeable pack between the formation and the well bore, an aqueous carrier solution is utilized to carry resin coated pack sand.

A variety of hardenable organic consolidating fluids can be utilized in accordance with the present invention. Particularly suitable such consolidating fluids are those comprised of a hardenable organic resin and a resin-to-sand coupling agent. The organic resin used is preferably a liquid at 80.degree. F. and is cured or hardened by heating or by contact with a hardening agent. Examples of commercially available organic resins which are particularly suitable for use in accordance with the present invention are epoxy resins, phenol-aldehyde resins, furfuryl alcohol resins and urea-aldehyde resins. Of these, furfuryl alcohol resin is the most preferred.

The above-mentioned organic resins are available at various viscosities, depending on the molecular weight of the resin. Preferably, the resin has a viscosity at 80.degree. F. in the range of from about 5 to 20,000 centipoises. The most preferred viscosity of the organic resin used in accordance with the present invention is in the range of from about 10 to about 500 centipoises at 80.degree. F. However, resins of higher viscosities can be utilized when mixed or blended with a diluent.

A variety of diluents for controlling the viscosity of the hardenable organic resin can be used in accordance with the present invention. Since the thickness of the resin coating which results on loose or incompetent sands in a formation, the surface area covered per volume of resin and the permeability and strength of the resultant hardened mass are in large part dependent on the viscosity of the resin, it is desirable to closely control the viscosity of the resin. This is accomplished in accordance with the present invention by combining a low viscosity liquid diluent with the resin used. Preferably, the diluent is a monomeric liquid capable of copolymerizing with the resin. Examples of suitable such diluents for epoxy resins are styrene oxide, octylene oxide, furfuryl alcohol, phenols, furfural, liquid monoepoxides derived from the reaction of epichlorohydrine and monohydroxyl compounds such as allyl glycidyl ether, butyl glycidyl ether and phenyl glycidyl ether; and liquid diepoxides such as diglycidyl ether or resorcinol. Examples of such diluents for furfuryl alcohol resins, phenol-aldehyde resins and urea-aldehyde resins include but are not limited to, furfuryl alcohol, furfural, phenol and cresol. Phenols, formaldehydes, furfuryl alcohol and furfural are preferred for use as diluents in accordance with the present invention.

When the consolidating fluid containing a diluent is combined with an aqueous or hydrocarbon carrier solution, a portion of the consolidating fluid is dissolved in the carrier solution and a portion is dispersed in an immiscible phase therein. In addition, a portion of the carrier solution is dissolved in the dispersed consolidating fluid. The quantitative distribution of the consolidating fluid between the dissolved and dispersed phases in the carrier solution is controlled to further achieve desired consolidating fluid viscosity and other properties. The step of controlling the quantitative distribution of the consolidating fluid between the dissolved and dispersed immiscible phases can be accomplished by controlling the particular quantities of consolidating fluid and the carrier solution used, and by controlling the temperature of the resulting consolidating fluid-carrier solution mixture. Another technique for controlling the quantitative distribution between dissolved and dispersed phases is to utilize a highly ionic aqueous carrier solution, i.e., a solution having a relatively high concentration of water soluble inorganic salts dissolved therein, which reduces the solubility of the consolidating fluid. Also, a liquid organic resin diluent can be utilized in the consolidating fluid which has a limited solubility in the aqueous carrier solution used. This control of the quantitative distribution between the dissolved and dispersed phases of the consolidating fluid and of the dispersed consolidating fluid viscosity, brings about superior formation treatment. For example, formations of relatively low permeability which have heretofore been difficult to treat due to the inability of relatively viscous consolidating fluids to penetrate and coat solids in the formation can be effectively treated. Further, a more effective utilization and spreading of a unit volume of consolidating fluid is achieved due to the presence of dissolved consolidating fluid in the carrier solution.

The resin-to-sand coupling agent is utilized in the consolidating fluid to promote coupling or adhesion of the consolidating fluid to sand and other siliceous materials in the formation to be treated. A particularly suitable such coupling agent is an amino silane compound or a mixture of amino silane compounds represented by the following formula: ##STR1## wherein:

R.sub.1 is a straight, branched or cyclic chain alkyl radical having in the range of about 1 to about 8 carbon atoms; R.sub.2 is hydrogen, an alkyl amine radical or an alkyl radical wherein the alkyl amine and alkyl radical have in the range of from about 1 to about 8 carbon atoms; R.sub.3 is a straight or branched chain alkyl radical having in the range of from about 1 to about 3 carbon atoms; and `n` is an integer within the range of from zero to about 10.

Examples of the foregoing amino silanes are gamma-aminopropyltriethoxysilane, N-beta-(aminoethyl)-gamma-aminopropyltrimethoxysilane, N-beta-(aminoethyl)-N-beta-(aminoethyl)-gamma-aminopropyltrimethoxysilane, N-beta-(aminopropyl)-N-beta-(aminobutyl)-gamma-aminopropyltriethoxysilane, and di-N-(beta-aminoethyl)-gamma-aminopropyltrimethoxysilane.

Preferred amino silanes are represented by the following general formula: ##STR2## wherein:

R.sub.4 is a straight or branched chain alkyl radical having in the range of from about 1 to about 4 carbon atoms; R.sub.5 is hydrogen, an alkyl amine radical or an alkyl radical wherein the alkyl amine and alkyl radicals have in the range of from about 1 to about 4 carbon atoms; R.sub.6 is an alkyl radical having in the range of from about 1 to about 2 carbon atoms; and `m` is an integer in the range of from about 1 to about 4.

Examples of the above amino silanes are N-beta-(aminoethyl)-gamma-aminopropyl-trimethoxysilane, N-beta-(aminoethyl)-N-beta-(aminoethyl)-gamma-aminopropyltrimethoxysilane and N-beta-(aminopropyl)-gamma-aminopropyltriethoxysilane.

The most preferred amino silane compound for use in accordance with the methods of the present invention is N-beta-(aminoethyl)-gamma-aminopropyltrimethoxysilane.

The consolidating fluid is preferably caused to harden by contacting the consolidating fluid with a hardening agent. The hardening agent can be included in the consolidating fluid composition (internal hardening agents) or the consolidating fluid can be contacted with the hardening agent (external hardening agents) after the consolidating fluid has been placed in the subterranean formation being treated. Internal hardening agents are selected such that the consolidating fluid hardens after a period of time sufficient to place the consolidating fluid in the subterranean formation. The most preferred technique for hardening the consolidating fluid placed in a formation in accordance with the methods of the present invention is to introduce an overflush solution containing an external hardening agent into the formation after the consolidating fluid has beed placed therein.

Suitable hardening agents for consolidating fluid compositions containing epoxy resins include but are not limited to, amines such as dimethylaminopropylamine, benzyldimethylamine, diethylaminopropylamine, diethylenetriamine, metaxylene diamine, metaphenylene diamine, diaminodiphenylmethane, piperidine, tridimethylaminomethylphenol; acid anhydride hardening agents such as oxalic anhydride, phthalic anhydride, pyromellitic dianhydride, dodecynyl succinic anhydride, hexahydrophthalic anhydride and methylbicyclo-(2,2,1)-5-heptene-2-3-dicarboxylic anhydride; and polymercaptan hardening agents.

Examples of internal hardening agents which can be used with consolidating fluids containing furfuryl alcohol resin, phenolaldehyde resins and ureau-aldehyde resins are hexachloroacetone, 1,1,3-trichloro-trifluoroacetone, benzotrichloride, benzyl chloride and benzal chloride.

Examples of external hardening agents for consolidating fluids including furfuryl alcohol resin, phenol-aldehyde resins and urea-aldehyde resins are acyl halide compounds such as phthaloyl, fumaryl and benzoyl chloride; halogenated organic acids and acid-producing chemicals such as trichloro-acetic acid, benzotrichloride, acetic acid, and formic acid; and inorganic acids such as hydrochloric acid. Generally, hardening agents selected from the group consisting of inorganic acids, organic acids and acid-producing chemicals are preferred for use in accordance with the methods of the present invention.

The consolidating fluid compositions preferably also include surfactants which function to improve the resin coating of sand or siliceous materials in an aqueous environment. The surfactants also help prevent the liquid consolidating fluid from becoming excessively tacky and agglomerating in aqueous carrier fluids thereby preventing undesirable gunky masses of resin coated solids which inhibit pumping from occuring. Particularly useful surfactants are cationic surfactants which are known as non-emulsifying surfactants and are commercially available as proprietary blends. When added to consolidating fluids, such surfactants maintain the portion of the consolidating fluid dispersed in the carrier solution from being converted to emulsions. Generally, a low concentration of such surfactants in the consolidating fluid is used, e.g., from about 0.1 to about 2 parts by weight surfactant per 100 parts by weight organic resin utilized.

Additives can be included in the consolidating fluid which function as dispersing agents, i.e., make the portion of the consolidating fluid dispersed in a carrier solution readily dispersable in a finely divided state. Particularly suitable such additives for facilitating the dispersal of consolidating fluids in aqueous carrier solutions are furfural, diethyl phthalate and mixtures of furfural and diethyl phthalate. These additives function as dispersing agents and prevent the consolidating fluid from becoming excessively tacky during placement into a subterranean formation. The portion of the consolidating fluid which is dispersed in the aqueous carrier solution can be readily extracted by sand or other siliceous materials in the formation, and since the consolidating fluid is prevented from becoming excessively tacky, agglomeration during pumping does not occur. Also, the finely divided dispersion of the consolidating fluid can be injected into low permeability formations without damaging the permeability of the formation. When brines are utilized as carrier solutions for the consolidating fluids, furfural is preferred as the dispersing agent, and when fresh water is utilized as the carrier solution, a mixture of furfural and diethyl phthalate is preferred.

The aqueous liquids which are useful as aqueous treating solutions in accordance with the methods of the present invention are those which do not contain contaminates which can plug the subterranean formation being treated. These include fresh water, formation brines, sea water and the like. When brines are utilized, those having alkali metal halides, alkaline earth metal halides or mixtures thereof dissolved therein are preferred. It has been found that aqueous treating solutions having high ionic strengths, i.e., solutions containing water soluble inorganic salts at concentrations of from about 5% to about 20% by weight have a greater tendency to allow the extraction of dispersed consolidating fluid therefrom onto siliceous surfaces and have less tendency to wash the consolidating fluid off of such surfaces as compared to low ionic strength aqueous solutions. This is due to the reduction of dispersion stability and resulting increase in dispersion coalescence in aqueous solutions of higher ionic strengths. Thus, brines are preferred for use as the aqueous treating solutions in accordance with the present invention. Small quantities of the above-mentioned non-emulsifying type of cationic surfactants are included in the aqueous solutions to prevent water blocks in the formation being treated, minimize emulsions and cause siliceous surfaces in the formations to readily accept the consolidating fluid in the presence of water, i.e., to render the siliceous surfaces wettable by the consolidating fluid.

In the procedures wherein liquid hydrocarbons are used, diesel oils, kerosenes, petroleum oil crudes, mineral oils and aromatic oils can be utilized. Liquid aliphatic or aromatic hydrocarbons having viscosities such that they can readily be injected through a subterranean formation are particularly suitable. Liquid hydrocarbons having a viscosity at 78.degree. F. in the range of from about 1 to about 25 centipoises are most preferred for the formations characterized by the lower permeabilities.

As will be understood by those skilled in the art, the consolidating fluids, aqueous treating solutions and liquid hydrocarbon solutions can all include a variety of other additives such as gelling or thickening agents, fluid loss additives, viscosity lowering agents, clay shrinking additives, friction reducing chemicals, etc.

In carrying out the present invention to consolidate loose or incompetent sands contained in a subterranean formation, an aqueous preflush solution is first introduced into the formation to condition the siliceous materials contained therein for the acceptance of the consolidating fluid used. While as stated above, a variety of aqueous fluids can be utilized, a brine comprised of water, a water soluble inorganic salt and a non-emulsifying type of cationic surface active agent is preferably utilized. The inorganic salt can be an alkali metal halide, an alkaline earth metal halide or mixtures thereof, and is preferably present in the aqueous solution in an amount in the range of from about 5% to about 20% by weight, most preferably from about 8% to about 15% by weight. The surface active agent is preferably present in the aqueous solution in an amount in the range of from about 0.1% to about 2.0% by weight. As the aqueous preflush solution is introduced into the formation, loose and/or incompetent sands contained therein are contacted by the solution and conditioned for the acceptance of the consolidating fluid. Further, the preflush prevents emulsions, water blocks and the like from forming in the formation.

Following the aqueous preflush solution and if the formation being treated has a relatively high premeability, the consolidating fluid can be displaced as a neat consolidating fluid, i.e., in a continuous quantity, directly into the formation so that the consolidating fluid contacts the formation and coats the loose or incompetent sands therein. In this procedure, the consolidating fluid is preferably a liquid composition comprised of a hardenable organic resin selected from the group consisting of epoxy resin, phenol-formaldehyde resin, urea-formaldehyde resin, furfuryl alcohol resin and mixtures thereof, a monomeric liquid diluent capable of copolymerizing with said resin selected from the group consisting of phenols, formaldehydes, furfuryl alcohol, and furfural present in an amount by weight about equal to the amount of resin used, and an amino silane coupling agent of the type described above present in an amount of from about 0.1 to about 10 parts by weight per 100 parts by weight of the resin. The most preferred consolidating fluid for direct introduction into the formation is a liquid composition comprised of furfuryl alcohol resin, furfural present in an amount in the range from about 50 to about 150 parts by wieght per 100 parts by weight of furfuryl alcohol resin therein, a non-emulsifying cationic surfactant present in an amount of about 1 part by weight per 100 parts by weight of furfural alcohol resin and N-beta-(aminoethyl)-gamma-aminopropyltrimethoxysilane present in an amount of about 1 part by weight per 100 parts by weight of furfuryl alcohol resin.

The consolidating fluid is displaced into the formation by an aqueous spacer solution which also functions to wash excess consolidating fluid from tubular goods disposed in the well bore and to distribute or spread the consolidating fluid into the formation and onto the loose or incompetent sands contained therein. Preferably, the spacer solution is a brine containing one or more of the above-described water soluble inorganic salts in an amount in the range of from about 5% to about 20% by weight, most preferably from about 15% to about 20% by weight, and a non-emulsifying cationic surface active agent present in an amount in the range of from about 0.1% to about 2.0% by weight.

The spacer solution is followed by an aqueous solution containing a hardening agent which causes the consolidating fluid to harden. The hardening agent is preferably an inorganic acid, and the aqueous solution containing the acid is preferably a brine of the same composition as the spacer solution described above. Most preferably, the hardening agent is hydrochloric acid contained in the brine solution in an amount of about 10% by weight. The contact of the consolidating fluid with the hardening agent causes the consolidating fluid to harden and consolidate the loose or incompetent sands contained in the formation into a hard permeable mass.

If the formation to be treated is of relatively low permeability, the consolidating fluid is placed into the formation by an aqueous carrier solution. That is, instead of displacing the consolidating fluid as a neat consolidating fluid, i.e., in a continuous quantity, directly into the formation after the preflush solution, the consolidating fluid is combined with an aqueous carrier solution so that a portion of the consolidating fluid is dissolved therein and a portion is dispersed in an immiscible phase therein. The aqueous carrier solution is preferably a brine containing one or more of the above-described water soluble salts in an amount in the range of from about 5% to about 20% by weight, most preferably from about 8% to about 15% by weight, and containing a non-emulsifying type of cationic surface active agent present in an amount in the range of from about 0.1% to about 2.0% be weight. The consolidating fluid is generally combined with the aqueous carrier solution in an amount in the range of from about 20 to about 200 parts by weight per 100 parts by weight of aqueous carrier solution, but the quantitative distribution of the consolidating fluid between the dissolved and dispersed phases in the carrier solution is controlled to obtain desired viscosity and other properties by utilizing specific quantities of consolidating fluid and carrier solution and controlling the temperature of the resultant mixture. The carrier solution containing dissolved and dispersed consolidating fluid is introduced into the formation so that loose or incompetent sands contained therein are coated by the consolidating fluid. The aqueous spacer solution and aqueous overflush solution containing a hardening agent described above are introduced into the formation following the consolidating fluid-aqueous carrier solution to form the loose sands into a hard permeable mass.

If it is desirable to form a permeable hard mass between the formation and the well bore in addition to consolidating at least a portion of the loose or incompetent sand contained in the formation, a quantity of consolidating fluid coated solid particles can be placed in contact with the formation prior to coating the loose or incompetent sands in the formation with additional consolidating fluid. In carrying out this aspect of the present invention, a brine preflush solution containing a non-emulsifying cationic surface active agent of the composition described above is introduced into the formation whereby the formation is conditioned to accept the consolidating fluid used, etc.

Following the introduction of the aqueous preflush solution, a first aqueous carrier solution of the same composition as the preflush solution containing a quantity of consolidating fluid coated solid particles, e.g., sand, is introduced into the formation so that the consolidating fluid coated particles are placed in contact with the formation adjacent the well bore. In preparing the consolidating fluid-solids-aqueous solution mixture, the consolidating fluid is first combined with the aqueous carrier solution whereby a portion of the consolidating fluid is dissolved in the solution and a portion is dispersed in an immiscible phase therein. The consolidating fluid is preferably dispersed in the aqueous carrier solution within the range of from about 0.5 to about 10 and preferably from about 0.75 to about 1.5 parts by weight consolidating fluid per 10 parts be weight of particulated solids used. A quantity of particulated solids are next introduced into the condolidating fluid-aqueous carrier solution mixture so that the solids are coated with the dispersed portion of the consolidating fluid. The particular quantity of particulated solids combined with the consolidating fluid-aqueous carrier solution mixture depends on the particular consolidating fluid utilized, its affinity for the particulated solid material and the portion of the consolidating fluid dispersed as an immiscible phase in the aqueous carrier solution. In some applications it may be desirable to add sufficient particulate material to attract only a portion of the dispersed consolidating fluid, leaving the remaining dispersed consolidating fluid to be placed in contact with loose or incompetent sands in the formation. If this procedure is used, it may also be desirable to eliminate the introduction of the second consolidating fluid-aqueous carrier solution mixture described below into the formation. A preferred particulated solid material is 20 to 60 mesh (U.S. Standard Sieve Series) sand which is generally mixed with the consolidating fluid-aqueous carrier solution mixture in an amount in the range of from about 3 to about 60, and preferably from about 6 to about 30 parts by weight per 100 parts by weight aqueous carrier solution. The particular concentration of particulated solids which can be mixed with the consolidating fluid-aqueous carrier solution mixture depends on a variety of factors such as the density and size of the particulated material, the viscosity and density of the aqueous carrier solution, the quantity of the consolidating fluid dispersed in the aqueous carrier solution and the flow rate at which the mixture is to be introduced into the formation to be treated.

The quantitative distribution of the consolidating fluid between the dissolved and dispersed immiscible phases is controlled in the manner described above to achieve desired viscosity and other properties. The consolidating fluid-solids-aqueous carrier solution mixture is introduced into the formation so that the consolidating fluid coated solid particles are placed in contact therewith. Excess solids are reverse circulated out of the well bore, and a second aqueous carrier solution containing dissolved and dispersed consolidating fluid is introduced into the formation so that loose or incompetent sands contained in the formation are contacted thereby. The second aqueous carrier solution is preferably a brine having a higher salt content than the preflush and first carrier solutions so that wash off of the consolidating fluid from the placed particulated solids is minimized. Most preferably the second carrier solution has a salt concentration of about 15% by weight. The quantitative distribution of the consolidating fluid between the dissolved and dispersed phases in the second carrier solution is controlled in the same manner as described above.

An aqueous spacer solution is next introduced into the formation to wash excess consolidating fluid from the tubular goods contained in the well bore and distribute and spread the consolidating fluid into the formation and onto the loose or imcompetent sands therein. The spacer solution is followed by an aqueous overflush solution containing a hardening agent so that the consolidating fluid is hardened and a hard permeable mass is formed between the well bore and the formation and a portion of the loose or incompetent sands in the formation are consolidated into a hard permeable mass. The spacer and overflush solutions are preferably brines of the same composition as the second carrier solution described above.

In carrying out the methods of the present invention in relatively low permeability formations containing high percentages of acid soluble materials such as calcium carbonate, dolomite, etc., and where aqueous solutions having high ionic strengths i.e., brines, are not available, liquid hydrocarbon solutions can be substituted for the spacer and overflush solutions described above. Such liquid hydrocarbon solutions resist wash off and acid or acid-forming hardening agents contained therein do not react with acid soluble materials in the formation as readily as do aqueous solutions containing such acids. In this application, an aqueous preflush solution is introduced into the formation so that loose or incompetent sands contained therein are contacted and conditioned for the acceptance of the consolidating fluid to be used. The preflush solution is made up of water containing a non-emulsifier type of cationic surface active agent in an amount of from about 0.1% to about 2.0% by weight.

Following contact of the formation with the preflush solution, an aqueous carrier solution of the same make up and composition as the preflush solution containing dissolved and dispersed consolidating fluid is introduced into the formation whereby loose or incompetent sands contained therein are coated by the consolidating fluid. The placement of the consolidating fluid is followed by a liquid hydrocarbon spacer solution and a liquid hydrocarbon overflush solution containing a hardening agent. Diesel oil containing a cationic surface active agent in an amount of about 0.1% to about 0.5% by weight is most preferred for use as the spacer and overflush solutions. As mentioned above, the liquid hydrocarbon solutions containing acid or acid-forming hardening agents do not react with acid soluble materials in the formation at a rate whereby hardening of the consolidating fluid is hindered or prevented and has less of a tendency to cause wash off of the consolidating fluid as compared to water of low ionic strength, i.e., fresh water.

A preferred consolidating fluid for use in carrying out this procedure is a liquid composition comprised of a hardenable organic resin selected from the group consisting of epoxy resin, phenolformaldehyde resin, furfuryl alcohol resin and urea-formaldehyde resin, a monomeric liquid diluent selected from the group consisting of phenols, formaldehydes, furfuryl alcohol and furfural present in an amount in the range of from about 20 to about 100 parts by weight per 100 parts by weight resin used, and an amino silane compound of the type described above present in an amount of from about 0.1 to about 2 parts by weight per 100 parts by weight resin.

The most preferred consolidating fluid for use in carrying out this procedure is a liquid composition comprised of furfuryl alcohol resin, furfuryl alcohol present in an amount in the range of from about 20 to about 100 parts by weight per 100 parts by weight of furfuryl alcohol resin used, a dispersing additive comprised of a mixture of furfural and diethyl phthalate present in an amount in the range of from about 50 to about 150 parts by weight per 100 parts by weight of resin, an amino silane compound of the type described above present in an amount of from about 0.1% to about 10 parts by weight per 100 parts by weight of resin, and a non-emulsifying cationic surface active agent present in an amount of from about 0.1 to about 2 parts by weight per 100 parts by weight of resin.

If it is desired to place consolidating fluid coated solid particles between the formation and the well bore so that a hard permeable mass is formed adjacent the well bore, in addition to forming a hard permeable mass in the formation, such coated solids are placed using an aqueous carrier solution. In carrying out this procedure, after the consolidating fluid coated solid particles are placed in contact with the formation, additional consolidating fluid is preferably introduced into the formation in a liquid hydrocarbon carrier solution so that loose or incompetent sands in the formation are coated by the consolidating fluid without excessive wash off of the consolidating fluid from the placed solid particles occurring. More specifically, the formation to be treated is first preflushed with an aqueous solution of the type described above, i.e., water containing a cationic surfactant, so that the formation is conditioned for the acceptance of the consolidating fluid utilized. A quantity of the consolidating fluid described above is combined with a quantity of an aqueous carrier solution of the same make-up and composition as the preflush solution so that the consolidating fluid is dissolved and dispersed therein. A quantity of particulated solids are next introduced into the consolidating fluid-aqueous carrier solution mixture so that the solids are coated with dispersed consolidating fluid, and the resultant consolidating fluid-solids-aqueous carrier solution mixture is introduced into the formation so that the coated solids are placed in contact with the formation. Excess solids are reverse circulated out of the well bore, and a liquid hydrocarbon solution, preferably diesel oil containing dissolved and dispersed consolidating fluid is introduced into the formation so that loose or incompetent sands in the formation are coated with consolidating fluid without excessive wash off of consolidating fluid from the placed solids occurring. A diesel oil-surfactant spacer solution is next introduced into the formation followed by a diesel oil-surfactant-hardening agent solution.

The following examples are given to present a clear understanding of and illustrate the present invention:

Furfuryl alcohol resin is tested with surfactants, diluents and various amino silanes to determine the effect of these components on a dispersion of furfuryl alcohol resin in an aqueous carrier liquid. The furfuryl alcohol resin has a viscosity at 25.degree. C. in the range of about 240 to 440 centipoises, a specific gravity in the range of about 1.205 to 1.220, a pH in the range of about 4 to 4.8 and an average molecular weight of about 225. One hundred twenty-one grams of the resin are homogeneously mixed with the concentrations of amino silanes, diluents and surfactants indicated in Table I. Five and five-tenths grams of the resin mixtures are then mixed with 0.66 grams of hexachloroacetone, an internal hardening agent for the resin. This mixture is then dispersed in 400 milliliters of an aqueous carrier liquid which is fresh water mixed with five parts by weight sodium chloride per 100 parts by weight water. Forty-eight grams of a 40-60 mesh U.S. Standard Sieve Series white sand is mixed with the dispersion and the mixture is agitated for a period of 30 minutes while heating the mixture at a constant rate from 72.degree. F. to 105.degree. F. The sand is then examined to determine if the resin coated the sand. The resin coated sand is then packed in a glass tube having an internal diameter of 0.875 inch to a height of 31/2 inches. The aqueous carrier fluid is flushed through the pack to simulate loss of the carrier fluid into a formation and the sample is allowed to harden in a 140.degree. F. bath for 24 hours. Samples are then cooled to 80.degree. F. and compressive strength measurements are made.

The data in Table I indicates that furfuryl alcohol resin mixed with amino silanes can be dispersed in an aqueous carrier liquid and that the resulting resin composition has an affinity for silica such that the resin composition will form a resin coating on silica surfaces when the resin is brought into contact with the silica.

This data also indicates that a sand pack coated with a mixture of furfuryl alcohol resin and an amino silane can be cured to a high strength matrix and that a surfactant can be added to the resin mixture to improve the compressive strength of a resin coated sand pack.

A resin formulation consisting of 121 grams of the furfuryl alcohol resin used in Example I, 113 grams of furfural and the concentration of surfactant shown in Table II are mixed with the silanes shown in Table II to determine the effect of the silanes on the ability of furfuryl alcohol resin to coat on silica particles. This series of tests is conducted in accordance with the procedure described in Example I except that the aqueous carrier fluid was fresh water and no hardening agent is mixed with the resin.

The data in Table II illustrates the coating properties of a resin mixture containing amino silanes. Resins containing amino silanes having at least two amino groups are shown to have good coating properties while an amino silane having one amino group is shown to enhance the coating ability of a resin when added to the resin formulation at a high concentration. Silanes which do not contain amino groups are shown to have no effect on the ability of the resin to coat silica particles unless used in combination with a cationic surfactant. Cationic surfactants are shown to improve the ability of a resin composition containing silanes to coat silica particles.

The compressive strengths of furfuryl alcohol resin coated sand packs prepared in accordance with the procedure described in Example I containing the silanes shown in Table III are measured. The aqueous carrier fluid in this example is fresh water containing 0.25 parts by weight of a proprietary blend of quaternary amines and diluents per 100 parts by weight water. The resin composition is a mixture including 0.95 grams of the silanes indicated in Table III, 121 grams of the furfuryl alcohol resin used in Example I, 113 grams of furfural and 0.96 grams of surfactant.

The data in Table III indicates that silanes which do not have amino groups produce low strength resin coated sand packs and that the strength of a resin coated sand pack increases with the number of amino groups in the silane structure.

the solubility of consolidated fluid dispersed in an aqueous carrier solution is determined at various temperatures. The consolidating fluid compositions are prepared by mixing 49.5 parts by volume of the furfuryl alcohol resin used in Example I with 49.5 parts by volume furfural, 0.5 parts by volume of N-beta(aminoethyl)-gamma-aminopropyltrimethoxysilane and 0.5 parts by volume of a proprietary blend of cationic surfactants per 100 parts by volume of the resin composition. The aqueous carrier solution is fresh water having dissolved therein eight parts by volume sodium chloride, 0.5 parts by weight calcium chloride, 0.2 parts by weight magnesium chloride and 0.25 parts by volume of a cationic surfactant blend per 100 parts by volume fresh water.

The data in Table IV illustrates the partial solubility of resin compositions dispersed in brine. It can be seen that the solubility of the resin composition in the brine does not increase in proportion to the concentration of resin compositions dispersed in the brine and that greater than about 20 parts by weight resin composition dispersed in the aqueous carrier liquid is required to maintain the viscosity of the resin composition. Therefore, the viscosity of the resin composition is reduced less as the concentration of the resin composition dispersed in the brine is increased. This data also indicates that the aqueous carrier liquid is partially soluble in the liquid resin composition and that the volume of the resin composition can be increased by the aqueous carrier liquid dissolving in the liquid resin composition.

The compressive strength and permeability of a sand pack consolidated with the resin used in Example IV and heated to 200.degree. F. are determined. After the resin composition dispersed in the brine and containing 20 parts and 30 parts by weight resin per 100 parts by weight of the resin brine mixture are heated to 200.degree. F. and the solubilities determined by the procedures described in Example IV, the dispersions are flushed through a pack of brine wet sand to coat the resin on the sand pack. The sand pack is 70 to 170 mesh U.S. Standard Sieve Series white sand packed in a glass tube having an internal diameter of 0.875 inch and a height of 3.5inches. The resin is cured by flushing 200 cc of 71/2% aqueous solution of hydrochloric acid in fresh water heated to 200.degree. F. through the sand pack. The aqueous solution used to harden the resin composition includes 0.1% of an acid inhibitor to reduce the corrosiveness of the acid to the metal components in the test system. The consolidated sand pack is cured for 16 hours at 200.degree. F. and then cooled to room temperature for measuring the permeability and compressive strength.

The data in Table V indicates that a resin composition dispersed in an aqueous carrier liquid can be flushed through a sand pack to consolidate the sand pack into a permeable matrix. The strength of the consolidated matrix and the permeability of the consolidated matrix are increased by increasing the concentration of the resin composition dispersed in the aqueous carrier liquid.

The ability of epoxy and phenol-formaldehyde resin compositions to coat silica particles and the strength of a pack of the resin coated particles is determined. The procedures described in Example I are used. The phenol-formaldehyde resin has a viscosity at 100.degree. F. of about 1000 centipoises and a pH of about 6.8. The epoxy resin has a viscosity at 80.degree. F. of about 100 to 160 centipoises and contains no diluents. The hardening agent for the epoxy resin is proprietary polymercaptan. The hardening agent for the phenol-formaldehyde resin is hexachloroacetone. The diluent for the epoxy and phenol-formaldehyde resin is furfural. The silane for both resins is N-beta (aminoethyl)gamma-aminopropyltrimethoxysilane.

The data in this table indicates that epoxy resin compositions and phenol-formaldehyde resin compositions can be dispersed in aqueous carrier fluids and that the resin compositions dispersed in the aqueous carrier fluids have an affinity for silica surfaces such that they will form coatings on the silica surfaces. This data also indicates that epoxy and phenolformaldehyde resin compositions containing amino silanes having at least two amino groups will form coatings on sand particles such that a pack of the resin coated sand particles will have high strengths after hardening.

A furfuryl alcohol resin composition containing 121 grams of the furfuryl alcohol resin used in Example I. 0.95 grams of N-beta-(aminoethyl)-gamma-aminopropyltrimethoxysilane, 0.96 grams of surfactant shown in Table VII, and 113 grams of furfural is tested with various surfactants. 5.5 grams of the resin composition are mixed with 0.66 grams of hexachloroacetone, and internal hardening agent for the resin. The resin composition is dispersed in 400 milliliters of a 5% sodium chloride brine. 48 grams of white sand having a particle size of 40-60 mesh U.S. Standard Sieve Series are mixed with the dispersion to coat the resin on the sand particles. The sand particles are then packed in a glass tube and the strengths are determined by the procedures described in Example I.

The data in Table VII indicates the surfactants can be included in the resin composition to increase the strength of a resin coated sand pack. This data also indicates that additional surfactant added to the carrier fluid can reduce the strength of a resin coated sand pack.

Various concentrations of a cationic surfactant are added to resin compositions containing amino silanes to determine the effect of surfactant concentration on the ability of the resin composition dispersed in an aqueous carrying fluid to coat silica particles. The ability to coat the silica particles is determined by measuring the strength of a pack of the particles in accordance with the procedure described in Example I. The resin composition is prepared by mixing 121 grams of the furfuryl alcohol resin used in Example I with 113 grams of furfural and 0.95 grams of the silane shown in Table VIII. Five and five-tenths grams of the resin composition is then mixed with the concentration of surfactant shown in Table VIII and 0.66 grams of hexachloroacetone, an internal hardening agent for the resin composition. This mixture is then dispersed in 400 milliliters of a 5% sodium chloride brine solution. Forty-eight grams of 40-60 mesh U.S. Standard Sieve Series white sand is then mixed with the dispersion to coat the resin on the sand. The coated sand is then packed in a glass tube and compressive strengths are determined by the procedures described in Example I.

The data in Table VIII indicates that cationic surfactants can increase the resulting strength of a resin coated sand pack. However, the concentration is critical and high concentrations of surfactant reduce the strength of a pack of resin coated sand particles.

A furfuryl alcohol resin composition containing 121 grams of the furfuryl alcohol resin used in Example I, 0.95 grams of N-beta-(aminoethyl)-gamma-aminopropyltrimethoxysilane, 113 grams of furfural and 0.96 grams of cationic surfactant is dispersed in the aqueous solutions shown on Table IX, and the ability of the resin to coat is determined in accordance with the procedures described in Example I.

The data in Table IX indicates that a resin composition comprising a curable organic resin and an amino silane can be dispersed in a variety of aqueous solutions and maitains its affinity for silica surfaces, i.e., the resin composition will coat the silica surfaces when placed in contact therewith. This data indicates that aqueous liquids containing acids can have deleterious effects on the ability of the resin dispersed in the aqueous liquid to coat silica surfaces.

The solubility of furfuryl alcohol in a brine solution comprised of 240 parts by weight water, 18.1 parts by weight NaCl, 1.34 parts by weight CaCl.sub.2 and 1 part by weight MgCl.sub.2 . 6H.sub.2 O at various temperatures is illustrated by the data given in Table X.

From the foregoing data it can be seen that the solubility of furfuryl alcohol in brine can be controlled by controlling the temperature of the brine-furfuryl alcohol mixture.

A consolidating fluid comprised of furfuryl alcohol resin and furfuryl alcohol in equal parts by volume is added to the brine solution described in Example X in controlled quantities at controlled temperatures. Before and after mixing, the volume of consolidating fluid is measured and the quantitative distribution of dissolved and dispersed phases determined. The results of these tests are shown in Table XI below:

From the data presented in Table XI, the control of the quantitative distribution of consolidating fluid in brine by controlling the quantitative ratio of consolidating fluid to brine used and the temperature of the mixture is illustrated.

The solubility of furfuryl alcohol in diesel oil (No. 2 standard commercial grade) at various temperatures is illustrated in Table XII:

From the data presented in Table XII, it can be seen that the solubility of furfuryl alcohol in diesel oil can be effectively controlled by controlling the temperature at which the furfuryl alcohol-diesel oil mixture exists.

A consolidating fluid comprised of furfuryl alcohol resin and furfuryl alcohol in equal parts by volume is added to diesel oil in controlled quantities at controlled temperatures. Before and after mixing, the volume of consolidating fluid is measured and the quantitative distribution of dissolved and dispersed phases determined. The results of these tests are shown in Table XIII below:

From the data presented in Table XIII, the control of the quantitative distribution of consolidating fluid in diesel oil by controlling the quantitative ratio of consolidating fluid to oil used and the temperature of the mixture is illustrated.

Various quantities of a consolidating fluid comprised of 3.3 parts by volume furfuryl alcohol resin, 1 part by volume furfuryl alcohol, 1 part by volume furfural and 1.4 parts by volume diethyl phthalate are mixed with the aqueous solutions given in Table XIV at the temperatures indicated and the viscosities of the dispersed phases of the consolidating fluid are determined.

From Table XIV it can be seen that the viscosity of the portion of consolidating fluid dispersed in various aqueous solutions can be effectively controlled by varying the quantitative ratio of aqueous solution to consolidating fluid and the temperature of the resultant mixture.

The dispersibility and placement properties of the various consolidating fluid compositions shown in Table XV are determined by observation in fresh water and brine. Ten (10) c.c. portions of the consolidating fluids are mixed with 100 c.c. portions of fresh water and brine at the temperatures indicated.

From Table XV it can be seen that furfural and diethyl phthalate function as dispersing agents and improve pumpability when combined with various consolidating fluids dispersed in aqueous solutions.