Method of Consolidating Porous Formations Using Vinyl Polymer Sealer With Divinylbenzene Crosslinker

There are numerous prior art consolidation systems which are used for forming gravel packs, consolidating permeable formations and sealing permeable formations. Many of these systems are limited to specific uses and have problems associated therewith. For instance, many use high viscosity resins or prepolymer compositions which are sensitive to water, carbonates or high pH formations, or are adversely affected by low or high temperatures or result in a relatively low strength consolidation.

A particular combination of monomers and catalyst systems have been discovered and make it possible to overcome many of these disadvantages. By this invention particular compositions and methods are provided for consolidating a particulate formation using a polymerizable organic liquid mixture having low viscosity with a catalyst system comprising a polymerization promotor, such as an organo metallic compound or an amine, and a polymerization initiator selected from organic peroxides, azo compounds and combinations thereof. This invention can be used for consolidating a portion of a particulate formation into a high strength, water resistant mass which is either permeable or impermeable. The compositions can be added to particulate formations in place or combined with particulate material and placed into the desired location to form a gravel pack or sand mass consolidation. The compositions can be used as a low viscosity mixture of neat monomers with catalyst components and optional additives or with a solvent. In addition, certain monomers such as styrene, divinylbenzene, acrylic acid or acrylonitrile can be used as the only monomer for a certain application, or as a reactive diluent monomer, or as a reactive diluent monomer which also serves as a catalyst. The consolidating composition can be applied to a formation, coated onto a particulate material, combined or mixed with a particulate material or injected into a particulate formation as long as the consolidating composition is in contact with the particulate formation to be consolidated and is maintained under suitable polymerization conditions until the monomers polymerize to form a high strength, water resistant mass including the particulate material. Preferred compositions include solvents, particulate fillers, chelating agents, and binders.

The compositions can be considered basically a mixture of low viscosity monomers. This mixture comprises polymerizable liquid, low viscosity monomers which consist essentially of monomers serving two functions. For certain applications one type of monomer can serve both functions. The polymerizable liquid mixture includes the catalyst system, preferred additives and optional additives, if desired, mixed with the polymerizable liquid monomers.

Monomers which serve the first function can be considered as a first group of preferred vinyl tape hydrocarbon monomers. These monomers are basically low molecular weight, low viscosity hydrocarbon monomers having about 3-12 carbon atoms and containing at least one group or radical selected from phenyl, carboxyl or nitrile. The monomer liquid mixture should be substantially all hydrocarbon monomers having at least one of these reactive groups or radicals. A small amount of other monomers can be tolerated but are not preferred. For example, monomers with ester linkages should be avoided since they are sensitive to water and temperature extremes. The low viscosity monomer mixture can include mixtures of monomers having the preferred reactive groups indicated above. Vinyl type monomers are those which have at least one reactive vinyl group represented by the formula:

the reactive groups phenyl, carboxyl or nitrile are represented by the following formulae respectively: ##STR1##

The second group of monomers are monomers which serve the second function required for the composition of this invention are the divinyl or difunctional monomers. These monomers have at least two vinyl reactive groups which can be polymerized and result in a crosslinked polymer network. These monomers are basically the same type as those for the first function except for the difunctional feature. For certain applications the difunctional monomer can be omitted. For example, for certain applications only one monomer such as styrene, acrylic acid or acrylonitrile can be used. However, a concentration of at least 1% by weight difunctional monomer or equivalent is preferred for the compositions of this invention. Examples of preferred difunctional monomers are divinylbenzene, 1,4-dibutylacrylate and polyester resin in low concentrations. The polyester resin contains maleic or fumaric groups which are actually polyfunctional and can be used, preferably in small concentrations, e.g., up to about 5%.

Examples of preferred vinyl type monomers are styrene, acrylic acid, methacrylic acids, acrylonitrile, methacrylonitrile, divinylbenzene and combinations thereof. Each of monomers should be of a type which is soluble in a low viscosity liquid aromatic hydrocarbon solvent. For low temperature applications, acrylic acid or acrylonitrile monomers should be present.

Monomers such as dimethyl itaconate, 2-ethylhexyl acrylate, methyl methacrylate, and d-2-ethylhexyl fumarate can be used.

The catalyst system or composition of this invention comprises promoters and initiators. Preferred catalyst systems for the composition of this invention have a latent period or in effect provide a delayed polymerization which allows placement of the polymerizable, low viscosity, liquid mixture before polymerization significantly affects the viscosity of the mixture. This is especially advantageous where the liquid mixture is to be pumped through a well into a subterranean formation and injected into that formation. When conventional preflushes and afterflush phases are used to control the location and coating characteristics of the polymerizable liquid mixture, this latent period can be especially advantageous.

The promoter portion of the catalyst system can be characterized as an organo metallic compound wherein the metallic portion or ion has a valence which varies with conditions. Organo metallic compounds of cobalt, nickel, iron, titanium, tin, antimony, zinc, and vanadium are preferred. These metals are generally from Classes IV through VIII of the periodic table of elements. The organic portion of the organo metallic promoter is preferably a low molecular weight hydrocarbon such as an ester which allows the metallic ion to function and promote the formation of free radicals from the other portion of the catalyst system. The organic radical can be aryl, alkyl or combinations thereof wherein the aryl or alkyl radical contains about 3-12 carbon atoms. A preferred class of organo metallic initiators are the cobalt arylates and cobalt alkylates such as cobalt naphthenate and cobalt octoate. Naphthenic acid is an old name for hexahydrobenzoic acid or cyclohexanecarboxylic acid. Generally, the class of coordination catalysts can be used for the catalyst systems of this invention. Another type of promoter which can be used is the substituted amines such as N,N-dimethyl aniline as described by: Brauer, G. M.; Davenport, R. M.; and Hansen, W. C.; "Accelerating Effect of Amines on Polymerization of Methyl Methacrylate;" November 1956, Breskin Publications, 575 Madison Ave., New York 22, N.Y., which is incorporated herein by reference.

The second portion of the catalyst system is a polymerization initiator. These are generally organic peroxides or an azonitrile type compound. The organic peroxides are preferably alkyl, aryl or combinations thereof wherein the alkyl or aryl radical has from about 3 to 12 carbon atoms. Examples of the preferred organic peroxides are t-butyl peroxide, ketone peroxide, methylethyl ketone peroxide, benzoyl peroxide, 2,5-dimethylhexane-2,5-diperbenzoate and t-butyl peroctoate. A preferred azonitrile initiator is azoisobutyronitrile. The formulas for methylethyl ketone and derived "peroxide" initiator are shown as follows:

Methylethyl ketone: ##STR2##

One of the forms of Methylethyl ketone peroxide: ##STR3##

A preferred but optional class of additives is the binders. This includes silanes, organo silanes and surfactants which affect or control the dispersibility and coating characteristics of the consolidating fluid. These silanes are called "silane adhesion promoters" by Union Carbide and are also referred to as silicon compounds. The surfactants and silane materials are described in the following U.S. patents which are incorporated herein by reference, U.S. Pat. Nos.: 3,123,137; 3,415,320; 3,199,590; 3,416,601; 3,221,814; 3,437,145; 3,291,214; 3,625,287; 3,625,287.

Preferred silanes or organo silicon compounds are listed as follows:

gamma aminopropyltriethoxysilane,

N-(beta-aminoethyl)-gamma-aminopropyltrimethoxysilane,

delta-aminobutylmethyldiethoxysilane,

N-methyl-gamma-aminoisobutyltriethoxysilane,

N-methyl-gamma-aminopropyltriethoxysilane,

delta-aminobutyltriethoxysilane,

N-(beta-aminoethyl)-gamma-aminopropyltriethoxysilane,

gamma dialkylaminopropyltriethoxysilane,

glycidoxyproplytrimethoxysilane, and

3,4 epoxycyclohexylethyltrimethoxysilane.

The surfactants which can be used in the compositions of this invention are those which are soluble or readily dispersible in an organic liquid such as the low viscosity monomers or the aromatic solvents used herein. The surfactants generally control dispersion of the various components in the organic liquid mixture and affect the attraction or coating ability of the polymerizable liquid on to the particulate formation. The surfactants also help to dissolve or maintain the various additives dispersed within the organic liquid phase. Preferred surfactants are blends of anionic, cationic and nonionic surfactants. Examples of preferred surfactants include hydrocarbon quaternary ammonium salts, alkylaryl sulfonates, ethoxylated hydrocarbon alcohols wherein each hydrocarbon radical, e.g., alkyl, aryl or combinations thereof, has about 6-18 carbon atoms.

Several preferred but optional additives include solvents, particulate fillers and chelating agents. Solvents which can be used with compositions of this invention are normally liquid aromatic hydrocarbon solvents. This can be mineral oil but the polymer is not soluble in mineral oil. The solvent serves to reduce the viscosity and dilute the polymerizable liquid. This dilution effect can be used to increase the permeability of the resulting consolidated mass and to reduce the amount of monomers required to coat and consolidate a given particulate mass. This in effect reduces the resulting volume of polymerized network which also reduces the ultimate strength attainable. For permeable consolidations careful control of coating, removal and distribution of monomer mixture in the particulate mass may be necessary which may require the use of various preflush and afterflush systems. Chlorinated solvents should be avoided. Chlorinated hydrocarbons have an adverse effect on refinery catalysts. In extreme cases explosive hyperactivity results. Most of the time organo halogens are bad for polymer strength because of chain transfer effects. For certain applications monomers such as styrene, acrylonitrile and acrylic acid can be either a reactive monomer or a diluent or solvent which reduces the viscosity of the polymerizable liquid mixture.

Particulate fillers which can be used for compositions of this invention are preferably relatively inert solid particles. The intended use will determine the particle size, particle size distribution and reactivity required. The particulate filler should be wet by the polymerizable liquid mixture for maximum strength. Preferred fillers include silica flour which is a finely divided silica, sand and biotite, exploded vermiculite (groupd up), ground granitic and basaltic materials. Chelating agents such as 2,4-pentanedoine can be used to improve the consolidation where the polymerizable liquid mixture must pass through the particulate formation. The chelating agent combines with the promoter (cobalt salts) and other organo metallic salts to maintain them dispersed in the polymerization liquid to assure complete polymerization of the monomers. In some cases, a particulate formation can extract or adsorb components from the polymerizable liquid mixture and adversely affect the resulting polymerized structure. Other conventional additives and methods can be used with the compositions and processes of this invention in view of this disclosure. Where the consolidating mixture is used to fill or plug a large void space or vug or it is desirable to attain a high compressive strength, a particulate filler is preferred. For applications where the particulate formation or gravel pack is to be impermeable, any reactive diluent or solvent concentration should be maintained at a minimum level. The use of filler and absence of solvent maintains shrinkage of the polymerized structure to a minimum. Since the compositions of this invention are insensitive to pH fluctuation, have no effect on pH and are not dependent on pH for initiating polymerization like phenol-formaldehyde, urea-formaldehyde, etc., they can be readily used where high carbonate materials present a problem.

The following preferred formulations and examples illustrate the invention and would enable one skilled in the art to practice the invention. Numerous variations will be obvious in view of this disclosure. The optimum concentrations, reaction conditions and optional components can be readily determined for specific formulations and application with minimum experimentation in view of this disclosure.

Generally, the polymerization rate is directly proportional to the temperature. For conventional batch polymerization the temperature can be controlled by addition or removal of heat from the polymerization vat. With subterranean or in situ polymerization the temperature and heat transfer is governed by the temperature of the well and formation. Therefore, the polymerization rate and conditions must be controlled as taught herein by adjusting the concentration of various monomers, initiators, promoters, solvents and other components. For example, at high temperature a low concentration of initiator and promoter can be used for a low polymerization rate and a low heat accumulation from the polymerization. Solvent can also be used to adsorb some heat, act as a diluent to help control polymerization rate and the viscosity as polymerization progresses. For certain high temperature applications (down to about 100.degree. F), certain monomers such as styrene can be used alone as the only monomer, although the resulting polymer will be a gel with a softening point rather than a crosslinked gel. Solid filler can be used to increase strength and reduce problems due to softening of the gel. For a low temperature (below about 100.degree. F), high initiator and promoter concentration or certain preferred monomers such as methacrylic acid, acrylic acid, acrylonitrile or methacrylonitrile can be used for a high polymerization rate. Esters are of little or no benefit at low temperature.

Table I describes the components used in various formulations. Table II shows preferred formulations with solvent. Table III lists preferred formulations without solvents.

It is preferred to omit solvents because the resultant strength reduction outweighs the volume gain. Fillers are used where macrovoids are to be sealed while fillers are omitted when capillaries are to be sealed.

The above tests serve to indicate the scope of this invention with respect to monomers that can be used.

Test 7 is the control test. It shows that it is difficult to obtain a set with styrene and divinylbenzene alone at low temperatures such as 75.degree. F.

The methacrylate esters Tests 4, 5, and 6 yield only modest aid in speeding up the gel time. However, methacrylic acid gives definite aid in speeding up gel time in Test Test 9 through 13.

Tests 6 and 7 indicate that with the proper Peroxide-Promoter System that the 75.degree. F compressive strength can be raised to a respectable level.

In Table IX, it can be seen that a gel time and compressive strength system can be made by varying the acrylonitrile-styrene ratio; note the orderly series with Tests 1 through 6. Also, Tests 7, 8 and 9 show that with additional manipulation of the promoter-initiator system that greater flexibility is possible.

When the monomer system of this invention is placed in vugs and cracks as contrasted to capillary systems, it is desirable to reduce the shrinkage caused by polymerization. This is done by using fillers. In Table X, it can be seen that the shrinkages in Test 2 are considerably less than the corresponding runs in Test 1. The purpose of the attapulgite is to prevent the ground silica flour filler from sedimentating.

Certain organosilicon compounds promote adhesion between silica flour and organic polymers. Examples are gammaglycidoxypropyltrimethoxysilane and cloropropyltrimethoxysilane. However, in this invention it is preferred to use a binding agent (adhesion promoter) with a reactive double bond in it so that it can participate in polymerization with the other monomers and thus firmly stitch the polymer to the silica by continuous chemical bonds. Examples are vinyltrichlorosilane, vinyltriethoxysilane, vinyltrimethoxysilane, and gamma-methacryloxypropyltrimethoxysilane. Table XI demonstrates that there is a definite improvement in compressive strength of the polymerized slurry (compare Test 2 with Test 4) when the binding agent is used. The binding agent should also promote adhesion to the formation surface. Because of this the binding agent is useful even when no filler is used.

When injected into a water producing 70-170 mesh sand with a permeability of approximately 10 darcies, the results were 99.61% and 99.95% water shut off for two tests (170.degree. F in 24 hours).

When the formula is squeezed into a wet sand, the cobalt plates out on the sand. Lack of cobalt in the lower part of the injected interval causes a failure to polymerize. A chelating agent such as acetylacetone (also called 2,4-pentanedione) controls the dispersibility of the initiator and/or promoter in the polymerization mixture in the presence of materials which would cause the initiator to separate from the mixture.