CA1144298A

CA1144298A - Aqueous drilling fluid additive, composition and process

Info

Publication number: CA1144298A
Application number: CA000326926A
Authority: CA
Inventors: James M. Lucas; Alphonse C. Perricone; Dorothy P. Enright
Original assignee: Milchem Inc
Current assignee: Milchem Inc
Priority date: 1978-09-27
Filing date: 1979-05-04
Publication date: 1983-04-05
Also published as: FR2441049A1; MX150927A; GB2032929A; GB2032929B

Abstract

ABSTRACT OF THE DISCLOSURE
The invention relates to an aqueous drilling fluid composition, a filtration control agent for utilization in said aqueous drilling fluid, and a method of forming a filter cake on the wall of a well for the reduction of filtrate from said drilling fluid, which are ef-fective at high temperatures and pressures, by utilization of a terpolymer of: (1) a monovalent alkaline metal salt of acrylic acid;
(2) an hydroxy alkyl acrylate; and (3) acrylamide.

Description

~144Z98 ACKGROUND OF THE INVENTION

1. FIELD OF THE INVENTION: The invention relates to the utili~ation of a terpolymer of: (l) a monovalent alkaline metal salt of acrylic acid; (2) an hydroxy alkyl~acrylate; and (3) acryl-amide,to effectively reduce the filtrate loss of an aqueous drillingfluid used in the drilling of a subterranean well.

2. DESCRIPTION OF THE PRIOR ART: It is generally agreed among those skilled in the art that a rotary system is a most ac-ceptable form of drilling an oil or gas well. This system depends upon the rotation of a column of drill pipe to the bottom of which is attached a multi-pronged drilling bit. The bit cuts into the earth causing the cuttings to accumulate as drilling continues. As a result,a drilling fluid must be used to carry these cuttings to the surface for removal, thus allowing the bit to continue function-ing and the bottom hole to be kept clean and free of cuttings at all times. Drilling systems other than the rotary system are sometimes employed during drilling operations. Nevertheless, these systems still require a drilling fluid to remove the bore hole cuttings and to otherwise perform functions related to drilling fluids.

Oil-producing formations are generally porous layers having varying degrees ofpermeability to the flow of fluids such as oil, water, or gas. Consequently, the rate of oil production is largely determined by the rate of flow through these permeable formations which, in turn, is dependent upon the porosity or permeability of the sand or stone present. In drilling through such a porous layer, it is desirable to employ a drilling mud having such characteristics that excessive amounts of liquids or solids are prevented from pen-etrating the porous formation. The ability of the drilling mud to prevent excessive formation fluid penetration is called filtration control.
Materials that have been used in the past to control fil-tration rates of aqueous drilling fluids by plugging, producing cakes, or similar methods, have included materials such as 1~44298 pre-gelatinized starchl sodium carboxylmethylcellulose, sodium polyacryaltes, and lignites. Each of these materials have cer~ain limitations. For example, lignite becomes inneffective in high salt concentrations.
Acrylic and methacrylic derivitives, such as those which are co-polymerized with hydrocarbon substituted styrenes, such as alpha methyl styrene, para methyl styrene, 2-4 dimethyl styrene, and the like have been utilized in drilling fluids. For example, U. S. Patent No. 2,718,497, to Oldham, et al, teaches the use of relatively high molecular weight polymers of these materials to control water loss characteristics of aqueous muds and clay dis-persions. Additionally, U. S. Patent No. 2,650,905, to Fordyce, et al, teaches the use of water soluble sulfonated polystyrene derivitives for filtration control in water-based drilling fluids.

The prior art has utilized acrylic acid derivitives as thickeners for numerous commercial purposes, including utilization in drilling fluids. For example, U. S. Patent No. 4,059,552, to Zwei~le, et al, teaches the use of acrylamide-sodium acrylate or acrylic acid-substituted acrylates. A similar thickening material is disclosed in U. S. Patent 4,037,035, to Blanc, et al, by util-ization of an acrylamide-sodium acrylate constituent with an acryl-amide-acrylic acid alkanolamine. Similarly, copolymers of acryla-mide and sodium acrylate and acrylate derivitives thereof formed by irradiat;on polymerization are utilized as thickeners, as dis-closed in U. S. Patent No. 3,926,576 to Restaino. U. S. Patent No. 3,8~7,404 ~o Korte, et al, teaches utilization as thickeners for printing paste and the like of substituted acrylamide-acrylic acid-acrylate derivitives.

1~442g8 Hydrophilic gels derived from 2-hydroxyethyl methacryla~e have been found to be useful in a number of medical applications as material for gel filtration, such as copolymers of acrylamide, acrylic ester-2-hydroxyethyl methacrylate, as disclosed in V. S.
Patent No. 3,948,841, to Dusek.
Acrylamide-sodium acrylate-2-hydroxyethyl acrylate cross-linked agents of a comparatively high molecular weight are utilized as soil stabilizers as disclosed in U. S. Patent No, 3,651,002, to Higashimura, et al.
Acrylic acid derivitives such as copolymers of acrylamide and sodium acrylate derivitives have been frequently and commercially utilized as flocculants for drilling fluids, and are disclosed in U. S. Patents No. 3,558,545, and No. 3,472,325 to Lummus. Similarly, a copolymer derived from acrylic acid and acrylamide is disclosed in U. S. Patent No. 3,323,603 to Lummus et al, as a flocculant for aqueous drilling fluids.

In the present invention, enhanced filtration control is obtained by incorporation into an aqueous drilling fluid of a fil-tration control agent consisting essentially of a terpolymer of:
(1) a monovalent alkaline metal salt of acrylic acid; ~2) an hydroxy alkyl acrylate; and (3) acrylamide. Although it is not fully understood, it is believed that the terpolymer will produce a filter cake along the bore hole to maintain effective filtration control during circulation of the drilling fluid within th~ well.
Thus this invention provides a filter cake which is substantially unaffected by comparatively high bore hole temperatures and pressures and which will not materially affect the viscosity of the utilized drilling fluid system.

11~4Z98 Also this invention provides a comparatively low cost, easily prepared, filtration control agent for use in aqueous drilling fluids. This ~iltration control agent for aqueous drilling fluids is comparatively insensitive to salt environments and concentrations within the aqueous syste~ and may be utilized in highly weighted drilling fluids.

Other ad~antages of the present invention will be easily appreciated by those skilled in the art from a reading of the description, examples and claims which follow.
SUMMARY OF THE INVENTION
~ The present invention provides a filter cake-producing substance which is effective at high temperatures and is compara-tively insensitive to salt environments and concentrations found in aqueous drilling fluidsby utilization of a terpolymer of: (1) a monovalent alkaline metal salt of acrylic acid; (2) an hydroxy alkyl acrylate; and (3) acrylamid~.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
The preparation of the terpolymer of the present invention incorporates three monomeric materials,which are: (1) a monovalent alkaline metal salt of acrylic acid; (2) an hydroxy alkyl acrylate;
and (3) acrylamide.
Any monovalent alkaline metal salt of acrylic acid, such as the sodium, potassium, or cesium salt, may be utilized as a starting monomeric additive for preparation of the present filtra-tion control agent. Di- and tri-valent salts have been found to be comparatively unacceptable because of their inherent precipita-tion characteristic when incorporated into aqueous systems. Ad-ditionally, acrylic acid variatives, such as methacrylic acid salts, ~ ~.44298 are not acceptable for use in the practice of the present invention because their comparative solubility parameters are significantly less in aqueous systems than that of the aforementioned acrylic acid water soluble salts. Additionally, since the acrylic acid derivi-tives set forth above are comparatively highly water soluble in aqueous environments, their copolymerization activity is enhanced during the preparation reaction for the filtration control agent of the present invention.
Although any monovalent alkaline metal salt of acrylic acid may be successfully utilized in the preparation of the filtration control agent of the present invention, the sodium salt of acrylic acid is preferred.
Varying amounts of monovalent alkaline metal salt of acrylic acid, as selected, may be incorporated into the preparation of the terpolymer filtration control agent. It has been found that an amount of the selected monovalent alkaline metal salt of acrylic acid between a minimum of about 5 mole percent of the total composition of all monomeric materials and a maximum of about 62 mole percent may be utilized. A preferred range is from 10 to 30 mole percent.
When utilizing the sodium salt of acrylic acid, a preferred and satisfactory terpolymer filtration control agent may be prepared by incorporating therein about 23 mole percent of sodium acrylate.
The terpolymer of the present invention also utilizes as an initial constituent an hydroxy alkyl acrylate which is incorporated in order to provide hydrogen bonding between chains incorporating a carboxyl group and to provide a bulkier polymer end product.
Additionally, the utilization of an hydroxy alkyl acrylate also en-hances the viscosity of the terpolymer and renders it less sensitive to adverse effects of heavy salt concentrations, such as those found in aqueous brine solutions encountered as a base constituent of an aqueous drilling fluid. Also, by incorporating the hydroxy alkyl acrylate material into the terpolymer, good hydrogen-bonded cross-linking can be achieved between the chains which will aid in re-sisting salt sensitivity of the resultant terpolymer material.
Numerous hydroxy alkyl acrylates may be utilized, such as 2-hydroxy alkyl acrylate, 3-hydroxy alkyl acrylate, 2-hydro~yethyl-acrylate, 2-hydroxymethylacrylate, 2-hydroxybutylacrylate or, prefer-ably, 2-hydroxypropylacrylate.
The amount of the selected hydroxy alkyl acrylate for util-10 ization in the composition of the present invention will vary, but a satisfactory end product may be made by incorporating therein a minimum of about 2.1 mole percent of hydroxy alkyl acrylate. A sat-isfactory end product also may be produced by utilizing up to a max-imum of about 40 mole percent of hydroxy alkyl acrylate. Preferably, 15 when 2-hydroxypropylacrylate is selected as the hydroxy alkyl acryl-ate, it has been found that about 4.0 mole percent of 2-hydroxypropyl-acrylate may be utilized.
The third monomer for utilization in the terpolymer compo-sition for use in the present invention is acrylamide, which has been 20 found to have a certain electrolyte reaction when incorporated into the terpolymer utilized in the present invention. Although not fully understood, it is believed that the acrylamide monomer when polymer-ized with the other constituents of the terpolymer will act as a dispersant of carboxyl groups on the resultant polymeric chain.
25 Although methacrylamide may be substituted for the acrylamide monomer of the present invention, it has been found that it is less tolerant of the heavier concentrations of salt solutions and environments and is less water soluble than the acrylamide. Therefore, the acryl-amide monomer has been found to be more acceptable for use in 30 general in the present invention.
In our testing, we have found that ~a minimum of acrylamide monomer of about 31 mole percent may be incorporated into the ter-polymer to obtain a satisfactory end product. A maximum amount of . ( 1~4429~3 about 91 mole percent of acrylamide may also be incorporated to achieve a satisfactory terpolyme~. However, we prefer to utilize about 73 mole percent of acrylamide in the preparation of a pre-ferred composition for use in the present invention.
The terpolymer of the present invention may be prepared using a variety of known techniques. For examplel emulsion, suspen-sion or bulk polymerization techniques may be utilized.

As an effective filtration control agent, the terpolymer may be added to any aqueous base drilling fluid at the drilling or rig location in an amount from between about .25 p.p.b. to about 5 p.p.b. (pounds per 42 gallon barrel~. The amo~nt needed will vary, of course,depending upon the particular type of aqueous drilling fluid util-ized, such as brine, sea water, or the like, the weight of the given drilling fluid, ~he clayey substances appearing therein, and the presence and amount of other chemical additives, such as lignosulfonate deflocculants, and the like. Simple and com-mercially available testing techniques may be easily utilized at the well site to determine the amount of filtration control additive which must be added to the circulatable drilling fluid to provide effective filtratlon control in the subterranean well. Because of the loss of material in the weIl, such as through adsorption onto the ~rface of the drilled solids and the like, it may be necessary to incremental~y add additions of the terpolymer to the drilling fluid from time to time to maintain the required concentration.
A measure of the ability of the drilling fluid to form a thin impervious compressible filter cake may be determined by utilization of a simple filtration test in which the filter cake is formed and pressed against the membrane or filter which is permeable to water. A standardized procedure for determining the filatration rate is described in "API Recommended Practice RP 13 B Standard Procedure for Testing Drilling Fluids," 2nd Edition (April 1969).

1~44Z98 The preparation and use of the terpolymer to control filtrate in an aqueous d~illin~ fluid is further described in the examples which follow:
EXAMPLE I.
A terpolymer of sodium acrylate-2-hydroxypropyl acrylate and acrylamide was prepared utilizing an emulsion polymerization process. The mole ratios of acrylic acid to acrylamide, mole per-cent of 2-hydroxypropyl acrylate and molecular size were varied by controlling the reaction parameters. Six representative samples of the terpolymer were prepared with the compositions of the various terpolymers being estimated based upon their total nitrogen content.
In the reaction, ammonium persulfate was utilized as the polymer-ization initiator or catalyst. Reagent grade acetone and reagent grade anhydrous methanol were utilized to form the solvent. The emulsifier was sodium lauryl sulfate, and 2N aqueous sodium hydroxide was utilized to neutralize the reactants. The dried pro-ducts were thereafter milled and passed through a number 30 mesh screen. The reaction was conducted over a period of three hours at a reaction temperature of about 60C.
The six polymers prepared by this technique and the vary-ing amounts of monomers and reagents are given in the table below, together with the resultant product yield for the terpolym ~

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1~4429~3 EXAMPLE II.
The present example was conducted to determine the effect of exposure of various types and concentrations of inorganic salts to selected terpolymers made as in Example I, above. Polymer samples No. 2 and No. 3 of Example I, which contained a mole ratio of 2-to-1 of acrylamide-to-acrylic acid, were soluble in various aqueous-saturated salt solutions, while those polymer samples having a smaller mole ratio were precipitated by excess amounts cf calcium ion.

lo The effect of the selected salt concentrations on tne given polymer samples was determined by using swelling tests. The procedure for the swelling tests incorporated utilization of a lS milliliter centrifuge tube which was charged with 0.50 grams of the selected dry terpolymer which was powder-milled to pass through a No. 30 mesh screen. The tube also was charged with water or the selected aqueous solutions containing varying amounts of one of the salt samples. The total volume in the tube for each sampled material was 13 milliliters. The tubes were stoppered, shaken vig-orously to disperse the terpolymer and heated in a steam bath for about 10 minutes. Thereafter, the tubes were cooled to room temp-erature, shaken to disperse the terpolymer, and centrifuged at 1800 rpm for about 20 minutes using an International Clinical Centrifuge which was equipped with a head having an 8.5 cm radius of gyration. The volume of the swollen terpolymer was measured as the difference between the total volume of 13 milliliters and the volume of the supernatant. The volume of the unswollen polymer was measured utilizing isopropyl alcohol as the non-solvent.

-- 11 -- .

, ~144Z98 The criteria for measuring the degree of .swelling for the samples was based upon the application of q as a criterian for measurement of the chemical potential of an electrolyte in a given solvent containing a given amount of electrolyte which is based upon theoretical models developed by Flory, in "Principles of Polymer Chemistry", (Cornell University Press, 1953) and by Hildebrand, in "Regular and Related Solutions" (Van Hostrand Reinhold Company, 1970) which explains the unique solubility of a polymer in various solvents.
The results given in Table 2, below, indicate that the 10 polymer samples No. 2 and 3 of Example I were soluble in aqueous solu~ions which are saturated with various salts, while polymer Nos, 1, 4, 5 and 6 were somewhat precipitated by excess amounts of calcium ion. These tests indicate that these polymers have poten-tial application as filtration control agents exposed to high salt environments, ~ `

~ 12 -~144298 Table 2 DEGREES OF SWELLING, q, VERSUS IONIC
STRENGTH OF A~UEOUS SALT SOLUTIONS

Salt Salt Ionic ~ Terpolymer Number conc. Strength 1 2 3 4 .5 6 mole/kg mhomlkg(l) Degree of Swelling, q M
H20 0 0 gel gel gel gel gel gel CaSO4 0.01 0.04 -- gel gel 20 gel(2)g CA(OH)2 0.02 0.06 gel gel gel gel(2)gel(2)gel KCl 4.02 4.02 7 gel. gel(2)10 8 11 MgSO4 1.21 4.84 9 gel -- 8 gel(2) NaCl 6.00 6.00 7 gel gel(2) 8 12 12 CaC12 2.04 6.12 2 gel gel(2) 2 8 7 (1) S = 1/2 ~ (MV2), V is valence of ion.
(2) Gel formed with some swollen polymer particles suspended in solution.

1~44Z98 'EXAMPLE 'III.
The filtration control effectiveness of the terpolymer samples prepared as in Example I, together with a sample of a commercially available'filtration control agent generically de-scribed ac a polyanionic cellulose (hereinafter referred to as"P.A.C.") were tested in a 22 p.p.b. Wyoming Bentonite'3% sodium chloride suspension and also in a 15 p.p.b.' attapulgite-saturated sodium chloride'suspension. The'filtration control test was the API test as referred to above. The terpolymer and P.A.C. samples were'sifted into barrel equivalents of muds while shearing at moderate'speed on an electric mixer after which shearing was con-tinued for thi~ty minutes. Thereafter, the samples were'hot rolled at 150F for about 16 hours and thereafter cooled to room tempera-ture, before flow properties and API filtrate properties were determine, The results of this test clearly indicated that the ter-polymer samples were effective in reducing the'filtrate,' when com-pared to a sample'of each'drilling fluid containing no filtration control ad~itive.
The'results of this test are set forth in the tables below:

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From the rheological data given in each of Tables 3A
and 3B, above, it may also be observed that the addition of the terpolymer filtration control agent of the present invention did not adversely affect the rheological properties of the drilling 5 fluid, and each sample had satisfactory rheology properties at the given readings.
EXAMPLE IV
Nineteen terpolymer samples containing various mole per-cents of sodium acrylate, 2-hydroxypropyl acrylate and'acrylamide 10 were prepared for evaluation as filtration control agents. The pro-ced~re utilized to prepare the samples was as in Example I, above.
The monomers and about 70 to 75 grams of water were mixed and the acrylic acid was neutralized to about pH 7 with 5 M sodium hydroxide.
The temperature of the solution was kept below 30C with the aid of 15 an ice water bath. The monomers in solution and one-half of the initiator-amonium persulfate were added over a one-hour period to the'mixture of water, one-half of the initiator and about 10% of the solution of monomers. The temperature of the reaction was maintained at about 60C for a total reaction time of three hours. The terpolymer-20 water mixture was broken into small samples, added to 1 liter of iso-propyl alcohol, and allowed to stand for several hours. The solvent was'decanted and the residue was dried at 90C for about 24 hours, followed by drying in a vacuum oven at 90C for another 24 hours or to a constant weight. The samples were milled to pass throu~h a 30 25 mesh screen. In all cases, the product yield was quantitative.

The various terpolymers composed of varying mole percents of sodium acrylate, 2-hydroxypropyl acrylate and acrylamide '~ were prepared using the quantities of monomers, initiator and water given in the table below. The product yield was quantitative.
The reactants utilized in the preparation of the terpolymer samples are set forth in the table below.

:~144Z98 T~ble 4 MONOMERS AND INITIATOR CONCENTRATIONS
-OF TERPOLYMER PREPARATIONS

Sample No. (1) (2) (3) (4) 7 N^ 25.6 6.3 6~.1 M* 0.375 0.092 1.000 3.51 8 N 16.1 19.8 64.1 M 0.249 0.308 0.995 3.49 9 N 16.0 3.9 80.1 M 0.333 0.082 1.667 3.51 N 24.0 4.0 72.0 M 0.750 0.124 2.251 0.88 11 N 22 2 3.6 74.1 M 0 500 0.082 1.667 1.75 12 -N 24.0 4.0 72.0 M 0.750 0.124 2.251 1.75 13 N 8.0 4.0 88.0 M 0.250 0.124 2.750 1.75 14 N 8.0 27.8 64.2 M 0.116 0.404 0.931 3.27 N 30 4.0 66.0 M 0.627 0.083 1.378 5.86 19 N 0 0 100.0 M 0 0 1.352 3.51 N 10.0 15.0 75.0 M 0.200 0.299 1.498 1.75 21 N 10.0 25;0 65.0 M 0.231 0.575 1.494 1.75 22 N 5.0 14.9 80.1 M 0.093 0.275 1.482 1.73 23- N 6.1 2.9 91.0 M 0.142 0.069 2.132 1.75 24 N 15.0 40.0 45.0 M 0.267 0.713 0.802 1.75 N 12.9 2.6 . 84.5 M 0.306 0.062 2.001 1.75 * N mole %, M mole/kg 3 acrylamide 1 sodium acrylate 4 ammonium persulfate 2 2-hydroxypropyl acrylate ~44Z98 EXA~LE V.
The present Example demonstrates the effectiveness of the present terpolymer composition to provide effective filtration control at increased temperatures. For this test, selected samples 5 made as in Example I and Example IV were utilized in a mud system comprised of 17~ pounds of Wyoming Bentonite to which was added 1 p.p.b. of gypsum, 2 p.p.b. sodium chloride and 2 p.p.b. of chrome lignosulfonate. The initial mud system was adjusted to a pH of about 9.5 with sodium hydroxide. The selected samples of the terpolymer were added to aliquots of the base mud in concentrations cf ~ p.p.b. and 1 p.p.b. The samples were hot rolled at 150F
for 16 hours, and were permitted to cool to room temperature prior to rheological measurements being made and API filtrate being established for each san~le. Thereafter, the sample ccntaining 1 p.p.b. polymer was hot rolled in a 300F oven for a period of 3 hours and permitted to cool to room temperature before rheological data and API filtrate volumes were measured. Samples of the base mud treated with P. A. C. together with a base mud treated with another commercially available filtra-tion control agent identified as a sodium polyacrylate, (herein-after referred to as "S.P.A."~ also were prepared and tested, asabove, for comparative purposes. This test clearly indicated that the terpolymer of the present invention is an effective filtration control agent even after exposure to increased temperatures as high as about 300F. Additionally, this test also indicates that the terpolymer of the presen~ invention will not affect rheological properties of the drilling fluid. The results of this test are further illustrated in the following table:-.
_ 19 _ ~1~4298 FLOW PROPEKTIES AND API FILTRATE OF TERPOLYMER

API Fil-Fann Rheology, Rm. Temp. trate-600 300 200 100 6 3 lG 10G _ pH ml lb/bbl Sample Hot-Rolled __ _ __ 1.0 13 150F 62 35 26 16 3 2.5 3 10 9.2 6.1 1.0 300F 48 30 24 16 3 2 2 3 9.1 6.1 1.0 150F 69 40 30 20 5 4 4 23 9.0 4.8 1.0 300F 53 33 25 15 - 2 4 5 9.4 6.2 1.0 150F 36 20 15 9 1.5 1 2 3 - 4.8 1.0 300F 71 46 38 25 4 3 3 60 9.6 5.9 1.0 8 150F 66 39 29 18.5 3.5 2.5 3 7 8.9 6.2 1.0 300F 64 37 27.5 17 3 2 3 3 9.5 8.6 0.5 20 150F 36 21 16.5 9.5 2 1.5 1.5 2 9.2 8.2 1.0 150F 44 25 19 10 2 1.5 1.5 2 9.0 6.4 1.0 300f 52 30 22 13.5 2.5 2 2 2 8.3 8.1 0.5 22 150F 24 13.5 10 6 1.5 1 2 2 9.0 10.4 1.0 150F 42 24 17 10 2 1.5 2 3 9.0 7.2 1.0 300F 57 32.5 23 13.5 2 1.5 1.5 2 8.4 10 0.5 23 150F 19 11 8 5 1 1 1 1.5 9.2 7.4 1.0 150F 25 14 16.5 6.5 1.5 1 1 2 9.2 5.8 1.0 300F 39 23.5 18 11 2.5 2 2 3 8.6 6.5 0.5 24 150F 43 25 19 12 2.5 2 2 6 8.9 8.2 1.0 150F 53 31 23 14 2.5 2 2 6 8.7 8.8 1.0 300F 72 43 32 19 3.5 2.5 2.5 3 8.1 10.0 0.5 25 150F 19.5 11 8 5 1 1 1 11 9.1 9.0 1.0 150F 26 15 11 6.5 1.5 1 1.5 2 9.3 6.4 1.0 300F 42 25 18.5 11.5 2.5 2 2 2 8.4 6.5 1.0 7 150F 28 15.5 11.5 7 1 1 1 2 8.9 8.6 1.0 300F 26.5 14.5 10.5 6 1 1 1 1 8.1 12.6 1.0 19 150F 37 33.5 18 11.5 2.5 2 3 8 9.2 37.8 1.0 300F 13.5 7.5 6 3.5 1 1 1 1 8.2 38.0 1.0 150F ~300 295 200 20 13 10 13 25 - 14.6 1.0300F 29 16 12 7 1.5 1 1 2 8.9 9.0 0.25P.A.C. 150F 25 14.5 11 6.5 1.5 1 2 3 8.6 10.8 0.25150F 20 12 8.5 5 1.5 1 4 2 9.2 13.6 0.5150F 35 21 15.5 10 2 2 2 7 8.9 8.4 0.5150F 26.5 15 11 7 1.5 1 3 2 8.8 10.8 1.0150F 49 30.5 24 15.5 4 3.5 4 22 8.7 5.4 1.0300F 47 29 22 14 3.5 3 4 13 9.4 9.0 1.0150F 43.5 26.5 20 13 3 2 4 12 9.2 6.6 1.0300F 31 19 14 9 2 1.5 3 7 9.3 9.7 X

1~44Z98 APIFil-trate-600 300 200 100 6 3 lG 10GpH~l lb/bblSampleHot Rolled -0.25 3 150F68 45 35 23 14 14 5 63 - 12.8 0.5 150F59 37 28 17 2.5 2 2 35 8.7 7.6 1.0 150F59 37 29 19 3 2 2 8 8.7 5.2 1.0 300F61 35 25 15 2 1.5 2 2 9.3 13.0 0.25 14 150F44 29 23 15 3 2 2 55 8.8 11.0 0.5 150F73 43 33 20 5 4 4 38 8.4 9.6 1.0 150F93 58 45 29 6 5 6 49 8.6 6.8 1.0 300F82 52.5 41 27 4.5 3 4 5 9.4 14.6 0.25S.P.A. 150F93 59 48 33.5 20 19.5 19.5 68 9.1 22.0 0.5 150F76 43 32 18 3 2 3 3 9.0 15.2 1.0 150F85 48 35 20 3 2 2 4 9.2 9.0 1.0 300F169 119 95 64 13 8.5 9 - 9.4 20.6 1.0 150F49 28 20 12 2 1.5 1.5 2 9.6 9.0 1.0 300F69.5 41.5 31.5 18.5 2.5 1.5 1.5 2 8.8 16.4 0.5 11 150F61 38 28.5 17 3 2 2 21 9.2 6.8 1.0 150F80 60 45 30 7 6 5 47 9.2 5.4 1.0 300F78.5 45 35 21 3.5 3.5 4 8 9.0 6.6 1.0 150F77 49 38 26 4 3 3 55 9.2 4.8 1.0 300F72 42 30 18 - 2 3 5 9.3 7.9 0.5 12 150F80 51 39 25 6 5 3 47 9.0 7.0 1.0 150F88 62 49 40 18 14 12 95 9.3 5.0 1.0 300F80 50 38 23 4 3 4 6 9.0 6.7 0.5 15 150F49 31 23 14 2 1.5 2 13 9.2 7.2 1.0 150F52 31 23 13.5 2 1.5 2 3 9.1 6.6 1.0 300F59 34 25 14.5 2 2 2 3 9.3 9.3 0.5 10 150F68 42 33 21 7 6 5 40 9.2 8.8 1.0 150F97 65 53 39 20 18 19 51 9.3 5.0 1.0 150F87 58 47 34 11 9 7 103 9.4 4.8 1.0 300F115 66 47 26 4 3 3 4 8.9 8.2 1.0 150F86 54 43 37 5 4 4 66 8.9 5.0 1.0 300F115 67 53 30 - 3 4 4 9.0 8.6 0.25 4 150F174 146 135 111 70 61 54 55 9.2 19.8 0.5 150F88 49 35 20 3 2 2 4 9.0 14.6 1.0 150F64 38 28 17 2 1.5 2 3 9.1 7.2 1.0 300F125 86 69 47 10 7 9 17 - 19.3 0.25 1 150F92 67 55 44 33 32.5 34 70 9.1 21.6 0.5 150F57 34 25 15 2.5 2 4 6 9.2 14.8 1.0 150F44 24 18.5 10 1.5 1 2 2 9.3 7.2 1.0 300F139 96 77 53 11 8 8.5 13 9.6 18.8 0.5 9 150F26 15 11.5 7 2.5 2 3 4 9.0 7.4 1.0 150F35 20 15 9 2 1 2 3 9.1 5.2 1 0 300F61 35 26 16 3 2.5 3 3 9.0 6.1 1 0 150F39 23 17 10 2 1.5 1.5 2~5 9.2 5.4 1.0 300~52 32 24.5 15 3 2 3 9 9.2 5.6 BaseMud 150F18 9 6.5 3.5 1 1 1 1 9.3 16.4 300F20 10.6 7 4 1 0.5 1 1 9.0 20.6 150F21 11 7.5 4 1.5 1 1 1 9.7 20.8 300F26.5 14 9.5 5 1 0.5 1 1 9.7 21.4 X

~44Z98 EXAMPLE VI
The present Example demonstrates the ability of the ter-polymer of the present invention to provide effective filtration control in an aqueous drilling fluid after being subjected to 300F
over an extended period of time. For this test the base mud as in Example V, was utilized. To the base mud was added a i p.p.b. treat-ment of the samples identified in the Table below. The sample mud with the filtration control additive added thereto was first hot rolled for a period of 16 hours at a temperature of 150F. There after, each sample was permitted to cool to room temperature prior to measurements of rheological properties and API filtrate volumes.
Thereafter, the initial hot rolled sample was broken into four sep-arate test specimens, and each specimen was hot rolled in an oven at a temperature of 300F. The first test specimen was hot rolled for a time period of 3 hours, the second for 5 hours, the third for 7 hours and the 4th for 16 hours. After the respective time period of hot rolling for each sample, the sample was permitted again to cool to room temperature prior to rheological measurement made and API filtrate being established. The same procedure was utilized to measure the rheology and API filtrate of a blank sample of the base mud.
The results of this test clearly indicated that the ter-polymer of the present invention provided effective filtration control of the drilling fluid sample, even after exposure to a temperature of 300F, over extended periods of time, up to 16 hours Additionally, the present test indicates that the filtration control agent is more effective after exposure to a temperature of 300F
than comparative samples of commercLally available filtration control agents as described above.
The results of this test are further reflected in the Table below: -CHARACTERISTICS OF TERPOLYMER-TREATED MUD
Fann Rheology, Rm. Temp. API Fil-600 300 200 100 6 3 lG 10G pH trate 1 lb/bbl Sample 9 *HR 150F, 16 Hrs 39 23 17 10 2 1.5 1.5 2.5 9.2 5.4 HR 300F, 3 Hrs 52 32 24.5 15 3 2 3 9 9.2 5.6 5 Hrs 80 51 39 25 5.5 4 4 7 9.2 7.1 7 Hr6 80 51 38 24 5 3.5 4 5 9.3 9.0 16 Hrs 86 54 41 26 5 4 4 7 9.3 9.2 1 lb/bbl Sample 13 HR 150F, 16 Hrs 36 20 15 9 1.5 1 2 3 - 4.8 HR 300F, 3 Hrs 71 46 38 25 4 3 3 60 9.6 5.9 5 Hrs 102 65 49 31 7 5 6 15 9.3 7.0 7 Hrs 54 3 24.5 10.5 3.5 2.5 2.5 3 8.7 6.6 16 Hrs 48 29 22 14 2.5 2 2.5 3 9.0 8.0 1 lb/bbl P.A.C.
- HR 150F 16 Hrs 55 33.5 25.5 16.5 5 4 4 16 9.5 5.8 HR 300F 3 Hrs 51 33 26 17 7 5.5 7 22 9.4 7.8 5 Hrs 40 26 20 14 4 4 5 17 9.2 10.5 7 Hrs 39 24 18 11.5 3 2.5 3 11 9.8 10.4 16 Hrs 34.5 19.5 14.5 8.5 2 1 2 4 9.2 13.6 Base Mud HR 150F, 16 Hrs 21 11 7.5 4 1.5 1 1 1 9.7 20.8 HR 300F, 3 Hrs 26.5 14 9.5 5 1 0.5 1 1 9.7 21.4 5 Hrs 22 12 8.5 5 1.5 1 1 2 8.0 22.8 7 Hrs 18 9.5 7 4 1.5 1 1 1 8.0 21.6 16 Hrs 32 17 12 6.5 1 0.5 1 2 9.3 23.2 1 lb/bbl S.P.A.
HR 150F, 16 Hrs 49 28 20 12 2 1.5 1.5 2 9.6 9.0 HR 300F, 3 Hrs 69.5 41.5 31.5 18.5 2.5 1.5 1.5 2 8.8 16.4 5 Hrs 85 53 40 24.5 3.5 2.5 2.5 - - 20.2 7 Hrs 79 48.5 36.5 22 3 2 2 6 9.4 19.2 16 Hrs 95.5 58.5 43.5 26.5 4 3 3 6 8.4 22.8 * Hot Rolled 114~298 Although the invention has been described in terms of specified embodiments which are set forth in detail, it should be understood that this is by way of illustration only and that the invention is not necessarily limited thereto, since alternative embodiments and operating techniques will become apparent to those skilled in the art in view of the disclosure. Accordingly, modifica-tions are contemplated which can be made without departing from the spirit of the described invention.

- ~4 -

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a method of drilling a well into a subterranean formation in which an aqueous drilling fluid is circulated into the well, the steps of forming a filter cake on the wall of the well to decrease loss of fluid from the drilling fluid which comprises:
(1) admixing with said drilling fluid an amount of at least about .25 pounds per 42 gallon barrel of a terpolymer of: (a) a monovalent alkaline metal salt of acrylic acid in an amount of about 5 to about 62 mole percent based on the total amount of monomeric material present; (b) an hydroxy alkyl acrylate in an amount of about 2.1 to about 40 mole percent; and (c) acrylamide in an amount of about 31 to about 91 mole percent; and (2) circulating said drilling fluid in said well.

2. The method of Claim 1 wherein the amount of said monovalent alkaline metal salt of acrylic acid is from between about 10 and about 30 mole percent.

3. The method of Claim 1 wherein the amount of said hydroxy alkyl acrylate is about 4.0 mole percent.

4. The method of Claim 1 wherein the amount of said acrylamide utilized in said terpolymer is about 73 mole percent.

5. The method of Claim 1 wherein the amount of said monovalent alkaline metal salt of acrylic acid is about 23 mole percent; the amount of said hydroxy alkyl acrylate utilized in said terpolymer is about 4 percent; and the amount of said acrylamide utilized in said terpolymer is about 73 mole percent.

6. The method of Claim 1 wherein said hydroxy alkyl acrylate is 2-hydroxypropyl acrylate.

7. The method of Claim 1 wherein said monovalent alkaline metal salt of acrylic acid is sodium acrylate.

8. The method of Claim 1 wherein said monovalent alkaline metal salt of acrylic acid is sodium acrylate in an amount of about 23 mole percent; said hydroxy alkyl acrylate is 2-hydroxypropyl acrylate in an amount of about 4 percent; and said acrylamide is present in an amount of about 73 mole percent.

9. An aqueous drilling fluid comprising water, a clayey substance suspended in said water, and at least about .25 pounds per 42 gallon barrel of a terpolymer of: (1) a monovalent alkaline metal salt of acrylic acid in an amount of about 5 to about 62 mole percent based on the total amount of monomeric material present; (2) an hydroxy alkyl acrylate in an amount of about 2.1 to about 40 mole percent;
and (3) acrylamide in an amount of about 31 to about 91 mole percent.

10. The aqueous drilling fluid of Claim 9 wherein the amount of said monovalent alkaline metal salt of acrylic acid is from between about 10 and about 30 mole percent.

11. The aqueous drilling fluid of Claim 9 wherein the amount of said hydroxy alkyl acrylate utilized in said terpolymer is about 4.0 mole percent.

12. The aqueous drilling fluid of Claim 9 wherein the amount of said acrylamide utilized in said terpolymer is about 73 mole percent.

13. The aqueous drilling fluid of Claim 9 wherein the amount of said monovalent alkaline metal salt of acrylic acid is about 23 mole percent; the amount of said hydroxy alkyl acrylate is about 4 percent; and the amount of said acrylamide is about 73 mole percent.

14. The aqueous drilling fluid of Claim 9 wherein said hydroxy alkyl acrylate is 2-hydroxypropyl acrylate.

15. The aqueous drilling fluid of Claim 9 wherein said alkaline metal salt of acrylic acid is sodium acrylate.

16. The aqueous drilling fluid of Claim 9 wherein the said monovalent alkaline metal salt of acrylic acid present in said terpolymer is sodium acrylate in an amount of about 23 mole percent;
the said hydroxy alkyl acrylate is 2-hydroxypropyl acrylate present in said terpolymer in an amount of about 4.0 percent; and said acrylamide is present in said terpolymer in an amount of about 73 mole percent.

17. A filtration control agent for aqueous based drilling fluids, said agent consisting essentially of a terpolymer of: (1) a monovalent alkaline metal salt of acrylic acid in an amount of about 5 to about 62 mole percent based on the total amount of monomeric material present; (2) an hydroxy alkyl acrylate in an amount of about 2,1 to about 40 mole percent; and (3) acrylamide in an amount of about 31 to about 91 mole percent.

18. The filtration control agent of Claim 17 wherein the amount of said monovalent alkaline metal salt of acrylic acid utilized in said terpolymer is from between about 10 and about 30 mole percent.

19. The filtration control agent of Claim 17 wherein the amount of said hydroxy alkyl acrylate utilized in said terpolymer is from between about 2 mole percent and about 40 mole percent.

20. The filtration control agent of Claim 17 wherein the amount of said hydroxy alkyl acrylate is about 4.0 mole percent.

21. The filtration control agent of Claim 17 wherein the amount of said acrylamide utilized in said terpolymer is from between about 31 mole percent and about 91 mole percent.

22. The filtration control agent of Claim 17 wherein the amount of said acrylamide utilized in said terpolymer is about 73 mole percent.

23. The filtration control agent of Claim 17 wherein the amount of said monovalent alkaline metal salt of acrylic acid is about 23 mole percent; the amount of said hydroxy alkyl acrylate is about 4.0 percent; and the amount of said acrylamide is about 73 mole percent.

24. The filtration control agent of Claim 17 wherein said hydroxy alkyl acrylate is 2-hydroxypropyl acrylate.

25. The filtration control agent of Claim 17 wherein said monovalent alkaline metal salt of acrylic acid is sodium acrylate.

26. The filtration control agent of Claim 17 wherein said monovalent alkaline metal salt of acrylic acid is sodium acrylate in an amount of about 23 mole percent; the said hydroxy alkyl acrylate is 2-hydroxypropyl acrylate in an amount of about 4.0 percent; and said acrylamide is present in said terpolymer in an amount of about 73 mole percent.