NL8303610A - METHOD FOR DRILLING OIL AND GAS WELLS USING A VINYL POLYMER-CONTAINING DRILL FLUSH - Google Patents

Description

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Method of drilling oil and gas wells using a vinyl polymer-containing drilling mud.

Drilling muds are used in oil and gas well drilling to cool and lubricate the revolving chuck and drill columns, to transport rock debris to the earth's surface where it is removed, to prevent losses of water and drilling fluids in the formation in which the well is drilled, and to control the ingress into the well of liquids from the different formations that are penetrated during the drilling. To achieve these purposes, a drilling fluid, generally referred to as a drilling mud, consists of several components.

For example, heavy solids, such as barites, are often added to such drilling muds to give them the desired density, while bentonite or various clays are often added to increase the viscosity of the drilling mud, thereby enabling the drilling mud to be more suitable for rock debris through the well hole. from 15 the chuck up and remove the debris from the well.

It is also known to add various polymers to drilling fluids or drilling muds which act as viscous agents, dispersants and water loss additives in the drilling fluids. The use of polymers for this purpose has many problems. These polymers are often unstable at the higher well hole temperatures, e.g. temperatures around about 182 ° C, and have been found to lose their desired physical properties, such as plastic viscosity, pour point and resistance to water loss. The use of polymers to combat water loss in drilling fluids has historically often led to an undesirable increase in the viscosity of the drilling fluids.

The present invention provides polymers suitable for use as drilling mud water loss additives and methods for their preparation, which overcome the drawbacks encountered with the known polymers noted above.

It is a primary object of the present invention to provide improved drilling mud additives.

It is another object of the present invention to provide an improved method for preparing drilling fluid additives.

It is a further object of the present invention to provide an improved method of drilling a wellbore.

It is yet another object of the present invention to provide an improved drilling mud for use in drilling a wellbore.

It is yet another object of the present invention to provide an improved drilling mud which is stable for a long time at high temperatures. It is yet another object of the invention to provide an improved drilling mud that has improved properties. prevention of water loss.

It is a further object of the present invention to provide an improved drilling mud additive which is characterized by improved water loss control coupled with a minimal decrease in viscosity when used in a drilling mud.

The aforementioned and other objects, advantages and aspects of the present invention will become apparent from the following detailed description of the invention.

The polymers of this invention which are used in drilling muds as additives to prevent water loss after at least partial neutralization are preferably those polymers obtained by copolymerizing a hydrophilic vinyl monomer selected from acrylic acid (AA), methacrylic acid (MAA), other related mono lakes and mixtures of two or more thereof with at least one hydrophobic vinyl monomer selected from acrylic acid esters, such as, for example, methyl acrylate and ethyl acrylate, methacrylic acid esters, such as, for example, methyl methacrylate and ethyl methacrylate, vinyl esters of saturated monocarboxylic acids of 1-3 carbon atoms, such as for example, vinyl formate and vinyl acetate, other related monomers and mixtures or combinations of two or more thereof. Preferred polymers of the invention are selected from acrylic acid-methyl methacrylate copolymer (AA-MMA), methacrylic acid-methyl acrylate polymer (MAA-MA), methacrylic acid-35 methyl methacrylate copolymer (MAA-MMA), acrylic acid-vinyl acetate copolymer (AA-VA) ) and acrylic acid-methyl methacrylate-vinyl acetate terpolymer (AA-83 C 3 6 1 0 * 3 MMA-VA).

The polymers are prepared in any suitable inert / organic liquid medium with low free radical chain transfer. Non-polar diluents or solvents such as 5 n-hexane, cyclohexane, chlorofluorohydrocarbons such as 1,1,2-trichloro-1,2,2-trifluoroethane and mixtures of two or more thereof are preferred, since the polymer formed in the medium is insoluble and optionally by suitable means such as filtration from which it is easy to separate. The diluent or solvent 1,1,2-10 trichloro-1,2,2-trifluoroethane is commercially available under the registered trademark Freon-113. The isolated product can be washed, dried, suspended in water and treated with an appropriate amount of sodium hydroxide to obtain the sodium salt in the form of an aqueous solution. For example, an amount of sodium hydroxide suitable for this purpose is an amount sufficient to raise and maintain the pH of the slurry at a value in the range of about 5.3 to about 12, preferably about 5.5 to about 11, and most preferably from about 6 to about 8.

Normally, a free radical initiator is used in the polymerization. Such initiators are known and include azo compounds such as azobisisobutyronitrile and organic peroxy compounds such as t-butyl peroxypivalate. The amount of initiator used, based on a weight of the monomers used, depends on the selected monomers as well as on the selected reaction medium and the desired molecular weight of the polymer. So much initiator is used that the weight average molecular weight of the resulting polymers is in the range of about 100,000 to 500,000 seeds. For example, in the preparation of acrylic acid-methyl methacrylate copolymers in n-hexane with t-butyl peroxyvivalate as the initiator, the initiator level can range from about 0.05 to about 1.0% by weight, and is preferably about 0. 1 to about 0.8 wt% based on the weight of the monomer charge.

The molar ratio of hydrophilic monomer or hydrophilic monomers to the hydrophobic monomer or monomers may be any molar ratio to obtain a copolymer having the desired properties, but the molar ratio generally ranges from about 22 : 1 to about 1: 1, and is preferably about 7: 1 to about 1: 1, and most preferably about 3.5: 1 to about 2: 1. For the most preferred acrylic acid-methyl methacrylate copolymers, for example, the AA-MMA molar ratios can range from about 3.2: 1 to 2.1: 1, which corresponds to an AA-MMA weight ratio range from about 70:30 to about 60:40. For the methacrylic acid-methyl methacrylate copolymers, the weight ratios of MAA-MMA can range from about 95: 5 to about 10:46:54, the best results being obtained from about 95: 5 to about 65:35. equivalent molar ratios are from about 22: 1 to about 1: 1, and from about 22: 1 to about 2: 1.

For the acrylic acid-methyl methacrylate-vinyl acetate copolymer, the weight ratios of AA-MMA-VA can range from about 60-30-10 to about 60-10-30, with about 70-20-10 to about 70-10-20 give best results. The equivalent molar ratios range from about 2.8: 1: 0.33 to about 8.3: 1: 3.5 and from about 4.8: 1: 0.58 to about 9.7: 1: 2 , 3.

Generally, in preparing the polymers of the present invention, the total monomer level relative to the reaction medium can range from about 5 to about 30 wt%, and is preferably about 10 to about 20 wt%, based on the weight of the reaction medium. In other words, the weight ratio of monomers to the reaction medium is generally in the range of from about 5:95 to about 30:70, and is preferably about 10:90 to about 20:80.

The polymerization temperatures are generally in the normally used range and may range, for example, from about 25 ° C to about 100 ° C, preferably being from about 50 ° C to about 70 ° C, and most preferably about 50 ° C, which gives the best results. The polymers prepared at about 50 ° C give the best control of water losses in the tests used.

Each polymerization was conducted for a sufficient period of time to achieve a substantially quantitative conversion. Generally, a polymerization time in the range from about 10 minutes to about 30 hours is sufficient. More particularly, when about 20 g of total monomers are used in about 200 ml of reaction medium, that about 0.1 to about 1.5 wt%, and preferably about 0.1 to about 0.8 wt%, is t-butyl peroxypivalate and the reaction temperature ranges from about 50 ° C to about 70 ° C, conveniently used a polymerization time of about 15 to about 30 in; however, the conversion is almost complete in less than four hours. In commercial embodiments, it may be desirable to decrease the polymerization time to about an hour or less, or even to about 10 minutes.

In a typical laboratory scale preparation, acrylic acid and methyl methacrylate (20.0 g in total) were loaded in an appropriate molar ratio into a 296 ml crown cap beverage bottle containing 200 ml of reaction medium and a desired amount of t-butyl peroxypivalate initiator-15 solution, usually about 0.75 wt% based on the total weight of the monomers. The initiator, commercially available under the brand name Lupersol-li from Pennwalt Corp., was included in diluent in a 75 wt% solution. The monomers were of technical quality and used without purification.

Each bottle cap was degassed with argon for about 20 minutes after the components were loaded, then sealed and immediately placed in a water bath kept at a desired temperature such as 50 ° C or 70 ° C, then for the desired time was rotated- In all polymerization runs, 25 polymer suspensions were formed. Each polymer was isolated by filtration, dried and weighed to demonstrate that the conversion rate was nearly quantitative, for example from about 95 to about 100% of the theoretical value.

After the yields were determined, the polymers were suspended in distilled water to which a predetermined amount of sodium hydroxide was added sufficient to raise the pH of the polymer solution and maintain it in a range from about 6 to about 8, and to give an approximately 10% by weight solution of the neutralized polymer or dry polymer salt in the water.

The effectiveness of the polymers as water loss pesticides and theological pesticides was determined at various temperatures in a moderate saline drilling mud and in a brine-saturated drilling mud.

The first suspension, referred to as brine suspension A, comprised 3.5 wt% attapulgite clay in water containing 5 wt% NaCl. The second suspension, referred to as saturated brine suspension B, comprised 3.5 wt% attapulgite clay in water saturated with NaCl.

An appropriate amount of the polymeric saline was added to the suspension samples until the desired concentrations were obtained. While the concentration of the polymeric saline contained in a drilling mud or slurry may be any concentration capable of producing the desired results with the drilling mud or slurry, it is currently preferred to use a concentration in the range of about 1 up to about 3 pounds per barrel of drilling fluid or suspension. As used herein, the term "barrel" refers to a content of 42 U ~ S. gallons.

8303610 7

After the polymer sample was added to the drilling mud, with some of the water used to make the drilling mud retained to compensate for the water introduced through the polymer solution when used, the mud samples were mixed for 20 minutes with a Hamilton-Beach multi-mixer and then aged for at least 2 hours at room temperature, for example about 25 ° C. The samples were then mixed with the stirrer for an additional 2 minutes just before their initial plastic viscosities and pour points were determined at approximately 25 ° C with a model 35 Farm VG meter, a direct indicating viscometer, in accordance with API RP 13B 2nd Edition, April 1969, "Standard Procedure for Testing Drilling Fluids", American Petroleum Institute, Division of Production, Dallas, Texas. Initial water loss at approximately 25 ° C was also determined according to this reference. Also the pH of each The sample was then run again after the samples were aged at about 80 ° C overnight and cooled to room temperature.

Selected polymers were also evaluated under more stringent conditions. For these tests, the base slurry A was coated with 34 kg / m 3 bentonite, 5.8 kg / m 3 of a commercially available diluent sold under the trademark Desco and available from Chromalloy Corp., Conroe, Texas and 2, 9 kg / m? polymer and NaOH. A series of the treated rinses were additionally treated with gypsum to determine their effect on the polymers. For example, 2.9 kg / m gypsum when added to the suspension samples provides about 400 ppm of calcium ions in the suspension filtrates as determined by versenate titration.

These treated suspension samples were generally tested first at room temperature and then again at room temperature after aging overnight at about 182 ° C. After this second series of tests, an additional water loss test was performed at about 162 ° C at a differential pressure of about 35 kg / cm2. These tests were performed at a pressure of about 42 kg / cm2 on the water loss cell and about 7 kg / cm2 on the filtrate trap.

Example I

Three series of acrylic acid-containing polymers ill ill 8303610 δ were prepared in which the acrylic acid (AA) content ranged from about 60 wt% to about 100 wt% and the methyl methacrylate (MMA) content ranged from zero to about 40 wt. %, based on the total monomer weight. In each run, the total monomer weight was about 20.0 g; 0.20 g of t-butyl peroxypivalate (BPP) solution containing 0.15 g of BPP in concentrated diluent, which is equivalent to about 0.75 wt% BPP based on total monomer weight, was used; wherein the reaction was carried out in 200 ml of said liquid organic compound at about 50 ° C for about 16 to 25 hours until the conversion was nearly complete.

The polymers were isolated, washed with n-hexane, freon-113 and the like and dried in vacuo. Yields varied from about 95 to 100% of the theoretical value. Each polymer was suspended in about 135 g of distilled water and treated with enough 6 M 15 NaOH solution to obtain an aqueous solution with a constant pH in the range of about 6 to 8, which solution is about 10 wt% solid based on the total weight of the aqueous solution.

In one series, the reaction medium was n-hexane, where 200 ml of n-hexane is equivalent to about 132 g. In the second series, 200 ml of freon-113, equivalent to about 313 g, was used as the reaction medium. In the third series, 200 ml of t-butyl alcohol, equivalent to about 156 g, was used as the reaction medium.

Each polymer was evaluated at a content (dry polymer salt) of 2.9 kg / m3 and 8.5 kg / m3 in brine suspension A (5% salt water suspension) and in a saturated brine suspension B (saturated salt water suspension), which suspensions were previously are described.

The initial properties of each treated suspension sample were evaluated at room temperature (approximately 25 ° C) for plastic viscosity (PV) in centipoises (cp), pour point (YP) in lb / 100 ft2 (0.0487 kg / m *) and water loss (WL) in ml / 30 minutes, as described previously. The results are shown in Tables A1, A2 and A3.

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The data in Tables A1, A2 and A3 show that the performance of the polymers at moderate temperatures generally improves when the methyl methacrylate content of the copolymers approaches 30 or 40% by weight, based on these results the preferred concentration range is. At these concentrations of methyl methacrylate, the plastic viscosity and pour point of the suspensions are generally not significantly increased by the presence of the polymers. The data also demonstrate that the polymers made in n-hexane and Freon-113 are more effective than the polymers made in t-butyl-10 alcohol.

Example II

The effect of high molecular weight acrylic acid-methyl methacrylate copolymers (as the sodium salts), prepared in n-hexane in one series and in Freon-113 in another series, as water loss control-1? agents in the basic suspensions were examined. The polymeric samples were prepared as in Example I except that the BPP level was lowered from about 0.75 wt% to about 0.19 wt%. A change in the initiator concentration causes a decrease in the number of free radical fragments present in the monomer solution to initiate the polymerization *. This in turn leads to an increase in the molecular weight of the polymer. Thus, these polymers have a higher molecular weight than that indicated in Example I.

Each polymeric salt was evaluated as before in a saturated brine suspension B. The results are shown in Table 25B.

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Comparison of the results of Table B with those of Tables A1 and A2 shows that with the high-molecular polymers used at the moderate temperatures, somewhat better water loss control was achieved than with the equivalent lower-molecular polymers. It is noted that the 50:50 AA: MMA copolymer foaming occurred, which is usually not considered desirable for a drilling mud.

Example III

This example focused on the determination of the high temperature water loss properties. Three series of copolymers were prepared in the manner previously described. In one series the reaction medium was n-hexane, in the second series cyclohexane and in the third series Freon-113. Different introductory levels were also used in each series. A polymerization time of about 21 hours was used in the preparation of 60:40 AA: MMA copolymers in n-hexane 15 in the Freon-113. All other polymers were given a polymerization time of about 25 hours. Each polymer was prepared at about 50 ° C. As previously described, each polymer in treated brine suspension A was evaluated as a sodium salt in a 10 wt% solution at a pH in the range of about 6-8. The suspension was also treated with 34 kg / m 2. bentonite clay and 5.7 Desco thinner to prevent the adverse effects of high temperature aging of the clay and enough NaOH to give and maintain a pH in the range of about 10 to 11.

After the initial properties of the suspension samples were determined at room temperature, the samples were aged in a brass bomb at about 182 ° C and cooled to room temperature, after which the shear strength of the suspensions was measured. The suspensions were then removed, stirred with the previously described multi-mixer for about 20 minutes, and the plastic viscosity, pour point and room temperature water loss tests repeated. An additional water loss test was performed at about 163 ° C and at a differential pressure of about 35 kg / cm2. The results are summarized in Tables C1, C2 and C3.

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A comparison of the data summarized in Tables C1, C2 and C3 shows that the polymers prepared in n-hexane, cyclohexane or Freon-113 are all approximately equivalent in their behavior as water loss pesticides, especially used. 5 concentrations of 5.7 kg / m3 in the suspension examined. At this concentration, after aging for about 16 hours at about 182 ° C, the results indicate that the polymers may deteriorate slightly with regard to water loss control. The results in Example III show that 60:40 or 70:30 AA: MMA copolymers have approximately equivalent performance. The initiation level used in the preparation of the polymers was not found to be a determining factor in this series. The high temperature water loss properties exhibited by the polymers are good.

Example IV

This example is directed to the determination of the high temperature water loss properties of the polymers of the invention in gypsum suspensions. The polymers described in Example I and Table B1, prepared in Freon-113 at about 50 ° C, were also tested in the bentonite-clay / Desco thinner-treated suspension described in Example III, which suspension also contains 2, 9 or 5.7 kg / m3 of gypsum was treated. As described above, plastic viscosity, pour point and water loss were initially determined and again after aging for about 16 hours at about 182 ° C. The high temperature water loss values were also determined. Unless otherwise indicated, each treated slurry was also treated with 8.6 kg of polymer per m3 of slurry. The results are shown in Table D.

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The gypsum-contaminated suspensions are a rigorous test for the polymers evaluated, and the severity of this test is reflected by a fairly high high temperature water loss (HTV7L) as shown in Table 0. Based on this value, results 5 are an indication that 70 : 30 AA: MMA copolymer better results in a gypsum-contaminated suspension than with the other copolymers tested.

Example V

This example is directed to the evaluation of acrylic-10 acid-methyl-methacrylate-vinyl acetate (AA-MMA-VA) terpolymers as water loss agents. The polymers were prepared in the same manner as described in Example I. Thus, about 20 g of total monomers, about 200 ml of Ereon-113 and about 0.75 wt% BPP based on total monomer weight, were placed in the crown cap beverage bottle, followed by degassing and rotating for about 24 .5 hours to effect the polymerization. Conversions ranging from about 90 to 100% on average were achieved. Each sample was isolated and converted to the sodium salt as previously described. Each polymer was tested for water loss control in brine suspension A and saturated brine suspension B as previously described at room temperature.

The results are shown in Table E.

TABLE E

AA-MMA-VA terpolymers as water loss control agents

Brine suspension A Saturated brine suspension B 25 Wt. per -.- .- f. 2'9 ** / x '9'7- & fê-? / ..? jS / lS. 8'7 Vm * AA MMA VA_ WL (A) WL (a) WL (a) WL (a) 60 0 40 22 5.5 74 5.7 60 10 30 22 6.5 41 5.5 60 20 20 21 7.5 22 7.5 30 60 30 10 19 7.0 17 4.7 60 40 0 17 10.0 21 4.4 70 0 30 24 6.8 71 8.3 70 10 20 27 6.5 30 6 .8 70 20 10 35 8.0 22 10.0 35 70 30 0 33 10.5 19 7.0 (a) ml / 30 min.

83 0 3 6 1 0 -......— --------- ir * 21

The data summarized in Table E demonstrate that: The terpolymers are useful as water loss control agents at moderate temperatures. The results indicate that a 60:30:10 AA: MMA: VA terpolymer will be an effective water loss control agent in drilling muds.

Example VI

Copolymers containing 75 wt% methacrylic acid (MAA) and 25 wt% methyl acrylate (MA) based on the total weight of the monomers, as well as those containing 75 wt% acrulic acid (AA) and 25 wt% methyl acrylate (MA), based on the total weight of the monomers, were separately prepared in n-hexane as previously described. As previously described, the copolymers in hm sodium salt form were each tested at about 163 ° C and a differential pressure of about 35 kg / cm 2 for their high temperature water loss (HTWL) properties in the brine suspension at different copolymer suspension concentrations in the presence or not of determine gypsum in the suspension at different gypsum suspension concentrations. The gypsum-free brine suspension was prepared in water containing about 4 wt% NaCl, which suspension also contained 5.7 kg / m3 of the aforementioned Desco thinner and 14 kg / m3 of Tannathin lignite. The solids content of the final slurry, after calculation, was found to be about 2.7 wt% bentonite clay, about 2.19 wt% illite clay, and about 30 wt% barite, based on the total weight of the final slurry. The initial pH of the suspension samples ranged from about 10.0 to 10.9. The results are shown in Table F.

25 TABLE F

MAA-MA and AA-MA copolymers as high temperature water loss (HTWL) pesticides_

Copoly- Gypsum Copolymer HTWL, (c)

more (a) concentration, (b) at 163 ° C

30 (d) 0 2.9 28 (d) 0 5.8 30 (d) 2.9 5.8 51 (f) (d) 2.9 8.7 26 (d) 5.8 5.8 136 35 (d) 5.8 8.7 135 (e) 0 2.9 44 (e) 0 5.8 28 83 0 3 6 1 0 ________________________________ 22 TABLE F (Continued) MAA-MA and AA-MA copolymers as high temperature-water loss (HTWL) pesticides_

Copoly- Gypsum Copolymer HTWL, (c)

more (a) concentration, (b) at 163 ° C

5 (e) 2.9 8.7 120 (e) 2.9 5.8 (e) 5.8 8.7 260 (e) 5.8 5.8 258 (f) (a) kg gypsum per m3 suspension 10 (b) kg copolymer per m3 suspension (c) high temperature water loss, ml / 30 min

(d) MAA-MA copolymer, 75 wt% MAA, 25 wt% MA (d) AA-MA copolymer, 75 wt% AA, 25 wt% MA

(f) mean value for two separately prepared suspension samples 15 Note: a dash means that no determination was made.

The results show that the MAA-MA copolymer as a high temperature water loss control agent in gypsum-contaminated rinses is much better than the AA-MA copolymer under the conditions used.

As previously described, the polymers of this invention are preferably used as the sodium salts since the salts are water soluble. However, it is possible to use the acid forms of the polymers alone although this is less preferred because the copolymers in this form do not dissolve well in aqueous solutions.

When the methyl methacrylate content of these polymers is in the range of about 30 wt% or higher, the acid forms of the polymer are water insoluble. Despite this factor, the acid forms of the polymers are capable of acting as water loss control agents.

Although not previously emphasized, it is another peculiarity of the polymers of the present invention that they contribute little or no to the viscosity of the slurry into which they are introduced. This particularity is of utmost importance when the polymers are added to high solids suspensions.

In addition to the previously described suspension polymerization method 8303610 23, suitable copolymers of hydrophilic vinyl monomers with hydrophobic vinyl monomers can be prepared by various other methods. However, all of these methods used are characterized as free radical polymerizations, in which the polymer initiation, propagation and termination steps take place almost entirely as free radical reactions.

One suitable method of preparing the copolymers of the invention is an oil-in-water type polymerization process in which the monomers are copolymerized in the presence of a suitable surfactant, a free radical source, and water. A wide variety of surfactants and free radical sources can be used. Generally, surfactants are preferred which are effective at pH values below 7. In this system, the water / monomer weight ratio can vary over a wide range, but will usually be about 2/1 for a good balance of polymerization rates. , copolymer to obtain latex viscosity and sufficient heat transfer. As in the slurry polymerization method described previously, various free radical sources can be used, including both water-soluble and oil-soluble chemical compounds which are thermally decomposed into free radicals, for example, potassium persulfate or benzoyl peroxide or 2,2'-azo bis- isobutyronitrile. Also, irradiation with ultraviolet light or 60 gamma rays from a radioisotope, such as Co, can function as a free radical source for this polymerization system as well as for the previously described suspension polymerization method. When ultraviolet irradiation is used, sensitizing compounds can be used to promote the radical-forming reactions as known in the art.

The copolymer latex obtained as a product of the oil-in-water type polymerization method can be added directly to a drilling fluid already containing enough alkali metal base compound to neutralize the polymer in situ. Optionally, the polymer latex and the alkali metal base can be added simultaneously to a drilling fluid for in situ neutralization. As a further possibility, the polymer latex can be added to a drilling mud followed by addition of sufficient alkali metal base for in situ neutralization.

The copolymer latex can be reacted directly with sufficient alkali metal base, for example, aqueous NaOH, 50 wt%, to convert the latex to an aqueous neutralized polymer solution. The polymer solution can be directly added to a drilling mud to obtain the desired drilling mud composition. Optionally, the neutralized polymer solution can be heated under reduced pressure or finally dried by a suitable drying technique, such as, for example, microwave irradiation, to remove water to obtain a substantially dry finely divided product that can be easily mixed with a drilling fluid.

Another suitable method of preparing the copolymers of the invention involves a polymerization process of the water-in-oil type. In this system, the monomers are copolymerized in the presence of a water-insoluble organic liquid (usually a hydrocarbon), water, a suitable surfactant and a free radical source. Surfactants suitable for such systems are well known, for example, sorbitan monooleate. The weight ratio of "oil" to water in this system can vary widely, but will usually range from about 0.1 / 1 to about 5/1. The free radical sources described above can also be used in the water-in-oil polymerization method.

The various methods mentioned above in terms of the oil-in-water polymerization process can also be used to supply the neutralized polymer obtained by the water-in-oil polymerization method to a drilling fluid.

Carboxyl group-containing polymers may present difficulties in certain conventional molecular weight determination methods due to the intra- or intramolecular interaction involving the carboxyl groups. A suitable procedure to overcome these difficulties involves the quantitative esterification of the carboxyl-30 groups in such polymers without changing the chain length of the polymer. The esterified polymer can then be used in molecular weight analyzes, such as gel permeation chromatography (GPC) or intrinsic viscosity (I.V.), where calibration measurements have already been or can be performed for use in the calculations.

Different reaction component combinations and conditions are described in the article by H.L. Cohen, J. Polymer Sci .: 8303610 25 s

Polymer Chem. Ed./ Vol. 14, 7-22 (1976) for the quantitative esterification of polymeric carboxylic acids. A particularly suitable procedure is the extended (24-48 hours) heating of the polymer in dimethylformamide (DMF) diluent with an excess of trimethyl orthoacetate. The polymer may initially be insoluble, but as the reaction proceeds, it swells and then dissolves in DMF reaction diluent 1. DMF is believed to have a promoter effect on the esterification reaction.

As mentioned earlier, the esterified polymer can be easily handled in molecular weight determination procedures, such as GPC or I.V. measurements in which suitable calibration measurements have already been or can be carried out. For example, in the quantitative esterification of a methacrylic acid / methyl methacrylate (MAA / MMA) copolymer, the copolymer is converted into a poly (methyl methacrylate). This polymer has been extensively studied in a wide variety of solvents and its intrinsic viscosity to molecular weight ratio properties have been published. Furthermore, poly (MMA) standards for GPC analysis are commercially available, for example, from Polymer Laboratories, Stow, Ohio.

Thus, quantitatively esterified MAA / MMA copolymer can be used to determine the molecular weight of the "original" MAA / MMA copolymer.

A more direct method of determining the molecular weight of the carboxyl copolymers of this invention is possible by well known light scattering techniques. It is also known that this method is sometimes experimentally difficult to perform.

The carboxyl copolymers of this invention, in their neutralized (alkali metal salt) form, are particularly effective water loss control agents in drilling muds of various types, for example, KCl-containing delayed muds, recovery muds containing fiber-containing additives, etc. It has been found that the crylic acid (MAA) copolymers, ie MAA / MMA copolymer, and retain their effectiveness as water loss pesticides even in the presence of significant levels of commonly encountered contaminants, such as NaCl (brine), calcium ions (gypsum) and cement. Furthermore, the polymers of this application have been found to retain effectiveness as water loss control agents also at elevated temperatures. This is a very important feature as interest in drilling geothermal wells has increased and high temperatures are found in many deep gas and oil wells. It is known that cellulosic polymers which are otherwise very useful as drilling mud additives can decompose even when exposed to high temperatures for a relatively short period of time. In contrast, the polymers of the invention are resistant to thermal decomposition in drilling muds over relatively long periods of time, for example, up to 3-5 days or even longer. Thus, the copolymers 10 of the invention are particularly useful at well temperatures from about 75 ° C to about 371 ° C.

Example. VII

A series of methacrylic acid (MAA) / methyl methacrylate (MMA) copolymers were prepared by oil-in-water polymerization method at 50 ° C. Sulfonated castor oil (2 ppm of a 50 wt% active ingredient) was used as the surfactant and 0.3 ppm of potassium persulfate (KjSjOg) as initiator. The polymers were neutralized in situ with 5M NaOH and recovered from water by evaporation.

The copolymers were evaluated as water loss control additives in brine suspensions a and B at room temperature (Table G) and at about 163 ° C under a differential pressure of 35 kg / cm2 in the brine suspension of Example VI with and without gypsum or additional salt impurities ( Table H). The results for various acrylic acid (AA) copolymers are also indicated.

8303610 m 27

T AB EL · G

_KTWL values ^ _

Brine suspension ie A Saturated brine suspension -__ B

Polymer Monomer- 2.9 kg / m3 8.7 kg / m3 2.9 kg / m3 8.7 kg / m3 5 No. ratio _ MSA / MMA _ _ _ _ 1 95/5 29 7.4 33 7 2 90/10 24 8.8 30 5.5 3 85/15 28 7.8 26 5.5 10 4 80/20 20 7 28.5 5.5 5 75/25 17 7 32 5 6 70/30 16 6 , 8 43 6.5 7 65/35 19 8 69 12 8 60/40 20 7 - 1 2 3 28 15 9 55/45 30 8.7 - 56 10 50/50 49 9.5 - 86 'A & / MA (C) 11 75/25 18 9 21 5.6 AA / MMA4 '20 12 75/25 30 9.5 54 8.2 13 70/30 22 8.5 23 5.8 8303610 room temperature water loss, API, ml / 30 minutes 2 a dash means no determination was made 3 acrylic acid / methyl acrylate copolymer 4 (d) acrylic acid / methyl methacrylate copolymers.

* "ν '28 TABLE · Η _ (a) HTWL · values at 5.7 kg / m3 polymer

Polymer Ratio Suspension without Gypsum NaCl no_ MAA / MMA contamination 2.9 kg / m3 29 kg / m3 1 95/5 23 28 - 5 2 90/10 24 32 32 3 85/15 23 38 32 4 80/20 26 32 38 5 75/25 24 28 24 6 70/30 28 36 30 10 7 65/35 26 40 * 46 8 60/40 - - 9 55/45 - - 10 50/50 - -

Base suspension no polymer. 150 15 AA / MA

11 75/25 28 120 160 • t

AA / MMA

12 75/25 24 170 (b) 13 70/30 28. 94 (b) 140

20 (a) High temperature water loss, 35 kg / cm *, 163 ° C

(b) Average values from two tests.

The results in Tables G and H show that the MAA / MMA copolymers have satisfactory KTWL values and uncontaminated suspension HTWL values over a wide range, for example 95/5 to 65/35 of monomer ratios, but the values do not differ widely of those of acrylic acid / methyl acrylate and acrylic acid / methyl methacrylate copolymers 11, 12 and 13 in these suspensions. However, in suspensions contaminated with gypsum or NaCl, the high temperature MAA / MMA copolymers are clearly better at combating water loss than the AA / MA-30 or AA / MMA copolymers.

Example VIII

Other properties of the drilling mud composition used in Table H of Example VII, which contained polymers 1-7 (5.7 kg / m3 of 83 0 3 6 1 0; ___________ ___________ 29 mud} of Example VII, were measured. performed with and without added gypsum or NaCl impurities The results of these tests are shown in the following Table J.

TABLE J

5 Part A - No contamination added

Polymer_Start aged 16 hours at 182 ° C_

No. PV / YPCa) Gel (b) ph wl (c) SSPV / YP “Gel pH WL

1 23/59 92/140 10.3 3.8 810 14/68 11/40 7.7 5.2 2 27/59 92/144 10.3 3.8 855 16/36 14/45 7.6 4 .6 10 3 26/50 68/140 10.4 3.8 855 16/68 10/39 7.7 4.2 4 25/77 92/144 10.5 3.6 810 25/36 13/40 7 .5 4.3 5 24/95 92/162 10.3 - 900 15/68 8/35 7.7 4.5 6 27/122 99/234 10.3 2.7 855 10/77 8 / - 7 , 6 - 7 24/171 62/286 10.3 2.8 900 15/299 14 / - 7.6 4.5 15 Basic suspensions - 13/14. 27/59 10.7 - <270 9/45 11 / - 7.8 - sie. Part B - 2.9 kg / m3 added plaster 1 23 45/149 10.3 5.3 720 14/23 19/48 7.6 6.9 2 23 36/99 10.4 4.8 630 15/68 23/47 7.7 5.8 20 3 24 36/99 10.4 5.4 720 13/77 18/48 7.5 6.6 4 26 41/99 10.4 4.6 630 31/0 21 / 49 7.6 7.0 5 23 50/131 10.4 4.3 720 23/32 17/46 7.5 7.7 6 23 81/203 10.4 4.8 765 20/144 26/58 7.5 7.0 7 22 99/293 10.4 4.7 855 21/194 38/60 7.6 6.3 25 Part C - 28.5 kg / m3 added NaCl 2 28 68/135 9.8 5.0 495 13/72 11/36 7.2 8.2 3 23 63/131 9.8 4.5 428 11/72 12/35 7.1 8.0 4 18 72/162 9.8 5, 0 720 13/72 13/37 7.2 8.3 5 19; 90/189 9.9 4.2 540 14/59 9/31 7.2 8.5 30 6 25 126/216 9.9 4.7 540 12/90 13/37 7.0 8.6 7 21 99 / 248 9.8 5.2 540 13/95 21/47 7.0 6.8 (a) PV = plastic viscosity, cp; YP = pour point, kg / 100 m2 (b) Gel = gel strength at 10 sec (kg / 100 m2) / gel strength at 10 min (kg / ^ 100 m2) 8303610 30 (c) WL = API water loss, ml / 30 min ( d) SS = shear strength, kg / 100 m2.

The results in Table J demonstrate that the MAA / MMA copolymers tested did not drastically increase the suspension viscosity, gel-5 strength, pour point and shear strength values. Thus, rinses containing such polymers can be easily pumped or otherwise handled.

Example IX

Other tests were conducted in which the water loss control effectiveness of a (75/25) MAA / MMA copolymer (A) over a (70/30) AA / MMA copolymer (B) and a commercially available polymer (C ) based on a polyanionic cellulose under the name Dispac Superlo obtained from Drilling Specialties Co., Bartlesville, Oklahoma. These tests determined the high temperature water loss (HTWL) values of rinses containing different concentrations of polymer, gypsum or NaCl after aging under different conditions. The rinse (base) used for these experiments was the same as that used for the brine suspension of Example VI and also in Example VII (Table H). The results of these tests are shown in Table K below.

8303610 31

TABLE K

Suspensions aged at 121 ° C for 16 hours

Taste _Conc. 2.9 kg / m3_ HTWL at 163 ° C_ No. Polymer NaCl Gypsum 35 kg / cm2, ml / 30 min 1 (A) 2 0 1 28 5 2 (A) 2 0 1/5 46 3 (A) 1 15 0 37 4 (A) 1 20 0 40 5 (A) 1.5 20 0 32 6 (A) 2 20 0 32 10 7 (A) 2 50 0 28 8 (A) 2 60 0 66 9 (A) 2 70 0 124 10 (B) 2 0 1 38 11 (B) 1 20 0 126 12 (B) 1.5 20 0 92 13 (B) 2 20 0 36. i 14 (C) 2 0 1 · 36 15 (C) 1 15 0 48 20 16 (C) 1 20 0 72 17 (O 1.5 20 0 48 18 (C) 2 20 0 30 19 (C) 2 50 0 38 20 (C) 2 60 0 36 25 21 (C) 2 70 0 40

Suspensions aged at 80 ° C 22 (A) 2 0 1 26 23 (A) 2 0 2 150 24 (A) 2 20 0 28 30 25 (0 2 0 1 34 26 (0 2 0 2 37 27 (C ) 2 20 0 50

The above results indicate that the MAA / MMA copolymer (A) was more effective in the AA / MMA copolymer (B) 8303610 - ---------------

"V

32 and the commercial polymer (C) in a salt concentration range of 4% to near saturation values and at a gypsum concentration of 2.9 kg / m3 suspension. However, as the aging temperature increased, the MAA / MAA copolymer (A) became less tolerant of salt. At near saturation salt concentration, the polymer (C) also became more effective to combat water loss (HTWL) than the MAA / MMA copolymer (A). At a gypsum level of 5.7 kg / m3, polymer (C) was also more effective than (A).

Example X.

A large batch (about 4500 kg) of an 80/20 MAA / MMA copolymer was prepared in various reactor amounts according to an oil-in-water type polymerization process. The polymer latex was converted into a polymer solution of about 10% solids in water by neutralizing the polymer with NaOH.

An aqueous polymer solution for drilling mud testing was obtained by combining samples from different reactor lots to obtain a composite sample hereinafter referred to as polymer A.

The compatibility of polymer A with a commonly used additive in drilling muds, namely chrysotile asbestos flocked fibers under the name of Flosal from Drilling Spealties Co. Bartlesville, Oklahoma was determined in a series of tests with aqueous solutions containing both. For comparison, a commercially available high molecular weight polyanionic cellulose-like polymer (Drispac also from Drilling Specialties Co.) was simultaneously investigated. The results of the tests are shown in Table L.

8303610 33

TABLE L

Test Flosal, Polymer, Viscosity ^ no.kg / m3 2.9 kg / m3 cp _ _ _ at 600/300 RPM Gel C PV / YP WL ^ 1 2.9 A 28/20 0/0 8/54 200 5 2 2.9 Drispac 26/18 0/0 8/45 65 3 5.8 A 32/22 4.5 / 9 10/54 168 4 5.8 Drispac 30/20 0/0 10/45 64 5 11, 6 A 37/30 4.5 / 9 7/104 116 6 11.6 Drispac 36/26 13/22 10/72 31.5

10 Overnight aged at 80 ° C

7 2.9 A 27/17 0/0 8/41 140 8 2.9 Drispac 25/15 0/0 10/23 39 9 5.8 A .29 / 19 1/2 10/41 108 10 5.8 Drispac 29/20 0/1 9/50 30 15 11 11.6 A 38/28 4/6 10/81 '96 12 11.6 Drispac 36/26 3/5 10/72 27 (a) Determined with Farm viscometer (b) API water loss determined at room temperature, 7 kg / cm2 in ml / 30 min.

(c) Gel = gel strength at 10 sec (kg / 100 m2) / Gel strength at 10 min (kg / 20 100 m2) (d) PV = plastic viscosity, cp? YP = pour point, kg / 100 m2.

The results in Table L demonstrate that polymer A is compatible with Flosal in rinses containing both. However, the water loss control with the Flosal-polymer A combination was not as good as with the Flosal-Drispac polymer combination.

Other tests were performed with rinses containing other materials besides the Flosal (11.4 kg / m3) and polymer (Polymer A or Drispac) at 5.7 kg / m3. These tests were also performed after aging at elevated temperatures separately from the room temperature tests. The results of these tests are summarized in Table M.

8303610 i 34

TABLE M

Test Additive Begin Overnight aged No. Polymer 5.8 kg / m3 PV / YPC GelJ WLè at 149 ° C _ _ ____ PV / YPC GelQ WLë 1 A 0 14/99 4.5 / 9 64 10/23 4.5 / 23 139 5 2 Drispac 0 20/171 27/45 20 7/54 14/18 35 3 A bentonite 16/135 18/27 20 21/122 14/27 14 4 Drispac bentonite 25/293 50/50 13.2 9 / 50 23/41 19.8 at 204 ° C_ 5 A bentonite 17 27/36 28 9/50 1.4 / 14 30 10 6 A CaCO 3 16 23/32 22 18/126 23/32 20 7 A bentonite 3 25 36/50 28 9/72 14/32 26.8 and CaCO3 at room temp. (24 ° C) 8 A cement * 5 12/72 9/14 6 11/63 14/23 10.7 15 a) both present at 5.8 kg / m3 rinse.

b) present at 4.4 kg / m3 rinse.

c) PV = plastic viscosity, -cp; YP = pour point, 'kg / 100 m2 d) Gel «gel strength at 10 sec (kg / 100 m2) / gel strength at 10 min (kg / 100 m2) 20 e) API water loss determined at room temperature, 7 kg / cm2 in ml / 30 min.

The results of Table L demonstrate that the addition of bentonite or calcium carbonate can greatly improve the water loss control properties of rinses that polymer A such that the performance level is equal to or better than Drispac after aging at elevated temperatures. It has further been shown that cement contamination from a mud containing Flosal and polymer A does not dramatically increase the viscosity of the mud.

The tests summarized in Tables L and M demonstrate that polymer A is particularly well suited for use in a recovery flush containing Flosal fiber additive, especially in wells where high temperatures are encountered, such as in geothermal wells.

In operation, the above described drilling muds or slurries are preferably passed down through a tubular drill string and through the drill bit at the bottom of the drill string into the bottom of a well. The drilling muds are further fed upwardly through the ring between the drill string and the borehole wall / through which debris from the bottom of the borehole is transported to the surface of the earth and the polymeric water loss control agent from the drilling mud comes into contact with the penetrated formations to combat water loss from the borehole in the formations thus processed. After each passage of the drilling mud through the drill string and the borehole ring, the drilling mud is preferably passed through a settling tank or trough where sand and drill cuttings are separated / with or without screening. The drilling mud is then pumped back into the drill string by means of a mud pump to continue the circulation described above.

From the foregoing, it is clear that the polymers of the present invention accomplish the above-described objects and advantages easily. While the invention has been described in specific embodiments, it is understood that this is only by way of illustration and that the invention is not necessarily limited thereto / since other embodiments and processing techniques will become apparent to those skilled in the art upon reading this specification.

8303610

Claims (24)

A method of drilling a well in the earth of the type in which the well is formed by drilling means which penetrate the earth to the bottom of said well, wherein the well penetrates at least an underground zone with a temperature of at least 79 ° C, 5 characterized in that a drilling mud is circulated through said well and said at least one underground zone to the bottom of said well, said drilling mud comprising: an amount of water and an amount of a copolymer prepared by copolymerizing a hydrophilic vinyl monomer with at least one hydrophobic vinyl monomer under polymerization conditions for a sufficient period of time to give a copolymer having a weight average molecular weight within a predetermined range. 2. A method according to claim 1, characterized in that said hydrophilic vinyl monomer is selected from acrylic acid, methacrylic acid and combinations thereof. 3. Process according to claim 1, characterized in that at least one hydrophobic vinyl monomer is selected from acrylic acid esters, methacrylic acid esters, vinyl esters of saturated monocarboxylic acids with 1-3 carbon atoms, and combinations of two or more thereof. Process according to claim 3, characterized in that said hydrophilic vinyl monomer comprises methacrylic acid. Process according to claim 4, characterized in that said at least one hydrophobic vinyl monomer comprises methyl methacrylate. 6. A method according to claim 1, characterized in that said hydrophilic vinyl monomer comprises acrylic acid and said at least one hydrophobic vinyl monomer comprises methyl methacrylate. A method according to claim 5, characterized in that the weight ratio of said hydrophilic vinyl monomer to said at least one hydrophobic vinyl monomer present during said copolymerization is in the range from about 95: 5 to about 46:54, based on the total weight of said monomers present in said copolymerization. A method according to claim 5, characterized in that the weight ratio of said hydrophilic vinyl monomer to said at least one hydrophobic vinyl monomer present during said copolymerization is in the ranges from about 95: 5 to about € 5: 35 based on the total weight of said monomers present in said copolymerization. The process according to claim 1, characterized in that the weight ratio of said hydrophilic vinyl monomer to said at least one hydrophobic vinyl monomer present during said copolymerization is in the range from about 95: 5 to about 46:54, based on the total weight of said monomers present in said copolymerization. 10. A process according to claim 1, characterized in that the weight ratio of said hydrophilic vinyl monomer to said at least one hydrophobic vinyl monomer present during said copolymerization is in the range of from about 95: 5 to about 65: 35 based on the total weight of said monomers present in said copolymerization. 11. A process according to claim 1, characterized in that the molar ratio of said hydrophilic vinyl monomer to said at least one hydrophobic vinyl monomer present during said copolymerization is in the range from about 22: 1 to about 1: 1. A method according to claim 1, characterized in that the molar ratio of hydrophilic vinyl monomer to said at least one hydrophobic vinyl monomer present during said copolymerization is in the range from about 22: 1 to about 2: 1. Process according to claim 1, characterized in that said hydrophilic vinyl monomer comprises acrylic acid and said at least one hydrophobic vinyl monomer comprises methyl methacrylate and vinyl acetate, wherein the acrylic acid, methyl methacrylate and vinyl acetate are present in a molar ratio in said copolymerization range from about 2.8: 1: 0.33 to about 8.3: 1: 3.5. A method according to claim 1, characterized in that said hydrophilic vinyl monomer comprises acrylic acid and said at least one hydrophobic vinyl monomer comprises methyl methacrylate and vinyl acetate, said acrylic acid, methyl methacrylate and vinyl acetate being present in a weight ratio in the range of about 60:30:10 to about 60:10:30 based on 8303610 * the total weight of the monomers present in said copolymerization. A method according to claim 3, characterized in that said hydrophilic vinyl monomer comprises acrylic acid. A method according to claim 6, characterized in that the 5 molar ratio of said acrylic acid to said methyl methacrylate during said copolymerization is in the range from about 7: 1 to about 1: 1. 17. A process according to claim 6, characterized in that the molar ratio of said acrylic acid to: said methyl methacrylate during said copolymerization is in the range from about 3.2: 1 to about 2.1: 1. Method according to claim 1, characterized in that said at least one underground zone has a temperature of at least 163 ° C. A method according to claim 1, characterized in that said at least one underground zone has a temperature in the range of from 163 to about 371 ° C. A method according to claim 1, characterized in that said one underground zone has a temperature in the range of 79 to 20 about 371 ° C. A method according to claim 5, characterized in that said at least one underground zone has a temperature in the range from about 79 ° C to about 371 ° C. 22. A method according to claim 5, characterized in that said at least one underground zone has a temperature of at least about 190 ° C. A method according to claim 5, characterized in that said at least one underground zone has a temperature in the range from about 190 ° C to about 371 ° C. The method of claim 1, characterized in that said weight average molecular weight is in the range from about 100,000 to about 500,000. 8303610