Aqueous-based wellbore fluids

Abstract

The invention provides a wellbore fluid which comprises an aqueous continuous phase and, dissolved in said aqueous continuous phase, at least one salt containing an imidazolium cation having at least 6 carbon atoms, and a method of carrying out a wellbore operation, which comprises introducing into a wellbore in a clay-containing formation, a wellbore fluid according to the invention. The described salts are effective shale inhibitors.

Claims

1. A method of carrying out a wellbore operation, which comprises: introducing into a wellbore in a clay-containing formation, a wellbore fluid which comprises: an oil-in-water emulsion comprising an aqueous continuous phase and a discontinuous oil phase, said aqueous continuous phase comprising at least one salt containing an imidazolium cation having at least 6 carbon atoms dissolved in said aqueous continuous phase, wherein the introducing of the wellbore fluid reduces the swelling of the clay-containing formation.

2. The method of claim 1, in which said cation contains at least 8 carbon atoms.

3. The method of claim 1, in which said cation contains at least 12 carbon atoms.

4. The method of claim 1, wherein the quaternising substituent on the nitrogen atom of the imidazole ring is a hydrogen atom or an alkyl group having up to 16 carbon atoms optionally substituted by one or more of the same or different substituents selected from phenyl, carboxyl, amine, amide, sulfate, cyanate and thiocyanate groups or halogen atoms and optionally interrupted by one or more oxygen, nitrogen and/or sulfur atoms.

5. The method of claim 4, in which said substituent is an unsubstituted alkyl group having from 1 to 8 carbon atoms.

6. The method of claim 5, in which said cation is 1-ethyl-3-methylimidazolium.

7. The of method claim 1, wherein said salt exists in a liquid state at a temperature below 150° C.

8. The method of claim 1, wherein the continuous phase is water or a sodium chloride brine.

9. A method of inhibiting shale, comprising: introducing into a wellbore in a clay-containing formation, a wellbore fluid which comprises an oil-in-water emulsion having an aqueous continuous phase and, dissolved in said aqueous continuous phase, at least one salt containing an imidazolium cation having at least 6 carbon atoms.

10. A method of carrying out a wellbore operation, which comprises: introducing into a wellbore in a clay-containing formation, a wellbore fluid which comprises: an oil-in-water emulsion comprising an aqueous continuous phase and a discontinuous oil phase, said aqueous continuous phase comprising at least one salt containing an imidazolium cation having at least 6 carbon atoms dissolved in said aqueous continuous phase, wherein the wellbore fluid comprises the at least one salt containing an imidazolium cation in an amount of from 1 to 5% weight/volume, and wherein the oil phase is present in an amount of from 1% to 65% by volume of the emulsion, wherein the introducing of the wellbore fluid reduces the swelling of the clay-containing formation.

11. A method of inhibiting shale, comprising: introducing into a wellbore in a clay-containing formation, a wellbore fluid which comprises an oil-in water emulsion having an aqueous continuous phase and, dissolved in said aqueous continuous phase, at least one salt containing an imidazolium cation having at least 6 carbon atoms, wherein the wellbore fluid comprises the at least one salt containing an imidazolium cation in an amount of from 1 to 5% weight/volume, and wherein the oil phase is present in an amount of from 1% to 65% by volume of the emulsion.

12. A method according to claim 10 or 11, wherein the salt comprises an anion selected from: haloalkyl or aryl sulphates, trifluoromethanesulfonate, tosylate, dimethyl phosphate, diethyl phosphate, phosphinates or phosphonates, alkyl or haloalkyl sulfonylamides, carbonate or alkyl carbonates, dicyanamide, azolates, perhalides, or metal anions.

13. A method according to claim 12, wherein the specific gravity of the wellbore fluid is in the range 0.9 to 2.5.

14. A method according to claim 13, wherein the oil phase comprises droplets with an average particle diameter of less than 40 microns.

15. A method according to claim 12, wherein the oil phase comprises droplets with an average particle diameter of less than 40 microns.

16. A method according to claim 10 or 11, wherein the specific gravity of the wellbore fluid is in the range 0.9 to 2.5.

17. A method according to claim 10 or claim 11, wherein the oil phase comprises droplets with an average particle diameter of less than 40 microns.

Description

EXAMPLE 1

(1) 16.5 grams of 1-ethyl-3-methylimidazolium chloride was dissolved in 285 ml of distilled water to produce the “inhibitive solution” (approximately 5 weight % in 1-ethyl-3-methylimidazolium chloride). 10.0 grams of London clay chippings, with particle size range between 4.0 mm and 2.0 mm, was placed in a 110 ml glass sample bottle, and 100 grams of the previously prepared solution (5 weight % 1-ethyl-3-methylimidazolium chloride) was added. The sample bottle was then sealed, and placed on a rolling table for 24 hours at room temperature. After 24 hours, the sample was filtered through a 500 micrometer sieve and washed with a KCl/water solution (42.75 grams KCl/litre). The sieve containing the recovered clay particles was then placed in a drying oven overnight (at 110° C.) and the recovered particles were then carefully weighed. The procedure was repeated three times, and the results averaged. 79% of clay was recovered, representing a high level of inhibition.

EXAMPLE 2

(2) The method of Example 1 was repeated except that the 285 ml of distilled water was replaced by 285 ml of NaCl/water solution (71.3 grams NaCl in distilled water). A recovery of 75.0% was obtained.

EXAMPLE 3

(3) The method of Example 1 was repeated except that the 285 ml of distilled water was replaced by 285 ml of KCl/water solution (71.3 grams KCl in distilled water). A recovery of 70.0% was obtained.

EXAMPLES 4 TO 8

(4) The general method of Example 1 was repeated using different salts for comparison purposes, and using either distilled water, NaCl (71.43 g/l) solution, or KCl (71.43 g/l) solution. The results (% of recovered clay) are summarized in Table I.

(5) TABLE-US-00001 TABLE I Distilled NaCl KCl Example No. Salt water solution solution 4 (comparative) Choline chloride 36 37 33 5 (comparative) tetrabutylammonium 66 — 58 bromide 6 1-ethyl-3- 84 74 66 methylimidazolium methylcarbonate 7 (comparative) None 1.8 — — 8 (comparative) sodium methylsulfate 1 — —

(6) It can be seen that the compositions according to the invention exhibited a much higher degree of inhibition than a composition containing no inhibitor, or a composition containing a salt not according to the invention.

EXAMPLES 9 TO 11

(7) The general method of Example 1 was repeated in a second series of experiments. The results—recovery of clay—are shown in Table II. Glycol DCP208 is a commercially-available shale inhibitor used in aqueous-based wellbore fluids.

(8) TABLE-US-00002 TABLE II Distilled NaCl KCl Example No. Salt or other inhibitor water solution solution  9 1-ethyl-3- 70 76 75 methylimidazolium ethylsulfate 10 (comparative) None 1 0.2 0.6 11 (comparative) Glycol DCP208 1 6 59

(9) It can be seen that the compositions according to the invention exhibited a much higher degree of inhibition than a composition containing no inhibitor, or a composition containing a commercially used inhibitor. The commercially-used inhibitor, Glycol DCP208, required the presence of KCl to exhibit any inhibiting properties; the inhibitors according to the invention exhibited high levels of inhibition in all of water, KCl brine and NaCl brine.

EXAMPLES 12 AND 13

(10) Cage rolling tests were carried out as follows. Around 100 g of 4-8 mm of London Clay chips were accurately weighed into rolling cages. The cages were rolled at 20 rpm for 4 hours at room temperature in 1500 ml of various test fluids, after which the cages were rinsed well with water to remove all traces of the test fluids from the surviving clay chips. The chips were dried at 130° C. for 16 hours, weighed, and the percentage recovery was calculated taking the original moisture content into account. The moisture content was 22.01%. The composition of the test fluids, which modelled wellbore fluids, are shown in Table III, and the results—recovery of clay—of the cage rolling tests are shown in Table IV.

(11) TABLE-US-00003 TABLE III KCl 0 or 129 g Starch (Flotrol) 129 g PAC L 4.3 g XC polymer Duovis 5.1 g tributyl(ethyl)phosphonium diethylphosphate or 75 ml 1-ethyl-3-methylimidazolium ethylsulfate pH (adjusted with KOH) 10 Water to 1500 ml

(12) TABLE-US-00004 TABLE IV Example Clay recovery No. KCl Salt (wt %) 12  0 1-ethyl-3-methylimidazolium 64 ethylsulfate 13 129 g 1-ethyl-3-methylimidazolium 72 ethylsulfate