Method to reduce the water loss in slurries or solutions used in oil field and gas field operations

Abstract

The present invention relates to a method to reduce the water loss in slurries and solutions used in oil field or gas field operations, for example for drilling, cementing and completion operations by adding a copolymer having a high molecular weight characterized by a K value of at least 300, said copolymer comprising structural units derived from monomers having sulfonic acid or derivative thereof, phosphonic acid or derivative thereof and acrylamide functionality.

Claims

1. A method for reducing water loss in aqueous slurries of particulate solids and/or in aqueous solutions for oil field and/or gas field operations, said process comprising the steps of: adding to the said slurry or to said solution a copolymer having a high molecular weight characterized by a K value of at least 300, determined as 0.1 weight % copolymer concentration in deionized water, said copolymer comprising (i) 0.1 to 20 weight % of structural units of formula (I), ##STR00009## and (ii) 5 to 90 weight % of structural units of formula (II), ##STR00010## and (iii) 5 to 75 weight % of structural units of formula (III) ##STR00011## and (iv) up to 20 weight % of structural units of formula (IV), said structural unit of formula (IV) is different from structural units of the formula (II), ##STR00012## wherein B is a two-valent organic bridge group, and if structural units of formula (IV) are present, B can also be a covalent bond forming a direct linkage, R9 is hydrogen or C.sub.1-C.sub.6-alkyl, R10 is hydrogen, a cation of an alkaline metal, of an earth alkaline metal, and/or of ammonia, wherein the sum of the structural units of formulae (I), (I), (III), and (IV) if present, amounts to 100 weight % of the total mass of the copolymer, and R1, R4 and R6 are independently of one another hydrogen or C.sub.1-C.sub.6-alkyl, R2, R3 and R5 are independently of one another hydrogen, a cation of an alkaline metal, of an earth alkaline metal, of ammonia and/or of an organic amine, R7 and R8 are independently of one another hydrogen or C.sub.1-C.sub.6-alkyl, A is a covalent CP bond or a two-valent organic bridge group, and B is a two-valent organic bridge group, with the proviso, that the copolymer is added to said slurry or to said solution in the absence of any glycol and/or glycol-ether compounds.

2. The method according to claim 1, wherein R1, R4 and R6 are independently of one another hydrogen or methyl and R2, R3 and R5 are independently of one another hydrogen or a cation of an alkali metal, of an earth alkaline metal, or of ammonia and R7 and R8 are independently of one another hydrogen, methyl or ethyl, preferably hydrogen.

3. The method of claim 1, wherein A is a CP covalent bond or a C.sub.nH.sub.2n group with n being an integer between 1 and 6, and B is a CONHC.sub.mH.sub.2m group with m being an integer between 1 and 6.

4. The method of claim 1, wherein R9 is hydrogen or methyl.

5. The method according to claim 1, wherein the copolymer comprises (i) 40 to 80 weight % of structural units of formula (II) and its alkali salts and/or ammonium salts, (ii) 1 to 10 weight % of structural units of formula (I) and its alkali salts and/or ammonium salts and (iii) 10 to 59 weight % of structural units of formula (III).

6. The method according to claim 1, wherein the copolymer is added to aqueous suspensions of particulate solids, cement slurries, gypsum slurries, mortars, or drilling muds or wherein the copolymer is added to aqueous solutions, including saline solutions.

7. The method according to claim 6, wherein concentration of the copolymer added to the aqueous suspensions of particulate solids is between 0.1 to 4 weight %.

8. The method according to claim 7, wherein the solids content of the final aqueous suspension of particulate solids is between 2 and 75 weight %.

9. The method according to claim 1, wherein the concentration of the copolymer added to the aqueous solutions is between 0.2 and 8 weight %.

10. The method according to claim 1, wherein to the aqueous solutions comprising the copolymer with structural units of formulae (I), (II) and (III), and (IV), adding CaCl.sub.2 and/or CaBr.sub.2 to increase the density of said aqueous solution above 1 g/ml.

11. The method of claim 3 wherein n is 1.

12. The method of claim 3 wherein m is between 2 and 4.

13. The method of claim 3 wherein B is CONHC(CH.sub.3).sub.2CH.sub.2.

14. The method of claim 10 wherein the density of said aqueous solution is in a range of 1.4 to 1.81 g/ml.

Description

EXAMPLE 1: PREPARATION OF COPOLYMER 1

(1) 37 g sorbitan monooleate were dissolved in 160 g C11-C16 iso-paraffin. 100 g water in a beaker was cooled to 5 C., and then 200 g 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and 10 g vinylphosphonic acid (VPS) were added. The pH was adjusted to 7.1 with aqueous ammonia solution. Subsequently 160 g acryl amide (AM) solution (60 weight % in water) were added.

(2) Under vigorous stirring the aqueous monomer solution was added to the iso-paraffin mixture. The emulsion was the purged for 45 min with nitrogen.

(3) The polymerization was started by addition of 0.5 g azoisobutyronitrile in 12 g iso-paraffin and heated to 50 C. To complete the reaction the temperature was increased to 80 C. and held at this temperature for 2 h. The polymer emulsion was cooled to room temperature.

(4) For the tests the inverse copolymer emulsion is inverted by adding the corresponding quantity of the emulsion to achieve the desired copolymer concentration to an aqueous or saline solution containing 1 weight % of a surfactant with a HLB>12.

EXAMPLES 2 TO 7

(5) In Table 1 the copolymers synthesized according to the inverse emulsion polymerization are summarized, the compositions are given in weight %:

(6) TABLE-US-00001 TABLE 1 Example no. AMPS VPS AM NNDMA VSS K-value 2 62 2 36 381 3 68 2 30 398 4 61 1 38 405 5 80 1 19 410 6 (comp.) 50 0 50 422 7 (comp.) 85 0 5 5 5 375 NNDMA = N,N-dimethlyacrylamide VSS = Vinylsulfonic acid

EXAMPLE 8: PREPARATION OF COPOLYMER 8

(7) 1000 nil water, 80 g AMPS and 2 g vinylphosphonic acid are added with stirring. The solution is adjusted to pH 7.2 with 20 weight % NaOH solution. Then 50 g N,N-dimethylacrylamide are added.

(8) The solution is then purged with a gentle N2 stream and slowly heated to 40 C. Then a 10 weight % solution of Na.sub.2S.sub.2O.sub.8 is added to start the polymerization which is indicated by an increase in temperature and viscosity. The mixture is heated to 80 C. and held for 2 h to complete the reaction.

(9) During cooling the obtained gel is diluted with 500 ml water to ensure a better handling of the copolymer solution.

EXAMPLES 9 TO 11

(10) Copolymers which were synthesized according to the gel polymerization described in example 8 are summarized in table 2:

(11) TABLE-US-00002 TABLE 2 Example no. AMPS VPS AM NNDMA K-value 9 74 4 22 336 10 85 2 30 398 11 (comp.) 61 0 10 29 405

(12) Copolymers according to the present invention and comparative copolymers were characterized by measuring the fluid loss of cement slurry. The slurry was prepared by adding 700 g of the cement to a stirred solution of 3.5 g copolymer in 308 g water. The cement slurry was transferred into a HTHP filtration cell and pressurized with 70 bar. The filtrate within 30 min was collected. For tests at elevated temperature a retarder was added to the slurry.

(13) The cement used in all testings is a Dykerhoff Class G cement which satisfies the API Spec. 10A. issued by the American Petroleum Institute.

(14) The fluid loss testing was performed in the absence of any glycol and/or glycol-ether compounds.

(15) In Table 3 the results are summarized.

(16) TABLE-US-00003 TABLE 3 Copolymer according to Temperature Fluid loss Example no. ex. ( C.) (ml/30 min) 12 3 25 38 13 4 50 43 14 4 180 70 15 6 (comp.) 150 >150

(17) It is evident that copolymers according to the Invention are effective fluid loss additives in cement slurries. The incorporation of vinylphosphonic acid into the copolymer ensures a good fluid loss behavior even at elevated temperatures.

(18) To characterize the fluid loss properties of the copolymers according to the present invention for drilling applications, a drilling mud consisting of 4 weight % bentonite, 25 weight % NaCl, 1 weight % CaSO.sub.4 and 1.5 weight % of copolymer was used.

(19) The fluid loss of this drilling mud was determined in a HTHP filtration cell at ambient temperature applying 70 bar and measuring the fluid loss of the bentonite slurry. In addition the fluid loss of the slurry was determined after aging the suspension at 200 C. for 15 h and after cooling to ambient temperature again.

(20) The fluid loss testing was performed in the absence of any glycol and/or glycol-ether compounds.

(21) In Table 4 the results are summarized:

(22) TABLE-US-00004 TABLE 4 Copolymer Fluid loss, Fluid loss according to (ml/30 min) (ml/30 min) Example no. ex. without aging after aging 16 1 27 32 17 2 22 21 18 10 34 36 19 7 (comp.) 40 102

(23) Also for drilling muds it is shown that the copolymers according to the invention ensure a low fluid loss compared to comparative copolymers without vinylphosphonic acid.