Degradable Polymers for Hydrocarbon Extraction

Abstract

The present disclosure is directed degradable polymers. The polymers are solid when maintained under substantially dry conditions at a temperature of up to about 90 degrees C. When contacted with water at a temperature of up to about 90 degrees C., however, the polymers initially remain solid for a period of up to about 6 to about 24 hours, then depolymerize to provide a liquid having a viscosity of from about 1 to about 200,000 centipoise after a period of time from about 8 hours to about 3 days and then further depolymerizes to water-soluble components after a period of time at least about 3 days. Also disclosed are sand screen coatings made with the polymers and hydraulic and acid fracturing methods using the polymers.

1 . A method for hydraulic fracturing of a subterranean rock formation adjacent a well borehole, the method comprising the steps of:
 mixing solid pellets with a pumpable fluid, the solid pellets comprising at least one degradable polymer and a proppant dispersed within the degradable polymer;   pumping the fluid and the solid pellets mixed therein down the borehole and into the rock formation;   partially depolymerizing the degradable polymer into a viscous liquid having a viscosity of from about 1 to about 200,000 centipoise;   applying pressure to the viscous liquid within the well borehole sufficient to induce fracturing of the adjacent rock formation and force both the viscous liquid and proppant dispersed therein into the resultant fractures; and   further depolymerizng the viscous liquid into water-soluble components while leaving the proppant disposed with the fractures in the rock formation.   
     
     
         2 . The method of  claim 1 , wherein the at least one degradable polymer is a solid when maintained under substantially dry conditions at a temperature of up to about 90 degrees C., and
 where the degradable polymer, when contacted with water at a temperature of up to about 90 degrees C., initially remains solid for a period of up to about 6 to about 24 hours, then begins to depolymerize to provide a liquid having a viscosity of from about 1 to about 200,000 centipoise after a period of time from about 8 hours to about 3 days and then further depolymerizes to water-soluble components after a period of time at least about 3 days.   
     
     
         3 . The method of  claim 2 , wherein the at least one compound which is capable of reacting with either the first monomer or the second monomer to form an ester is selected from the group consisting of (i) a monofunctional or multifunctional alcohol; (ii) a monofunctional or multifunctional carboxylic acid; (iii) an anhydride that yields a monofunctional or multifunctional carboxylic acid upon reaction of the anhydride; and (iv) a monofunctional or multifunctional epoxide. 
     
     
         4 . The method of  claim 2 , wherein the first monomer is L-lactic acid, the second monomer is glycolic acid and wherein the degradable polymer comprises from about 70 to about 80 mole percent monomer residues of the first monomer and from about 20 to about 30 mole percent monomer residues of the second monomer. 
     
     
         5 . The method of  claim 2 , wherein the first monomer is L-lactic acid, the second monomer is D-lactic acid and wherein the degradable polymer comprises from about 70 to about 80 mole percent monomer residues of the first monomer and from about 20 to about 30 mole percent monomer residues of the second monomer. 
     
     
         6 . The method of  claim 2 , wherein the first monomer is L-lactide, the second monomer is D-lactide and wherein the degradable polymer comprises from about 50 to about 99.5 mole percent monomer residues of the first monomer and from about 0.5 to about 50 mole percent monomer residues of the second monomer. 
     
     
         7 . The method of  claim 2 , wherein the composition further comprises up to about 5 weight percent of polylactic acid having a number average molecular weight of greater than about 25,000. 
     
     
         8 . The method of  claim 2 , wherein the at least one compound which is capable of reacting with either the first monomer or the second monomer to form an ester is selected from the group consisting of (i) a monofunctional or multifunctional alcohol having from 1 to 16 hydroxyl groups; (ii) a monofunctional or multifunctional carboxylic acid having from 1 to 16 carboxylic acid groups; (iii) and an anhydride that yields a monofunctional or multifunctional carboxylic acid having from 2 to 16 carboxylic acid groups upon reaction of the anhydride. 
     
     
         9 . The method of  claim 2 , wherein the at least one compound which is capable of reacting with either the first monomer or the second monomer to form an ester comprises a multifunctional alcohol selected from the group consisting of pentaerythritol, glycerine, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, trimethyolpropane, dendritic polyols having up to 16 hydroxyl groups, dipentaerythritol, and mixtures thereof. 
     
     
         10 . The method of  claim 2 , wherein the at least one compound which is capable of reacting with either the first monomer or the second monomer to form an ester comprises a polymer. 
     
     
         11 . The method of  claim 2 , wherein the at least one compound which is capable of reacting with either the first monomer or the second monomer to form an ester comprises a polyvinyl alcohol. 
     
     
         12 . The method of  claim 2 , wherein the at least one compound which is capable of reacting with either the first monomer or the second monomer to form an ester comprises a polyacrylic acid. 
     
     
         13 . The method of  claim 2 , wherein the at least one compound which is capable of reacting with either the first monomer or the second monomer to form an ester comprises pentaerythritol. 
     
     
         14 . The method of  claim 2 , wherein the at least one compound which is capable of reacting with either the first monomer or the second monomer to form an ester comprises a multifunctional carboxylic acid selected from the group consisting of adipic acid, succinic acid, sebacic acid, and mixtures thereof. 
     
     
         15 . The method of  claim 2 , wherein the at least one compound which is capable of reacting with either the first monomer or the second monomer to form an ester comprises a cyclic anhydride that yields a multifunctional carboxylic acid selected from the group consisting of trimellitic anhydride, pyromellitic anhydride, and mixtures thereof. 
     
     
         16 . The method of  claim 2 , wherein the degradable copolymer has a number average molecular weight of from about 3000 to about 22,000. 
     
     
         17 . The method of  claim 2 , wherein the degradable copolymer has a polydispersity index of from about 1.0 up to about 3.0.