Methods and compositions for sealing subterranean zones

Abstract

Methods and compositions for sealing subterranean zones having temperatures in the range of from about 80° F. to about 300° F. are provided. A method of the invention is basically comprised of the steps of providing a subterranean zone sealing composition that becomes substantially rigid when exposed to subterranean zone temperatures above about 80° F. and has a pH above about 8.5 comprised of water, a substantially fully hydrated depolymerized polymer and a cross-linking agent. The sealing composition is introduced into the subterranean zone whereby it becomes rigid and seals the zone. The sealing composition can subsequently be removed by contact with a fluid having a pH below about 8 when a boron compound is utilized as the cross-linking agent.

1 . A subterranean zone sealing composition that becomes rigid when exposed to subterranean zone temperatures above about 80° F., that has a pH above about 8.5 and that can be removed by contact with a fluid having a pH below about 8 comprising: 
 water;    a substantially fully hydrated depolymerized polymer; and    a cross-linking agent comprising a boron compound for said polymer.    
     
     
         2 . The sealing composition of  claim 1  wherein said water is selected from the group consisting of fresh water and salt water.  
     
     
         3 . The sealing composition of  claim 1  wherein said water is present in said sealing composition in an amount in the range of from about 97% to about 99% by weight of said composition.  
     
     
         4 . The sealing composition of  claim 1  wherein said substantially fully hydrated depolymerized polymer is a substantially fully hydrated depolymerized guar or cellulose derivative polymer selected from the group consisting of hydroxypropylguar, carboxymethylhydroxypropylguar, carboxymethylguar, hydroxyethylguar, carboxymethylhydroxyethylguar, hydroxyethylcellulose, grafted hydroxyethylcellulose, carboxymethylcellulose and carboxymethylhydroxyethylcellulose.  
     
     
         5 . The sealing composition of  claim 1  wherein said substantially fully hydrated depolymerized polymer is substantially fully hydrated depolymerized hydroxypropylguar.  
     
     
         6 . The sealing composition of  claim 1  wherein said substantially fully hydrated depolymerized polymer is present in said sealing composition in an amount in the range of from about 0.5% to about 2% by weight of said composition.  
     
     
         7 . The sealing composition of  claim 1  wherein said cross-linking agent is selected from the group consisting of dehydrated boric acid and dehydrated sodium tetraborate.  
     
     
         8 . The sealing composition of  claim 1  wherein said cross-linking agent is dehydrated sodium tetraborate.  
     
     
         9 . The sealing composition of  claim 1  wherein said cross-linking agent is present in said sealing composition in an amount in the range of from about 0.025% to about 0.1% by weight of said composition.  
     
     
         10 . The sealing composition of  claim 1  wherein said sealing composition further comprises a pH adjusting compound.  
     
     
         11 . The sealing composition of  claim 10  wherein said pH adjusting compound is selected from the group consisting of sodium hydroxide, lithium hydroxide, fumaric acid, formic acid, acetic acid, acetic anhydride and hydrochloric acid.  
     
     
         12 . The sealing composition of  claim 10  wherein said pH adjusting compound is present in said sealing composition in an amount in the range of from about 0.05% to about 5% by weight of said composition.  
     
     
         13 . The sealing composition of  claim 1  wherein said sealing composition further comprises a buffer.  
     
     
         14 . The sealing composition of  claim 12  wherein said buffer is selected from the group consisting of sodium carbonate, sodium bicarbonate, potassium bicarbonate, sodium diacetate, potassium diacetate, sodium phosphate, potassium phosphate, sodium dihydrogen phosphate and potassium dihydrogen phosphate.  
     
     
         15 . The sealing composition of  claim 12  wherein said buffer is present in said sealing composition in an amount in the range of from about 0.05% to about 15% by weight of said composition.  
     
     
         16 . The sealing composition of  claim 1  wherein said sealing composition further comprises a surfactant to prevent emulsions.  
     
     
         17 . The sealing composition of  claim 16  wherein said surfactant is selected from the group consisting of alkyl sulfonates, alkyl aryl sulfonates, dodecylbenzene sulfonic acid, alkyl trimethylammonium chloride, branched alkyl ethoxylated alcohols, phenol-formaldehyde nonionic resin blends, cocobetaines, dioctyl sodium sulfosuccinate, imidazolines, alpha olefin sulfonates, linear alkyl ethoxylated alcohols and trialkyl benzylammonium chloride.  
     
     
         18 . The sealing composition of  claim 16  wherein said surfactant is present in said sealing composition in an amount in the range of from about 0.01% to about 1% by weight of said composition.  
     
     
         19 . The sealing composition of  claim 1  wherein said sealing composition further comprises a clay stabilizer.  
     
     
         20 . The sealing composition of  claim 19  wherein said clay stabilizer is selected from the group consisting of potassium chloride, sodium chloride, ammonium chloride and tetramethyl ammonium chloride.  
     
     
         21 . The sealing composition of  claim 19  wherein said clay stabilizer is present in said sealing composition in an amount in the range of from about 2% to about 20% by weight of said composition.