Self-degrading ionically cross-linked biopolymer composition for well treatment

Abstract

A method of treating a well including the steps of: (A) forming a treatment fluid comprising: (i) water; (ii) a water-soluble β-polysaccharide selected from the group consisting of a β-galactomannan, a water-soluble derivative thereof retaining β-O-glycosidic linkages and a mannose:galactose of at least 5:1; and any combination thereof; (iii) a borate cross-linker; (iv) a base to adjust the pH of the water in the treatment fluid to be at least 8.5; and (v) a water-soluble α-polysaccharide or water-soluble derivative thereof retaining α-O-glycosidic linkages; and (B) introducing the treatment fluid into the well.

What is claimed is: 
     
         1 . A method of treating a well, the method comprising the steps of:
 (A) forming a treatment fluid comprising:
 (i) water; 
 (ii) a water-soluble β-polysaccharide selected from the group consisting of a β-galactomannan, a water-soluble derivative thereof retaining β-O-glycosidic linkages and a mannose:galactose of at least  5 : 1 ; and any combination thereof; 
 (iii) a borate cross-linker; 
 (iv) a base to adjust the pH of the water in the treatment fluid to be at least 8.5; and 
 (v) a water-soluble α-polysaccharide or water-soluble derivative thereof retaining α-O-glycosidic linkages; and 
   (B) introducing the treatment fluid into the well.   
     
     
         2 . The method according to  claim 1 , wherein the β-polysaccharide is selected from the group consisting of guar, a guar derivative, and any combination thereof. 
     
     
         3 . The method according to  claim 2 , wherein the guar derivative is selected from the group consisting of: a carboxyalkyl derivative of guar, a hydroxyalkyl derivative of guar, and any combination thereof. 
     
     
         4 . The method according to  claim 1 , wherein the borate cross-linker is selected from the group consisting of: boric acid, boric acid anhydride, a borate, and any combination thereof. 
     
     
         5 . The method according to  claim 4 , wherein the borate is water soluble. 
     
     
         6 . The method according to  claim 4 , wherein the borate is selected from the group consisting of: an alkali metal borate. 
     
     
         7 . The method according to  claim 1 , wherein the water in the treatment fluid is not buffered to maintain the pH in any pH range above 8.5. 
     
     
         8 . The method according to  claim 1 , wherein the treatment fluid does not include a strong base or water-soluble carbonate. 
     
     
         9 . The method according to  claim 1 , wherein the α-polysaccharide comprises a partially hydrolyzed starch. 
     
     
         10 . The method according to  claim 1 , wherein the concentration of the α-polysaccharide or derivative thereof in the water is at least sufficient to produce in-situ via hydrolysis at least a sufficient concentration of H+ to reverse the borate cross-linking of the β-polysaccharide. 
     
     
         11 . The method according to  claim 10 , wherein the concentration of the α-polysaccharide or derivative thereof in the water is at least sufficient to produce in-situ via hydrolysis at least a sufficient concentration of H+ to degrade the β-polysaccharide via hydrolysis of the β-O-glycosidic l linkages. 
     
     
         12 . The method according to  claim 1 , wherein the treatment fluid additionally comprises an alginate. 
     
     
         13 . The method according to  claim 1 , wherein the treatment fluid is substantially free of any solid particulate larger than 400 US mesh. 
     
     
         14 . The method according to  claim 1 , wherein the treatment fluid has a viscosity at the time of introducing or develops a viscosity in the well that is greater than 10 cP. 
     
     
         15 . The method according to  claim 14 , wherein the step of introducing into the well is at a design temperature that is less than 120° C. 
     
     
         16 . The method according to  claim 15 , wherein the treatment fluid has less than a sufficient concentration of a non-polysaccharide breaker to break the viscosity of the treatment fluid at the design temperature in the absence of the α-polysaccharide. 
     
     
         17 . The method according to  claim 16 , wherein the treatment fluid is essentially free of any non-polysaccharide breaker. 
     
     
         18 . The method according to  claim 16 , wherein the non-polysaccharide breaker is selected from the group consisting of: (a) an acid having a pKa(1) less than 5, (b) an oxidizer, (c) an enzyme, or any combination thereof. 
     
     
         19 . The method according to  claim 15 , wherein the treatment zone is not over flushed before flowing back fluid from the treatment zone with a second treatment fluid that comprises a sufficient concentration of a non-polysaccharide breaker to break the viscosity of the treatment fluid in the treatment zone. 
     
     
         20 . The method according to  claim 1 , wherein treatment fluid is allowed to break in a treatment zone of the well before flowing back fluid from the treatment zone.