Modification of solid polysaccharide with transesterification agent

Abstract

Polysaccharides, for example xanthan, diutan, scleroglucan, gums, celluloses, and starches, and derivatives of the foregoing, are reacted with organic carbonates forming products that: (1) have increased viscosifying efficiency, i.e., higher viscosities at reduced concentrations compared to the unmodified polysaccharide; or (2) are insolubilized at temperature ranges for which the unmodified polysaccharide would hydrate fully; or (3) both properties. In some cases, the insolubilized polysaccharides can be activated to dissolve and viscosify at specific temperature ranges by using pH modifiers. A method of treating a well is provided, including the steps of: (a) obtaining a modified polysaccharide characterized by having been made by the process of combining: (i) a water-soluble polysaccharide, wherein the polysaccharide is in a solid form during the combining step; and (ii) a transesterification agent, wherein the transesterification agent is in liquid form; wherein the step of combining is in the presence of less than 10% by weight water relative to the water-soluble polysaccharide and wherein any water present is at a pH of 8 or less; (b) forming a treatment fluid comprising the modified polysaccharide and water; and (c) introducing the treatment fluid into the well.

1 . A method of treating a well, wherein the method comprises the steps of:
 (a) obtaining a modified polysaccharide characterized by having been made by the process of chemically combining:
 (i) a water-soluble polysaccharide, wherein the polysaccharide is in a solid form during the combining step; and 
 (ii) a transesterification agent, wherein the transesterification agent is in liquid form during the combining step; 
 wherein the step of chemically combining is under substantially dry conditions; 
   (b) forming a treatment fluid comprising the modified polysaccharide and water; and   (c) introducing the treatment fluid into the well.   
     
     
         2 . The method according to  claim 1 , wherein the water-soluble polysaccharide is selected from the group consisting of xanthan, diutan, scleroglucan, and any combination thereof. 
     
     
         3 . The method according to  claim 1 , wherein the water-soluble polysaccharide is selected from the group consisting of guar, a guar derivative, cellulose, a cellulose derivative, starch, a starch derivative, and any combination thereof. 
     
     
         4 . The method according to  claim 3 , 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. 
     
     
         5 . The method according to  claim 3 , wherein the guar derivative is selected from the group consisting of carboxymethylguar, carboxymethylhydroxyethylguar, hydroxyethylguar, carboxymethylhydroxypropylguar, ethylcarboxymethylguar, and hydroxypropylmethylguar. 
     
     
         6 . The method according to  claim 3 , wherein the cellulose derivative is selected from the group consisting of a carboxyalkyl derivative of cellulose, a hydroxyalkyl derivative of cellulose, and any combination thereof. 
     
     
         7 . The method according to  claim 6 , wherein the cellulose derivative is selected from the group consisting of carboxymethylcellulose, carboxymethylhydroxyethylcellulose, hydroxyethylcellulose, methylhydroxypropylcellulose, methylcellulose, ethylcellulose, ethylcarboxymethylcellulose, hydroxypropylmethylcellulose, and any combination thereof. 
     
     
         8 . The method according to  claim 1 , wherein the transesterification agent is an organic carbonate. 
     
     
         9 . The method according to  claim 8 , wherein the organic carbonate is selected from the group consisting of ethylene carbonate, propylene carbonate, glycerine carbonate, butylene carbonate, diethyl carbonate, and any combination thereof. 
     
     
         10 . The method according to  claim 1 , wherein during the step of combining, includes heating within a temperature range from about 40° C. to about 160° C. 
     
     
         11 . The method according to  claim 1 , wherein the step of combining is in the presence of less than 5% by weight water relative to the water-soluble polysaccharide. 
     
     
         12 . The method according to  claim 1 , wherein the modified polysaccharide is further characterized as having an increased average molecular weight relative to the water-soluble polysaccharide. 
     
     
         13 . The method according to  claim 1 , wherein the modified polysaccharide is further characterized as having a slower hydration rate or increased hydration temperature relative to the water-soluble polysaccharide under pH of less than 8. 
     
     
         14 . The method according to  claim 1 , wherein the modified polysaccharide is further characterized as having a slower hydration rate or increased hydration temperature relative to the water-soluble polysaccharide under pH of less than 8, but the hydration rate can be increased or the hydration temperature can be decreased by adjusting the pH to be greater than 9. 
     
     
         15 . The method according to  claim 1 , further comprising the step of: before, during, or after the step of introducing, adjusting the pH of the treatment fluid to be greater than 9. 
     
     
         16 . The method according to  claim 1 , further comprising the step of flowing back fluid from the well. 
     
     
         17 . The method according to  claim 1 , wherein the step of forming the treatment fluid comprises forming a treatment fluid having a concentration of the modified polysaccharide in the range of from about 0.02% to about 15% by weight of the aqueous treatment fluid. 
     
     
         18 . The method according to  claim 1 , wherein the step of forming the treatment fluid comprises forming a treatment fluid having at least a sufficient concentration of the modified polysaccharide to be capable of forming a cross-linked gel with the addition of a cross-linking agent, wherein the treatment fluid is used as a suspending fluid for a particulate. 
     
     
         19 . The method according to  claim 1 , wherein the step of forming the treatment fluid comprises forming a treatment fluid having less than a sufficient concentration of the modified polysaccharide to be capable of forming a cross-linked gel, whereby the treatment fluid is used as a friction reducing fluid. 
     
     
         20 . The method according to  claim 1 , wherein the step of forming the treatment fluid comprises forming a treatment fluid comprising at least 2% by weight of an inorganic ionic salt. 
     
     
         21 . The method according to  claim 1 , wherein the step of forming the treatment fluid comprises forming a treatment fluid having at least one additive selected from the group consisting of: a surfactant, an anti-scaling agent, a crosslinker, corrosion inhibitor, and a breaker. 
     
     
         22 . The method according to  claim 1 , wherein the aqueous treatment fluid is introduced into the subterranean formation at or above a pressure sufficient to create at least one fracture in the formation. 
     
     
         23 . The method according to  claim 1 , wherein the treatment fluid is a drilling fluid, a spacer fluid, a gravel packing fluid, or a completion fluid. 
     
     
         24 . A method of treating a well, wherein the method comprises the steps of:
 (a) chemically combining:
 (i) a water-soluble polysaccharide, wherein the polysaccharide is in a solid form; and 
 (ii) a transesterification agent, wherein the transesterification agent is in liquid form during the combining step; 
 wherein the step of chemically combining is under substantially dry conditions; 
   (b) forming a treatment fluid comprising the modified polysaccharide and water; and   (c) introducing the treatment fluid into the well.