Methods of Controlled Release pH Adjustment for Oilwell Stimulation

Abstract

A method for treating subterranean formations by the use of delayed release pH control agents in subterranean formations during fracturing operations includes providing a fracturing fluid comprising a base fluid, a viscosifying agent, a pH sensitive crosslinking agent, and a delayed release pH-adjusting material. The delayed release pH-adjusting material includes a pH-adjusting agent and a binder. The fracturing fluid is introduced into a subterranean formation, and the pH of the fracturing fluid is changed through at least partial degradation or disassociation of the delayed release pH-adjusting material, thereby allowing the viscosifying agent to be crosslinked through activation of the pH sensitive crosslinking agent.

1 . A method comprising:
 providing a fracturing fluid comprising: a base fluid, a viscosifying agent, a pH sensitive crosslinking agent, and a delayed release pH-adjusting material, the delayed release pH-adjusting material comprising a pH-adjusting agent and a binder;   placing the fracturing fluid into a subterranean formation;   changing the pH of at least a portion of the fracturing fluid through at least partial degradation or disassociation of the delayed release pH-adjusting material; and   allowing at least a portion of the viscosifying agent to be crosslinked through activation of the pH sensitive crosslinking agent by the change in pH.   
     
     
         2 . The method of  claim 1 , wherein the delayed release pH-adjusting material further comprises an outer coating. 
     
     
         3 . The method of  claim 2 , wherein the outer coating is comprised of a water-insoluble material and the outer coating has a melting point of about 100° F. to about 500° F. 
     
     
         4 . The method of  claim 2 , wherein the outer coating comprises at least one selected from the group consisting of: a polysaccharide; dextran, starch, cellulose, chitin, lipid, latex, wax, chitosan, protein, aliphatic polyester, poly(lactide), poly(glycolide), poly(ε-caprolactone), poly(hydroxybutyrate), poly(anhydride), aliphatic polycarbonate, orthoester, poly(orthoester), poly(amino acid), poly(ethylene oxide) and polyphosphazene, any derivative thereof, any copolymer or blend thereof, and any combination thereof. 
     
     
         5 . The method of  claim 2 , wherein the outer coating is configured to delay the degradation of the delayed release pH-adjusting material until the delayed release pH-adjusting material is in the portion of the subterranean formation to be fractured. 
     
     
         6 . The method of  claim 1 , wherein the pH-adjusting agent is a base. 
     
     
         7 . The method of  claim 6 , wherein the base comprises at least one selected from the group consisting of: a hydroxide, sodium hydroxide, ammonium hydroxide, potassium hydroxide, magnesium hydroxide, a metal alkali salt, an organic base, a hydroxide of an organic base, a methyl amine, tetramethylammonium hydroxide, tetrabutylammonium hydroxide, any derivative thereof, and any combination thereof. 
     
     
         8 . The method of  claim 1 , wherein the binder comprises at least one selected from the group consisting of: silica gel, aluminosilicate, chitosan, starch, sugar, and cellulose, derivatives thereof, and combinations thereof. 
     
     
         9 . The method of  claim 1 , wherein the viscosifying agent comprises at least one selected from the group consisting of: cellulose, modified cellulose, cellulose derivative, methylcellulose, hydroxyethyl cellulose, carboxyethylcellulose, carboxymethylcellulose, carboxymethylhydroxyethylcellulose, polysaccharide, guar gum, hydroxyethyl guar, hydroxypropyl guar, carboxymethyl guar, carboxymethylhydroxyethyl guar, carboxymethylhydroxypropyl guar, locust bean gum, gum ghatti, gum karaya, tamarind gum, tragacanth gum, xanthan, scleroglucan, succinoglycan, diutan, biopolymers, and/or derivatives thereof that contain one or more of these monosaccharide units: galactose, mannose, glucoside, glucose, xylose, arabinose, fructose, glucuronic acid, or pyranosyl sulfate, any derivative thereof, and any copolymer, combination or blend thereof. 
     
     
         10 . The method of  claim 9 , wherein the viscosifying agent comprises guar, and any derivative thereof. 
     
     
         11 . The method of  claim 1 , wherein the delayed release pH-adjusting material has an average particle diameter of about 0.1 mm to 5 mm. 
     
     
         12 . The method of  claim 1 , wherein the fracturing fluid further comprises proppant particulates. 
     
     
         13 . The method of  claim 1 , wherein the base fluid comprises at least one selected from the group consisting of: fresh water, municipal water, wastewater, saltwater, seawater, brine, produced water, and flowback water, any derivative thereof, and any combination thereof. 
     
     
         14 . The method of  claim 12 , wherein the proppant comprises at least one selected from the group consisting of: sand, bauxite, ceramic material, glass material, polymer material, polytetrafluoroethylene material, nut shell piece, seed shell piece, fruit pit piece, cured resinous particulate, wood, and composite particulate, any derivative thereof, and any combination thereof. 
     
     
         15 . A method comprising:
 providing a fracturing fluid comprising: a base fluid, a viscosifying agent, a alkali pH sensitive crosslinking agent, and a delayed release pH-adjusting material, the delayed release pH-adjusting material comprising a basic pH-adjusting agent and a binder;   placing the fracturing fluid into a subterranean formation;   raising the pH of the fracturing fluid through at least partial degradation of the delayed release pH-adjusting material, and   allowing the viscosifying agent to be crosslinked downhole through activation of the pH sensitive crosslinking agent through the raising of the pH.   
     
     
         16 . The method of  claim 15 , wherein the basic pH-adjusting agent comprises at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, magnesium hydroxide, and a metal alkali salt , any derivative thereof, and combination thereof. 
     
     
         17 . The method of  claim 15 , wherein the alkali pH sensitive crosslinking agent comprises at least one selected from the group consisting of aluminum, antimony, chromium, zirconium, magnesium and titanium, any derivative thereof, and combination thereof. 
     
     
         18 . The method of  claim 15 , wherein the delayed release pH-adjusting material further comprises an outer coating. 
     
     
         19 . The method of  claim 18 , wherein the outer coating is comprised of a water-insoluble material and the outer coating has a melting point of about 100° F. to about 500° F. 
     
     
         20 . The method of  claim 18 , wherein the outer coating comprises at least one selected from the group consisting of: a polysaccharide; dextran, starch, cellulose, chitin, lipid, latex, wax, chitosan, protein, aliphatic polyester, poly(lactide), poly(glycolide), poly(ε-caprolactone), poly(hydroxybutyrate), poly(anhydride), aliphatic polycarbonate, orthoester, poly(orthoester), poly(amino acid), poly(ethylene oxide) and polyphosphazene, any derivative thereof, any copolymer or blend thereof, and any combination thereof.