Recyclable foamed fracturing fluids and methods of using the same

Abstract

Fracturing fluids and methods of fracturing a subterranean formation using such fluids are provided. A fracturing fluid having a first pH is foamed by introducing a gas to the fluid. The fracturing fluid comprises a surfactant that facilitates formation of the foam at the first pH. The foamed fracturing fluid is subsequently pumped to the subterranean formation to fracture it. The pH of the fracturing fluid is then changed to a second pH at which the surfactant facilitates reduction of the foam. The fracturing fluid releases proppant contained in the fluid to the subterranean formation. The fracturing fluid is then allowed to flow back to the surface. It can be recycled by changing the pH of the fracturing fluid back to the first pH and adding a gas to the fluid, causing it to foam again.

1 . A foamed fracturing fluid, comprising: water; proppant; a gas dispersed in the water; and a tertiary alkyl amine ethoxylate for facilitating the formation of foam at a basic pH and facilitating the reduction of foam at an acidic pH, wherein the foamed fracturing fluid has the basic pH, wherein the tertiary alkyl amine ethoxylate is represented by the following formula:  
       
         
           
           
               
               
           
         
       
       wherein R is an alkyl group, X is from about 2 to about 15, and Y is from about 2 to about 15.  
     
     
         2 . The foamed fracturing fluid of  claim 1 , wherein X is from about 10 to about 15, and Y is from about 10 to about 15.  
     
     
         3 . The foamed fracturing fluid of  claim 1 , wherein the basic pH is greater than about 9, and the acidic pH is less than about 6.  
     
     
         4 . The foamed fracturing fluid of  claim 1 , wherein the fracturing fluid comprises a gelling agent.  
     
     
         5 . The foamed fracturing fluid of  claim 1 , wherein the foamed fracturing fluid comprises a delayed release acid in an amount sufficient to lower the pH of the foamed fracturing fluid from the basic pH to less than about 6 when acid is released.  
     
     
         6 . The foamed fracturing fluid of  claim 5 , wherein the delayed release acid is selected from the group consisting of an encapsulated acid and an acid producing compound.  
     
     
         7 . The foamed fracturing fluid of  claim 1 , wherein the delayed release acid comprises a compound selected from the group consisting of an encapsulated formic acid, an encapsulated citric acid, an encapsulated fumaric acid, an encapsulated mineral acid, an ethyl acetate, and an ethyl formate.  
     
     
         8 . A foamed fracturing fluid, comprising: water; proppant; a gas dispersed in the water; a base in an amount sufficient to provide the foamed fracturing fluid with a basic pH; a delayed-release acid in an amount sufficient to lower the pH of the foamed fracturing fluid from the basic pH to an acidic pH when acid is released; and a surfactant mixture for facilitating the formation of foam at the basic pH and facilitating the reduction of foam at the acidic pH, the surfactant mixture comprising an amphoteric surfactant and an anionic surfactant.  
     
     
         9 . The foamed fracturing fluid of  claim 8 , wherein the amphoteric compound comprises at least one surfactant selected from the group consisting of a lauryl amine oxide, a myristyl amine oxide, a cocoamine oxide, a lauryl betaine, and an oleyl betaine.  
     
     
         10 . The foamed fracturing fluid of  claim 8 , wherein the anionic surfactant comprises at least one surfactant selected from the group consisting of a C 4-12  alcohol ether sulfate, an α-olefin sulfonate, a sulfonated C 15  alcohol substituted with ethylene oxide, a sodium laureth-2-sulfate, and a laureth-3-sulfate.  
     
     
         11 . The foamed fracturing fluid of  claim 8 , wherein the anionic surfactant comprises a sulfonated C 15  alcohol substituted with from about 12 to about 40 moles of ethylene oxide.  
     
     
         12 . The foamed fracturing fluid of  claim 8 , wherein the amphoteric surfactant is present in the surfactant mixture in an amount in the range of from about 32% to about 45% by weight of the surfactant mixture, and the anionic surfactant is present in the surfactant mixture in an amount in the range of from about 55% to about 68% by weight of the surfactant mixture.  
     
     
         13 . The foamed fracturing fluid of  claim 8 , wherein basic pH is greater than about 9, and the acidic pH is less than about 6.  
     
     
         14 . The foamed fracturing fluid of  claim 8 , wherein the delayed release acid is selected from the group consisting of an encapsulated acid and an acid producing compound.  
     
     
         15 . The foamed fracturing fluid if  claim 8 , wherein the delayed release acid comprises a compound selected from the group consisting of an encapsulated formic acid, an encapsulated citric acid, an encapsulated fumaric acid, an encapsulated mineral acid, an ethyl acetate, and an ethyl formate.  
     
     
         16 . The foamed fracturing fluid of  claim 8 , wherein the fracturing fluid comprises a gelling agent.  
     
     
         17 . The foamed fracturing fluid of  claim 8 , wherein the fracturing fluid comprises a bacteriacide.  
     
     
         18 . A foamed fracturing fluid, comprising: water; proppant; a gas dispersed in the water; an acid in an amount sufficient to provide the foamed fracturing fluid with a pH of less than about 6; a delayed release base in an amount sufficient to raise the pH of the foamed fracturing fluid from the pH of below about 6 to a basic pH; and a surfactant mixture for facilitating the formation of foam at the pH of below about 6 and facilitating the reduction of foam at the basic pH, the surfactant mixture comprising an amphoteric surfactant and a cationic surfactant.  
     
     
         19 . The foamed fracturing fluid of  claim 18 , wherein the cationic compound comprises at least one surfactant selected from the group consisting of cocoalkyltriethyl ammonium chloride and hexadecyltrimethyl ammonium chloride.  
     
     
         20 . The foamed fracturing fluid of  claim 18 , wherein the amphoteric compound comprises at least one surfactant selected from the group consisting of a lauryl amine oxide, a myristyl amine oxide, a cocoamine oxide, a lauryl betaine, and an oleyl betaine.  
     
     
         21 . The foamed fracturing fluid of  claim 18 , wherein the amphoteric surfactant is present in the surfactant mixture in an amount in the range of from about 30% to about 40% by weight of the surfactant mixture, and the cationic surfactant is present in the surfactant mixture in an amount in the range of from about 60% to about 70% by weight of the surfactant mixture.  
     
     
         22 . The foamed fracturing fluid of  claim 18 , wherein the basic pH is greater than about 9.  
     
     
         23 . The foamed fracturing fluid of  claim 18 , wherein the foamed fracturing fluid comprises a gelling agent.  
     
     
         24 . The foamed fracturing fluid of  claim 18 , wherein the foamed fracturing fluid comprises a bacteriacide.  
     
     
         25 . The foamed fracturing fluid of  claim 18 , wherein the acid is selected from the group consisting of an acetic acid, a formic acid, and a mineral acid.  
     
     
         26 . The foamed fracturing fluid of  claim 18 , wherein the delayed release base is selected from the group consisting of an encapsulated base and a base producing compound.