Methods of fracturing subterranean zones, fracturing fluids and breaker activators therefor

Abstract

This invention provides methods of fracturing subterranean zones, fracturing fluids and breaker activators for use in the fracturing fluids. The fracturing fluids are basically comprised of water, a gelling agent, a particulate proppant material, a delayed viscosity breaker and a breaker activator.

1 . A fracturing fluid for fracturing a subterranean zone penetrated by a well bore at temperatures below about 200° F. comprising: 
 water;    a viscosity increasing gelling agent;    a particulate proppant material;    a delayed viscosity breaker for causing said fracturing fluid to revert to a thin fluid; and    a breaker activator comprising a mixture selected from the group consisting of a mixture of cobaltous acetate and the sodium salt of ethylenediaminetetraacetic acid and a mixture of thioglycolic acid and sodium molybdate.    
     
     
         2 . The fracturing fluid of  claim 1  wherein said delayed viscosity breaker comprises one or more members selected from the group consisting of alkali metal and ammonium persulfates, alkali metal chlorites, alkali metal hypochlorites and calcium hypochlorite.  
     
     
         3 . The fracturing fluid of  claim 2  wherein said delayed viscosity breaker is present in said fracturing fluid in an amount in the range of from about 0.003% to about 0.3% by weight of water in said fracturing fluid.  
     
     
         4 . The fracturing fluid of  claim 1  wherein said breaker activator is a mixture of cobaltous acetate and the sodium salt of ethylenediaminetetraacetic acid.  
     
     
         5 . The fracturing fluid of  claim 2  wherein the weight ratio of cobaltous acetate to the sodium salt of ethylenediaminetetraacetic acid in said mixture is in the range of from about 1:0 to about 1:2.  
     
     
         6 . The fracturing fluid of  claim 2  wherein the weight ratio of cobaltous acetate to the sodium salt of ethylenediaminetetraacetic acid in said mixture is about 1:0.5.  
     
     
         7 . The fracturing fluid of  claim 1  wherein said breaker activator is a mixture of thioglycolic acid and sodium molybdate.  
     
     
         8 . The fracturing fluid of  claim 2  wherein the weight ratio of thioglycolic acid to sodium molybdate in said mixture is in the range of from about 1:0 to about 1:4.  
     
     
         9 . The fracturing fluid of  claim 2  wherein the weight ratio of thioglycolic acid to sodium molybdate in said mixture is about 1:2.  
     
     
         10 . The fracturing fluid of  claim 1  wherein said breaker activator is present in said fracturing fluid in an amount in the range of from about 0.003% to about 0.5% by weight of said water in said fracturing fluid.  
     
     
         11 . The fracturing fluid of  claim 1  wherein said water is selected from the group consisting of fresh water and salt water.  
     
     
         12 . The fracturing fluid of  claim 1  wherein said gelling agent comprises one or more members selected from the group consisting of guar and its derivatives, cellulose and its derivatives, xanthan gum and succinoglycon.  
     
     
         13 . The fracturing fluid of  claim 1  wherein said gelling agent comprises one or more members selected from the group consisting of guar, hydroxypropylguar, carboxymethylhydroxypropylguar, hydroxyethylcellulose, carboxymethylhydroxyethylcellulose, carboxymethylcellulose and hydroxyethylcellulose grafted with vinyl phosphonic acid.  
     
     
         14 . The fracturing fluid of  claim 1  wherein said gelling agent is present in said fracturing fluid in an amount in the range of from about 0.17% to about 0.84% by weight of water in said fracturing fluid.  
     
     
         15 . The fracturing fluid of  claim 1  wherein said fracturing fluid further comprises a cross-linking agent selected from the group consisting of borate releasing compounds, a source of titanium ions, a source of zirconium ions, a source of antimony ions and a source of aluminum ions.  
     
     
         16 . The fracturing fluid of  claim 1  wherein said cross-linking agent is included in said fracturing fluid in an amount in the range of from about 0.5% to about 15% by weight of said gelling agent therein.  
     
     
         17 . The fracturing fluid of  claim 1  wherein said particulate proppant material is selected from the group consisting of graded sand, bauxite, ceramic materials, glass materials, walnut hulls, polymer beads and mixtures thereof.  
     
     
         18 . The fracturing fluid of  claim 1  wherein said particulate proppant material is present in said fracturing fluid in an amount in the range of from about 12% to about 239% by weight of water in said fracturing fluid.  
     
     
         19 . A breaker activator for activating delayed alkali metal and ammonium persulfate breakers, alkali metal chlorite breakers, alkali metal hypochlorite breakers and a calcium hypochlorite breaker at temperatures below about 200° F. comprising a mixture selected from the group consisting of a mixture of cobaltous acetate and the sodium salt of ethylenediaminetetraacetic acid and a mixture of thioglycolic acid and sodium molybdate.  
     
     
         20 . The breaker activator of  claim 19  which comprises a mixture of cobaltous acetate and the sodium salt of ethylenediaminetetraacetic acid.  
     
     
         21 . The breaker activator of  claim 20  wherein the weight ratio of cobaltous acetate to the sodium salt of ethylenediaminetetraacetic acid in said mixture is in the range of from about 1:0 to about 1:2.  
     
     
         22 . The breaker activator of  claim 20  wherein the weight ratio of cobaltous acetate to the sodium salt of ethylenediaminetetraacetic acid in said mixture is about 1:0.5.  
     
     
         23 . The breaker activator of  claim 19  which comprises a mixture of thioglycolic acid and sodium molybdate.  
     
     
         24 . The breaker activator of  claim 23  wherein the weight ratio of thioglycolic acid to sodium molybdate in said mixture is in the range of from about 1:0 to about 1:4.  
     
     
         25 . The breaker activator of  claim 23  wherein the weight ratio of thioglycolic acid to sodium molybdate in said mixture is about 1:2.