Hydraulic fracturing methods using cross-linking composition comprising delay agent

Abstract

A method for hydraulically fracturing a subterranean formation comprises introducing into the formation a cross-linking composition which comprises (a) an aqueous liquid, (b) a pH buffer, (c) a cross-linkable organic polymer, (d) a cross-linking agent which comprises an organic titanate, an organic zirconate, or combinations thereof, and (e) a delay agent which is a hydroxyalkylaminocarboxylic acid. The method can be used over a wide range of pH conditions.

1 . A method for fracturing a subterranean formation which comprises introducing into said formation a cross-linking composition at a flow rate and pressure sufficient to create, reopen and/or extend a fracture in said formation, wherein said composition comprises (a) an aqueous liquid, (b) a pH buffer, (c) a cross-linkable organic polymer, (d) a cross-linking agent which comprises an organic titanate, an organic zirconate, or combinations thereof, and (e) a delay agent which is a hydroxyalkylaminocarboxylic acid.  
   
   
       2 . The method of  claim 1  wherein the cross-linkable organic polymer is a solvatable polysaccharide selected from gums, gum derivatives, and cellulose derivatives.  
   
   
       3 . The method of  claim 2  wherein the delay agent is selected from the group consisting of bishydroxyethylglycine, bishydroxymethylglycine, bishydroxypropylglycine, bishydroxyisopropylglycine, bishydroxybutylglycine, monohydroxyethylglycine, monohydroxymethylglycine and their alkali metal salts.  
   
   
       4 . The method of  claim 3  wherein the delay agent is bishydroxyethylglycine.  
   
   
       5 . The method of  claim 3  wherein the cross-linking agent is an organic zirconium complex selected from the group consisting of zirconium α-hydroxycarboxylic acid salt, zirconium polyol complexes, zirconium alkanol amine complexes, zirconium hydroxyalkylated alkylenediamine complexes, and combinations thereof.  
   
   
       6 . The method of  claim 3  wherein the cross-linking agent is an organic titanium complex selected from the group consisting of titanium α-hydroxycarboxylic acid salt, titanium polyol complexes, titanium alkanol amine complexes, and combinations thereof.  
   
   
       7 . A method for fracturing a subterranean formation which comprises 
 (a) preparing a base gel by mixing an aqueous liquid with a cross-linkable organic polymer;    (b) preparing a delayed cross-linking composition by mixing a cross-linking agent which comprises an organic titanate, an organic zirconate, or combinations thereof with a delay agent which is a hydroxyalkylaminocarboxylic acid;    wherein a pH buffer is added to the base gel, the delayed cross-linking composition or both;    (c) contacting the base gel with the delayed cross-linking composition;    (d) permitting the base gel and the cross-linking agent to react after a controllable amount of time to form a cross-linked aqueous gel; and    (e) introducing the cross-linked gel into the formation at a flow rate and pressure sufficient to create, reopen, and/or extend a fracture in the formation.    
   
   
       8 . The method of  claim 7  wherein the subterranean formation is penetrated by a wellbore and wherein said contacting step (c) occurs in the wellbore.  
   
   
       9 . The method of  claim 8  wherein the delay agent is bishydroxyethylglycine.  
   
   
       10 . The method of  claim 9  wherein the cross-linking agent is an organic zirconium complex selected from the group consisting of zirconium α-hydroxycarboxylic acid salt, zirconium polyol complexes, zirconium alkanol amine complexes, zirconium hydroxyalkylated alkylenediamine complexes, and combinations thereof.  
   
   
       11 . The method of  claim 9  wherein the cross-linking agent is an organic titanium complex selected from the group consisting of titanium α-hydroxycarboxylic acid salt, titanium polyol complexes, titanium alkanol amine complexes, and combinations thereof.  
   
   
       12 . A method for fracturing a subterranean formation which comprises: 
 (a) preparing a base gel by mixing an aqueous liquid with a cross-linkable organic polymer and a delay agent which is a hydroxyalkylaminocarboxylic acid;    (b) contacting the base gel with a cross-linking agent which comprises an organic titanate, an organic zirconate, or combinations thereof;    wherein a pH buffer is admixed with the base gel, the cross-linking agent or both, prior to contacting;    (c) permitting the base gel and the cross-linking agent to react after a controllable amount of time to form a cross-linked aqueous gel; and    (d) introducing the cross-linked gel into the formation at a flow rate and pressure sufficient to create, reopen, and/or extend a fracture in the formation.    
   
   
       13 . The method of  claim 12  wherein the subterranean formation is penetrated by a wellbore and wherein said contacting step (b) occurs in the wellbore.  
   
   
       14 . The method of  claim 13  wherein the delay agent is bishydroxyethylglycine.  
   
   
       15 . The method of  claim 14  wherein the cross-linking agent is an organic zirconium complex selected from the group consisting of zirconium α-hydroxycarboxylic acid salt, zirconium polyol complexes, zirconium alkanol amine complexes, zirconium hydroxyalkylated alkylenediamine complexes, and combinations thereof.  
   
   
       16 . The method of  claim 14  wherein the cross-linking agent is an organic titanium complex selected from the group consisting of titanium α-hydroxycarboxylic acid salt, titanium polyol complexes, titanium alkanol amine complexes, and combinations thereof.  
   
   
       17 . A method for hydraulically fracturing a subterranean formation penetrated by a wellbore which comprises: 
 (a) preparing a base gel by mixing an aqueous liquid with a cross-linkable polymer;    (b) introducing the base gel into the wellbore;    (c) simultaneously with or sequentially after, introducing the base gel into the wellbore, introducing a cross-linking agent which comprises an organic titanate, an organic zirconate, or combinations thereof into the wellbore;    wherein a pH buffer and a delay agent which is a hydroxyalkylaminocarboxylic acid are independently admixed with the base gel, the cross-linking agent or both prior to introducing the base gel and the cross-linking agent into the wellbore;    (d) permitting the base gel and the cross-linking agent to react after a controllable period of time to form a cross-linked aqueous gel; and    (e) introducing the cross-linked gel into the formation from the wellbore at a flow rate and pressure sufficient to create, reopen, and/or extend a fracture in the formation.    
   
   
       18 . The method of  claim 17  wherein the delay agent is bishydroxyethylglycine.  
   
   
       19 . The method of  claim 18  wherein the cross-linking agent is an organic zirconium complex selected from the group consisting of zirconium α-hydroxycarboxylic acid salt, zirconium polyol complexes, zirconium alkanol amine complexes, zirconium hydroxyalkylated alkylenediamine complexes, and combinations thereof.  
   
   
       20 . The method of  claim 18  wherein the cross-linking agent is an organic titanium complex selected from the group consisting of titanium α-hydroxycarboxylic acid salt, titanium polyol complexes, titanium alkanol amine complexes, and combinations thereof.  
   
   
       21 . The method of  claim 1 ,  7 ,  12 , or  17  further comprising introducing a cross-linking composition comprising (a) an aqueous liquid, (b) a pH buffer, (c) a cross-linkable organic polymer, (d) a cross-linking agent which comprises an organic titanate, an organic zirconate, or combinations thereof, (e) a delay agent which is a hydroxyalkylaminocarboxylic acid and (f) proppant, into the fracture.