Viscous fluid applicable for treating subterranean formations

Abstract

A viscous fluid is shown which is useful in treating subterranean formations. The fluid is formulated from an aqueous base, an alkyl sarcosinate surfactant and a buffer suitable for adjusting the pH of the blended fluid to a range in which the fluid is suitably viscosified. The fluid can also include an additional source of anions, such as chloride or fluoride ions, in order to increase the temperature stability of the fluid. The fluids have application for conventional well fracturing, coiled tubing fracturing, gravel packing and frac packing, as well as for use as selective water control additives and other applications.

We claim:  
     
         1 . A viscous fluid for use in well bore operations, the fluid comprising: 
 an aqueous base;    a surfactant comprising an alkyl sarcosinate having from 12 to 24 carbon atoms;    a buffer for adjusting the pH of the combined aqueous base and surfactant above about 6.5.    
     
     
         2 . The viscous fluid of  claim 1 , wherein the alkyl sarcosinate is present in the range from about 0.5 to 10% by weight, based upon the weight of the total fluid.  
     
     
         3 . The viscous fluid of  claim 1 , wherein the pH of the viscous fluid is in the range from about 6.5 to 10.0.  
     
     
         4 . A viscous fluid for use in well bore operations, the fluid comprising: 
 an aqueous base;    a surfactant comprising an alkyl sarcosinate having from 12 to 24 carbon atoms;    an additional source of anions;    a buffer for adjusting the pH of the combined aqueous base, source of anions and surfactant above about 6.5.    
     
     
         5 . The viscous fluid of  claim 4 , wherein the source of anions is a carboxylic acid salt present in the range from about 0.1 to 2% by weight, based upon the weight of the total fluid.  
     
     
         6 . The viscous fluid of  claim 4 , wherein the additional source of anions is a chloride salt present in the range from about 0.5 to 15% by weight, based upon the weight of the total fluid.  
     
     
         7 . The viscous fluid of  claim 2 , wherein the carboxylic acid salt is selected from the group consisting of monovalent acetates, divalent fumerates, trivalent citrates and tetravalent EDTA.  
     
     
         8 . A viscous fluid for transporting particulate through a conduit to a subterranean location, the fluid comprising: 
 an aqueous base;    a source of fluoride ions;    a surfactant comprising an alkyl sarcosinate having an alkyl group with 12 to 24 carbon atoms.    
     
     
         9 . The viscous fluid of  claim 8 , wherein the source of fluoride ions is a fluoride salt or acid compound present in the range from about 0.5 to 10% by weight, based upon the weight of the total fluid.  
     
     
         10 . The viscous fluid of  claim 7 , wherein the viscous fluid contains a buffer to adjust the pH of the resulting viscous fluid within the range from about 6.5 to 10.  
     
     
         11 . The viscous fluid of  claim 7 , wherein the alkyl sarcosinate is present in the range from about 0.5 to 10% by weight, based upon the weight of the total fluid.  
     
     
         12 . The viscous fluid of  claim 7 , further comprising: 
 an additional source of anions.    
     
     
         13 . The viscous fluid of  claim 12 , wherein the source of anions is a carboxylic acid salt present in the range from about 0.1 to 2% by weight, based upon the weight of the total fluid.  
     
     
         14 . The viscous fluid of  claim 13 , wherein the carboxylic acid salt is selected from the group consisting of monovalent acetates, divalent fumerates, trivalent citrates and tetravalent EDTA.  
     
     
         15 . A viscous fluid for transporting particulate through a conduit to a subterranean location, the fluid comprising: 
 an aqueous base;    a surfactant having the structural formula:                        wherein R 1  is a fatty acid hydrocarbon chain having from 12 to 24 carbon atoms, R 2  is selected from the group consisting of hydrogen, methyl, propyl, butyl and ethyl and X is selected from the group consisting of carboxyl and sulfonyl; and      a buffer for adjusting the pH of the combined aqueous base and surfactant above about 6.5.    
     
     
         16 . A method of fracturing a subterranean formation, the method comprising the steps of: 
 combining an aqueous base fluid with a surfactant comprising an alkyl sarcosinate having from 12 to 24 carbon atoms;    buffering the combined fluid with a buffer to thereby adjust the pH of the combined aqueous base and surfactant above about 6.5, thereby creating a viscous fluid capable of supporting proppant;    pumping the viscous fluid through a wellbore and into a surrounding formation at a pressure sufficient to fracture the formation.    
     
     
         17 . The method of  claim 16 , further comprising the steps of: 
 allowing the viscous fluid to contact the formation for a period of time sufficient to break the fluid viscosity without the use of additional breaker materials.    
     
     
         18 . A method of fracturing a subterranean formation, the method comprising the steps of: 
 combining an aqueous base fluid with a surfactant comprising an alkyl sarcosinate having from 12 to 24 carbon atoms;    adding a source of chloride or fluoride ions to the combined fluid;    buffering the combined fluid with a buffer to thereby adjust the pH of the combined aqueous base and surfactant within the pH range from about 6.5 to 10, thereby creating a viscous fluid capable of supporting proppant;    pumping the viscous fluid through a wellbore and into a surrounding formation at a pressure sufficient to fracture the formation.    
     
     
         19 . The method of  claim 18 , wherein the source of fluoride ions is a fluoride salt or acid compound present in the range from about 0.5 to 10% by weight, based upon the weight of the total fluid.  
     
     
         20 . The method of  claim 18 , wherein the source of fluoride ions is selected from the group consisting of ammonium bifluoride, sodium fluoride, potassium fluoride and fluoride based acids.  
     
     
         21 . The method of  claim 18 , further comprising the steps of adding an additional source of anions to the combined fluid.  
     
     
         22 . The method of  claim 18 , wherein the source of anions is a carboxylic acid salt present in the range from about 0.1 to 2% by weight, based upon the weight of the total fluid.  
     
     
         23 . The method of  claim 22 , wherein the carboxylic acid salt is selected from the group consisting of monovalent acetates, divalent fumerates, trivalent citrates and tetravalent EDTA.  
     
     
         24 . A method of fracturing a subterranean formation, the method comprising the steps of: 
 preparing a base solution comprising an aqueous fluid which is buffered within the pH range from about 7.0-10.0;    dispersing a surfactant comprising an alkyl sarcosinate having from 12 to 24 carbon atoms within the base solution to form a combined fluid, thereby reducing the pH of the combined fluid within the pH range from about 5.0 to 10.0;    slowing increasing the pH of the combined fluid within the range from about 7.0 to 9.0 by adding caustic to the combined fluid to produce a viscous fluid capable of supporting a proppant;    pumping the viscous fluid through a wellbore and into a surrounding formation at a pressure sufficient to fracture the formation.    
     
     
         25 . The method of  claim 24 , further comprising the steps of: 
 allowing the viscous fluid to contact the formation for a period of time sufficient to break the fluid viscosity without the use of additional breaker materials.    
     
     
         26 . A method of reducing the amount of water produced from a subterranean oil producing formation, the method comprising the steps of: 
 combining an aqueous base fluid with a surfactant comprising an alkyl sarcosinate having from 12 to 24 carbon atoms;    buffering the combined fluid with a buffer to thereby adjust the pH of the combined aqueous base and surfactant sufficiently to produce a viscous fluid;    pumping the viscous fluid through a wellbore and into a surrounding formation having an aqueous zone and a hydrocarbon zone, the aqueous zone comprising water;    allowing the viscous fluid to contact the aqueous zone and the hydrocarbon zone, contact with the hydrocarbon zone serving to thin the viscous fluid while contact with the aqueous zone serves to preferentially block the flow of water from that portion of the formation.    
     
     
         27 . The method of  claim 26 , wherein the aqueous base fluid also has added thereto a source of chloride or fluoride ions.  
     
     
         28 . The method of  claim 27 , wherein an additional source of anions is added to the aqueous base fluid.  
     
     
         29 . The method of  claim 28 , wherein the additional source of anions is a carboxylic acid salt present in the range from about 0.1 to 2% by weight, based upon the weight of the total fluid.  
     
     
         30 . The method of  claim 29 , wherein the carboxylic acid salt is selected from the group consisting of monovalent acetates, divalent fumerates, trivalent citrates and tetravalent EDTA.  
     
     
         31 . The method of  claim 27 , wherein the source of fluoride ions is a fluoride salt or acid compound present in the range from about 0.5 to 10% by weight, based upon the weight of the total fluid.  
     
     
         32 . The method of  claim 27 , wherein the source of fluoride ions is selected from the group consisting of ammonium bifluoride, sodium fluoride, potassium fluoride and fluoride based acids.  
     
     
         33 . The method of  claim 32 , wherein the source of fluoride ions is a fluoacid.  
     
     
         34 . The method of clam  33 , wherein the source of fluoride ions is fluosilicic acid.