Viscoelastic Surfactant Gels With Reduced Salt Concentration

Abstract

A well bore treatment fluid of viscoelastic surfactants and methods for increasing the viscosity of the fluid at high temperature without increasing its salt concentration by adding a organic hydrophilic-lipophilic compound and reducing the salt concentration below 6 percent.

1 - 23 . (canceled)  
   
   
       24 . A wellbore fluid for injection into subterranean formation, comprising an anionic surfactant for forming a viscoelastic (VES) gel; a hydrophilic-lipophilic organic compound with one or more polar groups; and a salt at a concentration in the range of 0 to less than 1.0 wt %.  
   
   
       25 . The wellbore fluid of  claim 24 , wherein the organic compound is miscible with the VES gel formulation.  
   
   
       26 . The wellbore fluid of  claim 24 , wherein the organic compound is non-ionic.  
   
   
       27 . The wellbore fluid of  claim 24 , wherein the organic compound is composed of a linear or branched saturated or partially unsaturated carbon chain comprising one or more polar groups.  
   
   
       28 . The wellbore fluid of  claim 24 , wherein the polar groups are —OH, —SH or —NH 2 .  
   
   
       29 . The wellbore fluid of  claim 24 , wherein the compound contains at least one other group selected from an ether, ketone, amide, ester, phosphate ester or phosphonate ester group.  
   
   
       30 . The wellbore fluid of  claim 24 , wherein the organic compound is a mono-alcohol, a diol, an ethoxylated alcohol, ethyoxylated amine, alkanolamide or fatty acid ethoxylate.  
   
   
       31 . The wellbore fluid of  claim 24 , wherein the organic compound is propan-2-ol, butanol, octan-1-ol, oleyl alcohol, versatyl alcohol, butanediol, butyl amine, oleyl amine or a dimeric oleyl amine.  
   
   
       32 . The wellbore fluid of  claim 24 , wherein the surfactant is a carboxylate or modified carboxylate, a compound of formula R—X—Y-Z, in which R is the hydrophobic tail of the surfactant, Z is the hydrophilic head of the surfactant, preferably carboxylate, COO −  or sulphonate, SO 3   − , said hydrophilic head group being charged, X is a stabilising group and Y is a linear, saturated or unsaturated chain of 1, 2 or 3 carbon atoms or a branched, saturated or unsaturated hydrocarbon chain wherein the main chain is of 1, 2 or 3 carbon atoms, with or without incorporating an aromatic ring; a quaternary ammonium compound; an alkyl betaine/sulphobetaine or an alkyl amido betaine/sulphobetaine.  
   
   
       33 . The wellbore fluid of  claim 24 , wherein the surfactant is derived from oleic acid, linoleic acid or mixtures thereof, erucic acid, tallow acid, dimeric/trimeric/oligomeric carboxylic acids; oleic acid dimer gels, oleyl ester succinate, oleyl amide succinate, oleyl sarcosinate or N-erucyl-N,N-bis(2-hydroxyethyl)-N-methyl ammonium chloride.  
   
   
       34 . The wellbore fluid of  claim 24 , wherein the molar ratio of organic compound to surfactant is in the range of 0.05 to 5.  
   
   
       35 . The wellbore fluid of  claim 24 , wherein the viscosity of the fluid at the point of injection is above 20 cp at 100 s−1 at a temperature of above 50 degrees Celsius.  
   
   
       36 . The fluid of  claim 24 , having a viscosity above 50 cp at 100 s−1 at a temperature of above 50 degrees Celsius.  
   
   
       37 . The fluid of  claim 24 , having a viscosity above 50 cp at 100 s−1 at a temperature of above 60 degrees Celsius.  
   
   
       38 . The fluid of  claim 24 , having a viscosity above 60 cp at 100 s−1 at a temperature of above 60 degrees Celsius.  
   
   
       39 . The wellbore fluid of  claim 24 , wherein the molar ratio of organic compound to surfactant is in the range of 0.05 to 5 and the viscosity of the fluid at the point of injection is above 20 cp at 100 s−1 at a temperature of above 50 degrees Celsius.  
   
   
       40 . The wellbore fluid of  claim 24 , wherein the salt concentration is the concentration of inorganic salts.  
   
   
       41 . The wellbore fluid of  claim 24 , wherein the salt concentration is the concentration of organic and inorganic salts.  
   
   
       42 . The wellbore fluid of  claim 24 , being a fracturing fluid or a diverting fluid.  
   
   
       43 . A method of treating a subterranean formation using the wellbore fluid of  claim 24 .  
   
   
       44 . A wellbore fluid for injection into a subterranean formation, comprising a cationic surfactant for forming a viscoelastic (VES) gel; a hydrophobic-lipophilic organic compound with one or more polar groups; and an inorganic salt at a concentration in a range of 0 to less than 2.0 wt %.  
   
   
       45 . A wellbore fluid for injection into a subterranean formation, comprising an anionic, cationic, or zwitterionic surfactant for forming a viscoelastic (VES) gel; a compound selected from an organic amine, an organic mercaptan, and an organic alcohol, said organic alcohol further comprising an ether, ketone, amide, ester, phosphate ester, or phosphonate ester group; and a salt at a concentration in a range of 0 to less than 6.0 wt %.  
   
   
       46 . A method for increasing the temperature at which viscosity of a wellbore treatment fluid comprising a surfactant for forming a viscoelastic (VES) gel decreases, said method comprising adding an effective amount of a hydrophilic-lipophilic organic compound having one or more polar groups to the treatment fluid.