Drag-reducing agent for use in injection water at oil recovery

Abstract

The present invention relates to the use of a drag-reducing agent in an amount of 50-400 ppm in water having an electrolyte content of 0.01-7% by weight. The drag-reducing agent comprises two zwitterionics, each comprising acyl containing surfactant and an anionic surfactant, where the hydrophilic group is a sulphate, a sulphonate or an ether sulphate. The water containing the drag-reducing agent is suitable to be used in injection water at oil recovery.

1 . A drag-reducing agent containing 
 a) a zwitterionic surfactant of the formula                          where R 1  is acyl group with 12-16 carbon atoms, R 3  and R 4  are independently of each other an alkyl group of 1-4 carbon atoms or an hydroxyalkyl group of 2-4 carbon atoms and R 5  is an alkylene group of 1-4 carbon atoms, preferably CH 2  or a group                          where R 6  is an alkyl group of 1-3 carbon atoms,    b) a zwitterionic surfactant of the formula                          where R 2  is an acyl group with 18-22 carbon atoms, and R 3 , R 4  and R 5  have the meanings mentioned above, and    c) an anionic surfactant of the formulae      R 7 (OA) n B or R 7 E    or a mixture thereof, where R 7  is an aliphatic group of 8-14 carbon atoms, A is an alkylene group having 2-4 carbon atoms, n is a number from 1 to 10, B is a sulphate group OSO 3 M, E is a sulphate group OSO 3 M or a sulphonate group —SO 3 M and M is a cationic, preferably monovalent group;    the weight of a), b) and c) being 20-95% by weight, 0-70% by weight and 1-50% by weight, respectively, based on the total amount of a), b) and c);    in an amount of a), b) and c) of 50400 ppm in water having an electrolyte content from 0.01-7% by weight.    
   
   
       2 . The drag reducing agent of  claim 1 , wherein the component a) and b) are present in an amount of 20-85% by weight and 10-70% by weight, respectively.  
   
   
       3 . The drag reducing agent of  claim 1 , wherein R 2  contains at least 50% by weight of unsaturated acyl groups.  
   
   
       4 . The drag reducing agent of  claim 3 , wherein R 2  contains at least 20% by weight of two or more double bonds.  
   
   
       5 . The drag reducing agent of  claim 1 , wherein c) is lauryl sulphate, a lauryl (oxyethylene) n  sulphate, where n is 1-3, or lauryl sulphonate.  
   
   
       6 . The drag reducing agent of  claim 1  wherein the water has an electrolyte content of 0.3-6% by weight.  
   
   
       7 . (canceled)  
   
   
       8 . Injection water for the treatment of oil reservoirs, wherein said water contains 
 a) a zwitterionic surfactant of the formula                          where R 1  is acyl group with 12-16 carbon atoms, R 3  and R 4  are independently of each other an alkyl group of 1-4 carbon atoms or an hydroxyalkyl group of 2-4 carbon atoms and R 5  is an alkylene group of 1-4 carbon atoms, preferably CH 2  or a group                          where R 6  is an alkyl group of 1-3 carbon atoms,    b) a zwitterionic surfactant of the formula                          where R 2  is an acyl group with 18-22 carbon atoms, and R 3 R 4  and R 5  have the meanings mentioned above, and    c) an anionic surfactant of the formulae      R 7 (OA) n B or R 7 E    or a mixture thereof, where R 7  is an aliphatic group of 8-14 carbon atoms, A is an alkylene group having 2-4 carbon atoms, n is a number from 1 to 10, B is a sulphate group OSO 3 M, E is a sulphate group OSO 3 M or a sulphonate group —SO 3 M and M is a cationic, preferably monovalent group;    wherein the total amount of the components a), b) and c) is from 50-400 ppm and said water has an electrolyte content of 0.01-7% by weight.    
   
   
       9 . Injection water according to  claim 8 , wherein said water contains electrolytes in an amount of 0.3-6% by weight.  
   
   
       10 . Injection water according to  claim 8  wherein the water is sea-water or production water.  
   
   
       11 . A method of reducing drag in waters containing electrolytes which comprises adding to said waters at least one drag-reducing agent containing 
 a) a zwitterionic surfactant of the formula                          where R 1  is acyl group with 12-16 carbon atoms, R 3  and R 4  are independently of each other an alkyl group of 1-4 carbon atoms or an hydroxyalkyl group of 2-4 carbon atoms and R 5  is an alkylene group of 1-4 carbon atoms, preferably CH 2  or a group                          where R 6  is an alkyl group of 1-3 carbon atoms,    b) a zwitterionic surfactant of the formula                          where R 2  is an acyl group with 18-22 carbon atoms, and R 3 , R 4  and R 5  have the meanings mentioned above, and    c) an anionic surfactant of the formulae      R 7 (OA) n B or R 7 E    or a mixture thereof, where R 7  is an aliphatic group of 8-14 carbon atoms, A is an alkylene group having 24 carbon atoms, n is a number from 1 to 10, B is a sulphate group OSO 3 M, E is a sulphate group OSO 3 M or a sulphonate group —SO 3 M and M is a cationic, preferably monovalent group;    the weight of a), b) and c) being 20-95% by weight, 0-70% by weight and 1-50% by weight, respectively, based on the total amount of a), b) and c);    in an amount of a), b) and c) of 50400 ppm in water wherein said water has an electrolyte content from 0.01-7% by weight.    
   
   
       12 . The method of  claim 11 , wherein the component a) and b) are present in an amount of 20-85% by weight and 10-70% by weight, respectively.  
   
   
       13 . The method of  claim 11  wherein R 2  contains at least 50% by weight of unsaturated acyl groups.  
   
   
       14 . The method of  claim 11  wherein R 2  contains at least 20% by weight of two or more double bonds.  
   
   
       15 . The method of  claim 11  wherein c) is lauryl sulphate, a lauryl (oxyethylene) n  sulphate, where n is 1-3, or lauryl sulphonate.  
   
   
       16 . The method of  claim 11  wherein the water has an electrolyte content of 0.3-6% by weight.