Compositions and methods for treating subterranean formations

Abstract

Methods for treating subterranean wells in which the producing formation is a carbonate comprise preparing a treatment fluid comprising either: (a) an aqueous solution of a multivalent-cation reacting polymer; (b) a solution comprising a fatty acid and an ethanolamine; (c) an aqueous acidic solution of one or more compounds whose calcium salts are insoluble; or (d) an aqueous solution comprising urea or alkane derivatives thereof or both and polyvinylpyrrolidone (PVP). The treatment fluid is placed in the well such that the solution contacts the carbonate formation at a pressure lower than the fracturing pressure. The treatment fluid is allowed to react with the carbonate formation, thereby depositing a film onto the formation surface or part of the formation surface. Then an acid solution is placed in the well such that the acid contacts the carbonate formation at a pressure lower than the fracturing pressure.

1 . A treatment fluid system, comprising
 (i) a first fluid comprising either:
 an aqueous mixture of a multivalent-cation reacting polymer; 
 a mixture of a fatty acid and an ethanolamine; 
 an aqueous acidic mixture of one or more compounds whose calcium salts are insoluble; or 
 an aqueous solution comprising polyvinylpyrrolidone (PVP) and urea or alkane derivatives thereof or both; and 
   (ii) a second fluid comprising an acid.   
     
     
         2 . The system of  claim 1 , wherein the multivalent-cation reacting polymer is sodium alginate, present at a concentration between 0.1% and 3.0% by weight. 
     
     
         3 . The system of  claim 1 , wherein the ethanolamine comprises monoethanolamine, diethanolamine or triethanolamine or combinations thereof. 
     
     
         4 . The system of  claim 1 , wherein the fatty acid has a chemical formula CH 3 (CH 2 ) n COOH, wherein n is between 10 and 24 inclusive, and the fatty acid is present at a concentration between 1.0% and 2.5% by weight. 
     
     
         5 . The system of  claim 1 , wherein the compounds whose calcium salts are insoluble comprise sodium (or other monovalent cation) sulfate, sodium (or other monovalent cation) phosphate dibasic, sulfamic acid, sodium (or other monovalent cation)-4-hydroxybenzenesulfonate, oxalic acid, tetrapotassium (or other monovalent cation) pyrophosphate, potassium (or other monovalent cation) periodate or potassium (or other monovalent cation) phosphate monobasic or combinations thereof. 
     
     
         6 . The system of  claim 1 , wherein the aqueous solution of the multivalent-cation reacting polymer further comprises urea or derivatives thereof or both. 
     
     
         7 . The system of  claim 1 , wherein the second fluid further comprises urea, derivatives thereof or both. 
     
     
         8 . The system of  claim 1 , wherein the first fluid further comprises methanesulfonic acid or alkane, benzene or naphthalene derivatives thereof or mixtures thereof, at a concentration between 0.1% and 1.0% by weight 
     
     
         9 . A method for treating a subterranean well having a borehole and a carbonate formation with a fracturing pressure, comprising:
 (i) preparing a treatment fluid comprising either:
 an aqueous solution of a multivalent-cation reacting polymer; 
 a solution comprising a fatty acid and an ethanolamine; 
 an aqueous acidic solution of one or more compounds whose calcium salts are insoluble; or 
 an aqueous solution comprising urea or alkane derivatives thereof or both and polyvinylpyrrolidone (PVP); 
   (ii) placing the treatment fluid in the well such that the solution contacts the carbonate formation at a pressure lower than the fracturing pressure;   (iii) allowing the treatment fluid to react with the carbonate formation, thereby forming a film onto the formation surface or part of the surface; and   (iv) placing an acid solution in the well such that the acid contacts the carbonate formation at a pressure lower than the fracturing pressure.   
     
     
         10 . The method of  claim 9 , wherein the multivalent-cation reacting polymer is sodium alginate, present at a concentration between 0.1% and 3.0% by weight. 
     
     
         11 . The method of  claim 9 , wherein the ethanolamine comprises monoethanolamine, diethanolamine or triethanolamine or combinations thereof. 
     
     
         12 . The method of  claim 9 , wherein the fatty acid has a chemical formula CH 3 (CH 2 ) n COOH, wherein n is between 10 and 24 inclusive, and the fatty acid is present at a concentration between 1.0% and 2.5% by weight. 
     
     
         13 . The method of  claim 9 , wherein the compounds whose calcium salts are insoluble comprise sodium (or other monovalent cation) sulfate, sodium (or other monovalent cation) phosphate dibasic, sulfamic acid, sodium (or other monovalent cation)-4-hydroxybenzenesulfonate, oxalic acid, tetrapotassium (or other monovalent cation) pyrophosphate, potassium (or other monovalent cation) periodate or potassium (or other monovalent cation) phosphate monobasic or combinations thereof, 
     
     
         14 . The method of  claim 9 , wherein the treatment fluid further comprises methanesulfonic acid or alkane, benzene or naphthalene derivatives thereof or mixtures thereof, at a concentration between 0.1% and 1.0% by weight 
     
     
         15 . (canceled) 
     
     
         16 . (canceled) 
     
     
         17 . (canceled) 
     
     
         18 . (canceled) 
     
     
         19 . (canceled) 
     
     
         20 . (canceled) 
     
     
         21 . (canceled)