Matrix treatment of damaged sandstone formations using buffered HF-acidizing solutions

Abstract

Sandstone formations of oil and gas and geothermal wells are effectively stimulated when a buffered HF-sandstone acidizing solution is employed without the prior introduction of an acid containing preflush solution. By not using a preflush solution, buffered HF-sandstone acidizing solutions are highly effective in dissolving and removing siliceous material while minimizing the formation of calcium fluoride.

1 . A method for dissolving acid-soluble siliceous material in a sandstone formation of an oil or gas or geothermal well which comprises introducing into the well, in the absence of a preflush solution, a buffered HF-sandstone acidizing solution.  
     
     
         2 . The method of  claim 1 , wherein the pH of the acidizing solution is between from about 1.9 to about 4.8.  
     
     
         3 . The method of  claim 2 , wherein the pH of the acidizing solution is between from about 2.5 to about 4.5.  
     
     
         4 . The method of  claim 1 , wherein the acidizing solution further comprises a phosphonate of the formula:  
       
         
           
           
               
               
           
         
       
       wherein R1, R2 and R3 are independently selected from hydrogen, alkyl, aryl, phosphonates, phosphates, acyl, amine, hydroxy and carboxyl groups and R4 and R5 are independently selected from hydrogen, sodium, potassium, ammonium or an organic radical.  
     
     
         5 . The method of  claim 2 , wherein the acidizing solution further comprises a phosphonate of the formula:  
       
         
           
           
               
               
           
         
       
       wherein R1, R2 and R3 are independently selected from hydrogen, alkyl, aryl, phosphonates, phosphates, acyl, amine, hydroxy and carboxyl groups and R4 and R5 are independently selected from hydrogen, sodium, potassium, ammonium or an organic radical.  
     
     
         6 . The method of  claim 4 , wherein the acidizing solution further comprises citric acid or formic acid.  
     
     
         7 . The method of  claim 6 , wherein the acidizing solution comprises about 1 to about 50 weight percent citric acid, up to about 20 weight percent HF and from about 0.5 to about 50 weight percent phosphonate compound.  
     
     
         8 . The method of  claim 1 , further comprising introducing into the well, subsequent to the introduction of the acidizing solution, an overflush solution.  
     
     
         9 . The method of  claim 1 , which further comprises introducing into the well a neutral chelant pickling agent.  
     
     
         10 . In a method of well remediation in which a wellbore fluid is employed, the improvement comprising using a wellbore fluid comprising a buffered HF-sandstone acidizing solution.  
     
     
         11 . The method of  claim 10 , wherein the pH of the sandstone acidizing solution is between from about 1.9 to about 4.8.  
     
     
         12 . The method of  claim 10 , wherein the sandstone acidizing solution further comprises a phosphonate of the formula:  
       
         
           
           
               
               
           
         
       
       wherein R1, R2 and R3 are independently selected from hydrogen, alkyl, aryl, phosphonates, phosphates, acyl, amine, hydroxy and carboxyl groups and R4 and R5 are independently selected from hydrogen, sodium, potassium, ammonium or an organic radical.  
     
     
         13 . The method of  claim 12 , wherein the sandstone acidizing solution further comprises citric acid or formic acid.  
     
     
         14 . A method of stimulating or remediating a sandstone formation consisting essentially of introducing into the formation a buffered HF-acidizing solution.  
     
     
         15 . The method of  claim 14 , wherein the pH of the acidizing solution is between from about 1.9 to about 4.8.  
     
     
         16 . The method of  claim 14 , wherein the acidizing solution further comprises a phosphonate of the formula:  
       
         
           
           
               
               
           
         
       
       wherein R1, R2 and R3 are independently selected from hydrogen, alkyl, aryl, phosphonates, phosphates, acyl, amine, hydroxy and carboxyl groups and R4 and R5 are independently selected from hydrogen, sodium, potassium, ammonium or an organic radical.  
     
     
         17 . The method of  claim 14 , wherein the acidizing solution further comprises citric acid or formic acid.  
     
     
         18 . A process for dissolving acid-soluble siliceous material in a sandstone formation of an oil or gas or geothermal well consisting essentially of introducing into the well a buffered HF-acidizing solution.  
     
     
         19 . The method of  claim 18 , wherein the pH of the acidizing solution is between from about 1.9 to about 4.8.  
     
     
         20 . The method of  claim 18 , wherein the acidizing solution further comprises at least one member selected from the group consisting of: 
 (a.) a phosphonate of the formula:                          wherein R1, R2 and R3 are independently selected from hydrogen, alkyl, aryl, phosphonates, phosphates, acyl, amine, hydroxy and carboxyl groups and R4 and R5 are independently selected from hydrogen, sodium, potassium, ammonium or an organic radical; and    (b.) citric acid, formic acid and mixtures thereof.