Acidizing and scale treatment of subterranean formation

Abstract

A one step squeeze treatment of a subterranean formation involves the treatment with a treating solution comprising an acid, a scale inhibitor, and a reducing agent. The presence of the reducing agent prevents the iron ions in the system from reacting with and forming a precipitate with the scale inhibitor and maintains the iron ions in the ferrous state.

What is claimed is  
     
         1 . In a method of treating a subterranean formation with a treating solution containing acid and iron ions, the improvement wherein the treating solution further contains 
 (a) a scale inhibitor, and    (b) an additive capable of preventing or inhibiting the iron ions from forming a precipitate with the scale inhibitor:    
     
     
         2 . The method of  claim 1  wherein the iron ions enter the treating solution by the acid reacting with downhole equipment or materials.  
     
     
         3 . The method of  claim 1  wherein the acid is HCl.  
     
     
         4 . The method of  claim 3  wherein the additive is a reducing agent for reducing the iron ions to the ferrous state.  
     
     
         5 . The method of  claim 4  wherein the reducing agent is erythorbic acid.  
     
     
         6 . The method of  claim 4  wherein the scale inhibitor is selected from the group consisting of phosphonates, phosphate esters, polyacrylates, sulfonates, copolymers and terpolymers of acrylates, sulfonates and phosphonates, phosphinico polycarboxylic acid.  
     
     
         7 . A method of treating a subterranean formation comprising the steps of 
 (a) mixing an aqueous solution of 
 (i) HCl,  
 (ii) a scale inhibitor, and  
 (iii) an additive for preventing or inhibiting the scale inhibitor from forming a precipitate with any iron ions in the water,  
   (b) injecting the treating solution into the formation whereby the reaction of the HCl with downhole equipment or materials forms iron ions and whereby the presence of an effective amount of the additive (iii) inhibits the iron ions from reacting with and forming a precipitate with the scale inhibitor.    
     
     
         8 . The method of  claim 7  wherein the HCl is present in a concentration of 1 to 38%.  
     
     
         9 . The method of  claim 7  wherein the scale inhibitor is selected from the group consisting of phosphonates, phosphate esters, and polyacrylic acid.  
     
     
         10 . The method of  claim 7  wherein the scale inhibitor is selected from the group consisting of phosphonates, phosphate esters, polyacrylates, sulfonates, copolymers and terpolymers of acrylates, sulfonates and phosphonates, phosphinico polycarboxylic acid, phosphoric acid and salts thereof and is present in the treating solution at a concentration of between 0.5 and 50 wt. %.  
     
     
         11 . The method of  claim 7  wherein the additive is a reducing agent and is present in the treating solution at a concentration of between 0.05 and 30 wt. %.  
     
     
         12 . The method of  claim 11  wherein the reducing agent is selected from the group consisting of erythorbic acid, ascorbic acid, citric acid, thioglycolic acid, oxalic acid and mixtures thereof.  
     
     
         13 . An aqueous solution for treating a subterranean formation which comprises: 
 (a) From 5 to 28 wt. % HCl,    (b) From 0.5 to 10 wt. % of a scale inhibitor, and    (c) From 0.05 to 5 wt. % of a reducing agent for maintaining any iron in the treating solution in the ferrous state.    
     
     
         14 . The treating solution of  claim 13  wherein the scale inhibitor consisting of phosphonates, phosphate esters, polyacrylates, sulfonates, copolymers and terpolymers of acrylates, sulfonates and phosphonates, phosphinico polycarboxylic acid.  
     
     
         15 . The treating solution of  claim 13  wherein the reducing agent is erythorbic acid.