Fracture fluid alteration to mitigate barite scale precipitation in unconventional oil/gas shale systems

Abstract

An acid spearhead formulation for mineral scale reduction that includes a sulfuric acid solution having an acidity that is substantially equivalent to a hydrochloric acid solution in an acid spearhead formulation, a sodium citrate compound, where an acid spearhead formulation for mineral scale reduction is formed, the acid spearhead formulation is disposed in a well bore to stabilize mineral scales, the acid spearhead formulation is disposed in the well bore to chelate solubilized calcium in a rock bed of the well bore, and the well bore includes a temporal thermodynamic subsurface barite cycling having a subsurface barite dissolution temporal phase, a subsurface barite transport to fractures temporal phase, a subsurface barite precipitation to fracture temporal phase and a subsurface barite dissolution to fracture space temporal phase, where the acid spearhead formulation for mineral scale reduction reacts with the well bore within the subsurface barite dissolution temporal phase.

1 . A method to mitigate barite scale precipitation in unconventional oil/gas extraction, the method comprising:
 preparing an acid spearhead formulation having as its acid either sulfuric acid or a mixture of sulfuric acid and hydrochloric acid that is 10% or more sulfuric acid, wherein the acid spearhead formulation includes sodium citrate in an amount effective to suppress gypsum formation; and   injecting the acid spearhead formulation into a subsurface.   
     
     
         2 . The method of  claim 1 , wherein the mixture of sulfuric acid and hydrochloric acid is between 40% and 60% sulfuric acid. 
     
     
         3 . The method of  claim 2 , wherein a concentration of the sodium citrate in the acid spearhead formulation is about 1 M, whereby gypsum formation from subsurface rock having 40% or more calcite by weight is alleviated. 
     
     
         4 . The method of  claim 1 , wherein the mixture of sulfuric acid and hydrochloric acid is between 60% and 80% sulfuric acid. 
     
     
         5 . The method of  claim 4 , wherein a concentration of the sodium citrate in the acid spearhead formulation is between about 0.05 M and about 1 M, whereby gypsum formation from subsurface rock having 15-40% calcite by weight is alleviated. 
     
     
         6 . The method of  claim 1 , wherein the mixture of sulfuric acid and hydrochloric acid is 80% or more sulfuric acid. 
     
     
         7 . The method of  claim 6 , wherein a concentration of the sodium citrate in the acid spearhead formulation is about 0.05 M, whereby gypsum formation from subsurface rock having 0-15% calcite by weight is alleviated.