Formulation of a New Acid Fluid for Blocking Removal in Carbonate Formations and Analysis of Factors Affecting Blocking Removal

Drilled cuttings and particles from drilling fluids generally cause severe blocking of the pores in carbonate reservoir rocks. A blocking removal acid fluid was developed to cope with this problem. The acid fluid is formulated with a new ethyl iodosulfonate which was synthesized based on the principles of organic chemistry and the principles of preparing acid fluids. In laboratory test, the effect of several factors, such as HCl content, ethyl iodosulfonate content, temperature of the acid fluid and initial permeability, on the blocking removal performance of the new acid fluid was analyzed using the dissolution rate of carbonate rocks and permeability as the evaluation indices. It was found that increases in the contents of HCl and ethyl iodosulfonate, the temperature of the acid fluid and the initial permeability all are beneficial to the increases of dissolution rate and the permeability of the carbonate rocks; Using the new acid fluid containing 7% HCl, the dissolution rate and percent recovery of permeability of the formation rocks were as high as 96.1% and 111.3%, respectively, far greater than these two indices for conventional clay acid, which are 80.3% and 76.1%, respectively. The existence of ethyl iodosulfonate in the acid fluid helps extend the time for the dissolution of the carbonate rocks, and enhance efficiency of blocking removal, exhibiting excellent blocking removal and environment protection performance.