Acid Emulsified in Xylene: A Cost-Effective Treatment To Remove Asphaltene Deposition and Enhance Well Productivity

Abstract

Summary Emulsified acid (30 vol% diesel and 70 vol% HCl) has been used in both matrix and acid fracturing treatments. Injecting the acid in this form has several advantages including retarding the reaction of the acid with rock, reducing corrosion to well tubulars, and minimizing acid additives. However, using this acid to treat wells with asphaltene deposition requires removing asphaltene first using a suitable aromatic-based solvent, and then using a matrix acid treatment. This additional step increases the cost and time needed to execute acid treatments. To remove asphaltene deposition and enhance well productivity, hydrochloric acid was emulsified in xylene. Xylene was the external phase, and was used to dissolve asphaltenes. Then the acid as the dispersed phase dissolved the carbonate rock, enhancing well productivity. Extensive laboratory work was performed to ensure the stability of acid-in-xylene emulsion and measure its apparent viscosity. Acid concentration was 15 wt% HCl, the acid volume fraction was 0.7, and the balance was xylene with demulsifier. All tests were conducted at room temperature and 160°F (bottomhole temperature). The stability and apparent viscosity of emulsified acids were found to be a function of the type of hydrocarbon phase used to prepare the emulsified acid. Emulsified acids prepared with xylene had a lower apparent viscosity and were stable for relatively shorter times. A matrix acid treatment based on xylene-emulsified acid was applied in four wells without encountering operational problems. Unlike previous matrix acid treatments using regular acids, the four wells responded to the new treatment without increasing water cut, except in one well that was wet before the treatment.