Use of Emulsified Acid System with Corrosion Protection up to 350°F

Abstract Acidizing operations increasingly present challenges in deeper formations. The formation of wormholes and inhibition of corrosion are particularly becoming significant because both are drastically affected in deeper wells with higher temperatures. In emulsified acid fluids, the direct contact between the acid and formation is reduced, thus enhancing the formation of wormholes at high temperatures. Emulsions also reduce the direct contact between acid and metal, thus improving the inhibition of corrosion. This makes emulsified acids one of the most promising fluids for high-temperature acidizing operations; however, the primary challenge is stabilizing the emulsion system at increased temperatures and in the presence of corrosion inhibitors. Using the existing emulsifiers, it is often difficult to formulate a stable emulsified acid that can pass corrosion testing above 300°F. This paper discusses the study of a new emulsifier with a high molecular weight and branched nature. Because of these structural aspects, the new emulsifier retained its emulsifying power at high temperatures and in the presence of corrosion inhibitors. This helped enable the use of appropriate quantities of corrosion inhibitors within the system. The emulsified acid system was further optimized to pass static high-pressure/high-temperature (HP/HT) corrosion testing at 350°F with 20% hydrochloric acid (HCl) strength. The same fluid also passed corrosion testing with 28% HCl strength at 325°F. Per the data, the use of this new emulsifier helped improve both emulsion stability and corrosion inhibition because of better separation between the acid and metal surface. The new emulsifier system also has a lower chemistry scoring index (CSI) than existing emulsifiers. The acidizing operation of carbonate reservoirs with bottomhole static temperatures (BHSTs) up to 350°F become attainable using the new emulsified acid system. Guidelines for designing acidizing fluids with this higher temperature limit are presented.