Novel Emulsified Acid Boosts Production in a Major Carbonate Oil Field with Asphaltene Problems

Abstract

Abstract When performing matrix-acid treatments, the goal is to stimulate the formation as deeply as possible, distributing the acid uniformly over the total zone of interest. Uniform distribution is even more important when intervals are long, horizontal, or several zones with natural fractures predominantly take the reactive fluid. In Italy's major oil-producing field, all of these challenges are faced. In addition, during production, asphaltenes form and are deposited in the well, making it even more difficult to distribute the acid evenly. Because the field is located in an environmentally sensitive area, all fluids need to be mixed and pumped using a zero-operational-risk philosophy. Some of the matrix-stimulation challenges were overcome as a result of the development of a novel emulsified acid that combines the practiced asphaltene-dissolving technique with proven acid-diversion technology. The environmental challenges are overcome by creating an oil-external/acid-internal emulsion, on-the-fly, just before the fluid is pumped downhole. This paper describes the engineered process of finding solutions to the challenges, beginning with laboratory testing to develop and optimize the solvent part of the innovative acid system. Further, an overview of how operational difficulties were resolved and how the innovative fluid system was applied is presented. The first section of the paper outlines laboratory testing, showing that an emulsified-acid system can be mixed with custom-tailored asphaltene-solving blends and provide the desired benefits for matrix acidizing, such as a slower acid reaction, higher base viscosity, and excellent emulsion stability in temperature. The second part of the paper explains the equipment setup used to create the acid system ready for field application in an environmentally sensitive area. The third part of the paper describes how the novel acidizing approach in its first field application boosted production to unexpected highs.