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

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.

Field Experience Leads to Effective Bypass of Formation Damage Caused by Asphaltenes Deposition and Improves Production from a Naturally Fractured Carbonate Oil Reservoir

“…To keep the field alive, research efforts were made to reduce the production loss caused by the asphaltene deposits. To remedy the decreasing efficiency of the solvent system used in the field, extensive lab testing was initiated and several different compositions tested (Appicciutoli et al 2010). In parallel to research for a solvent composition with a higher dissolving power, the nature of the individual wellbores and their fluidabsorption regimes were studied, and a new approach in stimulation technique was developed.…”

“…In this instance, it was not possible to use diesel oil because it destabilizes the produced crude and increases the asphaltene deposition, and it was not possible to use produced oil because of logistical difficulties. Therefore, to replace the oil phase in the emulsified-acid system, the solvent blends developed for the improved asphaltene removal were tested for compatibility with the emulsifier and acid system to use (Appicciutoli et al 2010).…”

A Review on Use of Emulsified Acids for Matrix Acidizing in Carbonate Reservoirs

“…Water in oil emulsions provide better retardation due to the low diffusivity created by the oil phase around acid droplets, which allows for minimum acid volume contact with t h e r o c k − t u b u l a r s u r f a c e . T h u s , m o s t r esearch 18,26,[29][30][31][32][33][34][35][36][37]39,40,[42][43][44][45][46][47][48][49][50][51]53 has adapted W/O emulsions due to their desirable retardation effect and corrosion inhibition in comparison to O/W emulsions, 27,28 as depicted in Figure 5.…”

“…Coarse emulsions have until now been considered more cost efficient in matrix acidizing operations due to having low amount of surfactants and the ability to hold large volume of acid in contrast to microemulsions, which require large volume of surfactants for stability. Hence, very few publications − created microemulsions, whereas research studies ,− created coarse emulsions, as illustrated in Figure .…”

Effect of Presence of Crude Oil on the Performance of Emulsified Acids

“…The emulsified acid in xylene was applied in 4 wells with success and no problems. Appicciutoli et al (2010) showed that emulsified acid systems can be mixed with custom-tailored asphaltene-solving blends, and this system provided the desired benefits for matrix acidizing, such as stability, high viscosity, slow reaction, and at the same time it was able to remove asphaltene.…”