A Novel Approach to Quantify Emulsion and Sludge Formation Damage During Matrix Acidizing

Summary Matrix acidizing can damage formations by forming acid-crude oil emulsions and sludges. These damages contradict the benefits of acidizing and reduce well productivity. Given the limited understanding of mechanisms for acid-crude oil emulsion formation and insufficient and sometimes contradictory data in the literature, a reliable quantitative approach is crucial for thoroughly analyzing emulsions under various conditions. In this study, we introduce three novel parameters based on image analysis to quantify emulsion tests at reservoir temperature (366.5 K), and define the emulsion-specific parameters of the number, average size, and average spacing of acid droplets in a crude oil emulsion. These three parameters allow for a quantitative evaluation of acid-crude oil emulsions, their stability, the amount of formation damage, and the amount of emulsion and sludge formed under various conditions. We further consider the impacts of acid concentration [hydrochloric acid (HCl)], ferric ions, and various acidizing additives [i.e., corrosion inhibitor (ACI), corrosion inhibitor intensifier (ACII), iron chelating agent (IC-3), iron sequestering agent (IC-4), non-ionic surfactant (PA), anti-emulsion (NE) agent, and anti-sludge (AS) agent]. A stability test was designed to validate the emulsion test results. The results show that, as the number and average size of acid droplets increase and their spacing decreases, the emulsion stability and subsequent sludge formation increase. The availability of ferric ions causes the highest sludge formation (and the greatest formation damage), the highest emulsion-to-sludge conversion (39%), and an emulsion stability of 100%. In the presence of these ions, both the number and size of droplets increase by 168% and 1,400%, respectively, while the droplet spacing decreases by 97%. The sludge created because of acid concentration increase from 15 wt% to 28 wt% was less than that when ferric ions were available in the acid solution. The emulsion-to-sludge conversion changes from 16% to 20%, and the number and size of acid droplets rise by 5% and 50%, respectively, while the droplet spacing decreases by 10%. This results in an emulsion stability increase of 5% (from 10% to 15%), and a sludge increase of 4%. Our findings indicate that most additives not only fulfill their intended roles but also decrease the amount of emulsion and sludge as well. For example, when all additives, excluding the AS agent, are mixed with the acidizing fluid, the lowest emulsion-to-sludge conversion (8.9%) was achieved. The quantity and size of acid droplets show a 48% and 95% decrease, but the droplet spacing raised 2,916% for the designed optimal acidizing fluid. Moreover, a complete loss of emulsion stability was achieved. Through this study, we provide new insights into acid-crude oil emulsion analysis by quantifying emulsion properties, aiding in designing and developing compatible acidizing fluids for a target crude oil.