Development of emulsified acid system (EAS) using organoclays (OC): Rheology and implication to the acidizing

Abstract

Matrix acidizing is a well-stimulation technique extensively used in the petroleum industry to increase well productivity by removing scales and creating channels in the rocks. However, conventional acidizing fluids used in this process have some limitations such as rapid reactions with scale and fines, high acid strength, and corrosion of equipment at high temperatures. To address these issues, emulsified acid system (EAS) is used in fracturing and acidizing operations for carbonate reservoirs to improve well productivity by removing formation damage. EAS can help to improve well productivity by creating deeper and narrower wormholes through reduced reaction rates of acid due to the external oil phase. However, EAS has limitations such as low stability at high temperatures, high viscosity that restricts pumping rates, potential formation damage, and difficulty in achieving homogenous mixing. Pickering emulsions, which use solid microparticles as a stabilizer instead of surfactants, show promise in overcoming these challenges due to their easy preparation, good thermal stability, and low viscosity at high shear rates.This study investigates the use of different types of organoclays (OC) for the development of an emulsified HCl acid systems for carbonate reservoirs. Several experiments were conducted to demonstrate and evaluate the use of OC for EAS and to improve field operations. To advance the development of EAS, a meticulous process was undertaken to select and optimize OCs as the key component. It include mineral characterization by XRD and XRF techniques, optimization of OC concentration (250–1000 ppm), and mixing speed (4000–8000 RPM). The thermal stability of the EAS was evaluated for a temperature range of 25–160 °C and a comprehensive analysis of EAS rheology (0.1–1000 sec−1) was performed. The conductivity, drop-test analysis, as well as micrographic analysis, were carried out to ensure the formation of invert emulsion. It was found that the required mixing speed was 6000 RPM and the optimum OC concentration was 500 ppm for developing a stable invert emulsion. The viscosity of the EAS shows increasing trends with an increase in temperature at the low shear rates (below 10 sec−1); however, at high shear rates (higher than 10 sec−1), the EAS viscosity decreases with temperature. The study found that OCs are promising emulsifiers for creating EAS with good thermal stability and low viscosity at high shear rates. The EAS formulated using OC were robust and thermally stable, making them suitable for field mixing procedures. Additionally, the OC used in the study are cost-effective, readily available, environmentally friendly, and have a high surface area, making them advantageous as an emulsifier.