Development of gelled acid system in high-temperature carbonate reservoirs

Abstract

Acid fracturing technology is an effective way to reconstruct carbonate reservoirs. However, considering the characteristics such as strong heterogeneity, deep burial, and high temperature, the conventional acid fracturing system cannot be used in the low-permeability area effectively. Aiming at resolving this problem, Tarim Oilfield was taken as the research object and a new high-temperature-resistant gelled acid system with modified xanthan gum was developed in the present study. Then the temperature resistance and acid resistance of the thickening agents were tested through experiments. Moreover, the conductivity of acid-etched fractures was studied. The acid flow in the fracture was simulated to study the deep penetration capacity of the acid system. The obtained results show that the gelled acid system has good temperature resistance, acid resistance, and shear resistance, and the viscosity of the acid system at 160 °C remains 21 mPa s. The acid pressure experiment with a developed gelled acid system shows that the acid pressure effect is significant at indoor high temperatures of 160 °C. At a confining pressure of 30 MPa, the acid-etched fracture has a conductivity of 9.39D•cm. It was found that as the experimental ambient temperature increases, the conductivity of acid etching fracture gradually increases and stabilizes at 9.5D•cm. Finally, a “pink-out” gradient reduction appears in the acid concentration of the fracture, and flows along the fracture to the deep part of the formation, and propagates the fracture. It is concluded that the proposed method can be applied to communicate with the reservoir to increase production and injection. This article is expected to provide a theoretical foundation for the exploration of high-temperature resistance xanthan gum in the field of acid compression.