Triaxial experimental investigation into the characteristics of acid-etched fractures and acid fracturing

Abstract

Abstract A high-strength pressure-resistant material and acid-resistant thickener are developed, and natural cores extracted from the Changqing Oilfield in China are wrapped in three dimensions to study the initiation, propagation, and characteristics of cracks. Conventional hydraulic fracturing, acid fluid fracturing, and thickener compound acid fluid fracturing were carried out through physical and numerical simulations. The results show that under the simulated environmental pressure, the fracture pressure in the core increases significantly. Ordinary hydraulic fracturing produces a fixed-direction fracture. The acid fluid effectively corroded the wellbore, thereby reducing the fracture pressure, but only some cracks were produced with pure acid pressure. Fracturing with the acid plus the thickener produced a single main fracture. The acidic fluid flowed in a fixed direction and effectively corroded the wellbore, thereby reducing the fracture pressure. A large number of microcracks are due to the thickener slowing down the acid nucleus reaction, which greatly increases the acid transmission distance. The shape of acid-etched cracks is significantly different from hydraulic fracturing because of the acid-rock reaction. Compared with other fracturing simulation studies, this study has the advantage of effectively reducing the initiation and propagation direction of fractures induced by acid fracturing in the presence of underground confining pressure. This experimental method restores the actual underground situation to the greatest extent. This paper combines physical simulation with numerical simulation to study acid erosion fracturing experiments, which provides guidance for optimizing the effect of acid fracturing.