Mechanism study on steering acid fracture initiation and propagation under different engineering geological conditions

Steering acid fracturing is a new way which can significantly increase oil and gas production. However, it is still unknown how to appropriately use steering acid in carbonate reservoir. Therefore, four true tri-axial acid fracturing experiments were carried out to study fracture initiation and propagation during steering acid fracturing. The experimental results reveal the following. 1. The results of the acid fracturing are easily affected by natural vugs, which can change the direction of the acid-etched fracture propagation. When there are few vugs in the reservoir, the steering acid etches the surface of the acid-etched fractures and forms crowds of acid-etched vugs. 2. When using high pumping rate, it is easy for the steering acid to plug the top of the acid-etched fracture and force the fracture to change its propagation direction. 3. The acid will etch the fracture surface, which results in a strong conductivity. The acid-etching phenomenon is obvious in the area near the wellbore and the turning area. The steering acid etches multiple channels with high conductivities rather than etching the entire area of the fracture surface. 4. Acid fatigue fracturing can effectively reduce the fracturing pressure. However, when using this method, there will be few acid-etched vugs in the area far from the wellbore. Article Highlights When acid is used as fracturing fluid, it would react with the carbonate, and form complex fracture networks.