Simulation and analysis of reactive flow in fractured carbonate reservoir using extended finite element method

Acidizing is one of the effective means to increase oil and gas production in carbonate reservoirs, which improves the fracturing process by forming high conductivity oil and gas seepage channels. However, there are few studies on the acid flow reaction of matrix-fracture dual media. In order to solve the problem of acid flow reaction discontinuity in fractured media, this paper introduces the extended finite element method into the carbonate acid flow reaction model, and the migration level set method is combined to characterize the discontinuity of fractures. The model of matrix-fracture transfer of acid flow reaction in carbonate is established based on the double scale model, and the fully implicit method is used to discretely solve the established model. The effect of fracture parameters and geological engineering parameters on acid flow reaction are studied. The results show that the fracture length and azimuth angle have a great influence on the acid flow reaction. The width of acid fracture can reach 0.0015 m under the condition of 20 m, while the condition of 60 m can reach 0.00103 m. Compared with the condition of 90 °and 50°, when the length of fracture reaches 25 m, the width of acid fracture increases by 0.00025 m. The acid filtration and direction of wormhole propagation are only affected by the anisotropy of matrix permeability, and the wormhole development and fracture width of acid etching are less affected. Natural fractures have a great influence on the formation of complex acid-etched fracture network. Compared with the case of connecting main fractures, more acid is needed to form complex fracture networks when natural fractures are not connected to main fractures. The simulation and discussion show that the modeling of acid flow reaction in carbonate rock is of great significance to improve the effect of acidizing.