Volume 54

Field-scale Simulation of Closed-Fracture Acidizing for Acid Etching Patterns and Conductivity Prediction Panpan Lu , Jianye Mou , Shicheng Zhang, Sinan Li , Xinliang Wang , Xiaoyi Sun

Abstract

Maintaining fracture conductivity in acid-fractured carbonate reservoir presents a significant challenge as the fractures tend to close due to closure pressure. A viable approach to prevent the decline of conductivity is closed-fracture acidizing (CFA). In this study, we introduce a field-scale numerical model to simulate the acid-etching pattern in CFA and its effect on the conductivity of acid-fractured fractures. The accuracy of the CFA model is validated through experiments under identical acid-etched fracture morphology. The simulation results indicate that the morphology of closed fractures determines the acid-etching patterns. When the mean fracture aperture is small (≤2 mm), roughness is high (SD>0.05), and the dimensionless correlation length is extensive (≥0.05), acid etching becomes non-uniform, forming grooves and channels. In this case, the live acid reaches farther, and the conductivity remains high under closure stress (improved 8 to 33 times compared to before acidizing). Conversely, the acid uniformly etches the fracture surface, the acid treatment distance is short, and the conductivity rapidly decreases, making the acidizing performance negligible. In short, acid tends to flow into areas with the least resistance, and ultimately affecting acid-etching patterns and conductivity.

Keywords Closed-fracture acidizing; Numerical model; acid-etching pattern; Conductivity prediction