Volume 51

Classification of Well Test Models and Characterization of Opening Pressure for Water-Induced Fractures Jinbao Liu, Linsong Cheng, Pin Jia, Zheng Zhang, Jiangpeng Hu, Cong Peng

Abstract

For low permeability reservoirs, water-flooding development is usually adopted, which leads to induced fractures near the wellbore, increasing reservoir heterogeneity, making the residual oil distribution more complex, and significantly increasing development costs. This study focuses on low-permeability reservoirs. Based on well test pressure monitoring data from production sites and their characteristic patterns on log-log pressure response plots, and considering the characteristics of water injection-induced fracture composite zones, four typical models and their corresponding water flooding types were identified. Through analyzing the dynamic mechanisms of opening and closing of water injection-induced fractures, a new method for interpreting the opening pressure of these fractures was proposed. This method accurately characterizes the opening pressure thresholds of water injection-induced fractures under different classification models. Subsequently, several water injection wells in the J Oilfield were selected to verify the opening pressure thresholds and analyzed the opening pressure thresholds for water injection-induced fractures corresponding to different reservoir depths, permeabilities, and the four classification models. The results show that this method of interpreting the opening pressure of induced fractures based on well test pressure monitoring data exhibits high rationality and accuracy in characterizing the opening pressure thresholds of induced fractures. The opening pressure of induced fractures in Mode 2 and Mode 3 is higher than that in Mode 4; with increasing depth, the opening pressure of induced fractures tends to increase; and as the interpreted permeability from well testing increases, the opening pressure of induced fractures tends to decrease.

Keywords Low permeability reservoirs, well test pressure monitoring data, water injection-induced fracture, the opening pressure thresholds