Numerical Simulation Study of 3D Crosswell Measurement for Hydraulic Fracture Zone Diagnostics in Steel-Cased Boreholes

Abstract

Summary Electrical signals in the vicinity of excited steel-cased borehole sources offer significant potential for monitoring fracture zones filled with highly conductive proppant. However, despite this potential, it is difficult to accurately monitor fracture zones in steel-cased boreholes due to various challenges, such as interference from background noise and the complexity of the geological environment. To address these challenges, we propose a novel crosswell measurement method specifically designed for diagnosing hydraulic fracture zones in steel-cased boreholes. During dynamic monitoring of fracturing, high-power direct current (DC) is applied to the steel-cased borehole, and the potential on the other open borehole is measured. This method uses a 3D finite element algorithm to establish a fracture detection model, and its accuracy has been verified by comparing the results with a benchmark model. Furthermore, the relationships between the geometric parameters of both fracture zones and boreholes, and the obtained measurement signals, are investigated. To evaluate the effectiveness of our proposed method in complex underground conditions, a case study is conducted. Numerical results indicate that the measurement signals are highly sensitive to a fracture’s size, thickness, and conductivity but less so to its shape. Moreover, whenever feasible, minimizing the distance between the measurement line and the asymmetrical fracture zone is essential for improving signal quality. In a case study focusing on segmented-fracturing monitoring, the signal difference observed before and after hydraulic fracturing clearly reveals the orientation of fracture zones during the fracturing process. This study demonstrates that the crosswell measurement method is an effective technique for dynamically monitoring hydraulic fracturing in steel-cased boreholes and holds promising applications.