Characterization of electrically conductive hydrofractures with cross-borehole electromagnetic measurement

Geometric analysis of hydraulic fractures in unconventional shale oil reservoirs is essential for enhancing production efficiency. This paper proposes a new method for evaluating large-scale fractures using cross-borehole electromagnetic measurement technique based on numerical simulation. The three-dimensional finite element method (3D FEM) is used to establish a hydraulic fracture model of horizontal wells, and the accuracy and validity of algorithm are verified using a benchmark model. The relationships between the geometric parameters of fractures 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 coaxial component signal (xx,yy,zz) is effective in characterizing hydraulic fractures. The signals exhibit greater sensitivity to the T-R spacing, fracture conductivity, fracture half-length, and fracture number, compared to transmitter frequency and fracture aspect ratio. Furthermore, the opening angle of asymmetrical fractures should be wider than 120° to ensure proper fracturing. In the segmented fracturing monitoring case study, positioning the transmitter source inside the fracturing borehole greatly aids in determining the orientation of fractures, while deploying it in the monitoring borehole conveniently improves the collection of response signals with a more prominent amplitude. This study demonstrates that the cross-borehole measurement method is an effective technique for monitoring hydraulic fracturing in open boreholes and offers promising applications.