3-D numerical study on cross-hole monitoring of hydraulic fractures in vertical steel-cased wells

Electrical and electromagnetic methods are increasingly used in environments containing steel infrastructure and are reliable tools for imaging and monitoring hydraulic fracture zones and other subsurface targets. However, despite the potential of these methods, accurately monitoring fracture zones in steel-cased boreholes remains challenging due to interference from ambient noise and the complexity of the geological environment. To overcome these challenges, this study proposes a novel cross-hole measurement technique specifically developed for diagnosing hydraulic fracture zones in vertical steel-cased boreholes. First, we derive the finite element formulation for numerical computation and develop a three-dimensional (3D) finite element algorithm specifically tailored to model fractured formations. Second, we perform a quantitative analysis of the fracture zone response characteristics under varying parameters using the cross-hole measurement technique. Finally, we conduct a multi-stage fracturing analysis to evaluate the effectiveness of the proposed method under complex subsurface conditions. Numerical results demonstrate that the measurement signals are highly sensitive to both fracture size and conductivity. Additionally, monitoring wells positioned closer to the direction of fracture zone propagation yield higher signal amplitudes. Furthermore, the proposed approach proves to be highly effective, even in multi-stage fracturing scenarios. This study demonstrates that the cross-hole measurement technique is a robust method for dynamically monitoring hydraulic fracturing in steel-cased boreholes and holds significant potential for practical applications.