Analytical and Numerical Investigations of the Impact of Anisotropic Elastic Properties on Hydraulic Fracture Geometry

Abstract

This study investigates the impact of transverse isotropic vertical (TIV) characteristics on fracture geometry, spacing, and stress shadow development in shales. Shales exhibit transverse isotropic characteristics due to their rich organic content and laminated depositional environments. The lamination planes are horizontal in shale formations having a symmetric axis vertical to the bedding plane. Neglecting the TIV nature of shale formations leads to erroneous in-situ stress estimates, resulting in inefficient fracture design and reduced recovery. The study employs analytical modeling and numerical simulations to analyze the effects of TIV medium properties. Analytical modeling shows that Young's modulus anisotropy significantly impacts fracture width, while Poisson's ratio has minimal influence. Stress anisotropy is also examined, revealing that high-stress anisotropy allows for closely spaced fractures, theoretically eliminating minimum spacing concerns. Numerical simulations confirm that higher anisotropic stiffness reduces fracture width in TIV formations, aligning well with analytical modeling results. Wide fracture spacing produces a uniform and symmetric geometry, while narrow spacing results in non-uniform and asymmetric growth, with some fractures failing to initiate. Fracture turning due to stress anisotropy was also investigated, and the fracture propagation results clearly demonstrated the starting of fracture turning between 1000 to 1500 psi stress anisotropy. Micro-seismic was used to validate and calibrate fracture geometry. Economic-based optimization determines the optimal fracture spacing.