Electrical–Elastic Joint Inversion Method for Fracture Characterization in Anisotropic Media

Fracture networks are omnipresent in unconventional energy reservoirs. The inversion of fractures is of vital importance to oil and gas exploration and production. Most of the existing inversion methods are developed based on homogeneous media theory and rely on a solitary physical descriptor. For instance, one commonly employed single property inversion approach is the determination of water saturation through the use of the media's electrical conductivity. With the fast development of multi-physics geological survey, a joint inversion framework that is suitable for anisotropic fractured media is needed. In this paper, we propose an electrical-elastic joint inversion method involving both electrical tensor and elastic tensor to invert the fracture characteristics (e.g., fracture shape, inclination angle, and porosity). We conduct numerical experiments with two-phase geometries containing idealized ellipsoidal fractures. The resistivity tensor and Young's moduli of different directions are calculated and used to construct an anisotropy diagram and a joint inversion chart. The method is validated by comparing the predicted fracture geometry with the actual geometry of the fracture embedded in media. Both ideal homogeneous media and digital rock samples are used to test the inversion framework. A comparison between the single and joint property inversion is also presented, the joint property inversion shows a higher accuracy in predicting fracture volume and tilting angle. This work indicates that the proposed electrical-elastic joint method can capture the anisotropy of the formation rock, and the multi-physics inversion framework exhibits the potential to recover fracture features with high fidelity.