Hydraulic fracturing monitoring: New concept of electromagnetics linked to elastic modeling

Abstract

We have developed a simulation of the electromagnetic (EM) response and its joint interpretation with fracking monitoring simulation during hydraulic fracturing in an unconventional reservoir. A multiphysics workflow is presented, using a criterion based on a breakdown pressure to generate and propagate the hydraulic fracturing, where the pressure response and EM response were jointly constructed. The approximate solution of Maxwell equations was obtained using a mixed finite-element method (FEM) combined with a leapfrog time-stepping procedure. The spatial discretization of the Maxwell’s equations is achieved using the mixed finite-element spaces of Nedelec, in which the electrical fields have a continuous tangential component across the edges of the computational mesh. Leapfrog time stepping was used for the time discretization, so that the fully discrete sequence is first solving for the electric field using preconditioned conjugate gradient iteration and then solving for the magnetic field. A stability analysis of this FEM method is provided. The results indicate that the EM response might be sensitive enough to be monitored and the magnetic field correlates better with the saturation distribution than the electric field. Furthermore, due to its relation to water saturation and effective connectivity, it is shown that EM monitoring yields additional information to determine the stimulated reservoir volume. An error analysis of estimations from EM and the actual saturation size indicates that the petrophysical assumption is perhaps the most sensitive part of this study.