Efficient fully coupled 3D poroelastic modeling of geomechanical deformation during depletion and reinjection: An asymptotic transformation of Biot's poroelasticity from a dynamic to a quasistatic response

We develop an approach for efficient 3D simulation of the quasistatic fully coupled poroelastic response of a reservoir during depletion and subsequent reinjection. The approach uses a scaling of the solid and fluid densities in Biot's po-roelastic equations. This scaling impacts the critical fre-quency fc of Biot's slow wave that defines diffusive flow (f < fc) and wave propagation (f > fc). We find the cri-terion for the density scaling range over which the poroelas-tic response is accurately modeled and benchmark the approach against Terzaghi's 1D and Rudnicki's 3D analytic solutions. The density scaling approach is presently limited to single-phase fluid flow. To illustrate the utility of this ap-proach, we simulate microseismic depletion delineation (MDD) in a fractured unconventional reservoir. The reser-voir, which is subjected to an anisotropic stress field, is first produced for 1000 days, and then a reinjection (below the in situ pressure) is performed for 100 days. We find that stress reorientation during production produces favorable condi-tions for the generation of Mohr-Coulomb slip-related mi-croseismicity. The locations of these microseismic events are found to be consistent with depleted portions of the frac -ture system, in accordance with the MDD concept.

Automated summary

We have developed an efficient method for simulating the 3D poroelastic response of a reservoir during depletion and reinjection. The method uses a scaling of solid and fluid densities in Biot's equations to accurately model the response. We have tested the method against analytic solutions and applied it to simulate microseismic depletion delineation in a fractured unconventional reservoir.