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Estimates of hydraulic transport parameters using microseismicity induced by nonlinear fluid‐rock interaction

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Abstract

We consider an impact of a borehole fluid injection on rock permeability. Such fluid injections create a heterogeneously distributed (pressure‐dependent) permeability. Simultaneously, microseismicity is being induced. We analyze nature of hydraulic diffusivity estimates obtained from the spatio‐ temporal behaviour of fluid‐injection induced microseismicity. Under the assumption of transport properties being independent of time and pressure the concept of the so‐called triggering front is well established and provides diffusivity estimates of the reservoir rock. In this paper we investigate what kind of diffusivity estimates are provided by the triggering front if hydraulic transport properties are functions of pore‐ fluid pressure. We numerically solve nonlinear diffusion equations accounting for a power‐law and an exponential dependence of hydraulic diffusivity on pore‐fluid pressure. Based on the spatio‐temporal pore‐fluid pressure evolution we generate synthetic clouds of microseismicity. We apply the triggering front to the simulated synthetic event clouds. We compare the obtained diffusivity estimates with effective diffusivity values which we compute for the medium stimulated by a nonlinear pressure diffusion. We do this kind of analysis for 1‐, 2‐ and 3‐D media. Our results show that the triggering front provides reasonable diffusivity estimates characterizing the medium after stimulation including hydraulic fracturing of rocks.