Geomechanical Interpretation of Pore Pressures Triggering Microseismicity

Abstract

Fluid injections from boreholes into hydrocarbon and geothermal reservoirs can lead to the triggering of seismic events. In this paper we analyse the influence of elastic heterogeneities in rocks on magnitude and distribution of critical pore pressures, leading to the triggering of these events. For this purpose we apply an external homogeneous stress field to an elastically heterogeneous rock volume. The elastic parameters as well as the applied external stress field used for the analysis are taken from literature and correspond to the setting at the German Continental Deep Drilling Site (KTB). By finite element modelling using the FE program ABAQUS we determine the stress field inside the rock volume. The modelling results in a heterogeneous stress field from which we compute critical pore pressures. Furthermore, we analyse correlations between the distribution of assigned elastic parameters, the computed stress field and the resulting critical pore pressures. We conclude that pre-existing fractures in stiffer parts of a rock are characterized by lower critical pore pressures. With the here presented approach we elaborate a geomechanical interpretation of pore pressures triggering microseismicity.