ABSTRACT:

Natural fractures are the primary pathways for fluid migration and production in unconventional geothermal and petroleum reservoirs. In geothermal reservoirs, reactivation (and possible propagation) of natural fractures is an important component of stimulation. Slip on these fractures induced Microearthquakes (MEQs) and the locations of MEQ events reveal aspects of stimulation. In this paper, we discuss a technique for extracting information about fractures orientations from MEQs. This is achieved by combining geomechanics and geostatistics to better constrain uncertainties in natural fracture properties. We develop a new Geomechanics-Based Stochastic Analysis of Microseismicity (GBSAM) to provide quantitative estimate of fractures orientations. In this work, the rock response to pore pressure is modeled using a line injection source to simulate water injection into a natural fracture network. Mahalanobis distance is then used to quantify the similarity between the distribution of MEQs (GMEQs) from the forward model and field-observed distribution of MEQs (TMEQs) to find the best GMEQs that fits the TMEQs. As an example, the GBSAM is applied to a data set of 344 MEQs recorded during phase 2.2 of Newberry Volcano EGS demonstration project, located 37 km south of Bend, Oregon. Borehole televiewer (BHTV) was used successfully to map the geometry of 351 fractures in the wellbore. Results from GBSAM show that the dip and dip direction of those fractures have good agreement with the field results from BHTV. This proposed method is a simple but effective way for interpreting MEQs for better characterizing reservoir stimulation.

1. INTRODUCTION
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