Abstract:

The Northwest Geyser EGS Demonstration Project aims at creating an Enhanced Geothermal System (EGS) by directly and systematically injecting cool water at relatively low pressure into a known High Temperature (400°C) Zone (HTZ) located under the conventional (240°C) steam reservoir. In this paper we present the results of coupled thermal, hydraulic, and mechanical (THM) modeling conducted to investigate injection strategies and effects of cold water injection upon the EGS system, in particular to predict the extent of the stimulation zone for a given injection schedule. We present a comparison of model predictions with micro-earthquake (MEQ) monitoring data, as well as comparison with reservoir pressure and ground surface deformation data over the first several months of injection. Using a simplified model in terms of geology and geometry, we were able to make a reasonable prediction of the extent of the stimulation zone and with reasonable parameter adjustments we could reproduce the observed evolution of reservoir pressure and surface deformations. However, we also found that the detailed evolution of reservoir pressure, MEQ and ground-surface movements display prominent effects of more complex geology, including minor faults and fractures that provide preferential flow paths or are hydraulically bounding.

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