A three-dimensional structural model of The Geysers geothermal field is being developed by Calpine Corporation using Paradigm Geophysical SKUA GOCAD software originally designed for the oil and gas industry. Structural model building constraints include lithology logs, surface geologic maps and seismicity hypocenters available from the Northern California Earthquake Data Center (NCEDC) and Lawrence Berkeley National Laboratory (LBNL), as well as temperature logs, pressure logs, tracer analysis patterns, heat flow patterns, and reservoir history matching. A field-wide ArcGIS digital surface map compiled in 2014 from existing hard copy surface geology maps and refined in 2015 now provides improved constraint on the surface-to-subsurface structural relationships. Recent advances to the SKUA GOCAD 3D seismicity analysis and time animation software provide an additional and substantial constraint on structural model building through enhanced visualization of the spatiotemporal relationships between induced seismicity, fracture orientations and water injection at The Geysers. The result is a refined understanding of structural relationships, fluid flow paths, fluid boundaries, reservoir heterogeneity and compartmentalization at The Geysers. We can now demonstrate that The Geysers reservoir is subdivided by intersecting zones of faulting and fracturing, the majority of which are oriented NNW-SSE and ENE-WSW and sometimes expressed in the surface geology. The 3D structural model development is part of a program to honor a vast collection of field data and more closely link geoscience, reservoir engineering and drilling. This is anticipated to contribute to reservoir management and induced seismicity mitigation efforts at The Geysers.

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