Anisotropic Seismic Imaging and Inversion for Subsurface Characterization at the Blue Mountain Geothermal Field in Nevada

Abstract

The Blue Mountain geothermal power plant is located at the base of Blue Mountain, west of Winnemucca, Nevada. The power plant was built in 2009 with an installed gross capacity of 49.5 MW and net capacity of 40 MW. Currently, the net power production is 29 MW because production temperatures declined steeply for the first 4 years of production but have been mitigated recently. Now, the project owner, AltaRock Energy is implementing an aggressive improvement plan to increase the production to plant capacity. Subsurface characterization is crucial for new well placement. In 2007, seismic data along seven 2D lines were acquired at Blue Mountain for subsurface characterization. The data contain strong ground-roll noise, resulting in a great challenge for full-waveform-based anisotropic inversion and migration imaging. We employ our newly developed wavenumber-adaptive frequency-space filtering technique to successfully remove the ground-roll noise and obtain high-quality pre-stack seismic waveform data for seismic inversion and imaging. We build anisotropic models along the seven 2D lines using anisotropic full-waveform inversion of the processed seismic data. We then conduct anisotropic reverse-time migration using the anisotropic models and our newly processed seismic data to obtain high-resolution subsurface images at Blue Mountain. The high-resolution subsurface images reveal steeply dipping features west of the mountain front that could be interpreted as faults not previously recognized on the seismic profiles or Miocene diabase dykes offset by normal faulting from those exposed on Blue Mountain. The new seismic images can provide valuable information for design and selection of future geophysical studies to further characterize these features and eventually for optimizing the placement of new wells.