The Raft River geothermal field in southern Idaho is the site of a successful DOE Enhanced Geothermal System demonstration project. Prior to the drilling of sidetrack RRG-9 ST1, the stimulated well, a vertical seismic profile (VSP) survey was conducted in 2010 in the original well to image subsurface structures. The survey included a zero-offset VSP and eight walkaway VSP lines. The VSP data were recorded using 40 three-component receivers in well RRG-9, with a receiver interval of approximately 15 m, located at measured depths from 15 m to 600 m. Vibroseis sources with intervals of approximately 30 m to 60 m were used for the VSP survey. The maximum source offset from the well was around 2 km. We have processed the raw VSP data to separate the down-going and up-going wavefields, and built 1D and 2D velocity models using tomographic inversions of the first-arrival times of the down-going waves. We have then applied reverse-time migration to the up-going waves of the VSP data and obtained high-resolution subsurface images along the eight walkaway lines at the Raft River geothermal field.

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