| Abstract |
A series of 9 2D and 2D swath surface reflection seismic profiles were acquired over the Brady's Hot Springs producing geothermal field in Churchill County, Nevada. These lines were acquired with much finer source and geophone spacing than that used in typical seismic acquisition. This allowed for more effective filtering of ground roll and other near surface interfering events. Post stack time migration images were produced. Typical of geothermal environments, profiles showed clear coherent reflections over the valley fill, but were less than ideal over the highly faulted producing area. Nonetheless, as discussed by Siler et al., (2016) in a companion paper, the profiles were found to be useful for mapping faults and lithological boundaries. As part of the same effort, in June 2015, a vertical seismic profile (VSP) survey was conducted at Brady's. The purpose of the survey was to better characterize the subsurface fractures and faults. In conjunction, numerical modeling of fracture impacts on the seismic wave propagation was performed. This modeling suggests that VSP will be more effective than surface reflection seismic for imaging near vertical structures such as faults and fractures. The survey was conducted in a well which is being used for EGS treatment tests at Brady's. A novel high-temperature, 36-level, 3-component, fiber optic accelerometer array with 20 ft spacing between sensor levels was used. The seismic source was a triaxial vibroseis truck capable of generating 3 independent, linear components of ground motion (x, y, and z). Combining the 3 source components with the 3 sensor components at each depth gives a 9-component VSP and allows investigation of the full tensor of seismic wave motion. This type of survey is especially important to aid understanding of converted waves (e.g. P-wave to S-wave) and seismic anisotropy, both of which can be controlled by fracturing and can be used to image fracture/fault zones and potentially invert for fracture properties. Data were recorded between 300 ft and 2020 ft depths, above the EGS reservoir. Initial data analysis and modeling results will be discussed. |