| Abstract |
In March 2016 an extensive integrated survey was performed at the geothermal field at Brady Hot Springs, Nevada, where highly permeable conduits along faults appear to channel fluids from shallow aquifers to the deep geothermal reservoir tapped by the production wells. The 15-day deployment included 4 distinct time intervals with intentional manipulations of the pumping rates in injection and production wells. The data set included, fiber-optic cables for Distributed Acoustic Sensing (DAS) and Distributed Temperature Sensing (DTS) arranged vertically in a borehole to ~400 m depth and horizontally in a trench 8700 m in length. The vertical installation in well 56-1 was organized quickly after an initial deployment in well 55-1 failed when an in-well calcification collapsed under the weight of sand which was intended to improve coupling between the fiber cable and borehole wall. Well 56-1 was drilled to 732m in 1991 and completed with a cemented production casing to 314m and a slotted liner between 314m and 369m. (All depths referenced to KB 6.7m above ground level.) 369m of 3.2mm (1/8 in) optical fiber in metal tube (FIMT) cable was deployed into the well. It contained both single-mode and multi-mode fibers with optical U-bends at the bottom. Silixa DTS and DAS interrogators were operated to continuously monitor the installation for 8 days. In addition to providing active and passive seismic waveform data, the DAS was processed to extract fiber slow strain at a rate comparable to the DTS (2 samples/min). Material will be presented that reviews and discusses observable phenomena that supplement and constrain processing algorithms and interpretations. The work presented herein has been funded in part by the Office of Energy Efficiency and Renewable Energy (EERE), U.S. Department of Energy, under Award Number DE-EE0006760. |