Fiber Optic High Temperature Seismic Sensor

The U.S. Department of Energy (DOE) is seeking development of seismic sensors, under its Geothermal Technologies Program, to support the subsurface monitoring of geothermal reservoirs during reservoir stimulation and operation. It is anticipated that these sensors will respond within the frequency range from sub-Hz to multi-kHz, be compatible with packaging for downhole deployment, including the capability to operate within the temperature range from -20oC to +250oC, and having an expected operating lifetime of 5000 hr. Physical Optics Corporation (POC) proposes an innovative Fiber Optic High Temperature Seismic Sensor (FOTSS) technology based on a microbending sensor design using multimode fibers, which is stable at elevated temperatures. Using optical time domain reflectrometry with a diode laser for interrogation, and digital signal processing, the sensor provides sensitivity over a wide frequency range (sub-Hz to multi-kHz). In Phase I POC successfully demonstrated the feasibility of the FOTSS approach through computer simulations, developing and demonstrating a working prototype based on a series of proof-of-concept experiments and tests. POC demonstrated that the FOTTS Phase I prototype has sensitivity down to sub-mg levels with a bandwidth of 1400 Hz and high temperature resistance up to +250oC. The results of the testing were in good agreement with the simulation and modeling results. In Phase II POC plans to further develop the FOTSS system. POC will bring to maturity the FOTSS technology proven feasible in Phase I, and build a full-scale prototype FOTSS system for geothermal energy source monitoring directly applicable to DOE tasks. Commercial Applications and Other Benefits: The proposed sensor addresses the major DOE requirements for high-temperature endurance (250oC for 5000 hr), wide (several kHz) bandwidth, seismic sensor solution. High-temperature-resistant, permanent downhole sensor technologies support the expansion of geothermal energy by improving safety and enabling the development of new techniques to identify and monitor geothermal resources. In addition to geothermal well monitoring, commercial applications include deep oil and gas well seismic profiling for exploration and monitoring, environmental monitoring, and vibration measurements in high-temperature environments (e.g., engines, motors, rockets, and wind turbines). Additional markets exist for