Development of a Low Noise Optical Interrogator for Interferometric Sensing Technologies

Geophone technologies cannot meet the ever-more demanding requirements for robust, high-temperature and resolution capabilities including the recording of small-amplitude, broad-band and high-frequency seismic data required for high-resolution imaging. Geophones cannot record low-magnitude (1,000 Hz) that are being produced by hydraulic fracturing and water and CO2 injection associated with oil and gas and geothermal energy production. The geophone systems deployed are also small-aperture, low-fidelity antennas which limit the location accuracy of mapped events. The industry also requires capabilities to deploy sensors at higher pressures and temperatures in vertical and horizontal boreholes for high-fidelity recording of low-magnitude high-frequency seismic events. Fiber-Optic Seismic Vector Sensors (FOSVS) have been shown to overcome most of the shortcomings found with legacy geophones because they are not as mechanically complex and are made entirely using high-temperature 572°F(300°C) tolerant components, making them more robust and suitable for long-term deployment in hostile and high-temperature environments. However, interferometric interrogators required for optical sensor applications are not commercially available. Effective use of FOSVS require an advanced optical interrogator that can operate in a surface field instrument-room. A fiber optic interferometric interrogator was designed, prototyped and successfully tested recording high-quality seismic sensor data. Our goal was to develop a fiber-optic interrogator technology capable of monitoring 300 FOSVS and 300 acoustic large-aperture Distributed Optical Sensors (DOS) simultaneously while supporting industry-standard seismic interfaces. The interrogator will support all interferometric fiber-optic sensors using an active modulation process. It was successfully tested and verified against current seismic acquisition technologies. A low-noise, Mach-Zehnder sensor was constructed to test the noise capabilities of the new interrogator. The interrogator will be used in a laboratory setting while recording low-amplitude, high-frequency data to validate and optimize the design. The results from that process will be used to develop, manufacture, and field test in a well a novel commercial grade interrogator for the FOSVS-DOS arrays. Unconventional Oil and Gas (UOG) development currently suffers from very poor economics. There are more than 100,000 wells in the United States that have already been hydraulically fractured with a significant backlog of already drilled but not fractured wells providing for a very large economic opportunity for better imaging. Cost effective solutions are required for real-time high-resolution imaging and monitoring of production for financial, environmental, and legal reasons. The proposed low-noise interrogator system will provide a technical and cost-effective means for continuous and real-time mapping and monitoring of UOG and conventional Oil & Gas production operations. Our fiber-optic sensor arrays and companion interrogator are suitable for Enhanced Geothermal Systems (EGS) applications since our FOSVS can tolerate temperatures over 572°F(300°C). The system can also be used to monitor CO2 injection for sequestration and oil & gas production.