Development of a Low Noise Optical Interrogator for Interferometric Sensing Technologies

Electronic geophones currently used in the oil and gas industry cannot meet the ever-more demanding requirements for robust, high-temperature capabilities and abilities to record the broad-band seismic data needed for high-resolution imaging. Electronic geophones are not capable of recording the low-magnitude and high-frequency signals that are being produced by hydraulic fracturing, water and CO2 injection and oil and gas production processes. The electronic systems deployed today are also effectively small-aperture low-fidelity antennas which limits the accuracy of the location of the mapped events. The industry needs capabilities to deploy sensors at higher pressures and temperatures in vertical and horizontal boreholes and to record low-magnitude and high-frequency seismic events in high-fidelity. Fiber-optic based point vector sensors have been shown to overcome most of the shortcomings found in the legacy electronic sensors. The fiber sensors themselves are not as mechanically complex as their electric counterpart making them more robust and suitable to be long-term deployed in hostile environments. However, optical interrogators are today not commercially available and they are not easy to design. Effective optical vector sensing requires an advanced optical interrogator that can operate in a controlled field environment at the earth surface. A prototype fiber optic interferometric interrogator was designed, prototyped and successfully tested recording high-quality seismic optical vector sensor data. A fiber-optic interrogator capable of monitoring 300 optical sensors simultaneously while supporting the industry standard seismic interfaces will be designed, built, laboratory tested and field deployed. The interrogator will support interferometric fiber-optic sensors using an active modulation process. The interrogator will be tested and verified against current interrogator technologies at our facilities. A low-noise, push-pull Michelson interferometer or Mach-Zehnder sensor will also be constructed to test the noise capabilities of the newly developed interrogator. At first, the interrogator will be used in a laboratory setting while recording low-amplitude high-frequency data to validate and optimize the design. Next, the results from that process will be used to develop, build and test an operational commercial unit for the Fiber Optic Seismic Vector Sensor (FOSVS) arrays developed by Paulsson, Inc.Commercial Applications and Other Benefits There are almost 100,000 wells in the United States that have already been hydraulically fractured with a significant fracturing backlog of already drilled wells. When cost effective solutions are available for high-resolution and continuous monitoring, hydraulic fracturing will be monitored for financial, environmental and legal compliance reasons. The proposed low-noise interrogator system will provide the technically and cost-effectively means to monitor and map hydro fracture and production operations in real time. Fiber-optic sensors are also well suited for geothermal applications since they can tolerate temperatures over 300°C. Fiber-optic arrays will also be used to monitor CO2 injection for sequestration and production enhancements.