FIBER OPTIC SEISMIC VECTOR SENSORS SET THE STANDARD FOR MONITORING CCS AND EGS PROCESSES

Paulsson, Inc. has designed, built, tested, and deployed novel Fiber Optic Seismic Vector Sensors (FOSVS) with a modeled vector fidelity of better than 90dB. Paulsson has furthermore, using field data from these sensors, processed and located events smaller than M-6 at frequencies over 2,000 Hz in the field at a depth of 5,500 ft by monitoring CO2 injection into a fractured carbonate reef. Paulsson deployed the new sensors at a CO2 injection site for Battelle in Michigan and for COSO in California. The development of Paulsson’s vector sensors was funded by several grants from US DOE. The FOSVS are now in their fourth-generation development stage.

Our third generation FOSVS were able to detect seismic events in our laboratory with an energy smaller than 1 micro-Joule (µJ) at frequencies over 10 kHz. This third-generation sensor was also tested at 320°C (608°F) for seven days in our high temperature oven. During the temperature, test tap tests confirmed that the three vector seismic sensors were operational and fully functional during the entire heating process.

Our recent fourth-generation fiber optic seismic vector sensor is even more sensitive. In the laboratory we have recorded events as small as 20 nano Joule with this new sensor which is still under development.

During the development of the FOSVS Paulsson designed and built a borehole deployment system designed around small diameter drill pipe that can safely deploy many 100s of optical 3C vector sensors to a drilled depth exceeding 20,000 ft in vertical and horizontal boreholes. This deployment system is critical for deploying and clamping the optical sensors to the borehole wall. Our deployment system eliminates borehole tube waves that so often destroy the quality of borehole seismic data.

During the successful monitoring of the CO2 injection working with Battelle and Core Energy we were able to record the sound of the CO2 fluid flow in fractures in the carbonate reef. This provides evidence that using arrays of optical borehole 3C vector sensors is effective to monitor and understand subsurface dynamic processes such as injection of CO2.

In comparison, acoustic sensors are not capable of detecting, monitoring and mapping complex structures such as earthquake fault zones or complex events such as injection or extraction of fluids including CO2 for CCS or H2O for fracturing the formation for Enhanced Geothermal Systems (EGS).