Theme 6: Integrated Monitoring

 General Assembly A

Fiber Optic accelerometers as point receivers are a mature technology with proven reliability. We developed a new tool to address an industry need for long-duration, high-fidelity wavefield measurement in the downhole environment. The main objective is to share this technology’s significance and applicability to CCUS monitoring. We provide a brief history of these FO sensors and contrast the point receiver interferometers against Distributed Acoustic Sensing (DAS) to demonstrate their technical advantages. These optical accelerometers use a laser interrogator to convert motion to optical interference phase with ultra-high dynamic range and high linearity. All components of the fiber optic sensors and telemetry are passive, with no electronics downhole, delivering long life and very high reliability at temperatures greater than 150 °C. Arrays are configurable from one to hundreds of receiver levels at custom spacings. The interrogator may be located any distance from the borehole up to tens of kilometers away. These characteristics make the tool particularly useful for both active and passive (microseismic) surveys for CCUS applications. The time-stationary response characteristics are necessary for deriving time-lapse (4D) characterization of a reservoir and surrounding geology. We performed a field test of a five-level, 3-component downhole tool at the Bureau of Economic Geology test site in Devine, Texas. The tool was deployed in a 1,417 meter deep, steel-cased well. We acquired a walkaway VSP and a circular array of near-offset source points at 22.5 degree increments, both using an accelerated weight drop source. The walkaway data clearly show both incident and reflected P- and S-waves with sufficient fidelity to characterize the stress concentration via shear-wave birefringence. The circular array of near-offset points demonstrates the dramatic vector fidelity of the system. This technology delivers these results with the noise performance of geophones, superior vector fidelity and higher reliability at high temperatures than any comparable downhole tool.

J. B. Bunn1, P. E. Murray2(1. OptoSeis, Geospace Technologies; 2. FIP Geophysical Services