Incremental Time-Lapse Monitoring of CO2 EOR and Geologic Storage Using a Scalable Automated Semipermeant Seismic Array

The Energy & Environmental Research Center conducted proof-of-concept field testing of a scalable automated semipermanent seismic array (SASSA) and trace-based processing and interpretation method that can detect CO₂ saturation changes at discrete locations in a reservoir undergoing CO₂ injection for enhanced oil recovery (EOR) or geologic storage. Using a sparse array of geophones and a stationary source, SASSA is capable of operating remotely and autonomously and has a greatly reduced environmental and operational footprint compared to traditional time-lapse 3-D seismic surveys. The trace-based method allows for rapid processing and interpretation that could ultimately contribute to same-day decision making. The SASSA technique was demonstrated at an active CO₂ EOR project during a 12-month field-test which acquired 41 sets of time-lapse data using 96 three-component geophones and a single remotely operated accelerated weight drop source. The technique detected CO₂ saturation changes that were validated against a conventional time-lapse 2-D line and advanced reservoir simulations. While the test resulted in a proof-of-concept, many of the records were impacted by noise.

A second field demonstration is under way that incorporates lessons learned from the initial field test to improve signal-to-noise ratio. Specifically, the demonstration will incorporate stronger sources, increase the shots-per-acquisition to improve stacking, incorporate strategic placement of geophones to reduce noise, and acquire complementary data sets regarding weather and ground conditions to develop tools for processing noise and to determine optimal conditions for system operation. Two orbital vibrators at offset source locations will operated consecutively during each acquisition as a technique to avoid the ground roll zone and improve coverage. The second field demonstration will provide key information about system performance, cost, designs and processing to advance the next-generation SASSA monitoring technique toward commercialization.