Site Characterization and Monitoring
Site characterization prior to injection of carbon dioxide (CO2) typically involves geological surface field surveys, geophysical methods (seismic reflection, gravity, magnetics) and drilling wells to generate site-specific information about geologic, hydrogeologic, and biogeochemical conditions underground. Such investigation is a crucial early stage in understanding the subsurface environment by evaluating its geologic carbon storage capabilities. Characterization data derived from these activities provide the foundation for associated numerical modeling and monitoring networks, which are designed based on the current conceptual understanding of a site, then modified as additional site-specific characterization data become available.
Carbon storage sites are characterized and monitored to verify that they operate as permitted and do not endanger underground sources of drinking water or cause other adverse ecological impacts. Potential release pathways and the possibility for associated environmental impacts considered during development of the monitoring strategy inform the design basis for various monitoring system components.
The injection and monitoring wells within a targeted injection zone are monitored for the duration of a project to characterize pressure and CO2 transport response and guide operational and regulatory decision-making. Site characterization, monitoring, and verification activities track the lateral migration and containment of CO2 within the targeted injection zone; characterize hydraulic, geochemical, or geomechanical changes that occur within the injection zone and overlying confining zones; provide for early detection of any unanticipated containment loss to ensure protection of underground sources of drinking water; and monitor for associated changes in land surface elevation. Tracking results derived from injection and monitoring wells may provide the first indication of any unanticipated containment loss, so these wells are critical monitoring locations. Comparing observed and simulated arrival responses at early-detection wells and shallower monitoring locations typically continues throughout the life of the project. The responses are used to calibrate and verify the model and improve its predictive capability for assessing the long-term environmental impacts of any loss of CO2 containment.
PNNL, in close association with Battelle, has been leading the characterization of storage sites for several major U.S. projects. PNNL is managed by Ohio-based Battelle for the U.S. Department of Energy.