Geophysical Monitoring of CO2 Sequestrations
Geologic CO2 sequestration is a process of capturing and storing CO2 in appropriate geological settings. By keeping the waste gas from escaping to the atmosphere, we hope to reduce the greenhouse effect and to assist in the mitigation of global warming. Depleted oil or gas reservoirs, deep saline aquifers and deep unminable coalbeds are believed to be good geological settings for CO2 storage. For safety and operational reasons, we must perform subsurface as well as surface monitoring.
We can use direct and/or remote sensing methods for CO2 monitoring. Examples of direct sampling methods include surface chemical sensors and monitoring wells, which provide high spatial resolution over a small volume of the storage reservoir. Geophysical methods, such as seismic, electromagnetics, gravity, and surface deformation, are remote sensing techniques, which generally provide large coverage but lower spatial resolution. Our research, supported by Global Climate and Energy Project (GCEP), has concentrated to seismic methods for quasi-continuous monitoring. A general investigation on other possible geophysical monitoring methods can be found in (Wynn, 2003), where we concluded that seismic methods will have the broadest applicability for the CO2 monitoring in various geologic settings. Special and advanced seismic monitoring techniques are being developed in our group.
Seismic monitoring on CO2 has special requirements. It is waste surveillance that may need decades of surveillance. Therefore it must be cost effective. We have proposed and developed a quasi-continuous monitoring strategy, named True4-D, for seismic monitoring of CO2 storage. We use sparse data acquisition, dynamic imaging and image integration to achieve cost-effective and quasi-continuous monitoring strategy. Our proposed strategy involves research in three distinct domains: data, processing, and image integration.