Lawrence Berkeley National Laboratory

Careful site characterization is critical for successful geologic sequestration of CO2, especially for sequestration in brine-bearing formations that have not been previously used for other purposes. Traditional site characterization techniques such as geophysical imaging, well logging, core analyses, interference well testing, and tracer testing are all valuable. However, the injection and monitoring of CO2 itself provides a wealth of additional information. Rather than considering a rigid chronology in which CO2 sequestration occurs only after site characterization is complete, we recommend that CO2 injection and monitoring be an integral part of the site-characterization process. The advantages of this approach are numerous. The obvious benefit of CO2 injection is to provide information on multi-phase flow properties, which cannot be obtained from traditional sitecharacterization techniques that examine single-phase conditions. Additionally, the low density and viscosity of CO2 compared to brine causes the two components to flow through the subsurface differently, potentially revealing distinct features of the geology. Finally, to understand sequestered CO2 behavior in the subsurface, there is no substitute for studying the movement of CO2 directly. Making CO2 injection part of site characterization has practical benefits as well. The infrastructure for surface handling of CO2 (compression, heating, local storage) can be developed, the CO2 injection process can be debugged, and monitoring techniques can be field-tested. Prior to actual sequestration, small amounts of CO2 may be trucked in. Later, monitoring accompanying the actual sequestration operations may be used to continually refine and improve understanding of CO2 behavior in the subsurface.