Basic Research Needs for Geosciences - Energetics Meetings and ...

APPENDIX 1: TECHNICAL PERSPECTIVES RESOURCE DOCUMENTconsequently is difficult to predict; however, standard techniques can measure residual phasetrapping directly. If a CO 2 plume does migrate from the injection point, residual phase trappingwill attenuate the plume and may eventually immobilize a substantial fraction. This mechanismacts over long time scales and CO 2 trapped this way may be considered permanently trappedbecause active injection is required to displace it.Once in the pore volume, the CO 2 will dissolve into other pore fluids, including hydrocarbonspecies (oil and gas) or brines. Depending on the fluid composition and reservoir condition, thismay occur rapidly (seconds to minutes) or over a period of tens to hundreds of years. Thevolume of CO 2 that may be dissolved into brines commonly ranges from 1–4% of the porevolume—this mechanism and these ranges served as the basis for many of the earliest estimatesof geological storage capacity potential (e.g., Bergman and Winter 1995). Once dissolved, theCO 2 –bearing brines are denser than the original brines, and so the strong buoyant forces of freephasegas are replaced by small downward forces.Over longer time scales (hundreds to thousands of years) the dissolved CO 2 may react withminerals in the rock volume to dissolve or precipitate new carbonate minerals. For the majorityof the rock volume and major minerals, this process is slow, and may take hundreds to thousandsof years to achieve substantial storage volumes (e.g., Wilson and Monea 2004). However, recentexperiments demonstrated that a small fraction of the mineral volume has rapid kinetics that maydissolve and precipitate on the time scale of seconds to hours (Knauss et al. 2005b). Subsurfacemicrobial activity might also accelerate mineralization or dissolution kinetics; additional researchFigure 3. Schematic diagram of large injection at 10 years time illustrating the main storagemechanisms. All CO 2 plumes (yellow) are trapped beneath impermeable shales (not shown). Theupper unit is heterogeneous with a low net percent usable porosity, whereas the lower unit ishomogeneous. Central insets show CO 2 as a mobile phase (lower) and as a trapped residualphase (upper). Right insets show CO 2 dissolution (upper) and CO 2 mineralization (lower). AfterMIT (2007).Appendix 1 • 10Basic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems