Risk Assessment Framework for Geologic Carbon Sequestration Sites Curtis M. Oldenburg1, Steven L. Bryant2, and Jean-Philippe Nicot1 1Lawrence Berkeley National Laboratory 2University of Texas, Austin 3Texas Bureau of Economic Geology ABSTRACT CF SUBMODELS Carbon Capture and Storage (CCS) mitigates the risk of climate change by directly reducing greenhouse gas emissions. Mitigating climate change by CCS entails costs (e.g., monetary for implementing the capture and storage technology) and risks (e.g., possibility of local impacts such as CO2 leakage or induced seismicity due to CO2 injection). We have developed a simple and transparent Certification Framework (CF) for certifying that the local risks of a given Geologic Carbon Sequestration (GCS) site are below agreed-upon thresholds. Leakage risk in the CF is based on the concept of effective trapping of CO2, whereby both the likelihood and impact of CO2 leakage are considered. The CF calculates CO2 (and brine) leakage risk by (1) estimating the probability of intersection of conductive faults and potentially leaky wells with the expected CO2 plume, and by (2) modeling fluxes or concentrations of CO2 under potential leakage scenarios as proxies for impacts to compartments (such as potable groundwater). Reservoir Simulation Reservoir Simulation (GEM or TOUGH2) is used to calculate the CO2 plume evolution and brine pressure perturbation footprints. Saturation and/or concentrations and pressures are either read from a catalog of pre-simulated results or computed on a site-specific basis. Well and Fault Leakage The CF calculates CO2 leakage flux using either simple models for flow up conduits (Oldenburg et al., 2008) or the more complex multicomponent drift-flux model (Pan et al., 2008). Fault Intersection Probability The CF calculates plume-fault intersection probability and considers likelihood of encountering a fault with an offset, e.g., larger than the seal thickness and therefore likely to be a leaky fault (Jordan et al., 2008). CF CONCEPTUALIZATION Fault Connectivity Intersecting fault networks can give rise to connected pathways from the storage region to shallow compartments. Our project is carrying out research on the use of percolation theory and fuzzy rules to model fault networks (Zhang et al., 2008; 2009). ECA Compartment NSE Compartment Dense Gas Dispersion Impact In the unlikely event that CO2 reaches the ground surface, the CF is carrying out research to use dense-gas dispersion modeling to understand how surface leakage of CO2 will disperse under various condiions of topography and ambient wind (Chow et al., 2009). USDW Compartment Conduits (wells and faults) . CASE STUDY (SOUTHERN SAN JOAQUIN VALLEY, CA) HMR Compartment Leakage Storage Region Injection into Vedder Bakersfield, CA Probability System input description Simulation output CF Output USDW is the main compartment vulnerable to impacts. USDW is approx. 1 km vertically above storage region. 250,000 t CO2/yr for four years into 160 m thick Vedder Fm at 2300 m depth. Very low probability that CO2 plume will encounter wells. Small chance (~3%) that CO2 will encounter fault with offset equal to seal thickness. Faults not expected to be conductive by shale-gouge ratio and oil trapping experience. Leakage risk found to be de minimis (effective trapping) for this site. CONCLUSIONS We have developed a simple and transparent framework for estimating local risks of GCS, e.g, due to CO2 or brine leakage. The CF simplifies the complex geologic and environmental system into a handful of compartments and relies on specialized submodels to calculate probabilities of various intersections and the resulting fluxes or concentrations that lead to impact. Research is continuing on the development of specialized submodels and on applications of the CF to specific sites (e.g., U.S. and international pilot and industrial-scale sites). ECA = Emission Credits and Atmosphere HS = Health, Safety, and Environment NSE = Near-Surface Environment USDW = Underground Source of Drinking Water HMR = Hydrocarbon and Mineral Resources CO2 = Injected CO2 source Fluxes and concentrations (j, C) of CO2 into/in compartments are proxies for impact to vulnerable assets. CF WORKFLOW REFERENCES Oldenburg, C.M., J.-P. Nicot, and S.L. Bryant, Case studies of the application of the Certification Framework to two geologic carbon sequestration sites, Energy Procedia, GHGT9 conference, Nov. 16-20, 2008, Washington DC. LBNL-1421E. Oldenburg, C.M., S.L. Bryant, and J.-P. Nicot, Certification Framework Based on Effective Trapping for Geologic Carbon Sequestration, Int. J. of Greenhouse Gas Control 3, 444–457, 2009, LBNL-1549E. Oldenburg, C.M., S.L. Bryant, J.-P. Nicot, N. Kumar, Y. Zhang, P. Jordan, L. Pan, P. Granvold, F.K. Chow, Model Components of the Certification Framework for Geologic Carbon Sequestration Risk Assessment, in Carbon Dioxide Capture for Storage in Deep Geological Formations, Volume 3, L.I. Eide (Ed.), CPL Press and BP, 2009. LBNL-2038E. Jordan, P.D., C.M. Oldenburg, and J.-P. Nicot, Characterizing fault-plume intersection probability for geologic carbon sequestration leakage risk assessment, Energy Procedia, GHGT9 conference, Nov. 16-20, 2008, Washington DC, LBNL-1522E. Zhang, Y., C.M. Oldenburg, and S. Finsterle, Percolation-Theory and Fuzzy Rule-Based Probability Estimation of Fault Leakage at Geologic Carbon Sequestration Sites, Env. Earth Sci., LBNL-2172E, in press. Zhang, Y., C.M. Oldenburg, P.D. Jordan, S. Finsterle, and K. Zhang, Fuzzy Rule-Based Probability Estimation of Fault Leakage at Geologic Carbon Sequestration Sites, Energy Procedia, GHGT9 conference, Nov. 16-20, 2008, Washington DC. LBNL-1415E. Chow, F.K., P.W. Granvold, and C.M. Oldenburg, Modeling the effects of topography and wind on atmospheric dispersion of CO2 surface leakage at geologic carbon sequestration sites, Energy Procedia, GHGT9 conference, Nov. 16-20, 2008, Washington DC., LBNL-1420E. ACKNOWLEDGMENTS This work was supported in part by the CO2 Capture Project (CCP) of the Joint Industry Program (JIP), and by Lawrence Berkeley National Laboratory under Department of Energy Contract No. DE-AC02-05CH11231. cmoldenburg@lbl.gov , steven_bryant@mail.utexas.edu , jp.nicot@beg.utexas.edu