Seal Analysis of Geologic Co2 Storage Sites
Seal analysis of hydrocarbon systems focuses on identifying effective seal horizons and understanding geologic controls on sealing ‘capacity’ (the hydrocarbon column contained by the seal under in situ conditions) based on capillary pressure measurements supplemented with other petrologic and stratigraphic data. While comparable seal analysis should also play a role in geologic CO2 storage, additional questions, not part of typical hydrocarbon seal analysis, must be addressed. These include: 1) What is the impact of CO2-rich fluids on chemical alterations of caprock minerals and sealing capacity? 2) What rate and amount of CO2 leakage would be acceptable? 3) What geomechanical impacts accompany CO2 injection? 4) Can impact on fluid flow of preexisting seal fractures and flaws be adequately characterized prior to CO2 injection? The Southwest and Southeast Regional Carbon Sequestration Partnerships, funded by the U.S. Department of Energy and managed by DOE’s National Energy Technology Laboratory, are investigating these questions by studying four formations identified as potential regional seals for geologic CO2 storage: the Gothic Shale in Utah; the Kirtland Shale/Formation in New Mexico; the Tuscaloosa Marine Shale in Mississippi; and the Selma Chalk in Mississippi. For these we compare results of typical seal analysis including lithofacies interpretation, mercury injection capillary pressure measurements, rock properties, XRD mineralogy, SEM/EDX, and thin section petrology while investigating the unique questions posed by CO2 storage. The comparison emphasizes differences in geologic controls on sealing capacity for continental and marine formations. CO2 column heights are compared for each site based on capillary pressure measurements. Fracture analyses and geomechanical testing of cores yield information on seal structural properties. Numerical models of poroelastic and inelastic processes evaluate deformational trends within seals, adjacent target reservoirs, and overburden. Coupled fluid flow and geomechanical modeling address impact of fractures on multiphase fluid transport. Chemical reactivity is addressed through geochemical modeling. Through this study we identify key considerations for effective seals for long-term geologic storage of CO2. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the U.S. Department of Energy under contract DE-ACOC4-94AL85000.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009