APPLICATION OF SEISMIC IMAGING TECHNIQUES TO THE GEOLOGIC SEQUESTRATION OF CO2 IN THE PACIFIC NORTHWEST

Geologic sequestration of carbon dioxide (CO₂) may be one of the highest potential technologies for addressing emissions from large, industrial sources of anthropogenic CO₂. The availability and quality of the geologic storage resource varies from one region of the United States to another, and in the Pacific Northwest, this resource varies significantly, even across short distances. In Washington and Oregon, there may be a number of likely geologic targets, located in tectonically stable areas and at suitable depths to ensure the pressures and temperatures necessary to maintain CO₂ in its supercritical state. These targets include deep, saline-filled sedimentary formations, unmineable coal beds, and flood basalts. Supercritical CO₂ can be injected into these formations and stored over very long timeframes via dissolution into the formation fluids, hydrodynamic trapping, or mineralization. Because of their ability to store significant amounts of CO₂ via all three of these mechanisms, and because they may represent the largest CO₂ storage resource available to the Pacific Northwest, the Columbia River Basalt Group represents an attractive target for sequestration. Though a high-potential target, the Columbia River Basalts also pose some of the greatest technical challenges for the critical seismic imaging component of reservoir characterization. Characterization of a potential storage formation includes an assessment of the ability of the formation to retain the injectate over very long periods of time, including assessing the integrity of the impermeable seal, determining and mitigating the presence of existing wellbores, and identification of transmissive faults and faults that may be near their critical stress limits. 3D seismic data, in combination with petrophysical log and rock data, represents one of the most valuable tools in assessing storage capacity, injectivity, and suitability for long-term retention of injected CO₂. 4D seismic analysis is a key technology in tracking the geometry of the injected plume over time. We review the role of multi-trace geometric attributes to assess structural aspects of potential geologic storage reservoirs, the role of seismic frequency attributes to help quantify CO₂ saturations, and some of the issues and advances in seismically imaging basalt reservoirs.