TEXTURAL FEATURES OF COLUMBIA RIVER FLOOD BASALTS: IMPLICATIONS FOR THE SEQUESTRATION OF ANTHROPOGENIC CARBON DIOXIDE

Continental flood basalts have potential as underground hosts for long-term storage of anthropogenic carbon dioxide. As a supercritical fluid, CO₂ is pumped into deep basalt, both of which react, creating stable calcite and other carbonate minerals. One potential sequestration site, the Columbia River Basalt Province (CRB), is attractive because tholeiitic basalt flows cover a total area and volume of basalt reaching 200,000 km² and 234,000 km³ respectively. The optimal location to inject supercritical CO₂ is between two basalt flows in the interflow zone. In the CRB, this zone is typically brecciated and highly vesicular, allowing fluid movement and reaction with the basalt. To identify and characterize interflow zones and their seals, the DOE Big Sky Regional Carbon Sequestration Partnership is conducting a basalt pilot test on the Boise White Paper Mill property at Wallula, Washington.

Although the stratigraphy, geochemistry and other aspects of the CRB have a long history of study, the implications of basalt textural features as related to CO₂ sequestration are less established. We present a review of breccias and other textural features in the Grande Ronde and Wanapum Formations, as observed in cores and rock cuttings from the 2009 Big Sky Basalt Pilot Well along with outcrop observations and published literature on CRB basalts in eastern Washington. We find that most reservoir-quality breccias in outcrop are pahoehoe flow tops; except for a variety of basalt/water interaction textures, few breccias are associated with flow bases. Resistivity-based image logs from the 2009 pilot well are particularly helpful in placing textures observed in core and cuttings into a flow-scale context. Image logs allow estimates of vesicle density and maximum vesicle diameter as well as direct images of brecciated areas, interior flow structures and a variety of cooling and tectonic fracture geometries and densities. These features, when integrated with other data, may allow important clues to type of flow, distance from lava source, and thickness of flow, and may provide a tool for predicting mechanical properties and vertical development of reservoirs and sequestration seals.