THE BIG SKY CARBON SEQUESTRATION WALLULA BASALT PILOT: STRATIGRAPHY AND IMPLICATIONS

Brecciated flow tops of the Columbia River Basalt Group (CRB) in eastern Washington form regional aquifers, and are targets for sequestration of anthropogenic CO₂ in areas where the basalts contain unpotable water and are at depths greater than 800 m. In laboratory experiments, CRB basalts react with formation water and supercritical CO₂ to precipitate carbonates, thus adding a potential mineral trapping mechanism to the dissolution and hydrodynamic trapping mechanisms of conventional sedimentary sequestration reservoirs. The DOE’s Big Sky Regional Carbon Sequestration Partnership has completed drilling the first pilot well to a depth of 1253 m on the Boise White Paper Mill property at Wallula, Washington. This well is being tested for reservoir capacity and seal integrity in the deeper basalt section. If characterization results are favorable, 1000 metric tons of food-grade CO₂ will be injected and studied over a multi-year period to obtain field data on in-situ mineralization.

Initiation of drilling was preceded by acquisition and processing of a 6.5 km, five line multi-component 2D seismic swath. The resulting migrated P-P data imaged a succession of approximately 2400 m of unfaulted basalt, suitable for wellbore characterization and testing. Subsurface stratigraphy at the pilot well was established through XRF geochemistry, tied to wireline logs and petrographic data from rotary sidewall cores and well cuttings. The Wanapum Formation contains numerous porous reservoir intervals, but few thick seal intervals. The Grand Ronde Formation contains more numerous containment intervals, but fewer porous flow tops. The new wellbore data, as integrated with data from outcrop and hydrocarbon exploration wells are consistent with the presence of a large Grand Ronde lava lake in the Pasco Basin. These new data are critical for developing an understanding of regional reservoir heterogeneity and seals of this important but unconventional sequestration target.