SITE CHARACTERIZATION AND MODELING FOR AN IN-SITU CARBON MINERALIZATION PILOT IN THE EASTERN SNAKE RIVER PLAIN BASALTS, IDAHO, USA

Chevron Technical Center and Idaho National Laboratory are collaborating to pilot carbon mineralization in basalts of the Eastern Snake River Plain Aquifer, Idaho, using aqueous CO₂ injection. Pilot planning requires site-specific geologic and hydrogeologic characterization to constrain subsurface uncertainty and inform pilot design and forecasts. Here we present results of the first phase of site characterization and modeling activities to be used in pilot-scale flow and transport models.

Subsurface geology at the proposed pilot site is constrained by numerous previous studies that investigated outcrops, well logs, and several thousand feet of core. Similarly, the hydrogeology of the Eastern Snake River Plain aquifer is constrained by aquifer tests, long term-aquifer monitoring, and groundwater simulation studies. In general, the aquifer is hosted in layered basalt flows of Pliocene to Holocene age with interbedded sedimentary layers. Individual basalt flows are commonly composed of flow tops and bottoms that may be highly vesicular, pillowy, fractured, and brecciated, whereas flow interiors are less vesicular and have variable amounts of fracturing. Well tests suggest flow is dominated by fractures and breccia zones, which also provide significant surface area for carbon mineralization. Additional outcrop characterization was completed utilizing scanlines and drone photogrammetry to further constrain the control of fractures and breccia zones on hydraulic conductivity heterogeneity and anisotropy.

Basalt flow stratigraphy, geometry, fracture hydraulic conductivity, and hydrogeologic boundary conditions are integrated to build a static subsurface model of the pilot site. The model will be integrated with reaction-transport modeling to test injection-production well placements, injection intervals, plume migration, and to optimize the pilot design to achieve necessary learning outcomes to inform commercialization of carbon mineralization in mafic rocks.