Geologic framework for the national assessment of carbon dioxide storage resources: Alaska North Slope and Kandik Basin, Alaska

This report presents fourteen storage assessment units (SAUs) from the Alaska North Slope and two SAUs from the Kandik Basin of Alaska. The Alaska North Slope is a broad, north-dipping coastal plain that is underlain by a thick succession of sedimentary rocks that accumulated steadily throughout much of the Phanerozoic during three major tectonic sequences: the Mississippian through Triassic Ellesmerian sequence, the Jurassic through Lower Cretaceous Beaufortian sequence, and the Cretaceous and Tertiary Brookian sequence. Stratigraphic packages associated with all three of these tectonic sequences are suited to geologic carbon dioxide (CO₂) sequestration. The lower part of the Ellesmerian sequence contains five potential SAUs, two of which have reservoirs within the Endicott Group and three of which have reservoirs within the Lisburne Group. Another potential SAU has sandstone-prone reservoir units interbedded with the upper part of the Ellesmerian Shublik Formation and the Beaufortian Kingak Shale. The Brookian sequence contains eight potential SAUs that have reservoirs that are defined by the various Cretaceous and Tertiary deltaic topset strata of the Colville foreland basin as well as associated slope aprons and submarine turbidite fan complexes.

In east-central Alaska, Kandik Basin is an extension of cratonic North America and straddles the border between Alaska and Canada. The basin contains a section of Neoproterozoic to Mesozoic rocks, which have been multiply deformed during the Phanerozoic. Paleozoic strata within the basin appear to be suited to geologic CO₂ sequestration. We defined two SAUs within this interval, which are the Upper Devonian and Mississippian Nation River Formation SAU and the Lower Permian to Lower Cretaceous Step Conglomerate and Tahkandit Limestone SAU.

For each SAU in both of the basins, we discuss the areal distribution of suitable CO₂ sequestration reservoir rock. We also characterize the overlying sealing unit and describe the geologic characteristics that influence the potential CO₂ storage volume and reservoir performance. These characteristics include reservoir depth, gross thickness, net thickness, porosity, permeability, and groundwater salinity. Case-by-case strategies for estimating the pore volume existing within structurally and (or) stratigraphically closed traps are presented. Although assessment results are not contained in this report, the geologic information included herein was employed to calculate the potential storage volume in the various SAUs. Lastly, in this report, we present the rationale for not conducting assessment work in fifteen sedimentary basins distributed across the Alaskan interior and within Alaskan State waters.