GEOCHEMICAL, MICROBIOLOGICAL, AND PERMEABILITY CHARACTERISTICS INDICATING VERTICAL ZONATION OF THE ARBUCKLE SALINE AQUIFER, A POTENTIAL CO2 STORAGE RESERVOIR
Permeability values derived from NMR wireline logs and estimated from DSTs are particularly low between 1332 m-1460 m, qualifying it as a potential baffle which coincides with the lower Jefferson City-Cotter formation, a tight, dense, primarily micritic dolomite. Seismic data collected within the study area also reported high seismic impedance for the middle Arbuckle (1339 m-1461 m) indicating high density rocks, which largely overlaps the zone of low permeability observed in the well logs. Microbiological data for drill stem fluids identify species belonging to the orders Bacteriodales, Firmicutes, Actinobacteria and Proteobacteria, with community diversity of 43% at a depth of 1277 m, 62% diversity at 1321 m, and 39% diversity at 1378 m, which follows the same trend as biomass. Analyses of δ18O and δ2H from DST fluids suggest some connectivity between the Arbuckle and overlying Mississippian units, as well as heterogeneity in the Upper Arbuckle with distinct separation between the Upper Arbuckle and Lower Arbuckle. Br/Cl and SO4/Cl ratios also point to a hydraulic separation between the Arbuckle and overlying Mississippian rocks as well as the Upper and Lower Arbuckle units.
Our petrophysical and geochemical data are consistent with hydraulic separation of the Upper and Lower Arbuckle, which could result in decreased storage capacity. However, they also indicate the presence of smaller, less influential baffles in the Upper Arbuckle, which could serve as important impediments to buoyant plume behavior, thereby increasing pore space and solubility trapping.