Paper No. 7
Presentation Time: 10:30 AM


JUNG, Na-Hyun1, HAN, Weon Shik1, KIM, Kue-Young2, WATSON, Zachary T.1, GRAHAM, Jack P.1 and THAO, Cheng1, (1)Geosciences, University of Wisconsin-Milwaukee, Milwaukee, WI 53201, (2)Korea Institute of Geoscience and Mineral Resources, Daejeon, 305350, South Korea,

Geologic CO2 sequestration has been proposed as a desirable option for reducing atmospheric CO2 emissions, but it can be an expensive failure if stored CO2 leaks from engineered sites. This study carried out a diffusive soil CO2 flux survey in conjunction with numerical simulations of CO2 leakage in the fault zones of the Colorado Plateau in east-central Utah, with the aim of having implications for geologic CO2 storage. 440 and 140 measurements of soil CO2 flux were made at 395 and 129 sites respectively in the Little Grand Wash (LGWFZ) and Salt Wash fault zones (SWFZ). CO2 flux anomalies in the SWFZ (~1,428 g m-2 d-1) are comparably smaller to the LGWFZ (~36,259 g m-2 d-1). Anomalously high CO2 fluxes were localized in close proximity of travertines on the northern fault traces (e.g. 5,917 g m-2 d-1), joint zones in sandstones (e.g. 120 g m-2 d-1), and brine discharge zones (e.g. 5,515 g m-2 d-1); however, there were also many fault/fracture zones, which gave no significant CO2 fluxes, indicating that the faults/fractures selectively behave as conduits for diffusive CO2 flow. In order to better understand CO2 and brine leakages processes in the LGWFZ, 2-D numerical simulations were performed with various scenarios for permeabilities of the faults and Navajo Sandstone. Henceforth, the simulation results were validated by matching with field CO2 flux observations. The results showed that CO2-brine flow regime depends primarily on the characteristics of fault permeabilities. Only anisotropic low permeabilities of the faults (0.01≤kh<0.1 and 0.1≤kv<1 md) led CO2 flow to be impeded across the faults and pooled in an anticlinal trap, which focuses high CO2 fluxes on the northern footwall similar to field observations. Nevertheless, the faults enhanced the vertical connectivity among the reservoirs compartmentalized by caprocks so that CO2 can accumulate in the reservoirs and even flow over a distance of several kilometers towards other fault zones. For a successful sequestration of CO2, therefore, it must: (1) take precedence to identify faults, joints/fractures, and groundwater discharge zones in a large region, (2) carefully monitor the proximity of injection/monitoring wells to CO2 plumes, (3) and have a dense spatial monitoring system of soil CO2 flux after injections.