Modeling Gas Transport in the Shallow Subsurface During the ZERT CO2 Release Test
We used the multiphase and multicomponent TOUGH2/EOS7CA model to carry out predictive simulations of CO{sub 2} injection into the shallow subsurface of an agricultural field in Bozeman, Montana. The purpose of the simulations was to inform the choice of CO{sub 2} injection rate and design of monitoring and detection activities for a CO{sub 2} release experiment. The release experiment configuration consists of a long horizontal well (70 m) installed at a depth of approximately 2.5 m into which CO{sub 2} is injected to mimic leakage from a geologic carbon sequestration site through a linear feature such as a fault. We estimated the permeability of the soil and cobble layers present at the site by manual inversion of measurements of soil CO{sub 2} flux from a vertical-well CO{sub 2} release. Based on these estimated permeability values, predictive simulations for the horizontal well showed that CO{sub 2} injection just below the water table creates an effective gas-flow pathway through the saturated zone up to the unsaturated zone. Once in the unsaturated zone, CO{sub 2} spreads out laterally within the cobble layer, where liquid saturation is relatively low. CO{sub 2} also migrates upward into the soil layer through the capillary barrier and seeps out at the ground surface. The simulations predicted a breakthrough time of approximately two days for the 100kg d{sup -1} injection rate, which also produced a flux within the range desired for testing detection and monitoring approaches. The seepage area produced by the model was approximately five meters wide above the horizontal well, compatible with the detection and monitoring methods tested. For a given flow rate, gas-phase diffusion of CO{sub 2} tends to dominate over advection near the ground surface, where the CO{sub 2} concentration gradient is large, while advection dominates deeper in the system.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- Earth Sciences Division
- DOE Contract Number:
- DE-AC02-05CH11231
- OSTI ID:
- 959421
- Report Number(s):
- LBNL-1529E; TRN: US200924%%724
- Journal Information:
- Transport in Porous Media, Journal Name: Transport in Porous Media
- Country of Publication:
- United States
- Language:
- English
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