HR: 1340h
AN: B33A-1013    [Abstracts]
TI: Feasibility of CO2 Sequestration with Simultaneous Enhanced Coalbed Methane Recovery in the Powder River Basin, Wyoming
AU: * Ross, H E
EM: hemiller@pangea.stanford.edu
AF: Geophysics Department, Stanford University, Stanford, CA 94305-2215 United States
AU: Zoback, M D
EM: zoback@pangea.stanford.edu
AF: Geophysics Department, Stanford University, Stanford, CA 94305-2215 United States
AB: CO2 sequestration in geological formations has been proposed as a means to reduce greenhouse gas concentrations in the atmosphere. Coal is an attractive geologic environment for CO2 sequestration because CO2 is retained in the coal as an adsorbed phase and the cost of sequestration can be offset by enhanced coalbed methane recovery. Using reservoir simulations of sub-bituminous coal in the Powder River Basin, Wyoming, we examined the feasibility of injecting and sequestering CO2 in this basin, particularly looking at whether hydraulically fracturing the coal would help increase CO2 injectivity. Our 3D model was built in an area where the least principal stress is equal to the overburden stress, resulting in horizontal hydraulic fractures, and gamma ray logs from coalbed methane wells were used to determine the depth and thickness of the coal. These wells produce from the Big George coal, which is approximately 20 m thick in this area, with a depth to the top of 310-360 m. Geostatistical techniques were employed to populate the coal matrix and cleats with permeability and porosity data taken from published reports. We conducted enhanced coalbed methane simulations using a commercial enhanced coalbed methane simulator. Our base case involved one injection well and one production well (1/4 of a 5-spot pattern). We then added a hydraulic fracture at the base of the injector and closed the rest of the well off. All our simulations were run with and without coal matrix shrinkage and swelling. The natural fracture system of the coal is the main pathway for gas migration. We found that gravity and buoyancy were the major driving forces behind gas flow within the coal, which reduced gas sweep efficiency and sequestration. Gravity caused the gas to migrate upwards at first and then along the top of the coal. The presence of the hydraulic fracture assisted in greater penetration of gas into the base of the reservoir, creating a more uniform vertical sweep as gas rose to the top. In addition, the hydraulic fracture enabled more CO2 to be injected into the coal and maintained high permeability close to the injection well during coal matrix swelling.
DE: 0545 Modeling (4255)
DE: 1699 General or miscellaneous
DE: 8168 Stresses: general
DE: 9350 North America
SC: Biogeosciences [B]
MN: Fall Meeting 2005