抄録
Coal beds adsorb abundant volume of methane gas, which is so-called coalbed methane gas and now utilized as an unconventional natural gas source in the U.S.A. Enhanced coalbed methane (ECBM) technology, which increases methane gas production by injecting carbon dioxide (CO2) into coal beds, is now viewed as one of the technologies to prevent the greenhouse effect. This technology may store the CO2 discharged from thermal power plants in coal seams in a stable state, and in the process, recover coalbed methane gas as a clean energy source. Many field experiments have been conducted in the world to investigate the possibility of this technology.
In Japan, General Environmental Technos. Co., Ltd. began “Japan CO2 Geosequestration in Coal Seams Project (JCOP)” in 2002 as a consignee of the project. As a part of the project, a micro pilot test started at the Minami Oh-Yubari district in the Ishikari coal filed in 2003, and will be continued until the end of 2007.
In this research, a numerical simulation model, which is named as Ishikari Model, has been constructed with a commercially available numerical simulator, which is widely used in coalbed methane gas industry. The model is based on the reservoir parameters obtained through the micro pilot test. Not all of the data necessary to construct the model were obtained; therefore a history matching study was conducted to estimate some unknown reservoir parameters such as pore compressibility and gas-water relative permeability curve. The developed Ishikari Model indicated the degree of enhancement effect observed in the micro pilot test, and also the degree of permeability decrease due to CO2 adsorption on coal.
