Enhanced coalbed methane recovery (ECBMR) has been paid attention as a new technology of both methane production and carbon dioxide sequestration. This paper describes sensitivity analysis of reservoir characteristics and development plan using ECBMR simulator (ECOMERS-UT) developed by the authors. The results provide basic data for economic evaluation of ECBMR and its optimum development planning. The validity of the simulation results was confirmed by the comparison with the study performed in GEO-SEQ project. The influence of permeability of coal seam, pore model considering matrix swelling, adsorptivity of carbon dioxide and gas composition of injection gas was evaluated. Coal seam of low permeability showed high enhancement effect and sequestration potential although such coal seam showed low production rate. In case of lowering of injectivity resulting from low permeability or large matrix swelling, ECBMR was not effective. High adsorptivity of carbon dioxide led to large sequestration and small enhancement effect. Also, nitrogen rich injection gas led to small sequestration, large enhancement effect and low methane concentration of produced gas.
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.
Unconventional natural gas resource including coalbed methane (CBM) is expected to be important in primary energy supply, although there is great uncertainty of its resource availability range in future. Enhanced coal bed methane (ECBM) technology is under development since it has advantage of CBM resource expansion as well as greenhouse gas mitigation by CO2 capture and storage (CCS). The author conducted sensitivity analysis of unconventional gas resource availability and existence of atmospheric CO2 concentration target, using global and long-term intertemporal optimization model. It is concluded that the unconventional gas resource amount uncertainty have substantial impact on global energy supply in the latter half of 21st century and ECBM enhances both CBM resource availability and CCS potential.
We made a study on the influence of presumable CBM (Coalbed methane) commercial production on the natural gas trades in Asia. Some possible scenario cases and a special scenario case assuming LNG trade between China and Indonesia were calculated. First, the supply rates of various natural gases were calculated so that the sum of total supply cost in an importing country would become the lowest. And next, similar calculations ware carried out so that the sum of total supply cost of an importing country and the production cost of an exporting country would become the lowest respectively. The following results were obtained by these calculations. (1) The climb rate of production cost of a conventional natural gas can be controlled by the alternative energy source CBM. (2) The above influence of CBM production becomes apparent by considering the profits of both countries. (3) CBM should play an significant role to satisfy ever increasing natural gas demand in the next 30 years in Asia.
In order to prevent adhesion of molten ash particles on the surface of heat exchanger tubes in coal combustion boilers, surface treatment of the tubes, using a thermal spray coating technique, is conducted in this study. As one of the important mechanisms of ash adhesion relates to liquid-bridge force between the tube surface and the molten ash particles, contact angle of the liquid-phase on the surface for the simulated molten ash particles was measured, varying types of coating metal species. The ash deposition experiments on the coated tubes were also conducted, using a vertical furnace under the high-temperature condition. The result showed that the two values of the wettability and the slagging factor of the ash particles deposited could evaluate the ash adhesion characteristics. The wettablity could be controlled by changing types of the coating metal species. The amount of ash deposition increased with an increase of the slagging factor. Especially, sodium and potassium compounds were concentrated in the position apart from 60 degrees from the stagnation point. These results suggest that the surface treatment of the tubes, using a thermal spray coating technique, can control the ash deposition behaviors.
Small-scale wood biomass gasification is considered as a suitable technology to utilize forest biomass such as logging residue and unused thinned wood. Recently, more than 10 demonstration plants have started to operate to verify both technical and economic feasibility of the system. This study analyzes the economic aspect of gasification system focusing on the regional distribution of biomass resources and technical characteristics such as scale merit. The authors developed BiRReT tool, which conducts the economic analysis of biomass energy system in a local region by finding the optimal conditions, namely plant size, plant location, and the number of plants. Case study in Miyagi prefecture had been carried out. Firstly, the economics of gasification system is compared with the steam-turbine-based CHP system that utilizes grate or fluidized-bed combustion technology. The result shows that gasification system has strong advantage in terms of low fuel transportation cost. Secondly, the economic feasibility of the system in a region is analyzed. The system with logging residue fuel has the possibility to gain economic competitiveness if technology learning and cost reduction will be seen in the capital cost and the fuel production process. Thinned wood will not be utilized only for the energy purpose.