CO
2 capture and storage (CCS) is one of expected methods to reduce CO
2 emissions into the atmosphere. The Japan consortium to proceed the CO
2 sequestration into coal seams carried out the project "Japan CO
2 Geosequestration in Coal Seams Project (JCOP) " on CO
2 injection and CH
4 production during 2002 to 2007 at Yubari City, Hokkaido, which is hereinafter called as Yubari ECBMR pilot test. A targeted coal seam at the project was located about 890m below the surface. The project had a problem on CO
2 injection with low injection rate of about 3ton/day. In the pilot-test data, it was observed as a common pattern that CO
2 injection rate was decreasing during 3 to 10 days after starting CO
2 injection, because of decreasing permeability around the injector. The maximum decreasing ratio of the permeability was evaluated as 1/50 of the initial one. The reason was assumed by swelling of the coal seam around the injector by injection liquid CO
2.
In this study, an analytical model has been presented in consideration of permeability reduction by swelling. Present predictions on CO
2 injection rate with the model have been matched with monitoring data measured at the Yubari ECBMR pilot test. The ratio of permeability reduction of coal seams by the swelling (swelling factor) has been evaluated as 1/50 to 1/16.
In this research, numerical simulations, which use double porosity model and Palmer & Mansoori model to express permeability reduction by shrinkage of micro-pores caused by CO
2 adsorption, called as coal matrix swelling, has been carried out with the ECLIPS (CBM option) . A history matching study was conducted to estimate CH
4 desorption time and production bottom-hole pressure (BHP). Other reservoir parameters such as pore compressibility and gas-water relative permeability curve, were set based on the report of Yubari pilot test and previous researches by Yamaguchi et al. (2007) and Pekot & Reeves (2002) .
The numerical simulations for sensitivity studies on CO
2 injectivity and CH
4 productivity have been carried out by giving CO
2 and CH
4 adsorption capacities and viscocities of CO
2 and water as a function of the coal seam temperature (30 to 60 °C) . Finally, the numerical simulation results with five spot model have been presented to evaluate CO
2 injectivity and CH
4 productivity by changing the well spacing. The results show that CO
2 injection is roughly proportional to number of injectors, however the time at the maximum CH
4 production rate is delayed with area including four production wells. From view of economical evaluation, drilling cost of wells and accumulated present value of revenue of CH
4 production will be important to decide the optimum well spacing.
抄録全体を表示