Economic Assessment of Enhanced Coalbed Methane Recovery for Low Rank Coal Seam

摘要

Enhanced Coalbed Methane Recovery (ECBMR) is usually targeted for the bituminous coals, for the methane content in such coals is rather high and it leads to the higher profit by methane sales. Generally, methane content of low rank coals is small. However, adsorption ratio of CO_2/CH_4 is high for low rank coal. It suggests that the CO_2 adsorption volume of low rank coal is large. Moreover, some low rank coal seams have high permeability. Low rank coal seams have advantage of high CO_2 adsorption volume and high permeability, and disadvantages of low methane content, possibility of large swelling from the viewpoint of ECBMR. When the carbon credit is expected, CO_2 storage in low rank coal seams is very promising due to their high CO_2 storage capacity. At the same time we must consider negative effect of CO_2 storage on the decrease of permeability caused by large swelling (CO_2 adsorption). A case study of economic assessment was made for low rank coal seams with sensitivity analysis. Well type of five spot patterns was employed. Well spacing, CO_2 concentration of injected gas and carbon credit is the parameter of sensitivity analysis. The results showed CO_2 concentration was the most important factor to determine the economy of the project affecting the permeability and the CO_2 storage rate. By selecting the optimum CO_2 concentration of the injected gas, the low rank coal would be one of the options for underground CO_2 storage under certain carbon credit.