| Coal bed methane (CBM) have very big geological reserves, and is treated as one of the potential unconventional resources. The geological reserves of CBM in China are very big, about 36.81×1012m3 within depth above 2000m, which is equal to those of the conventional natural gas. The exploration of CBM in Ningwu Basin is a potential project in CNPC CCDC, however, the weakness in CMB research has delayed the exploration and development of the resources.The gas content, permeability and reservoir pressure are important controlling factors for development of CBM. The 9# coal bed in Ningwu Basin is dominant by semidull-semibright type, with low ash content, and is classified as fat coking coal. The gas content is 17.44-18.72m3/t, and is classified as medium class. The reservoir pressure is 8.7～13.3MPa, and is a normal pressure reservoir. Fissures develop in the 9# coal bed, the porosity is ranging from 2%-8%, permeability is ranging from 0.01-1×10-3 μm2, the pressure coefficient is 0.96, and it is classified as the tight CBM reservoir. According to the observation under scanning electron microscope (SEM) and mercury injection capillary pressure (MICP) experiment, the pore geometry of coal bed reservoir is studied, and the results indicate that the pore sizes are mainly micro pores.The geological background study shows that the Ningwu Basin is flat towards south and north directions, and the thickness of 9# coal bed is steady. The overlying beds are dominant by shaly calcite and shale, which are good cap rocks. The underlying beds are dominant by shale, shaly calcite, sandstone, siltstone and calcite, and are good at sealing the gas. The shale formation above the 9# coal bed indicates the low possibility of wet zones. The water productions of CBM wells are low, and the pressure drop in the CBM reservoir is also good for the CBM development. The 9# coal bed of Taiyang Formation is a potential exploration target for CBM, and the risk of development is relatively low. |
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