Characteristics of coal reservoirs in Zhijin and Nayong regions, Guizhou province, China

Abstract：In order to Nayong regions, a se exp t of ore the production potential of coalbed methane (CBM) in testing methods were used to research the characteristics of coa ijin and 1 reservoirs from the angle of pore and fracture systems, and the adsorption and seepage capacities as well as their controlling factors were analyzed in this paper. It is considered that high degree of metamorphism of coal in the study areas and high gas adsorption capacities of coal reservoir are favorable for the adsorption and accumulation of the CBM; the low seepage capacities of coal reservoir and hypertonic conditions of local area are not conducive to the output of the CBM. The physical properties of coal reservoirs are controlled by complex geological factors. The burial metamorphism in the pre-Yanshan stage has resulted in the increase of the coal adsorption capacities and decrease of the seepage capacities; furthermore, the intense tectonic move- ments in the Yanshanian period have enhanced the coal adsorption capacities and improved the seepage capacities of the coal reservoirs that are near the fault zone. The results show that the pore structures of the samples in Zhijin and Nayong regions are dominated by adsorption pores, and the range of the adsorption pores is up to 50.61~--89.71~, resulting in the high adsorp- tion capacities. In contrast, the seepage pores poorly developed with an average content of 21.14%. In addition, the density of the microfraetures is generally less than 100 per 9 cm2 ,and the connectivity between the microfractures is relatively poor, which has reduced the permea- bility of the coal reservoirs. Faults are well developed in the districts with intensive tectonic movements, and the intrusion of magma in faulting zones not only sped up the coal metamor- phism, but also formed massive bility of coal the porosity CBM. reservoirs near the and permeability of pores and fractures, which improved the porosity and permea- fault zone. On the contrary, the later mineralization reduced the coal reservoirs, making it difficult for the output of the