The Differences of Physical Properties of Coal Reservoirs and Their Origin Mechanism between Zhijin and Panxian Areas, Western Guizhou, China

Western Guizhou has abundant coal resources, and it is considered as the most prospective area for coalbed methane (CBM) production in Southern China. To explore the potential of CBM production in this area, this study systematically addressed the differences of physical properties of coal reservoirs in the two typical areas (Zhijin and Panxian) of Western Guizhou, and on the base of that, deeply analyzed the forming mechanism of their differences. The results show that: the coal reservoirs in the Zhijin area are mainly high and medium rank coals with low porosity and poor permeability, and the pore structure is mainly dominated by micropores and transition pores; while the coal reservoirs in the Panxian area are mainly low and medium rank coals with high porosity and favorable permeability, and the pore structure is dominated by macropores and mesopores. The Langmuir volume and pressure of coal reservoirs in the Zhijin area are higher than those in the Panxian area, which indicates that coal reservoirs in the Zhijin area have much better adsorption capacity. The differences of physical properties of coal reservoirs in Western Guizhou are primarily controlled by the evolution degree of coal reservoirs. The evolution degree is dominated by the depositional and burial history as well as the tectonic thermal events afterwards: the depositional and burial history determines the difference of coal ranks between Zhijin and Panxian areas; while the tectonic thermal events are the main controlling factors of the internal differences of the coal ranks. Resulting from the various depositional and burial history or tectonic thermal events, different evolution process and physical-chemical structure generate, which in return determine the physical properties of coal reservoirs in Western Guizhou.