Study on pore properties of main coal seams of Yangmeishu syncline in Liupanshui coalfield

The main coal seams of Upper Permian in Yangmeishu syncline of Liupanshui coalfield were systematically sampled and tested by the low-temperature liquid nitrogen adsorption and mercury intrusion method to analyze pore properties and its influence factors,and favorable intervals were preliminarily selected.The results show that each coal sample tested by mercury intrusion is mainly composed of minipores and micropores,and micropores take the dominant position in pore specific surface area.The low-temperature liquid nitrogen adsorption test mostly consists of minipores and mesopores.The percentage of specific surface area of each coal sample is the largest with micropores and minipores.Mercury intrusion curve and adsorption loop can be divided into three types which represent respectively a certain pore morphology and connectivity.Mercury intrusion pore volume and specific surface area showed a trend of rising first and then falling with the the ratio Ro,max=1.65% as the cut-off point,and they were negatively correlated with the inorganic component and the dry ash content,while the Branauer-Emmett-Teller (BJH) pore volume and Branauer-Emmett-Teller (BET) specific surface area were positively correlated with the influencing factors.The relationship between the two test results and the vitrinite content was not obvious.Considering the pore properties of various coal seams,it is determined that coal seams such as No.5-2、5-3、13-1、33、34 have pore conditions for CBM development.