Research on law of coalbed methane enrichment and main controlling factors in Jiaozuo Machang exploration area

The paper is devoted to explore the rules and main control factors of coalbed methane enrichment in Machang exploration area.Field research，sampling，laboratory testing，and analysis of coal exploration data were used in this study.The distribution characteristics of coal seam gas content in Machang area were summarized and the intrinsic and extrinsic factors affecting coal seam gas content were analyzed systematically.The results show that the measured coalbed methane content in the Machang exploration area is 13.77～27.30 cm3/g，with an average of 20.26 cm3/g.The gas content is decreasing from west to east and south to north，with the highest in the southwest.The gas content distribution is controlled by four intrinsic factors.First，Ⅱ1 vitrinite group has a high content and has strong gas generating capacity，which is conducive to the formation of coalbed methane.Second，the coal ash content and moisture content of Ⅱ1 are low，and the adsorption capacity of is strong，which is conducive to the occurrence of coalbed methane.Third，Ⅱ1 coal seam is mainly composed of mi-cropores，which can provide a large specific surface area for coalbed methane adsorption and is conducive to the occurrence of coalbed methane.Fourth，under the action of tectonic stress，the soft coal has a change in the molecular and crystal structure of the coal，and the porosity and specific surface area have increased，which has enhanced the affinity of the methane and increased the gas content of the coal seam.Meanwhile，the gas content distribution is controlled by two extrinsic factors.First，with the increase of overlying bedrock thickness，the storage capacity is gradually enhanced，and the gas content of coal seam is gradually increased.Second，due to the effect of faults，theⅡ1 coal seam in the northern fault block is directly connected with Ordovician limestone，forming a relatively water-conducting boundary.The runoff of the groundwater will inevitably take a certain amount of coalbed methane，causing the gas content of the coal seam to decrease.Due to the action of the Fenghuangling strong runoff zone in the central fault block，the coalbed methane migrates with the water flow as the carrier，resulting in a decrease in the gas content of the coal seam，but relatively higher than the northern fault block.Ⅱ1 coal seam in the southern fault block is connected with the Permian weakly permeable rock stratum，which is beneficial to the preservation of coalbed methane，and the gas content of the coal seam is relatively high，forming the most favorable enrichment area of coalbed methane in Machang exploration area.