Quantitative Analysis of Gas Occurrence States and Its Controlling Factors in Deep CBM Reservoirs: An Integrated Model With Application in Linxing Block

Deep coalbed methane (CBM) is a crucial resource for ensuring energy security. Despite some successful localized deep CBM developments, the unclear understanding of gas content and gas occurrence state remains a key obstacle to the comprehensive development of deep CBM. This study utilizes data from pressure-preserved coring and wireline coring gas content tests, isothermal adsorption tests, and well test temperature and pressure data to establish a methodological model. This model corrects the gas content obtained from wireline coring and determines the gas occurrence state. The gas content, including adsorbed and free gas content, and gas/water saturation were calculated, and the controlling factors were analyzed. The results reveal that the high values of total gas content and adsorbed gas content are concentrated in the southwestern part of the study area. The adsorption capacity of the coal, influenced by its degree of metamorphism, is identified as the primary factor affecting the total gas content and adsorbed gas content. Furthermore, the high values of free gas content are primarily concentrated at the northwestern edge of the study area. The main factors affecting the porosity difference of free gas are coal metamorphism type and inertinite content. Areas affected by magmatic thermal metamorphism and those with high inertinite content tend to have higher porosity. Additionally, pressure, rather than temperature, is identified as the main factor determining the density of free gas. These findings provide a relatively simple indirect method for obtaining deep CBM content and occurrence state, particularly for studying the free gas content in deep coal seams. This approach is aimed at offering theoretical support for the development of deep CBM in the middle Linxing block.