The deep coalbed methane (CBM) resources in the Ordos Basin are enormous, and their exploration and development breakthrough are among the critical ways to improve CBM production in China. The occurrence state of deep CBM has unique characteristics caused directly by the change in methane density (ρ). By predicting key adsorption parameters and solving directly for adsorbed methane density (ρ_a), it is concluded that ρ_a decreases with increasing temperature and increases rapidly at first and then tends to stabilize with increasing pressure. Considering the characteristics of supercritical methane adsorption, a porosity (φ) prediction model for deep coal reservoirs was established based on these unique occurrence characteristics. A new equation for predicting gas content in deep coal seams was developed by combining the free gas content (V_fg) calculation method for unconventional oil and gas reservoirs and the adsorbed gas content (V_ad) method based on ρ_a. It was observed that the V_fg increased with pressure and φ but decreased with increasing water saturation and temperature. However, as temperature and pressure increased, the rate of increase in V_fg slowed down, probably because of the influence of φ decreasing with increasing temperature and pressure, which is similar to the change in ρ_a. Meanwhile, the V_ad increased with temperature and pressure, showing a trend of rapid increase followed by a decrease. These indicate that, as the depth and pressure increase and the temperature rises in deep coal seams, the negative effect of temperature gradually outweighs the positive effect of pressure. When φ increased to a specific value in low- to medium-rank coal, the V_fg can exceed the V_ad at depths between 2000 and 2500 m. Compared to high-rank coal, which has high V_ad, low- to medium-rank coals are more prone to experience the saturation phenomenon where the V_fg exceeds the V_ad.

鄂尔多斯盆地深层煤层气资源量巨大，其勘探开发突破是我国煤层气增产的关键途径之一。深层煤层气的赋存状态具有独特的特征，直接由甲烷密度（ρ）的变化引起。通过预测关键吸附参数并直接求解吸附甲烷密度（ρ _a ），得出结论：ρ _a 随着温度的升高而减小，先迅速增大，然后趋于稳定。压力越来越大。考虑超临界甲烷吸附的特点，根据这些独特的赋存特征，建立了深层煤储层孔隙度预测模型。将非常规油气藏游离瓦斯含量（V _fg ）计算方法与吸附瓦斯含量（V _ad 的方法。据观察，V _fg 随着压力和 φ 的增加而增加，但随着水饱和度和温度的增加而减少。然而，随着温度和压力的升高，V _fg 的增加速度减慢，可能是由于随着温度和压力的升高而减小的影响，这与ρ _a 随着温度和压力的增加而增加，呈现先快速增加后减少的趋势。这表明，随着深部煤层深度、压力的增加和温度的升高，温度的负面影响逐渐超过压力的正面影响。 当中低阶煤中 φ 增加到特定值时，在 2000 至 2500 m 深度，V _fg 可超过 V _ad 。与V _ad 较高的高阶煤相比，中低阶煤更容易出现V _fg 超过V _ad 。