The conglomerates of the Xiazijie (P₂x) Formation in the Mahu Sag are dominated by dissolution pores of zeolite cement as the primary hydrocarbon reservoir spaces. Consequently, the storage characteristics of conglomerates determine that the depositional environment is one of the key factors controlling reservoir quality. To address the lack of clarity regarding the types of paleo-depositional environments of the P₂x Formation and their controlling effects on reservoir characteristics, this study integrated elemental geochemical analysis with machine learning and other analytical approaches. A dynamic mapping relationship was established among elemental assemblages, depositional environments, and reservoir characteristics to elucidate the evolutionary features of the paleo-depositional environments of the P₂x Formation and their controlling effects on reservoir physical properties. The results indicate that the paleo-depositional environment of the P₂x Formation is subject to the coupled control of provenance supply and paleoclimatic conditions, exhibiting significant spatial heterogeneity. Spatially, the depositional water depth increased gradually from north to south, accompanied by a synchronous decrease in oxidizing condition of the environment. Meanwhile, the region featured a dual provenance supply system consisting of terrigenous debris and intermediate-mafic magmatic materials. The input intensity of terrigenous debris showed clear regional heterogeneity, accompanied by the differential supply of intermediate-mafic magmatic components. Influenced by peripheral tectonic uplift induced by plate collision, moisture transport to the basin center was obstructed. This factor resulted in the formation of an anomalous paleoclimatic distribution pattern characterized by increasing aridity trend from north to south. These regional variations in the depositional environment further control the spatial differentiation of zeolite cement types. In the Mabei area, Na- and Al-rich volcanic glass derived from terrigenous debris and intermediate magmatic materials, under the synergistic influence of a semi-humid climate and phasic salinization events, promoted the development of cements dominated by analcime and heulandite. The Manan area developed a dysoxic, open, and low-salinity water environment, where zeolite cement is dominated by laumontite. In contrast, the Maxi area developed a two-stage depositional environment evolution, resulting in the balanced development of the three types of zeolite cement. The spatial differentiation of zeolite cement and their coupling with the depositional environment further determined the variations in dissolution intensity. Ultimately, this characteristic resulted in a distribution pattern of reservoir physical properties in the P₂x Formation conglomerates that follows the distribution pattern of “Maxi > Mabei > Manan”.

The composition and isotopic characteristics of coalbed methane (CBM), as well as the genesis of CH₄ and CO₂, associated geological process and migration-accumulation model of CBM in typical mid- to low-rank coal-bearing basins were studied. The genesis of CBM is jointly influenced by the degree of coalification and biochemical processes, which in turn determine the composition and isotopic characteristics of CBM. Biogenic gas is extensively developed in mid- to low-rank coal-bearing basins, but its genesis varies. In the Baode area, China, and the San Juan Basin, USA, CBM is mainly secondary biogenic gas and thermogenic gas. In the Miquan area, China, CBM is characterized by primary biogenic gas. However, CBM in the Jiergalangtu area, China, Surat Basin, Australia, and Power River Basin, USA, are characterized by secondary biogenic gas. Microbial CO₂ reduction occurs in these coal-bearing basins, but with significant gas generation by acetate fermentation in some areas of these basins. Moreover, CO₂ in the Power River Basin, Surat Basin, and Jiergalangtu area mainly originates from microbial degradation of organic matter. However, in other basins studied, CO₂ initially derives from coal pyrolysis and is subsequently supplemented by CO₂ from microbial methanogenesis. The generation and isotope fractionation of CBM are affected and controlled by associated geological processes. Additionally, under the control of tectonic morphology and hydrogeological conditions, the genesis and migration-accumulation models of CBM in mid- to low-rank coal-bearing basins can be summarized into two models—the hydrodynamic active monoclinic model and the hydrodynamic differential syncline model—or a combination of the two.