关键词: 成煤时代, 成煤模式, 原型盆地, 煤层气, 煤岩气

Abstract: Coal serves as the bedrock and stabilizer in China’s energy supply system, and coalbed methane(CBM), which co-occur with coal, is a crucial alternative resource for continuously increasing reserve and production. To elucidate the geological conditions for the coordinated development of coal and CBM, this study systematically reviews the types of prototype basins in major coal-forming periods and evaluates their controls over the occurrence and distribution of CBM. Based on geological history analysis, tectonic evolution comparisons, and basin classification, combine with a comprehensive study of coal-forming plants, coal-forming periods, sedimentary environments, and coal-seam geological characteristics, the paper establishes coal-forming models under different tectonic settings in China. The results indicate that the amalgamation, extension, and subsequent transformation processes of three tectonic domains, namely the Paleo-Asian Ocean, Paleo-Tethys Ocean, and Paleo-Pacific Ocean, control the sediment provenance, accommodation space, and burial evolution of coal-bearing basins in China. Four main types of coal-forming basins are identified as below. (1) The Carboniferous-Permian cratonic depression-type basins in North China were characterized by the development of marine-continental transitional sedimentary systems. Benxi and Taiyuan formations were deposited during a transgressive-regressive cycle, promoting the continuous development of coal seams. The subsequent deposition of Shanxi Formation occurred under regressive conditions, with coal accumulation predominantly in fluvial-deltaic systems while exhibiting overall seam continuity. (2) The Late Permian cratonic depression-type and intracontinental rift-type basins in South China were characterized by frequent sea-level fluctuations and paleoland distribution controlling sedimentation, coexistence of tidal flat and delta systems, and numerous coal seams with thin individual layers. (3) The Early-Middle Jurassic intracontinental rift-type and intermontane depression-type basins in Northwest China were characterized by the development of medium- to low-rank thick coal seams in lake deltas, with significantly tectonic deformation. (4) The Early Cretaceous continental faulted sag-type basins in Northeast China were characterized by relatively independent depressions in the basin, with well-developed and numerous thick coal seams. In North China, coal seams within the Benxi, Taiyuan, and Shanxi formations exhibit continuous and stable distribution, and the spatial heterogeneity of CBM is primarily controlled by the maximum burial depth (which determines the coal vitrinite reflectance), later tectonic uplift, and preservation conditions. In South China, coal seams generally exhibit high thermal maturity and significant hydrocarbon generation potential, but individual coal seam is relatively thin. The study should focus on high-quality resources of individual coal seam and three-dimensional development of multi-seams. In Northwest China, the relatively low thermal maturity and extensive weathered-oxidized zones necessitate a focus on basin slope belts, deep-to-middle uplift zones, and structural trap areas. In Northeast China, coal seams are dominated by low-rank coals, where the regions with thick coal seams and the secondary biogenic gas recharge zones represent key areas for realizing future development potential. The geological characteristics and polycyclic tectonic evolution of coal-forming basins in China collectively control the distribution patterns of CBM. Therefore, it is essential to develop basin-specific, high-efficiency development models for multiple types of CBM resources, tailored to the geological characteristics of each basin type.

Key words: coal-forming period, coal-forming model, prototype basin, coalbed methane, coal-rock gas