关键词: 全油气系统, 煤层全油气系统, 煤层气, 煤岩气, 化石能源, 自然能源

Abstract: Significant breakthroughs have been made in exploration of deep coalbed methane (CBM) in China, demonstrating promising prospects for future development. However, due to the complex geological conditions and the high difficulty in CBM development, the existing basic theoretical researches cannot fully explain the deep-seated issues such as the enrichment mechanism and development prospects of CBM. The research progress of global CBM exploration and development shows that the enrichment and accumulation conditions for CBM in deep reservoirs are superior to those in shallow layers. However, the deepening research on deep CBM faces a series of challenges, including multiple genetic types with unclear genetic relationship, undetermined mechanism and key controlling factors of deep CBM accumulation, lack of discrimination criteria for enrichment modes and critical accumulation conditions of CBM, difficulties in predicting and evaluating high-yield sweet spots and fully applying the exploration experience of deep CBM in the eastern Ordos Basin to other regions. To solve the problems, the Whole Petroleum System (WPS) theory and the hydrocarbon accumulation model with dynamic field are introduced to expound the differences, correlations, and united symbiotic relationships between conventional and unconventional coal-formed gas reservoirs in petroliferous basin, in an attempt to provide new theoretical and methodological guidance for the prediction and evaluation of high-yield and rich CBM areas. The preliminary research results on CBM in major petroliferous basins of China indicate that during the evolution process of the Coalbed Whole Petroleum System (CWPS), the free hydrocarbon dynamic field is conducive to the enrichment and accumulation of CBM in an adsorbed state, whereas the confined hydrocarbon dynamic field is conducive to the enrichment of free gas in coal seams. In the free hydrocarbon dynamic field of coal seams, the amount of adsorbed gases increased with the increasing of burial depth and decreased after reaching a peak, while the free gas content has begun to increase. In the confined hydrocarbon dynamic field, the amount of gas trapped in coal seams in a free state continues to increase with the increasing of burial depth, and then decreases until it tends to disappear after reaching its peak. Vertically, the lower part of the free hydrocarbon dynamic field and the upper part of the confined hydrocarbon dynamic field (organic matter accumulation degree ranges from 0.50 % to 2.75 % ) are most favorable for multiphase enrichment and high production of CBM. The buried depths of the high heat flow basins of the eastern China, medium heat flow basins of the central China, and low heat flow basins of the western China are from 1 000 m to 3 600 m, 1 500 m to 7 500 m, and 3 000 m to 8 500 m, respectively. In these favorable fields, the total amount of coal resources is about 80 596×10⁸t, and the in-situ and recoverable resources of CBM are 115.91×10¹²m³ and 56.5×10¹²m³ respectively, showing broad prospects for development.

Key words: Whole Petroleum System, Coalbed Whole Petroleum System, coalbed methane (CBM), coal-rock gas, fossil energy, natural energy