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

摘要： 近年来,中国深部煤层气勘探取得重大突破,展示出全新的发展前景。由于深部煤层气地质条件复杂、开发难度大,目前的基础理论研究还不能完全阐述其富集成藏机制以及发展前景等深层问题。国内外煤层气勘探开发的研究进展表明,深部煤层气的富集和成藏条件较之浅层煤层气更为优越,但其深化研究面临着一系列挑战,包括深部煤层气的成因类型多且成因关系不明、成藏机制和主控因素不清、富集模式与成藏临界条件的判别标准尚未建立、高产甜点预测评价难度大以及鄂尔多斯盆地东部深部煤层气的勘探经验难以完全套用到其他地区。为解决这些难题,引入全油气系统理论和动力场成藏模式来阐述含油气盆地内常规与非常规煤成气藏之间的差异性、关联性及其联合共生规律,试图为煤层气高产富集区的预测评价提供新的理论与方法指导。中国主要含油气盆地煤层气资源的初步研究结果表明:在煤层全油气系统演化过程中,自由动力场有利于煤层气以吸附态富集成藏,局限动力场有利于煤层气以游离态富集成藏;在自由动力场中煤层吸附气含量随着埋深增大而增加,但在达到峰值后逐渐减小,而游离气含量开始增加;进入局限动力场后,煤层中的游离气含量随埋深继续增加,并在达到峰值后逐渐减少直到趋于消失;纵向上,自由动力场下部以及局限动力场上部(其有机质成熟度介于0.50%~2.75%)是煤层气多相态富集高产的最有利区域,其在中国东部高热流盆地、中部中热流盆地和西部低热流盆地分别对应的埋深范围为1 000~3 600 m、1 500~7 500 m和3 000~8 500 m,预计这些有利领域内的煤炭总量约为80 596×10⁸t,煤层气原地资源量和可采资源量分别为115.91×10¹²m³和56.5×10¹²m³,发展前景广阔。

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