Abstract: The development of shallow coalbed methane (CBM) has long been constrained by the traditional perception of coal as a solid mineral resource, resulting in its resource assessment confined to depths shallower than 1 500 m and global production stagnated by 2017. Since 2019, China National Petroleum Corporation has redefined coal-rock as a source-reservoir integrated reservoir rock and achieved an exploration breakthrough at a depth of over 1 500 m in Ordos Basin. The development of deep CBM in the basin has shown the characteristics of “gas production immediately upon well opening and then reaching peak rates rapidly”, which has promoted a strategic shift from shallow to deep exploration targets. However, the fundamental geological theory of coal-rock as both source rock and reservoir remains to be systematically advanced. Based on surveys of modern wetland swamps in Sanjiang Plain, Yellow River Delta, and Liaohe River Delta, etc., and by introducing sedimentological and petroleum geological perspectives, this study conducts research on the definition of the coal-bearing geological system, the controls of coal-forming environments, the classification of source rock types, the hydrocarbon generation and reservoir-forming evolution of coal-rocks, and the accumulation models of coal source rock petroleum system. The research results show as follows. (1) The continental coal-bearing geological system is innovatively defined as a composite system of terrestrial biological and geological construction, which initiates with the large-scale growth and preservation of lignin-rich plants and terminates with the completion of extensive swamping. It is controlled by five factors of tectonism, sedimentation, drainage network, soil, and climate, and constructed by an assemblage of coal seat, coal-rock and carbonaceous mudstone. (2) Coal source rock is the third type of high-quality source rock after marine and lacustrine source rocks, with a total organic carbon (TOC) content mostly exceeding 80% and a hydrocarbon generation capacity of up to 300 m³ per ton of coal. Based on the origin of hydrocarbon-generating parent material, source rocks are classified into aquatic organism-, terrestrial plant-, and mixed-type. The coal-rock belongs to a humic (Type Ⅲ kerogen) source rock dominated by woody plant input. (3) A four-stage thermal evolution scheme is proposed based on qualitative changes in hydrocarbon generation behavior [the low maturity, maturity, high maturity and over-maturity stages were divided respectively with the vitrinite reflectance (R_o) of 0.4%, 1.3% and 4.0% as nodes]. Hydrocarbon-generation evolution of coal source rocks can be classified into the biogas stage and the thermal evolution stage. In the mature stage, the contribution rate of the specific surface area of micropores is over 40%. Cleat density and gas yielding intensity peak at R_o=1.3%. The coal-rock reservoir is identified as a multi-scale pore-fracture-surface composite reservoir space system. (4) Coal source rocks constitute an independent petroleum system. Guided by “source-reservoir relationship, accumulation dynamics, occurrence state, and development response”, coal source rock petroleum system can be classified into CBM reservoir, coal seam oil-gas reservoir, and conventional oil-gas reservoir. They possess dual accumulation pathways of “self-generation and self-storage with pressure sealing” and “separate generation and storage driven by buoyancy”. (5) Volume development and three-dimensional development are the most favorable development methods for coal-rock gas fields in China. Drilling and segmented volume fracturing technologies of horizontal wells are the core for the development of coal-rock gas reservoirs. These findings deepen the geological connotation of source-reservoir integrated coal-rock reservoirs, improve the theories of hydrocarbon generation, reservoir formation, and hydrocarbon accumulation in coal-rocks, and provide scientific supports for the assessment, efficient exploration and development of coal-bearing oil and gas resources.

Key words: continental coal-bearing geological system, classification of source rock types, coal source rock, hydrocarbon generation and reservoir-forming evolution, multi-type reservoir space, coal source rock petroleum system

摘要： 浅层煤层气开发长期受到将煤岩作为固体矿产的传统认知束缚，其资源评价深度局限于1 500 m以浅，全球产量到2017年陷入停滞。2019年以来，中国石油天然气集团有限公司将煤岩厘定为源-储一体的储集岩，在鄂尔多斯盆地1 500 m以深取得了勘探突破，深层煤层气开发呈现出“开井即见气、快速达峰”的特征，由此推动了由浅向深的勘探开发战略转变，但煤岩作为源岩和储集岩的基础地质理论仍有待深化。基于对三江平原、黄河三角洲、辽河三角洲等现代湿地沼泽的观测，引入沉积学与石油地质学观点，围绕煤系地质体系的界定、成煤环境的控制、烃源岩类型的划分、煤岩的成烃-成储演化及其含油气系统的成藏模式开展了研究。研究结果表明：①通过创新定义陆相煤系地质体系，明确其为陆生生物建造与地质建造的复合体系，该体系始于木质素类植物大规模生长与保存，终于泛沼泽化的完成，主要受构造、沉积、水网、土壤、气候和植物种属6方面因素控制，其建造岩石为根土岩-煤岩-碳质泥岩组合。②煤源岩是继海相、湖相烃源岩之后的第3类优质烃源岩，其总有机碳（TOC）含量多大于80%、吨煤生烃量达300 m³；据母质来源将烃源岩划为水生生物类、陆生植物类与混合类，煤岩属以木本植物型为主的腐殖型（Ⅲ型干酪根）烃源岩。 ③提出以生烃质变节点为核心的热演化4阶段方案[以镜质组反射率（R_o）0.4%、1.3%和4.0%为节点分别划分出低成熟、成熟、高成熟和过成熟阶段]，煤源岩按成烃演化可分为生物气阶段与热演化阶段，在成熟阶段的微孔比表面积贡献率在40%以上，割理密度与产气强度在R_o=1.3%时达峰，明确煤岩储层为孔-缝-面多尺度集合体。④煤源岩自成含油气系统，以“源-储关系、成藏动力、赋存状态、开发响应”为主轴可划分为煤层气藏、煤层油气藏和常规油气藏，具备“自生自储、压力封存”与“他生他储、浮力驱动”双路径成藏能力。⑤体积开发、立体开发是中国煤岩气田最有利的开发方式，水平井钻井技术和体积分段压裂技术是煤岩气藏开发的最核心技术。研究成果深化了源-储一体煤岩储层的地质内涵，完善了煤岩成烃、成储、成藏理论，可为煤系油气资源评价与勘探开发提供科学支撑。

关键词: 陆相煤系地质体系, 烃源岩类型划分, 煤源岩, 成烃-成储演化, 多类型储集空间, 煤源岩油气系统