School of Energy Resources, China University of Geosciences (Beijing)
Coal Reservoir Laboratory of National Engineering Research Center of CBM Development & Utilization, China University of Geosciences

深部煤层气资源丰富、开发前景广阔，但对其与浅部煤层气地质条件的内在联系研究尚不够深入。从煤层形成演化角度出发，以鄂尔多斯盆地上古生界煤层为例，总结了煤层深埋深藏型、深埋浅藏型及浅埋浅藏型3种埋深演化模式。系统分析了深部和浅部煤层在温压条件与含气性、地应力与渗透率特征、变质程度与含水性等方面的差异性及其形成机制。研究指出，受埋深与演化过程影响，深部和浅部煤储层温度最多相差100℃以上，储层压力最大相差40 MPa左右，导致由浅部向深部，气体赋存状态以吸附气为主转变为吸附气与游离气共存，地应力场由水平应力主导转化为垂向应力主导，煤储层孔隙率、渗透率及含水性逐渐降低。明确了深部煤层气的典型特点，即：在高温高压条件下，以吸附态和游离态共存于一定深度以下煤储层中的甲烷气体，该类煤储层在垂向应力为主导的作用下，孔裂隙空间极度压缩，含水极少且矿化度极高，内生微裂隙为主要渗流通道。基于含气性临界深度和地应力场转换深度的不一致性，指出浅部向深部煤层演化过程中存在过渡区，该区内呈现出非典型深部煤层气的特点，或深部煤层气和浅部煤层气地质条件共存的情况，在勘探开发过程中，应具体分析，制定针对性开发方案，以实现浅部与深部煤层气的高效协同开发。

Deep coalbed methane (CBM) boasts abundant resources and great potential for exploitation. However, there is a lack of in-depth studies on the internal connections between deep and shallow CBM. This study investigated the Upper Paleozoic coalbed in the Ordos Basin. From the perspective of coalbed formation and evolution, it obtained three burial depth evolution modes of coalbed through summaries: both the maximum and present burial depths exceeding 2000 m, the maximum burial depth over 2000 m while the present burial depth less than 2000 m, and both the maximum and present burial depths less than 2000 m. This study systematically analyzed the differences in the temperature and pressure conditions, gas content, in-situ stress, reservoir permeability, metamorphic grade, and water content of deep and shallow coal seams, as well as their formation mechanisms. The results indicate that, due to the influence of burial depth and evolutionary process, deep and shallow coal reservoirs show maximum temperature and pressure differences of up to 100°C and about 40 MPa, respectively. As a result, from deep to shallow, the CMB occurrence state transitions from the predominance of adsorbed gas to the coexistence of adsorbed state and free gas, the in-situ stress field shifts from the predominance of horizontal stress to that of vertical stress, and coal reservoirs’ porosity, permeability, and water content gradually decreased. Accordingly, this study ascertained the typical characteristics of deep CBM. Specifically, under high-temperature and high-pressure conditions, deep CBM occurs as coexisting adsorbed and free gas in coal reservoirs below a certain depth. Under the action of predominant vertical stress, the coal reservoirs of deep CBM feature extremely compressed pore and fissure spaces, an extremely low water content, and an extremely high degree of mineralization, with microfissures acting as major seepage channels. Based on the differences in the critical depth for gas-bearing property and the transformation depth of in-situ stress field between deep and shallow coal reservoirs, this study proposed that there exist transitional zones between shallow and deep coal seams, exhibiting the characteristics of atypical deep CBM or the coexistence of geological conditions for deep and shallow CBM. During exploration and exploitation, it is necessary to figure out a tailored scheme based on specific analysis to achieve efficient and coordinated development of shallow and deep CBM.

国家自然科学基金项目(42172188)

许浩，汤达祯，陶树，等. 深、浅部煤层气地质条件差异性及其形成机制[J]. 煤田地质与勘探，2024，52(2)：33−39.

XU Hao，TANG Dazhen，TAO Shu，et al. Differences in geological conditions of deep and shallow coalbed methane and their formation mechanisms[J]. Coal Geology & Exploration，2024，52(2)：33−39.