Thin-interbedded coal measure reservoirs are important unconventional gas reservoirs. The lithology of these reservoirs is complicated, with rapid vertical changes, making accurate description difficult. Based on the thin-interbedded coal-bearing strata in the Wujiu Depression in eastern Inner Mongolia, China, this study constructs changes in lithofacies based on a Markov mathematical and statistical model. The Shengli subdepression mainly features a lithofacies sequence of uniform coal-mud-sand cycles and other small-scale symmetrical sedimentary cycles. In the Moguai–Shiwalu subdepression, lake hydrodynamics primarily affect coal–mudstone and mudstone–sandstone double-cycle lithofacies sequences and small-scale asymmetric sedimentary cycles. The Markov model and the Ward minimum variance method were used to quantitatively couple a reservoir lithologic sequence and bed thickness configuration, and five basic configurations of the composite reservoir of the Damoguaihe Formation in the study area were obtained: (1) multiseam interbedded configuration, (2) multiseam interbedded configuration with an intermediate number of seams, (3) interbedded configuration with an intermediate number or few seams (with thick mudstone or sandstone layers), (4) interbedded configuration with few seams (large spacings between adjacent coal seams) and (5) thickly interbedded configuration. The sedimentary facies mechanism controlling the spatial distribution pattern of composite reservoirs is discussed. It is concluded that the sedimentary system domain and lake size have a significant effect on the configuration of composite reservoirs. For small terrestrial lakes, the stability of sedimentary environment and the rapid and frequent rise and fall of the lake surface results in significant differences in coal accumulation in a short distance from the edge to the center.

中文翻译：

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内蒙古乌九凹陷薄互层煤系储层配置定量表征：沉积控制机制

薄互层煤系储层是重要的非常规气藏。这些储层岩性复杂，垂向变化快，准确描述困难。本文以内蒙古东部乌九凹陷薄互层含煤地层为背景，基于马尔可夫数学统计模型构建了岩相变化。胜利洼陷主要发育均匀煤-泥-砂旋回及其他小规模对称沉积旋回的岩相序列。在莫拐—石瓦路洼陷中，湖泊水动力主要影响煤—泥岩和泥岩—砂岩双旋回岩相序列和小规模不对称沉积旋回。采用Markov模型和Ward最小方差法对储层岩性序列与层厚配置进行定量耦合，得到了研究区大磨拐河组复合储层的5种基本配置：（1）多层互层配置，（ 2）中层多煤互层结构；（3）中层或少层互层结构（泥岩、砂岩层厚）；（4）少层互层结构（相邻煤层间距大）； (5)厚互层构造。探讨了沉积相控制复合储层空间展布格局的机制。结果表明，沉积体系域和湖泊规模对复合储层的配置有显着影响。对于小型陆地湖泊来说，沉积环境的稳定性和湖面快速频繁的升降导致了边缘到中心较短距离内煤炭堆积的显着差异。