Study on the accumulation conditions of coal-measure gas in the Shenfu Block
神府区块煤系天然气成藏条件研究

摘要

目的 为了明确鄂尔多斯盆地神府区块本溪组和太原组煤系天然气的富集规律，方法 本研究利用钻井及岩心分析资料，对烃源岩、储层、盖层及成藏模式进行系统剖析。结果 结果表明研究区内广泛发育煤层与泥岩两类优质烃源岩，本溪组煤层TOC均值为65.6%，泥岩TOC均值为4.1%，太原组煤岩TOC均值为63.7%，泥岩TOC均值为3.6%，均属优质烃源岩；Ro值介于0.8%～1.3%，平均1.1%，处于成熟生气阶段；致密砂岩储层以石英砂岩为主，平均孔隙度7.05%～7.54%，平均渗透率0.71~0.84mD，属典型特低孔－超低渗致密储层；上部发育区域性泥岩与组内煤泥岩共同构成了多级封盖体系。结论 该区天然气成藏主要受源储配置控制，表现为源储紧邻、短距离运移特征，主要发育下生上储与自生自储两种组合模式。未来勘探应聚焦于生烃中心与优质砂体配置的耦合区。

Abstract

Objective To elucidate the enrichment mechanisms of coal-measure gas in the Benxi and Taiyuan Formations of the Shenfu Block, Ordos Basin.
Methods Utilizing data from well drilling and core analysis, this study systematically investigated the source rocks, reservoirs, cap rocks, and hydrocarbon accumulation models within the study area.
Results The results indicate that two types of high-quality source rocks—coal seams and mudstones—are extensively developed in the region. In the Benxi Formation, the average Total Organic Carbon of coal seams is 65.6%, and that of mudstones is 4.1%; in the Taiyuan Formation, the average TOC of coal rocks is 63.7%, and that of mudstones is 3.6%. Both are classified as high-quality source rocks. The vitrinite reflectance RO ranges from 0.8% to 1.3%, with an average of 1.1%, indicating a thermally mature stage favorable for gas generation. The tight sandstone reservoirs are dominated by quartz sandstone, characterized by an average porosity of 7.05%–7.54% and an average permeability of 0.71–0.84 mD, representing typical reservoirs with extra-low porosity and ultra-low permeability. The regionally developed mudstones in the upper section, combined with intra-formational coal-mudstones, constitute a multi-level sealing system.
Conclusion   Natural gas accumulation in this area is primarily controlled by the source-reservoir configuration, characterized by the close proximity of sources to reservoirs and short-distance migration. Two main assemblage models are identified: "lower-generation and upper-storage" and "self-generation and self-storage." Future exploration should focus on the coupled zones where hydrocarbon generation centers align with high-quality sandbodies.