Scientific Development Research

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.

Shenfu Block; Benxi-Taiyuan Formations; Coal-measure gas; Accumulation conditions