Accumulation and Enrichment Model of Coal Series Gas in the Z Block on the Eastern Margin of the Ordos Basin

The Z Block is located in the eastern part of the Yishan Slope in the Ordos Basin, adjacent to the western margin of the Jinxi flexual fold belt and the volcanic rock massif to the west. The block has a thick and well-developed coal-bearing stratum in the Paleozoic Era, and exploration breakthroughs have been made in the multi-layered strata of the Paleozoic Era, indicating great exploration potential. However, the complex structural and enrichment conditions caused by the compression of the Jinxi flexual fold belt and the Zijinshan volcanic rock massif have seriously hindered the understanding of the structural, reservoir, and enrichment laws of the coal series gas, which has severely constrained the exploration and development progress of the area. Therefore, based on the comprehensive control factors of structure, reservoir, and magmatic thermal effects, this study explores the coal series gas accumulation model in this area. The research results show that: 1) The coal seam in the Z Block is well developed, with sufficient gas supply, and the sandstone reservoir in the coal-bearing stratum of the Paleozoic Era is well developed, providing a good foundation for the accumulation and enrichment of coal series gas; 2) Influenced by the Jinxi flexual fold belt in the east and the volcanic activity in the west, the block shows a two-uplift and one-depression feature, and the central gentle zone is a favorable area for coal series gas exploration; 3) Three sets of faults are developed in the Paleozoic Era, which play a controlling role in the vertical accumulation of tight gas in the area. The conclusion is that the central gentle zone of the Z Block is mainly composed of coalbed gas and tight sandstone gas, and its accumulation and enrichment are controlled by multiple factors such as structural evolution, magmatic activity, and sedimentary reservoir distribution. The research results provide a direction for the exploration of coal series gas in the area.