Abstract: The Carboniferous–Permian coal measure strata are widely distributed in Ordos Basin. There are abundant deep coal rock gas resources, showing a solid material basis for large-scale capacity construction, so it is crucial to systematically understand the geological characteristics and exploration methods of deep coal rock gas. Based on review of exploration history, and combined with well drilling,logging, and laboratory test data, the coal accumulation environment, coal quality, reservoir physical properties, and gas accumulation conditions of the Upper Paleozoic coal measure strata at the basin scale have been analyzed. By integrating with geological and engineering data from typical wells in recent years, the resource potential, enrichment patterns, and key development technologies have been summarized,and future exploration orientations have been determined. The study results show that: (1) No.8 coal seam in Benxi Formation and No.5 coal seam in Shanxi Formation are the main target layers for deep coal rock gas exploration, which are featured by thick coal seams, consistent distribution, relatively high maturity, high vitrinite content, and high gas generation capacity; (2) The coal rock reservoirs are dominated by primary structure coal, with bimodal pattern of pore structure, well-developed micropores and cleat–fracture system, and high proportion of free gas; (3) Hydrocarbon retention rate is generally high, which is about 40% in the central basin and exceeding 50% in the eastern basin,providing a material basis for gas accumulation; (4) Three types of reservoir and cap rock combinations were formed by coal rocks and the overlying strata, including coal–mudstone, coal–limestone, and coal–sandstone, which effectively controlled the distribution of free gas and formed a favorable hydrocarbon accumulation pattern of “continuous hydrocarbon generation, integration of source rock and reservoir, and box-type sealing”; (5) Based on field practice, a series of key engineering technologies applicable for deep coal rock gas have been developed, including differentiated geosteering, two-section wellbore structure optimization, high-displacement fracturing, and pressure-controlled production, significantly improving the drilling encounter rates, reservoir reconstruction efficiency, and single-well production capacity. The research results support the goal of deep coal rock gas development with “accurate identification, successful drilling, and steady production”, and demonstrate the feasibility and practical value of large-scale capacity construction promoted by integration of geology and engineering.

Key words: Ordos Basin, Benxi Formation, coal rock gas, geological characteristics, enrichment mode, engineering technology