Abstract: The natural gas in the He₈ Member of the Upper Paleozoic Shihezi Formation in the Ningxian-Zhengning Area, Ordos shows a good prospect for exploration, but the single-layer thickness of the effective reservoir is thin and the lateral change is rapid, and its natural gas accumulation characteristics and enrichment law are still unclear, which seriously restricts the natural gas exploration and development in this area. To this end, through a comprehensive analysis of the accumulation conditions of gas reservoirs in the study area, such as source bed, reservoir, caprock, trap, and migration, the accumulation characteristics and enrichment laws are summarized, and the gas layer-sensitive logging curves are screened. Combined with the lithology and physical properties of the reservoir, the effective reservoir division standard of the gas reservoir in the He₈ Member of the study area is established, and on this basis, the effective reservoir prediction is carried out by using 3D seismic data. The result shows: The Permian coal-measure source rocks are widely distributed and are in the high-to-over-mature stage, providing good gas source conditions for natural gas accumulation; the branched channel sandstone at the braided river delta front of the He₈ member is distributed in large-scale stripes in the near north-south direction, the lithology is mainly detrital quartz sandstone, followed by quartz sandstone, forming an effective reservoir sand body for natural gas reservoirs; the dominant reservoir in the He₈ Member and the underlying effective source rock form "lower source and upper reservoir" type near-source accumulation assemblages, generating widely distributed tight sandstone lithologic gas reservoirs. The near-source favorable sand body is preferred for accumulation, and the distribution of gas reservoirs and gas abundance are controlled by the distribution of effective sand bodies, the physical properties of the reservoir and the faults leading to the source. Through this study, the distribution of effective reservoirs in the He₈ Member in the area has been identified, which provides a basis for the optimization of the next natural gas exploration targets in this area.

Key words: Ningxian-Zhengning Area, Upper Paleozoic He₈ Member, coal-measure source rock, effective reservoir, lithologic gas reservoir