Distribution and genesis of large-scale Upper Paleozoic lithologic gas reservoirs on Yi-Shaan Slope

Lithologic reservoirs are widely distributed at Upper Paleozoic of Yi-Shaan Slope in Ordos Basin. With over 40 years of exploration, six large gas fields were discovered, including Sulige, Wushenqi, Yulin, Daniudi, Zizhou, and Mizhi, with total proved gas in place up to 13 126.54 × 108 m3. Based on the study on reservoir formation, the key factors of large-scale lithologic reservoirs include: widely distributed coal measure source rock and widely covered hydrocarbon generation, laying a physical foundation for wide gas accumulation; wide development of fluvial-delta sand deposits in the north of the basin, providing good reservoir spaces for wide gas accumulation; reservoir formation after densification of Upper Paleozoic reservoirs and stable structures in the basin ensure the later conservation of gas reservoirs. The effective allocation and interaction of these factors in space and time lead to the large-scale distribution of Upper Paleozoic lithologic gas reservoirs.