Abstract: Well Yuetan 1H in the Taipei Sag of the Tuha Basin made the first exploration discovery in the Badaowan Formation of the Xiaocaohu sub-sag, which achieved a comprehensive breakthrough in the exploration of the secondary sag area of the Taipei Sag and revealed the good exploration prospect of tight sandstone gas in the entire Taipei Sag area. Based on the Taipei Sag, this paper comprehensively analyzes the geological conditions of deep tight sandstone gas formation, and concludes that: (1) the development of three sets of source rocks in the Shuixigou Group provides a sufficient material basis for tight sandstone gas; (2) The development of delta front-scale sand bodies and near-coal seam sandstone dissolution pores are favorable reservoirs for deep tight gas accumulation; (3) The strata located in the lower part of the strike-slip thrust zone have good preservation conditions, which is a favorable area for tight sandstone gas enrichment. At the same time,based on the geological information obtained from the exploration and discovery of Well Yuetan 1H, the dominant accumulation conditions of Xiaocaohu sub-sag were clarified, and then the favorable geological conditions of tight gas in the entire Taipei Sag were re-understood, and it was pointed out that: (1) effective sand bodies were developed in the central area of the sub-sag; (2) The physical properties of the reservoir of the southern source sand body are better; (3) The source rock development zone with higher maturity is a favorable zone for natural gas enrichment. Based on the latest geological information and understanding, the evaluation of tight gas resources in Taipei Sag was re-carried out, and the predicted tight sandstone gas resources were 7070×10⁸m³, which was significantly higher than that in the previous period. Finally, the comprehensive evaluation selects two favorable exploration areas of tight sandstone gas in the northeast of Xiaocaohu sub-sag and north of Shengbei sub-sag.

Key words: Tuha Basin, Taipei sag, Middle-Lower Jurassic, Deep, Tight sandstone gas, Amount of resources, Xiaocaohu sub-sag