Structural preservation conditions analysis of oil and gas in complex structural area: A case study of structural analysis in the Well Wanjingdi-1, Anhui, China

The multi-stage tectonism of compression and extension occurred in the southern part of the Lower Yangtze region in the Mesozoic, which is one of the important factors restricting the breakthrough of oil and gas exploration in this area. This paper aims to reveal the influence of Mesozoic tectonisim on oil and gas preservation in the Lower Yangtze area. Based on the seismic profile interpretation data, field outcrop survey, regional tectonic evolution history analysis and the drilling core data and oil-gas display of the Well Wanjingdi-1, we comprehensively discussed the favorable structural preservation conditions in the southern part of the Lower Yangtze region. The results of seismic interpretation profile and surface survey show that the southern part of the lower Yangtze River has experienced two important tectonic processes since the Late Triassic. The first stage is fold deformation, thrust fault and uplift erosion caused by Indosinian compression, and the second stage is extension since the Late Cretaceous, resulting in the formation of fault basin and normal fault activity. Shale gas display was obtained from the Permian shale in the Well Wanjingdi-1, and light oil was found in the drilling of the Lower Triassic Yinkeng Formation, indicating that the southern Lower Yangtze region has good enrichment conditions and resource potential, which points out a new direction for oil and gas exploration in the region. The analysis of structural preservation conditions shows that the Well Wanjingdi-1 is located in the syncline of the fold-depression belt. The amount of uplift and denudation was small in the Indosinian period. Since the late Cretaceous, the depression has a small amplitude of extension and has good sealing and reservoir forming conditions. It is a favorable structural position for oil and gas preservation in this region. Based on the comprehensive analysis of regional structure and sedimentary basin evolution, it is considered that in the southern Lower Yangtze region, the syncline structural belt in the southern margin of the basin with small erosion amount of Triassic strata or the central zone of fault basin overlying thick Cretaceous-Cenozoic strata should be taken as the key target to search for favorable oil and gas zones.