Hydrocarbon accumulation model and controlling factors in the Upper Paleozoic in Jurong area, Lower Yangtze region

The main controlling factors of a hydrocarbon accumulation model of the upper Paleozoic in the Jurong area of the Lower Yangtze region were discussed. Regional geology and hydrocarbon accumulation processes in some key exploration wells were studied using the relationship between oil and gas accumulation elements and the spatial-temporal distribution of the marine strata in the Upper Paleozoic in the study area. The results showed that: (1) The Upper Paleozoic Longtan and Qinglong formations provided source rocks, carbonate fractures on the Indosinian unconformity surface and the tight sandstones in the Longtan Formation worked as reservoirs, and the shale in the Gecun and Pukou formations functioned as cap rocks. The tectonic and accumulation histories obtained from typical exploration wells indicated that traps were formed and adjusted continuously due to multiple tectonic activities. The tectonic uplift during the late Himalayan period destroyed hydrocarbon reservoirs, leading to a great loss of oil and gas in Jurong area. (2) Three classes of oil and gas reservoirs developed, including the secondary residual, primary preservation and the late reconstruction types. Preservation conditions for oil and gas were the key factors for hydrocarbon accumulation in Jurong area. The Qinglong Formation experienced erosion and leaching during the Indosinian and Yanshanian periods, forming a large number of caves and cracks, which controlled the late reconstruction of fractured-vuggy carbonate reservoirs on the unconformity surface.