Formation and evolution of Yin'gen-E'ji'naqi Basin and prospects for oil and gas exploration

The Yin'gen-E'ji'naqi Basin is located in the central and western part of the Inner Mongolia autonomous region, with an area of about 123×103 km2. It is a continental rift basin with a low exploration degree in North China. Due to the influence of complex surface and underground conditions, only the geological characteristics of the Chagan, Tiancao, Hari and other sags around the basin were studied during the early stage, which proved that each sag had the conditions for oil and gas accumulation, but the overall exploration potential was low. In recent years, on the basis of previous studies and combined with more field geology surveys, seismic and drilling data, the formation and evolution of the basin and the resource potential were re-evaluated. The Yin'gen-E'ji'naqi Basin basement was formed from the end of Permian to the Early Triassic, mainly composed of accretion-collision mélange, with moderate-shallow metamorphism generally occurring. Since the Mesozoic, affected by the Yanshanian and Himalayan movements, the basin has undergone six stages of structural evolution, with the characteristics of residual and reformed basins. The remaining Lower Cretaceous Bayin Gobi Formation is mainly distributed in the central and northern part of the basin, and is the main hydrocarbon generation and reservoir system. The total resources of the basin are estimated to be about 1.364 billion tons. Under the influence of strong late transformations, preservation conditions are the key factors for hydrocarbon accumulation. The tectonic activities in the northern part of the basin are relatively weak, and the effective source rocks in Bayin Gobi Formation remain in the depression area, which is the development area of overpressure oil and gas reservoirs and has become the key area for further exploration.