Carboniferous-Permian petroleum conditions and exploration breakthrough in the Yingen-Ejin Basin in Inner Mongolia

Lots of geological and petroleum studies have been conducted in the Yingen-Ejin (YE) Basin in such aspects as the evolution of the Carboniferous-Permian basin, the sedimentary filling, the regional distribution and geochemical characteristics of source rocks, the thermal evolution history of hydrocarbon source rocks, and the tectonic and sedimentary evolution and hydrocarbon preservation after the Carboniferous-Permian deposition. Based on the achievements obtained from these studies, the authors hold that the Yingen-Ejin Basin is composed of superimposed basins composed of a Carboniferous-Permian continental rift basin and Mesozoic inland basins. Petroleum prosperity is proved by the existence of several Carboniferous-Permian source strata characterized by great thickness, moderate-high abundance of organic matter, the existence of main kerogen type Ⅱ, and moderatehigh evolution stage. The preferred oil and gas prospecting areas were sold by the Ministry of Land and Resources, and the enterprises have increased the investment of the exploration. The first drilling hole (Guaican 1st Well) of the Guaizihu depression in the Wutaohe exploration area obtained the initial daily production of 51.67 m³ oil and 7290 m³ natural gas (open flow potential) with a small amount of condensate gas, and the first drilling hole (Yanhacan 1st Well) of the Hari depression in the Wentugaole exploration area received the industrial gas flow of 91500 m³ daily production (open flow potential) with a small amount of condensated oil. These achievements realize the great breakthrough of oil and gas exploration which started in 1955. Based on the age constraints on the oil and gas strata in the two wells and the comparison of oil and gas sources, the authors consider that the ages of oil and gas strata should be the Permian. Additionally, the Carboniferous-Permian strata should be the main objects of oil and gas exploration in that they have great prospects of resources.