Oil filling history of the Mesozoic oil reservoir in the Tabei Uplift of Tarim Basin, NW China

Abstract

Abstract The Tabei Uplift is one of the largest petroleum accumulation region in China. After decades of exploration and development a number of commercial oil reservoirs have been discovered in the Mesozoic formations suggesting a great potential for hydrocarbons. The Mesozoic oils were sampled from 18 wells in the Tabei Uplift. A total of 6 Ordovician oil samples were also collected for contrast analysis. On the basis of oil–oil correlation, all of the 24 crude oils belong to the same oil population and probably derived from the same source kitchen. Despite the coexistence of “UCM”,25-norhopane and intact n -alkanes which is generally interpreted as twice oil filling history, the homogenization temperature ( T h ) of brine inclusion indicates a single oil filling event which happened at 4–3 Ma, with the major frequency ranging from 110 °C to 120 °C. By means of T s /( T s + T m ), MPI−1, 4-/1-MDBT and total concentration of carbazole compounds, the oil filling orientation in Yakela and Yuqi areas were from NEE to SWW and NW to SE, respectively. The Luntai fault is believed to be an oil-migrating fault connecting the Ordovician reservoirs with Mesozoic reservoirs. Based on the physical properties, the geochemical characteristics and the oil filling histories, it can be concluded that the Mesozoic reservoirs in the Tabei Uplift were of secondary oil accumulations derived from the deeper Ordovician reservoirs.