Geological features and hydrocarbon accumulation in the Xinken oil field, Tarim Basin

Recently, a large-scale Ordovician oil and gas pool has been discovered in Xinken, north of the Tarim Basin, and it has strongly heterogeneous reservoirs and complicated fluid distribution. Through analyzing oil, gas and water samples collected from this area, in combination of field production and testing data, this study reveals that the Xinken oil pool contains dominantly normal oil characterized by low viscosity, low sulphur, and high wax. It has a low content of natural gas, which presents typical characteristics of wet gas and is oil-associated gas. Oil-gas correlation shows that the oil was from the Middle-Upper Ordovician source rocks and the charge and accumulation of oil and gas took place in the Late Hercynian Period. Controlled by paleogeomorphology, sedimentary facies, ancient karstification, faults, and other factors in the Caledonian Period, the Ordovician carbonate reservoirs are dominated by dissolved pores, cavities and fractures. The reservoir body of fractures and cavities is distributed in the shape of strip and laminate along faults and excellent reservoirs are mostly in the range of 70–100 m below the top of the Yijianfang Formation. As a whole, the Xinken oil pool is a fracture-cavity pool controlled by interbedded karst reservoirs and is a complex composed of stacked karst fractures and cavities of various sizes. It contains oil in large areas horizontally, which is quasi-laminated in distribution, and the accumulation of oil and gas is controlled by the distribution and development degree of the Ordovician carbonate reservoirs. The study shows that this area has abundant resources and a great exploration potential for oil and gas.