Hydrocarbon accumulation conditions and exploration directions of large-scale lithologic-stratigraphic oil and gas reservoirs in Upper Wuerhe Formation of Upper Permian in Junggar Basin

In recent years, large-scale lithologic-stratigraphic oil and gas reservoirs (groups) have been discovered in the Upper Permian in Mahu, Shawan, Fukang and Dongdaohaizi sags in Junggar Basin, thus making an overall breakthrough in exploration of the whole basin. Based on the comprehensive analysis of geological factors, such as tectonic setting, material basis for hydrocarbon supply, reservoir properties as well as trap and preservation conditions of large-scale lithologic-stratigraphic oil and gas reservoirs, it is considered that the development of low-level sandy conglomerates above unconformity in the transformation period of basin fault depression, fan delta front belt and high-quality sweet spot reservoirs provides a material basis for the large-scale accumulation and local enrichment of above-source allochthonous oil and gas in the whole basin. On this basis, the paper clarifies three main controlling factors for the development of large-scale lithologic-stratigraphic oil and gas reservoirs in the Upper Permian in Junggar Basin. The Middle and Lower Permian high-quality salinized lacustrine source rocks provide abundant oil and gas resources as a solid material basis; the three-dimensional pathway system of fault and unconformity provides an important guarantee for the large-scale accumulation and migration of oil and gas; the unconformity developed in the large slope zone around the sag provides favorable trap and preservation conditions for large-scale lithologic-stratigraphic oil and gas reservoirs. Based on this, two oil and gas accumulation models of "source-reservoir separation type and composite overlap-truncation combination" in the Upper Permian series of western Junggar Basin and "source-reservoir adjacent type and low-level overlap" in the Upper Permian series of eastern Junggar Basin have been established. Guided by the understandings, it is pointed out that the south slope of Mahu sag, west slope of Shawan sag, northeast slope of Pen 1 Well West sag, north slope of Dongdaohaizi sag and east slope of Fukang sag are the favorable exploration directions for large-scale lithologic-stratigraphic oil and gas reservoirs in the Upper Permian in Junggar Basin.