Recent progress in oil and gas geological exploration in the Qiangtang Basin, northern Xizang

The Qiangtang Basin lies as the largest petroleum basin on the Qinghai-Xizang Plateau and a potential strategic reserve area for petroleum exploration in China. Our results of recent petroleum geological survey in the Basin show that the excellent Palaeozoic source rocks mostly composed of the Carboniferous and Permian dark mudstones are characterized by higher contents of organic carbon, with the II₂ to III types of kerogen in organic matter, and maturities Ro values ranging between 1.50% and 2.40%, indicating the stages of oil-window maturity to overmaturity. The palaeo-weathering crust within the formerly Nadigangri Formation is believed to be the newly-discovered potential reservoir rocks in the Basin, which are overlain upon the Permian and formerly Triassic Xiaochaka Formation strata. The newly-discovered Upper Jurassic-Lower Cretaceous Bailongbing River Formation marls intercalated gypsum and shales are considered to be good seal rocks in the Basin. More than 250 sites of oil and gas showings have been distinguished in the Mesozoic formations in the Basin in recent years. Best of all, a large number of modern active mud volcanoes generated by the natural gas seepage have also been recognized in the northern Qiangtang Basin where the gas samples were collected. In the light of sedimentary facies, source rocks, reservoir rocks, seal rocks and preservation of oil and gas resources, six hydrocarbon exploration prospects are delineated, and the Tuonamu and Bandao Lake areas are selected as the potential targets for future petroleum exploration in the Qiangtang Basin.