Formation and Distribution of Giant Gas Fields in Northern West Siberian Basin

West Siberian Basin is the largest petroliferous basin of Russian Federation, which is one of the largest petroleum basins in the world newly developed since 1970s, with largest area, most hydrocarbon reserves and highest production. By the end of 2007, the ultimate recoverable reserves of natural gas of West Siberian petroleum basin is 16.1×1012m3, in which the reserves of undeveloped oil gas fields occupy 9.96×1012m3 and the undiscovered resources account for 31.6×1012m3. Based on the data of 57 large gas fields, combined with the tectono-depositional evolution process of the basin, applying the research idea and method of petroleum system, and through analyzing the reservoir-formation elements of generation, reservoir and cap rock, it is considered that Bazhenov Formation of Upper Jurassic and the equivalent ones are the most significant gas-generation rock of northern West Siberian Basin, in which the organic carbon content occupies more than 7%. Cenomanian rock located at the top of Cretaceous Formation is the reservoir of most large gas fields (80% natural gas), with 800m in average thickness. A vast number of complex structural-stratigraphic traps are generated in the basin and large gas fields that have been found concentrate in the uplift area of the northern margin of the basin including Nurmin and Medvezh, etc. In the future, the exploration target of increasing natural gas reserves will still be the oil-bearing provinces of Kara-Yamal and Nadym-Taz.