Controlling factors of hydrocarbon accumulation and play fairway in North Sakhalin Basin

Locating in the circum-Pacific fold belts of far-east in Russia, the North Sakhalin Basin is a back-arc basin developed from Mesozoic to Cenozoic. There are three sets of source rocks including shale in the Okobykay Formation of the Upper Miocene, shale in the lower Nutovo Formation of the Upper Miocene, and coal-bearing strata in the Weining Formation of the Lower Miocene and the Dagi Formation of the Lower Miocene. Its main oil production derived from the sandstones in the Dagi Formation of the Middle and Lower Miocene and the lower Nutovo Formation of the Upper Miocene. The major trap types are anticlines, complex faulted anticlines and fault blocks. Oil and gas mainly accumulated in the Sakhalin sub-basin in the northeast, with larger reserves offshore than onshore. Vertically, they were mainly found in the Dagi Formation of the Middle Miocene and the Nutovo Formation of the Upper Miocene. The comprehensive evaluation of reservoir conditions showed that the distribution of oil and gas were mainly controlled by structure and reservoir development. The structural traps formed during the late Pliocene provided spaces for hydrocarbon accumulation, and the folding event which took place from the late Pliocene to Holocene functioned as adjustment and even destruction to traps. The distribution of sandstones in the Dagi Formation of the Middle and Lower Miocene and the Nutovo Formation of the Upper Miocene controlled the plane and vertical distributions of hydrocarbon. Compared to the highly explored onshore area, the offshore area has a great potential, and the exploration targets should be focused on the structural-stratigraphic and stratigraphic traps in the Nutovo and Dagi Formations.