Abstract: The processes of natural gas accumulation in the deep water area of the Qiongdongnan Basin are complex. Through the comprehensive study of regional tectonic-sedimentary evolution, source-reservoir identification and evaluation, as well as hydrocarbon accumulation, the sources, dominant plays and zones of natural gas in the central depression are identified. The study shows that the development scale and paleo-geomorphology of the Oligocene delta controled the distribution of coal-series and terrestrial marine source rocks, and then formed the Oligocene terrestrial marine source rock which mainly generated natural gas but could also generate oil; Controlled by the distribution of early Oligocene delta, sedimentary filling rate and water depth since the Middle Miocene, it is predicted that the scale of high-quality source rocks in the south slope and Songnan low uplift area of the central depression is larger, its potential energy of reservoirs is lower than that of the northern steep slope zone at the same altitude depth, and the oil and gas transport capacity is better. The distribution of high-quality marine source rocks, large reservoirs and low-fluid potential areas controls the dominant migration of natural gas in deep waters, thereby southern slope of the central depression and the low convex are the potential breakthrough targets of large and medium-sized gas fields.

Key words: terrestrial marine source rock, primary migration, fluid potential, sandstone transfusion capacity, natural gas accumulation