Distribution and Hydrocarbon Geological Characteristics of Large and Medium Fields in Nansha Sea Area

Based on the extensive survey of relevant researches at home and abroad, and the latest drilling, oil&gas fields information from IHS, C&C, USGS database, the authors systemically analyzed the distribution and hydrocarbon geological characteristics of large and medium fields in Nansha sea area. Large and medium oil and gas fields discovered mainly in Brunei-Sabah and Zengmu Basins in Nansha sea area. Both the number of oil and gas fields and the size of hydrocarbon reserves are concentrated in the Miocene. There are mainly two types of source rocks, i.e. coal measures developed in the marine-terrestrial facies of rifting (drifting) period and the mudstones of prodelta facies in post-rifting period. The distribution of source rocks in the main sedimentary basins are characterized by the fact that the source rocks of marine facies are gas prone and those of the transitional and lacustrine facies are oil prone, which constitutes the material base of "deep water area rich in gas, shallow water area rich in oil". Controlled by the regional tectonic evolution and sedimentary environment, the distribution of reservoir rocks reveals the characteristics of "older reservoir (upper Oligocene to mid-lower Miocene) in the outside belt, younger (mid-upper Miocene) in the inside belt". The distribution of large and medium oil and gas fields also exhibits the regularity of "sandstone oil and gas reservoir in the outside belt, carbonate gas reservoir in the inside belt".