OIL AND GAS MIGRATION AND ACCUMULATION IN PEARL RIVER MOUTH BASIN,THE NORTHERN SOUTH CHINA SEA AND CONTROLLING FACTORS

Taking source and reservoir as the key points for oil and gas accumulation,there are three main mechanisms of oil and gas migration and accumulation in the Pearl River Mouth Basin.They are the hydrocarbon accumulation mechanism with autochthonous source from the half-graben-type depressions in Paleogene; the hydrocarbon accumulation mechanism in the deltaic sands-reef systems with allochthonus oil source; the hydrocarbon accumulation mechanism of deep-water fan system with oil and gas source from outside.For the first mechanism,both the oil and gas supply system and the migration and accumulation system occur within the Paleogene half-graben system,and characterized by autochthonous source and short distance of migration.For the second mechanism,delta sands-reef deposits are effective reservoirs,and oil and gas supply system and migration and accumulation system remain in the Paleogene half-graben system out of the delta sands-reef systems.Therefore,its main controlling factors are the migration systems including vertical crossing source fault system,the sandbodies on structural ridges and unconformities.The oil and gas supply system and migration and accumulation system of deep-water fan system are mainly located on the southern slope of deep water zone.Oil and gas are mainly from the half-graben system,even the marine source rocks in Oligocene may also contribute a little.The key factors to control oil and gas migration and accumulation are the vertical fault system crossing source rocks and the availability of good reservoir in the deep-water fan system.