Study on Differential Hydrocarbon Accumulation Conditions in Baiyun Sag under Continental Margin Crustal Background
The Pearl River Mouth Basin is located in the northern continental margin of the South China Sea.The crustal thickness is rapidly reduced from 29 km in the north to 17～18 km in the south,and the sea water depth is increased from＜0.1 km in the north to＞2 km in the south.The Baiyun Sag is located in the deep water zone of the strong thinning zone of continental margin crust in the southern part of the basin,leading to its special hydrocarbon accumulation conditions.Firstly,a wide and deep fault depression has de-veloped under the control of crust-mantle detachment fault,with a maximum sedimentary layer thickness exceeding 10 km and a sedi-mentary area exceeding 2×104 km2.Secondly,a highly variable geothermal field is developed,with the geothermal gradient rising from 3.5℃/100 m in the northern partofthe sagto8.5℃/100 min the south,with an average of 5℃/100 m.The high geothermaltem-perature accelerates the thermal evolution of the source rocks and the densification of reservoir.Thirdly,the reservoir-caprock assem-blage of shallow and deep water,terrestrial and marine sediments is developed.Finally,multiple hydrocarbon generating subsags were developed during the rift period of Baiyun Sag.Different hydrocarbon generating subsags have different scales,environments,and thermal evolution degrees of source rocks,resulting in differences in the scale and phase of hydrocarbon accumulation.The differences in numer-ous geological conditions result in significant variations in hydrocarbon accumulation conditions within the same subsag,and even in dif-ferent structural parts of the same subsag,further leading to differences in oil and gas distribution and enrichment level.The regional hy-drocarbon distribution and enrichment characteristics in the Baiyun Sag are clarified through the detailed analysis of the hydrocarbon ac-cumulation conditions,and the main controlling factors for oil and gas enrichment in different zones are points out,providing reference and basis for the next exploration of the Baiyun Sag.
northern continental margin of South China SeaBaiyun Sagstrong thinning zonewide-deep fault depressionhigh variable ground temperaturehydrocarbon accumulation conditionsmain controlling factors of hydrocarbon enrichment
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