Fluid Geochemical Features and Preservation Conditions of Marine Stratum in Typical Structure of Jianghan Plain Area

Many scholars carried out large quantity of researches on oil and gas preservative condi-tions of marine carbonate rocks from the aspects of cap rocks,faults,formation water,hydrodynamic,and tectonism.This article gives dynamic evaluation on oil and gas preservative conditions of marine stratum in Jianghan（江汉） plain of multiphase tectonic disturbance from the view of paleofluid geo-chemistry.The conclusion shows that there mainly existed fluid filling of two periods in the reservoir of Lower-Middle Triassic to Permian.The fluid filled in the earlier period came from Lower Palaeozoic.The interchange of fluid in Lower-Middle Triassic to Permian suggested the oil and gas in Lower Pa-laeozoic had been broken up.The fluid filled in the later period（Lower-Middle Triassic to Permian） came from the same or adjacent strata and lacked anatectic fluidogenous features coming from Palaeozoic.With good preservative conditions of bulk fluid at the time,the fluid of Lower-Middle Triassic to Permian and that of Lower Palaeozoic did not connect with each other.However,the hydrocarbon generation peak of marine source rocks had passed or the paleo-oil and gas reser-voirs had been destroyed at that time and the marine stratum of Palaeozoic to Triassic in the research area did not put out commercial oil and gas flow.

Cenozoic Sea-land Transition and its Petroleum Geological Significance in the Northern South China Sea

The process of Cenozoic sea-land changes in the northern South China Sea(SCS)controlled the sedimentary filling pattern and played an important role in the petroleum geological characteristics of the northern marginal sedimentary basins.Under the control of the opening process of the SCS,the northern SCS Cenozoic transgression generally showed the characteristics of early in the east and late in the west,and early in the south and late in the north.The initial transgression occurred in the Eocene in the Taixinan Basin(TXNB)of the eastern SCS,while the transgression occurred until the Pliocene in the Yinggehai Basin(YGHB)of the western SCS.International Ocean Discovery Program(IODP)expeditions(Expeditions 367/368)revealed that the initial transgression of the SCS basin occurred at approximately 34 Ma,which was the initial opening time of the SCS.The period of drastic changes in the sedimentary environment caused by large-scale transgression corresponded to the opening time of the southwestern subbasin(approximately 23 Ma),which also represented the peak of the spreading of the SCS.The sea-land transition process controls the distribution of alternating continent-marine facies,marine facies source rocks and reservoirs in the basins.The marine facies source rocks of the basins in the northern SCS have a trend of gradually becoming younger from east to west,which is consistent with the regional process of gradual transgression from east to west.Regional sea-level changes were comprehensively influenced by SCS opening and global sea-level changes.These processes led to the early development in the east and south and late development in the west and north for the carbonate platform in the SCS.Carbonate platforms form another type of"selfgenerating and self-accumulating"oil-gas reservoir in the northern SCS.The sea-land transition controlled the depositional filling patterns of different basins and laid the foundation of marine deposits for oil and gas resources.The source-reservoircap assemblage in the northern SCS was controlled horizontally by provenance supply and sedimentary environmental changes caused by sea-land transition and vertically by the tectonic evolution of the SCS and regional sea-level changes.