Study On The Hydrocarbon Accumulation Characteristics In The South Of Liaozhong Sag

The southern region of Liaozhong sag is one of the most hydrocarbon-rich zones discovered in recent years,which suggests a high value in exploration.However,the study area lacked a comprehensive research in the mechanism of hydrocarbon accumulation and there are still many questions about the hydrocarbon accumulation elements,oil and water distribution,and factors controlling hydrocarbon accumulation.On the basis of making full use of various geological,geochemical and geophysical data in the LD22-LD27 blocks of south of Liaozhong sag,this paper analyzes the ydrocarbon accumulation elements,hydrocarbon distribution characteristics,as well as the controlling factors of these two above.Together with the accumulation period and the hydrocarbon accumulation process,the reservoir forming pattern have been completed.The source rocks of the study area refer to the third member of Dongying Formation also with the Shahejie Formation.Reservoirs are allocated to the Guantao Formation and Minghuazhen Formation with middle to high permeability and high-porosity.As for the caprock,it is considered to be the well-developed mudstones or shale of E₃d₂^L,E₃d₃ and E₂s₃.There are two kinds of source-reservoir-caprock combinations being summerized,the lower generation to upper subsidence and self-generation to self-storage.In addition,it is known that the hydrocarbon reservoirs are mostly related to faults,such as fault lithologic reservoirs,fault block reservoirs,fault nose reservoirs and fault anticline reservoirs.There is significantly difference in hydrocarbon distribution of each block.In the block with well-developed faults,it is common to find the higher water mineralization degree with CaCl₂-type which reflects the upwelling of hydrothermal fluid from deep-seated fault.Affected by the central strike-slip fault,LD21-2,LD21-3 and LD27 blocks mainly develop Neocene reservoirs with poor hydrocarbon physical properties.However,blocks which are relatively far away from the major strike-slip fault like LD21-1,LD22-1 and LD22-1S develop deeper buried Paleocene reservoirs with better hydrocarbon physical properties.It is concluded that fault is vital for hydrocarbon accumulation and development of sand bodies take the second place.Threshold Fvs value of fault vertical sealing is 1.6.The time for oil and gas injection and accumulation in the studied area is suggested to occur in the middle and late Minghuazhen Formation.According to the oil source correlation,the crude oil of LD21-1 and LD27-2S show more than one source for hydrocarbons whereas that of other blocks are mostly from Liaozhong sag.Combined results of hydrocarbon accumulation,controlling factors of forming reservoirs,hydrocarbon source and the process of hydrocarbon filling,the reservoir forming pattern can be divided into three categories:hydrocarbon originates from dual-source and transported by fault-sand system with final forming in the deeper layers,hydrocarbon originates from single source and migrated mostly by faults with gathering in the shallow layers and shallow hydrocarbon reservoir with dual source migrated by fault-sand body.