The Characteristics And Accumulation Of Subtle Hydrocarbon Reservoirs In Gunan Sag Of Es3z And Es3x Member

Based on the analysis of the large amount of three-dimensional seismic data,logging data and core date,stratigraphic correlation and structural interpretation of Es3 z and Es3 x member in the Gunan sag.On the basis of above study,conducted the research of sedimentary facies and reservoir characteristics,established the deposit system mode of Es3 z and Es3 x member,evaluated the reservoir,pointed out the facies that have advantage to development of subtle reservoir,analyzed the main factors forming subtle reservoirs.By using the methods of geological,logging and drilling data,also using layer calibration,seismic coherence,attribute analysis,and logging constrained inversion technique,recognised subtle reservoirs target,interpretated forming conditions and finally pointed out the work area of favorable subtle reservoirs target.Gunan sag is a seeondary negative structural unit in Jiyang depression.Basal evolution of the sag can be divided into three developing stages,i.e.platform formation,evolution and Mesozoic rift.In Cenozoic rift stage,it consists of faulted basin in Paleogene period and the depression from Neogene to Quaternary period,and the faulted basin stage is the most important forming stage of reservoir rock andsource rock in the sag.According to the effects of the faulted basin,the south of Gunan sag is higher than the north.The Es3 z and Es3 x member in the Gunan Sag can be divided into six sand groups,and sub-faces of delta plain facies,deltafront facies,prodelta facies,fan delta-front facies,shore-shallow lakefacies and semi-deep lake and deep lakefacies were developedinthe sag,favorable reservoirs locate in delta-front facies,fan delta-front facies and beach bar facies.In term of reservoir parameters calculated by log interpretation,the reservoir in Gunan sag can be divided into the medium porosity and medium permeability,the low porosity and low permeability and the low porosity and special super-low permeability.Lithologic reservoir and composite reservoir assoeiated with it are the most important subtle reservoirs in the l Es3 z and Es3 x member in the Gunan Sag,which can be mainly divided into stratigraphic overlap reservoir,structural and stratigraphic reservoir,fault and lithology reservoir and sand lenticle reservoir.The sutble reservoir in Gunan is formed by the migration of oil in Es3 Sequence,oil bearing series contact direetly with source roek provides advantage for the gathering of oil,active faults,connecting sand and unconformity in latter Ed to Ng also provided good channel for oil migration and gathering from Es3 source rock upward to reservoir rocks.In the basis of this,the pattern of stratigraphic overlap reservoir in steep slope zone,the pattern of fault and lithology reservoir,the pattern of structural and stratigraphic reservoir in gentle steep zone,the pattern of stratigraphic reservoir in central groove are established.Fault and lithology reservoir tends to distribute in the area of beach bar sand in the shoreshallow lake facies and delta-front facies,lithology reservoir mainly locates in both sides of distributary channel,sheet sand in the delta-front,turbidite and the margin of beach bar,stratigraphic reservoir tends to distribute in glutenite fan at steep slope zone near the Gunan Fault.