Study On Sedimentary Facies Of Carboniferous S3 Sandstone Layers In Sangtamu Area

The Sangtamu fault zone is oil-bearing and located at the south of the Lunnan low uplift.S3 sandstone layers belonging to Carboniferous system are rich in hydrocarbon and serve as the emphases of this study.Sandstone of S3 sandstone layers is hard to predict because of its characteristics of thin thickness and poor continuity.The research of sedimentary facies has a long way to go to meet the requirements of the rolling exploration nowadays.Taking core,mud log,well logging,and seismic data into account,we made stratigraphic division and correlation by using the ‘cycle comparison and hierarchical analysis' method.Whereafter,the local sedimentary facies types were recognized and the characteristics of single well facies and profile facies were obtained by analyzing rock types,sedimentary structures,sedimentary tectonic,and log response in this area.Under the control of the stratigraphic framework,the plan distribution characteristics of the sand reservoir in the area were predicted using the seismic attributes,provenance and sand distribution.Finally,the distribution characteristics and evolution patterns of the sedimentary facies in the area can be determined and target zone can be predicted based on the above studies.In the research,the following conclusions are drawn: Carboniferous S3 sandstone layers can be divided into 3 medium-term cycles and 9 short-term cycles corresponding to 9 single sandstone layers respectively.The S3 sandstone layers contain mudstone,silty mudstone,siltstone,fine sandstone,medium sandstone,and pebbly coarse sandstone,in which the mudstone has the most widely distribution featuring classic muddy sand but with lower maturity.The main sedimentarystructures are cross bedding,scour surface,bioturbation,parallel bedding,and massive bedding.They are mainly developed in intertidal-subtidal depositional settings,and some area develop delta front deposition.Depositional environments include mud-flat,sand flat,sand bar,tidal channel,inter-distributary bay,estuary,and subaqueous distributary channel.The provenance source is mainly from the Lunnan buried hill in the northwestern.The delta facies are developed at the northwestern part of the study area meanwhile the rest are tidal flats horizontally,and there's obvious regressive phenomenon vertically.Sedimentary facies are the main influencing factors of reservoir properties.The reservoirs in this work area are divided into three types:Class I,Class II,and Class III,Class I reservoirs are developed in subaqueous distributary channel and tidal channel microfacies,Class II reservoirs are developed in estuary and sand bar microfacies,while Class III reservoirs are developed in sand flat microfacies.