Research Of Sedimentary Microfacies And Dominant Reservoir Distribution In Well P Area,Pinghu Formation,Xihu Sag

P well area is located in Pinghu structural belt in the middle of the western slope belt of Xihu Sag.It is a newly developed oil-gas well area.The target interval is the Eocene Pinghu Formation.P well area has an area of about 340km²,which is in the early stage of exploration and development.In addition,previous studies mainly focus on the sedimentary system of the whole sag or the secondary structural units in the sag There are some problems such as unclear understanding of sedimentary environment and distribution of favorable sand bodies,which hinder the exploration and development process.In this study,Pinghu Formation of P well area is the main research object.Based on the detailed observation and description data of the cores of 7 wells drilled in the well area,the lithofacies types developed in the study area are finely divided.The sedimentary microfacies types developed in the study area are analyzed by comprehensive utilization of petrology,lithofacies combination,well logging,analysis and test,3D seismic and other data,and the sedimentary model is summarized.On the basis of previous work,the characteristics of dominant reservoir in well P well area are analyzed.This study has a certain guiding role in the discrimination of sedimentary environment of P well area and the next oil and gas exploration.The results show that:?1?The lithology of Pinghu Formation are mainly mudstone,siltstone and sandstone,with a small amount of conglomerate,mainly gray and dark gray in color.Sedimentary structure is rich,which can be seen as scour structure,massive bedding,cross bedding,parallel bedding and other sedimentary structures.The double mud and tidal couplet are relatively developed,reflecting the presence of tidal shadow during deposition period.?2?Pinghu Formation in the study area mainly develops two sedimentary facies:tidal delta and tidal flat,which can be divided into three sedimentary subfacies:delta front,pre delta and intertidal zone,and can be further divided into eight sedimentary microfacies:underwater distributary channel,mouth bar,interdistributary bay,sheet sand,pre delta mud,mud flat tidal channel and mixed flat.?3?The sedimentary system of Pinghu Formation in the study area presents a tidal influence delta-tidal flat sedimentary model.The source is provided by the Western Hao Jiao uplift,and the delta deposits are formed from the west to the East.The tidal flat deposits are developed on the sides of the delta.?4?The porosity and permeability of Pinghu Formation are between 10%-17% and permeability reservoirs.The physical properties of massive bedding?gravel-containing?sandstone are the best,cross bedding?gravel-containing?sandstone is the second,and parallel bedding sandstone is the worst.In the sedimentary microfacies,the underwater distributary channel has the best physical properties,followed by sheet sand,the tidal channel is the worst.On this basis,combined with oil and gas bearing properties,it is considered that the dominant reservoir of Pinghu Formation is delta front underwater distributary channel sand body with porosity greater than 15%and permeability greater than 20×10^-3m ².The rock facies of the dominant reservoir are massive bedding?gravel-containing?sandstone facies and cross bedding?gravel-containing?sandstone facies.?5?The development of dominant reservoirs is affected by sedimentation and compaction,and the upper wall of syngenetic fault with thick sand body and wide distribution may be the favorable area for the development of dominant reservoirs.