Research On Sedimentary Facies Of Paleogene In Lunnan And Its Surrounding Area

Based on the core observation and description,through the comprehensive analysis of logging,core characteristic,seismic and regional geological data,this paper identifies and calibrates the standard layers of the three oil groups E?,E?,and E? of the Paleogene in the Lunnan area,carrying out fine stratigraphic division and comparison,identifying sedimentary facies types and distribution of Sand body,combined with the reservoir's physical properties,tectonic development characteristics,and oil test data to select favorable exploration blocks.There are seven standard layers developed in the Paleogene in this area,two of them are primary standard layers,two of them are secondary standard layers and three of them are tertiary standard layers.Under the constraint of the standard layer,the Paleogene strata in the study area was divided into three oil groups: E?,E?,and E?.These three oil groups were further subdivided and the E? oil group was divided into two sand groups: E?1 and E?2,a total of five small layers;E? oil group is divided into two sand groups:E?1 and E?2,a total of four small layers;E? oil group is divided into two sand groups:E?1 and E?2,a total of five small layers.The color of Paleogene sandstones are mainly grey and brown-red,mainly in medium,fine and silty sandstones,with a small amount of conglomerate developed locally.The mudstones are brownish-red and brown in color,and the overall environment is weakly oxidized and deposited.The sand-mud combination in the E? oil group is a typical sand-mud feature,in the E? oil group the sand-mud combination is a mud-sand feature,and the sand-mud combination feature in the E? oil group is a feature of the “half muddy sand”.The granularity probability curve is two-stage type or three-stage type.The sedimentary structures mainly contain parallel bedding,wavy bedding,trough-like cross-bed bedding,and the scour surface at the bottom of the channel.The maturity of sandstone composition and structure is relatively low.Above all,we can conclude that the Paleogene stratum in the working area is braided river delta front sedimentary subfacies,which mainly develops the microfacies of main channel,underwater distributary channel,the margin of river course,estuarine bar and interdistributary bay.It also develops shallow lake subfacies,which contains sand banks and mudflats.The main trend of braided river channel of this area is to extend in a nearly north-south direction.In the Lunnan area,the Paleogene as a whole is a lacustrine transgressive system,including two sub-lacustrine transgressive system and a sub-lacustrine regressive system.The E? and E? oil groups are lacustrine transgressive system,and the E? oil system is a lacustrine regressive system.The E? oil group is the main target for research,in which vertical multi-stage sand bodies of channel are vertically superposed,and the overall thickness is relatively large.Viewed from the plane,The main trend of braided river channel of this area are mainly distributed in strips in the north-south direction,and a few are in the northwest-southeast direction.The diversion and convergence of river channels can be seen in some areas.According to the distribution law of sand body and sedimentary facies in the study area,through the analysis of many factors such as reservoir physical properties,regional structural fracture characteristics,and oil test data,we can see that the main oil layer in the Paleogene strata is the small layer called E?2-1 in the Lunnan area.In the end,we can predicted that there are 5 favorable blocks in the upper part of the E?2 sand group in the area of LN2.