Sedimentary Facies Research And Lithological Trap Prediction Of The First Member Of Shahejie Formation In The Central And Southern Wen'an Slope

The Wen'an slope lies in the eastern Baxian depression,which is closed to the source sag of Baxian.It has been found nine oil bearing series here including Ng,Ed,Es1.The proved reserves centralized the medium and shallow layers of the slope.The study areas of this paper contain middle and south of Wen'an slope,which include two nose structure zones-Yilunbao and Changfengzhen.It has been found that the reservoirs concentrate on both sides of Wangxianzhuang fault,which main types are tectonic reservoirs,such as fault block and fault nose.There has been obtained certain progress in strengthening lithologic reservoir exploration in recent years.To realize the breakthrough of lithologic reservoir exploration,the key works are the further study of sedimentary phases and the finer sand bodies prediction.Using high resolution sequence stratigraphic theory,the thesis analyzed synthetically the southern structural history,drilling coring,logging,seismic data of Wen'an slope.It has redivided Sha 1 by cycles so that Sha 1 is one cycle process generally.There has been some mutation expansion phenomenon between the lower part and the upper part of Sha 1,which the upper part of Sha 1 changes deep positive cycle from down to up and the lower part of Sha 1 becomes shallow reverse cycle from up to down.The middle mutation boundary surface is the boundary of Es₁^s and Es1x because of their superposition.The bottom margin in lower part of Sha 1 is at the transform surface from the reverse cycle which becomes shallow on the top of Sha 2and the positive cycle which becomes deep on the bottom of Sha 1.Based on the identifiable sedimentary cycle of study layers,it is divided into seven middle-term cycles in two ? sequence surfaces of Sha 1.The seven cycles are MS1 and MS2 in lower part of Sha 1,MS₃,MS₄,MS₅,MS₆ and MS₇ in the upper part of Sha 1.Researching and analyzing deeply lithology distribution,quartz content distribution,ZTR index,heavy mineral characteristics,debris content distribution,it is believed that the main sediment source was from NE and the minor sediment source was from SE in study area.Using drilling data and abiding by a“point-line-surface”process flow,it recognized and divided the sedimentary facies and microfacies in Sha 1.The understandings are:the subsegments of the lower part of Sha 1 are shore-shallow lake sub-facies firstly,the sedimentary microfacies have shore-shallow lake sandy beach,shore-shallow lake sand bar and shore-shallow lake muddy beach.The regional lifting enhances obviously and basin reduces quickly at the later sedimentary period.The fluvial facies,especially the braided facies are mainly developed in the upper part of Sha 1.The meandering river sediment is developed in upper of Sha 1 subsegment?MSC6 and MSC7?,which include many types of microfacies such as channel bar,side bar,braided channel,floodplain,etc.They appear higher in the east while lower in the west totally.Based on the study of sedimentary facies in Sha 1,the paper predicted reservoirs through poststack seismic impedance inversion and attribute analysis.Looking for favorable facies,identifying sand bodies distribution characteristics,it has believed that the areas?i.e.,Wen 29 to Wen 80,Wen 79 to Wen 43,etc?which were at the two wings of Shigezhuang and Changfengzhen nose structure have formed a series of structural-lithologic traps,which had clear lithology and multiple faults.The layers of Sha 1?i.e.,Wen 34,Wen 33,Su 90,etc,in the outer zone of Wen'an slope?have formed a series of stratigraphic and lithologic traps,which the type of thinning from west to east until pinching-out.