The Control Function Of The Structural Break-slope Zone In Lishui Sag To The Oil And Gas Trap

The lishui sag is an important exploration areas in East Sea Shelf Basin. Thoughthe exploration in lishui sag has outset many years before, the major structural trapshaven’t been found. In recent years the exploration of lithologic trap has become thefocus of exploration work. This study applies the seismic facies analysis technique toestablish the sedimentary system based on the theory of the Sequence stratigraphy,Reservoir sedimentology and Petroleum geology as well as the seismic data and thewell-log information. This study analyses the distribution of the structural break-slopezone and then researches the influence of the structural break-slope to the sedimentarysystem. Through this study, the general conclusion of the influence is draw and thenguides the further exploration.At first, this study applies the well-log information and the seismic data toestablish the tectonic framework of lishui sag. Under the framework, the Paleoceneformation of lishui sag is divided into two secondary sequence and five third sequence.Then the yueguifeng formation, the lingfeng formation and the up segment ofmingyuefeng formation are divided into Transgressive Systems Tract and HighstandSystems Tract. The low segment of mingyuefeng is divided into Lowstand SystemTract, Transgressive Systems Tract and Highstand Systems Tract. So the sequencestratigraphic framework is established.The second study is distinguishing the structural break-slope zone. In the steepslope zone, three kinds of structural break-slope are distinguished, that is single faultstyle, positive step style and mountain ridge style. In the gentle slope, four kinds ofstructural break-slope are distinguished, that is flexural style, single fault style,positive step style and reverse step style. These kinds of structural break-slope arecombined to three break-slope zones in the plane, that is the west break-slope zone,the middle break-slope zone and the east break-slope zone.Many typical seismic facies, for example sheeted, divergence, S-foreset, composite foreset, wedge-shaped, messy-blank and so on, are detected. According toseismic reflection shape, there carved out4categories of seismic facies containingforeset, parallel-subparallel, hummocky and messy-blank seismic facies which aresubdivided into11subunits in accordance with reflection amplitude, frequency andcontinuity. Combine with the information of the core and well-log, the seismic faciesconvert to the sedimentary facies. The sedimentary facies of delta, slump turbidite fan,coastal subsea apron, fan delta, barrier bar, carbonate salt flats and so on, are detectedin this area.Summarizing all above work, the following conclusions could be drawn. Thewest break-slope zone controls the deposition of the slump turbidite fan. The middlebreak-slope zone controls the deposition of the barriers facies. The east break-slopezone controls the deposition of the coastal subsea apron and fan dalta. The lithologictrap may be developed in the barriers facies and the slump turbidite fan.