Hydrocarbon Accumulation Characteristics In Baiyun Sag,Pearl River Mouth Basin

Petroleum accumulation characteristics in Baiyun Sag in Pearl River Mouth Basin were studied from the following aspects:petroleum geochemistry characteristics,maturity,pathway system,oil and gas migration,reservoir characteristics,accumulation patterns,etc,and in combination with sedimentology、tectonics or other geology backgrounds,the oil accumulated characteristics in Baiyun Sag are analyzed in this paper.The source rocks in study area are deeply buried to 4-5km,nearly no source rock samples are obtained.Based on oil experiments and data analyses,parent material of crude oil has a notable higher plant input,Pr/Ph and other geochemistry parameters indicates an oxidizing type,lacustrine facies depositional environment.In according to featured biomarker compounds as oleanane and resin compound,combined with multi-parameter cluster analysis and C27-C29 triangular chart,the crude oil can be divided into two classes and five subclasses(Al-A3,B1-B2).Higher plant input degree regarded as the main differences between A and B.Oil-source correlation shows Enping source rock as the main rocks in class A,and that A3.adjacent to the center of depression,has relationship with Wenchang source rocks.Different contribution level between Enping and Zhuhai source rock offered favorable oil-source condition for class B,among these two formations,Enping source rock occupies the dominate position.The crude oils show mature-high mature oil characteristics.Class A has a high maturity compared to B.This also shows a good contrast relation with adamantine parameters.Three main pathway systems:permeability sandstone、fault and diapir structure,are the important oil-gas transportation in this Bayun Sag.Fault structures are highly developed,being the most significant longitudinal pass channel.Sandstone as the main lateral passageway,permeability in northern and southern sandstone is different.Fault produced by diapirism is also the important longitudinal pathway.In this study,aromatic maturity parameters that are effective in accessing oil and gas migration mechanism are discussed,for i.e.tricyclic terpane/hopane,TMNr,adamantine,nitrogen compounds,etc,indicate migration direction along the center of the Baiyun main depression to its surroundings;and adjacent to Panyu Lower Uplift,oil migration is from zones of high maturity in the west to zones of low maturity in the east.Fault developed areas,which are adjacent to the center of the main sag,are favorable migration and accumulation areas.Baiyun Sag is divided into two broad classes,seven small classes accumulation system,that is,four accumulation systems in Panyu Lower Uplift in western(N1-N4)and three accumulation systems in Liuhua-Liwan district in eastern(E1-E3).Three typical kinds of accumulation patterns are put forward on the basis of accumulation systems division,then comprehensively analyze the accumulation characteristics of three patterns.Based on the following analyses,W2,W3,W4 and E2,E3 are considered to be favorable migration and accumulation areas,and the research provides certain guidance for later oil and gas exploration in Bauyun Sag in Pearl River Mouth Basin.