Studies On Hydrocarbon Generation Potential Of The Source Rock Of The Zhuhai Formation In Baiyun Sag

The Baiyun Sag is located in the deep water area of the Zhu II depression in the Pearl River Mouth Basin.As the largest Cenozoic sedimentary basin in the Pearl River Mouth Basin,it has always been the focus of oil and gas exploration in deep water area.However,the research work on the source rocks of the Baiyun Sag has been concentrated in the Wenchang Formation and the Enping Formation for a long time,which means the research on the Zhuhai Formation is relatively rare.The factors affecting the tectonic-thermal evolution of the passive continental marginal basin are complex.Because of that,the selection of a suitable tectonic-thermal model is the basis for studying the hydrocarbon generation potential of source rocks.In this paper,the Zhuhai Formation of the Baiyun sag is selected as the research target layer,and the geophysical analysis data such as drilling and earthquakes and source rock samples are used to evaluate the source rock.With the help of the basin hydrocarbon simulation method,the investigation of the hydrocarbon generation potential has been done,in order to provide guidance for later oil and gas exploration work.The source rocks of Zhuhai Formation in the Baiyun sag are comprehensively evaluated from four aspects in this paper:basic characteristics of source rock,type of organic matter,abundance and maturity.The Zhuhai Formation in the Baiyun sag is in the transitional period between sea and land,and the delta-shore deposits are developed.The sedimentary thickness is large and widely distributed.The organic matter types of the source rocks are mainly type II₂,with both type II₁ and a few type III,with dual source characteristics.The organic matter has a high abundance and a large potential for hydrocarbon generation.It is mainly in the stage from immature to mature,and some of it can reach a high maturity stage.The main body belongs to a good source rock and partially belongs to medium class.Based on the data of statistical stratigraphic age,thickness,lithology and paleo-deep water,the simulation of stratigraphic burial history is carried out by using BasinMod-1D software.On this basis,combining the characteristics of current and paleo-temperature field,selecting the appropriate tectonic-thermal model,using positive and negative method,a thermal history simulation was performed.The results show that the tectonic subsidence has the greatest influence on the dolomite movement of the Baiyun sag since the Zhuhai Formation sedimentation,and the sedimentation rate of the Baiyun sag occurs mostly in the late stage of strong subsidence;the sedimentary thickness,effective burial depth,hydrocarbon generation threshold and maturity of the Zhuhai Formation source rocks are all reaching the highest in the main depression of the Baiyun sag,followed by the east depression the west depression and the south depression.They increase toward the center from the edge,and the north side is higher than the south side,looking from a plane perspective.Based on the research of thermal history,combined with the evaluation information of source rock,the hydrocarbon generation history simulation study is carried out.The results show that,due to the influence of source rock maturity and organic matter abundance,the comparison of fractional enthalpy shows that the cumulative hydrocarbon generation of the main depression is the largest,and it is now in the stage of cracking gas;the west and the east depressions are the second,and they are at the peak of hydrocarbon generation now;the south depression is the lowest,and it is still in the biogas stage.It also shows that the center of the depression is larger than the edge of the depression.On the plane,the northern part of the Baiyun sag has entered the peak of hydrocarbon generation,while the south has not yet entered.