Study On Wenchang Formation In Northern Zhu ? Depression Of Pearl River Mouth Basin

After many years' exploration,the hydrocarbon source rock of Wenchang formation has been proved to be the main hydrocarbon source rock in Zhu III depression.In the research area,only well YJ23-2-1 and well WC2-1-1 have reached Wenchang formation.For lack of controlling wells,the exploration,to a great extent,depends on the seismic data.The features about seismic facies of different sedimentary facies which summarize from similar sag such as wenchang A sag,wenchang B sag,Huizhou sag can be used in research area.Based on traditional sedimentary work,summarize the seismic reflection rules and distribution of different sedimentary facies,point out where high quality hydrocarbon source rocks is and provide scientific basis for an objective evaluation of the resources potential in the research area.The research shows that Wenchang formation is continental deposition.It mainly developed alluvial-fluvial-lake sedimentary facies.Near provenance area developed alluvial fan;gentle slope belt develop fluvial system;deep sinking belt develop lacustrine facies;steep slope belt develop fan delt-alluvial facies.Through the peripheral investigation,the corresponding principle of seismic facies and sedimentary facies in zhu I and zhu III deposition were summed up.There are six seismic facies identified in Yangchun-Yangjiang sag.Wedge shape mixed and disorderly weak amplitude blank phase,reflecting alluvial fan.Wedge shape mixed and disorderly blank foreset facies,or intermittent mixed disorderly strong amplitude phase,reflecting fan-delta.Sheeted parallel weak-middle amplitude phase,reflecting deep lake,middle-continuous parallel and weak-strong amplitude phase,reflectingmedium shore-shallow lake.Weak continuous,parallel-wave shape,variable amplitude phase,reflecting meandering river.Intermittent lenticular,weak-media amplitude phase,reflecting braided river.There are seven seismic facies identified in Qionghai sag.Wedge skew f-oreset media-strong amplitude phase,intermittent disorderly strong amplitude phase,intermittent skew foreset weak amplitude phase,reflecting alluvial fen.Intermittently disorder weak amplitude phase,reflecting braided fluvial river.Low frequency and weak continuous,sub-parallel,varying amplitude-media amplitude,reflecting meandering river.Media frequency,media continuous sub-parallel,media-strong amplitude,reflecting shore-shallow lake.Low frequency continuous parallel strong amplitude,reflecting deep lake.On the whole,the research area developed a large area of river-delta deposition.South Yangchun sag stable lacustrine sedimentation.Its range is very limited and the shore-shallow lake phase only 100 km2.East Yangjiang sag develop relatively large range of shallow lake-deep lacustrine deposition,of which the shore-shallow lake is 225 km2 and deep lake is 75 km2.Qionghai sag is mainly fluvial facies,the top of Wenchang formation is shore facies.Its shallow lake is 155 km2,and the top of center sag is deep lake facies(34 km2).Combined with Geochemistry analysis and basin modeling result,east Yangjiang sag and east Qionghai sag are the favorable exploration directions.What's more,east Yangjiang sag is the best sag which has the most potential resources in the research area.