The Research On Sedimentary System In The Wenchang And Enping Formation Of Pearl River Mouth Basin Baiyun West Depression And Panyu 27 Sag

Located in the northwestern part of the Baiyun depression and Panyu low uplift in the Pearl River Mouth Basin,Baiyun West depression and Panyu 27 sag are considered to have some potential for hydrocarbon generation.However,the research on this area has been relatively slow and the study on the distribution of sedimentary filling evolution and sedimentary systems lacks integrity and systematic.In this paper,the sequence stratigraphic framework of the Paleogene Wenchang and Enping Formation is established by studying the 3D seismic data in the whole region as well as some core and well logging data.The types of seismic facies and sedimentary facies are identified,and the distribution and filling evolution of sedimentary system are clarified.First of all,relying on the Vail sequence stratigraphy theory system,the seismic survey lines and some drilling and logging data of the study area are analyzed to identify three second-order unconformity sequence boundaries of the Paleogene,including Tg,T80 and T70.Three third-order sequence boundaries including wcsb2,wcsb3 and wcsb4 are identified in the Wenchang Formation,and one third-order sequence boundary of epsb2 is identified in the Enping Formation.The Wenchang Formation and Enping Formation of Baiyun West depression and Panyu 27 sag are subdivided into 6 third-order sequences.Six types of seismic facies of the Wenchang and Enping Formation of the Paleogene are identified.Among them,the Wenchang Formation steep slope mainly develops the wedge-shaped chaotic foreset seismic facies and the oblique or low-angle S-type foreset seismic facies;the deep belts mainly develop parallel to subparallel or hummocky seismic facies and the parallel sheet seismic facies;the slope zone mainly develops skewed or low angle S-type foreset seismic facies and chaotic foreset seismic facies;the Enping Formation mainly develops the middle-amplitude and low-continuity subparallel-hummocky sheet seismic facies and middle to strong-amplitude and middle to high-continuity parallel sheet seismic facies.The types of sedimentary system and sedimentary filling evolution of target layer in the study area are clearly identified,and types of sedimentary facies including fan delta,shore-shallow lake facies,mid-deep lake facies,braided river delta and braided river channel.The study shows that in the Wenchang Formation WCSQ1 initial rift stage,both north and south sides of Baiyun 3 depression develop large-scale fan delta facies;in the WCSQ2 rapid lift stage,the depositional area increases,each sag develops fan delta facies,and the study area is dominated by foreshore and shallow lake facies;in the WCSQ3 strong rift stage,the depositional area continues to expand,the lake level rises rapidly,the large-scale mid-deep lake facies develops,and fan delta develops in succession;in the WCSQ4 shrinking rift stage,each sag further intercommunicates with each other,and large-scale middle-deep lake facies and large-scale sandbodies develop in succession.The rift activities of the Enping Formation decrease during the depositional period.The braided river delta plain sedimentary system mainly develops in the whole area,and the source comes from north-west region.Each sag of EPSQ1 is basically connected,mainly developing the braided river channel facies with some braided river interchannel facies;In the EPSQ2,there are sediments throughout the region,mainly developing the braided river channel facies and a few braided river interchannel facies.By clarifying the distribution of sedimentary systems and sedimentary filling evolution in the study area,it provides a more reliable basis for the overall evaluation of the study area in the future,and provides reference and guidance for future exploration and development of such reservoirs.