The Research On Large-scale Sand Bodies And Transfer Zones In Paleogene Of Changchang-Heshan Sag,South China Sea

Changchang-Heshan(CC-HS)sag is a third-order tectonic unit in Zhu-? depression,Pear River Mouth Basin(PRMB),South China Sea(SCS).The study area closes to Xisha uplift and Shuangfeng basin in the south,Shunhe uplift in the north.It is a strategic exploration area of deep water region after oil and gas exploration outbreak of Baiyun and Liwan sag.Depending on the 2D seismic data,the research developed depositional system and tectonic-sedimentation response in Paleogene and discussed large-scale sandbodies under the control of transfer zones.First of all,guided by the Vail's theory of sequence stratigraphy,we constructed the sequence stratigraphic framework after the explanation of seismic data in study area.Consulting the partition scheme of Baiyun and Liwan depression,four second-order sequence surface were recognized including Tg,T80,T70 and T60.Wenchang,Enping and Zhuhai was devided into 4,3 and 6 sequences separately.Wenchang and Enping sedimented in each subsags,and Zhuhai mainly covered the whole region.Secondly,we recognized six types of continental seismic facies in Wenchang-Enping formation and seven types of marine seismic facies in Zhuhai formation in third-order sequence.Then we made seismic-sedimentation conversion template and analysed sedimentary system evolution in the study area.Finally,based on the planar fault explanation and stratum thickness,the research showed Wenchang and Enping formation experienced two tectonic stages successively,which respectively corresponded to early intensive rift stage and late weak rift stage.Zhuhai formation experience passive continental margin stage and the whole region step into balanced depression stage.In Wenchang and Enping tages,we recognized different levels and types of transfer zones.the research showed two levels(level-?and level-?)and six types(synthetic-approaching,synthetic-overlapping,synthetic-collateral,synthetic-collinear,antithetic-overlapping,divergent-overlapping)transfer zones.The degree of the fault activity controlled the sequence evolution and sedimentation system.In the plane,transfer zones were entrances of provenances and controlled the distribution of large-scale of sand bodies;In the section,slpe break controlled the types of large-scale of sand bodies.Furthermore,the research offers reliable evidence for favorable region exploration and supports a solid scientific evidence for the low degree oil and gas exploration in deep water area.