Analysis Of Sequence Stratigraphy And Sedimentary Facies Of Lingshui Formation In Yacheng Area, Qiongdongnan Basin

In this paper,the Lingshui Formation in Yacheng area of Qiongdongnan Basin is the main research object.Based on the analysis and research of the seismic data,drilling core data and analysis test data widely covered in the study area,the development model and evolution characteristics of the sedimentary system of the Lingshui Formation in Yacheng area are comprehensively discussed from the perspective of ’source-canal-sink ’ system.The source supply mode,the main types of sediment transport channels,the characteristics of sedimentary filling and the distribution of sand bodies in different periods are clarified,which provides a reference for finding favorable reservoir sand bodies in the next stage of the study area.Based on the comprehensive analysis of sequence stratigraphy,the key sequence boundaries of Lingshui Formation in Yacheng area are identified,divided and compared,and the isochronous sequence stratigraphic framework is established.The third-order sequences SQ70,SQ62 and SQ61 are divided,corresponding to the third,second and first members of Lingshui Formation.According to the core facies marks,logging facies marks,seismic facies marks and grain size analysis results,four sedimentary types of fan delta,braided river delta,coastal and shallow sea are identified in the third-order sequence framework.Based on the analysis of heavy minerals and seismic provenance system,the plane distribution and evolution law of the provenance system of Lingshui Formation in Yacheng area are clarified.The Lingshui Formation in the Yacheng area is mainly affected by the three major provenance systems inside and outside the basin,namely the Hainan uplift in the north of the basin,the large water system in the west of the basin and the Yacheng uplift in the basin.In the early stage of the Luolingshui Formation,influenced by the Yacheng uplift in the basin,the uplift and depression pattern in the study area is obvious,which is mainly supplied by the source system outside and inside the basin.In the middle-late period of the Tuolingshui Formation,with the increase of transgression,the Yacheng uplift in the basin was submerged into the water to receive sediments,which was mainly provided by the provenance system outside the basin.On the basis of macroscopic provenance tracing,the source channel types and plane distribution characteristics of Lingshui Formation in Yacheng area can be further described based on seismic data.The sedimentary paleogeomorphology and seismic reflection characteristics indicate that the study area mainly develops two types of source transport channels : ancient gully type and fault trough type(single fault and double fault type).Among them,the fault steep slope zone mainly develops fault trough type source transport channel-near source fan delta(such as the northern part of Yabei sag and the northern part of Yanan sag),and the gentle slope zone mainly develops ancient gully type source transport channel-braided river delta deposition(such as the western part of Yanan sag).Based on the systematic study of the provenance system,transport channel and corresponding sedimentary facies distribution characteristics of Lingshui Formation in Yacheng area,the development model of Lingshui Formation sedimentary system in Yacheng area is summarized into two types,namely:(1)the development model of near source-fault trough channel-fan delta sedimentary system,which is mainly developed in the periphery of Yacheng uplift and the steep slope of the northern margin of Yabei sag;(2)The development model of distal-gully channel-braided river delta sedimentary system is mainly developed in the western gentle slope of Yanan sag.Therefore,through the analysis of “source-canal-sink” system,the sequence stratigraphic framework,the distribution and evolution of provenance system,the characteristics of sediment transport channel,the types and spatial distribution of sedimentary system are integrated together,which enhances the reliability of reservoir sand body description under the condition of few wells and no wells.