| Ludong Sag is located in the east of Lujiabao sag in Kailu Basin.It is divided into three structural units: the eastern Sanshifangdi sag,the central tectonic belt and the western Jiaolige sag.The tectonic evolution of the Ludong sag can be divided into the initial fault depression stage,the rift and depression stage and the transition stage of fault depression.The Yixian Formation,Jiufotang Formation,Shahai Formation and Fuxin Formation of the Lower Cretaceous in Mesozoic are mainly developed.It is necessary to carry out this study because there are some problems in the Jiaolige area,such as disunity of understanding of sedimentary facies and unclear distribution facies of high-quality reservoir sand bodies.Aiming at the above problems,this thesis makes full use of geological data and drilling data in the study area to establish regional stratigraphic framework,and on this basis to identify and divide the sedimentary facies of Jiufotang Formation.Finally,ues the grey correlation analysis method to predict the distribution of high-quality reservoir sand of Jiufotang Formation during the period of sq2-4～sq2-5 and sq2-6～sq2-8,which reflected the control effect of sedimentary facies on the distribution of reservoir sand.The main insights are as follows:(1)The sequence interface of Jiufotang Formation can be identified by lithology combination,seismic reflection characteristics,well logging curve,single well characteristics,well shock combination and synthetic records.The Jiufotang Formation was divided into the lower member,the middle member and the upper member,and eight four-level sequences sq2-1～sq2-8 were identified under the control of three-level sequences.The stratigraphic framework of regional well connection was established,and the stratigraphic distribution characteristics of the south of the Jiufotang Formation was defined as thicker than the north and the west than the east.(2)The sedimentary facies were identified and divided by the characteristics of lithofacies,grain size,sedimentary structure,seismic facies and logging facies.The research results mainly identified fan delta,lacustrine facies and offshore subaqueous fan facies,and divided into underwater distributary channels,interdistributary channels,mouth bars,sheet sand(sheet lobes),deep lake mud,deep lake-semi-deep lake oil shale,turbidite thin sand,braided channel,and interbraided channel sedimentary microfacies.(3)The vertical and plane distribution of sedimentary facies was studied by fine characterization of microfacies features of single well,combined with provenance features,paleogeomorphic features and seismic attribute slice features.The results showed that the Jiufotang Formation mainly developed nearshore underwater fan facies in the sq2-1 and sq2-6～sq2-8 periods,the fan delta facies mainly developed in the sq2-4～sq2-5 period.Follow the direction of the source of the vertical up,the three systems of sedimentary facies are obvious.Tangent to the direction of the source,the sand bodies at different times are superimposed.In the sq2-4～sq2-5 period,fan delta front spreads over a wide area and is the main oil-bearing reservoir of the Jiufotang Formation.(4)Multiple evaluation parameters were selected by grey correlation analysis method to predict the distribution of high-quality sand bodies in sq2-4～sq2-5 periods and sq2-6～sq2-8periods of the Jiofutang Formation.Evaluation criteria were established,sand bodies were divided into high-quality,favorable and unfavorable types,and the plane distribution maps of sedimentary facies in different periods were integrated to find the main distribution facies zones of dominant sand bodies.The results show that sq2-4～sq2-5 high quality sand bodies with RQI(comprehensive evaluation factor)> 0.6 are mainly distributed in the area of well Jiao51,well Jiao49,well Jiao34 and well jiao47.In terms of sedimentary facies,such sand bodies are mainly distributed in the front facies zone of fan delta.The high-quality sand bodies with RQI > 0.6 in sq2-6～sq2-8 period are mainly distributed in the zone of well Jiao8,well Jiao33,well Jiao47 and well jiao22,and the sedimentary facies zone is mainly located in the nearshore underwater fan.At the same time,it also reflects the control effect of sedimentation relative to the distribution of reservoir sand body. |
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