Sedimentary Characteristics And Favorable Sandbody Predictions Of The Shahejie Formation In The Chaheji Area

Petroleum geological conditions in Chaheji area are very complex,in addition to the broken structure.Scattered reservoir longitudinal distribution,thin single layer thickness,small transverse distribution and poor interwell connectivity,result in sedimentary faces and micro-faces research relatively backward and restrict the in-depth development of reservoir evaluation.In order to further expand the oil and gas exploration areas,it is needed to have a comprehensive geological description in the study area.Guided by the theory of sedimentology,combined with the core,well logging,mud logging,seismic and testing data,the paper studies the sedimentary characteristics,micro-faces analysis and favorable sandbody prediction of the Shahejie formation of Chaheji area.By means of core data,grainsize analysis,thin section identification and analysis of seismic-faces and electro-faces,guided by the results of seismic faces,combining with the correlations of single well faces and profile faces,the systemic studies of sedimentary micro-faces of the Shahejie formation of Chaheji area are done.The result indicates that sediments in the research are maily grey,hoary fine sandstones-siltstones,and some grey argillaceous siltstone-silty mudstone.The color of mudstone is mainly black,gray green and purple.Through sedimentary microfacies identification,nearshore subaqueous fan,fan delta and XianHua lake are main sedimentary faces in study area,which are further classified as braided river and braided channel micro-faces of fan delta plain sub-face,underwater distributary channel and interchannel,mouth bar and sheet sand micro-faces of fan delta front sub-face.Dominated by the Niudong fault in the west,the delta passed through the study area from west to east.The research result shows that nearshore subaqueous fan is developed in northern part of this study area in the higher part of the third member of Shahejie formation,fan delta plain but not front sub-faces in southern.As for the second member of Shahejie formation,the contraction of lake basin results in the developments of fan delta in northern and XianHua lake in the large area southern.In the sedimentary period of the lower part of the first member of Shahejie formation,lake basin gradually expanded and the water level rised fluctually,the study area mainly developed nearshore subaqueous fan deposits.And on this basis,the paper established faces model of the Chaheji area.On the basis of sedimentary characteristics,tectonic setting and earthquake research,combining with sand body thickness distribution and adjacent wells in oil and gas shows,make a favorable sandbody scope prediction in the study area.The development of the sedimentary faces is mainly controlled by tectonic and climate,nearshore subaqueous fan and fan delta of the lower and middle part of the third member of Shahejie formation,nearshore subaqueous fan and subaqueous distributary channel,sheet sand of the higher part of the third member of Shahejie formation,fan delta of the second member of Shahejie formation and nearshore subaqueous fan of the lower part of the third member of Shahejie formation,sedimentary physical properties develop well,and favor oil gas accumulation.They are the next focal point of exploration.