Sedimentary Facies And Reservoir Evaluation Of Chang 7 In Tiebian Cheng Area

Shale oil of Member Ch-7 reservoirs group in Tiebian Cheng area of Ordos Basin is widely developed and has been initially developed in recent years.Due to the complicated oil-water relationship in the block,the production of single well is low at present,so it is urgent to master the reservoir status in the study area through fine reservoir characterization and secondary logging interpretation of some Wells.In this paper,Member Ch-7 reservoirs group in Tiebiancheng area of Ordos Basin is taken as the research object,guided by relevant theories and methods of sedimentology,and made full use of drilling core data to carry out analysis and research on stratigraphic subdivision,sedimentary facies types and characteristics,formation sand body distribution characteristics,reservoir characteristics and reservoir evaluation in the study area.In order to clarify the stratigraphic characteristics of the study area,according to the depositional cycle method,the marker layer and scour surface method,and the formation iso-thickness method,the Member Ch-7 reservoirs group is subdivided into seven sub-layers,namely Ch-7₁¹,Ch-7₁²,Ch-7₂¹,Ch-7₂^2-1,Ch-7₂^2-2,Ch-7₃¹and Ch-7₃².In addition,a"5transverse and 5 longitudinal"well pattern framework is established in the study area for stratigraphic correlation.The analysis shows that the characteristic of Member Ch-7 reservoirs group marker layer is obvious and its distribution is relatively stable.Based on the combination of the characteristics of rock color,grain size,rock structure and sedimentary structure in the sedimentary facies markers with the logging curve markers,it is concluded that the delta facies developed in the sedimentary period of Member Ch-7 reservoirs group in the study area,the delta front subfacies is the main one,and the sedimentary microfacies types are underwater distributary channel,bay between tributaries,underwater natural dike and estuary bar.The evolution law of sedimentary facies and the distribution pattern of sand body are further studied in vertical section and plane.It is clear that the extension direction of the sand body is from northeast to southwest,and the whole channel sand body of Member Ch-7 reservoirs group member reservoir is well developed,especially the Member Ch-7₂reservoirs group with large thickness,far extension and good contiguous property.Based on the observation and analysis of core samples,the reservoir petrological characteristics,reservoir pore-throat structure characteristics,reservoir physical characteristics and reservoir diagenesis were studied,and the study area was divided into four diagenetic facies zones.Based on the statistical characteristics of lithology,lower limit of oil bearing,lower limit of effective reservoir physical property and reservoir electrical property standard,the study area is classified into classⅠ,classⅡand classⅢreservoirs by combining with the previous evaluation and classification standard of reservoir.The evaluation results of Member Ch-7reservoirs were obtained,and Ch-7₃,Ch-7₂and Ch-7₁were graded as slightly poor,good and poor,respectively.Among them,high-quality reservoirs can lay a foundation for the development and stable production of oil reservoir of Member Ch-7 reservoirs group of Yanchang Formation in Tiebian Cheng area.