Reservoir Evaluation And Reserves Calculation Of Yan 9₂ Oil Formation In Feng 8 Well Area,Ordos Basin

Feng 8 well area belongs to Jihuang 32 block,Ordos Basin.At present,the problem of high water cut and the production of Yan 9₂ sandstone formation in the study area is becoming more and more serious.The fundamental reason is that the geological understanding is not precise.Specifically,the study on the contact relationship between sand bodies and the development of barrier and interlayer is not in-depth,thus affecting the effectiveness of injection and production scheme.For this reason,this paper makes use of geological and geophysical data of the study area,and on the basis of fine division of small layers and analysis of sedimentary microfacies,focuses on the fine analysis of single sand body and the establishment of a geological model.The reserves of the study area are recalculated by using the model.The main research results and understandings are as follows:Based on the logging data of the study area,the Yan 9₂ sand formation in the study area is further divided into three single sand layers:Yan 9₂³,Yan 9₂² and Yan 9₂¹.According to the methods of stratigraphic correlation such as marker layer,cycle analysis correlation and isoelevation correlation,the isochronous stratigraphic framework of single sand level is established.Combined with the regional sedimentary background data,it is clear that the study area is a braided river delta plain,and there are mainly four kinds of sedimentary microfacies:braided channel,central bank,overflowing bank and flood plain.Based on the study of sedimentary microfacies,the boundary of single sand body was identified by using different logging curves,different elevation of sand body top surface,interfluvial deposition,sand body thickness variation and river-dam-river identification markers.It was determined that there were 9 channel sand bodies,20core beach sand bodies and 14 bank overflow sand bodies in the study area.The spatial contact relationship of sand body is analyzed,which mainly shows isolated type,overlapping type,cut overlapping type,contact type and bay separation type.Two types of silty and physical barriers and intercalations are identified in the study area.In the vertical direction,the sand body is not connected where the barriers and intercalations are developed.Based on the study of the plane distribution characteristics of sand bodies and the contact relationship of sand bodies,the transverse connectivity of sand bodies can be divided into four types:first type connected(within the same channel),second type connected(between sand bodies of different channels),third type connected(between sand bodies of different genesis)and unconnected.Based on the detailed study of single sand body of reservoir,a three-dimensional structural model was constructed and the attribute model was established by the method of"facies control"to analyze its distribution in three-dimensional space.The geological reserve of Yan 9₂ sand group in the study area was calculated by using the geological model with single sand layer as unit,which was about 25×10⁴t in total.