| The H236 well area is located in the southwest of the Ordos Basin,and the Yan 7 oil layer group is main oil-producing layer.The research area has been put into production and development for more than ten years and has entered the middle stage of development.The early research grades for the composite channel sand body of the sand group can no longer meet the current development needs.Carrying out single sand body research has an important guiding role in subsequent development and adjustment.Based on core,logging,production data and other datum,this study carried out stratigraphic division and comparison with reference to sedimentary cycles,thicknesses and logging curves with the help of marker layers and auxiliary marker layers,and established an isochronous stratigraphic framework.On this basis,the microfacies types are determined and their distribution characteristics are analyzed by petrological characteristics such as color,lithology,grain size,sedimentary structure,and logging facies markers,which provide a reliable geological understanding for the study of single sand bodies.According to the identification marks,the single sand body is divided,its spatial relationship and its influence on connectivity are clarified,the lateral section and plane distribution characteristics of the single sand body are analyzed,the mathematical relationship between the width and thickness of the single channel for sand control is explored.And the connectivity of sand body is confirmed for providing injection and withdrawal adjustment measures.Mainly obtained the following knowledge:The Yan 7 oil layer group in the study area was divided into four sub-layers,Yan 711,Yan 712,Yan 721 and Yan 722,from top to bottom,with an average thickness ranging from 11.0 to 7.9 m,gradually decreasing by about 1 m.The strata of Yan 711 and Yan 712 were slightly thicker from the northwest to the middle and the east,and thin to the southwest;Yan 721 and Yan 722 were relatively thin as a whole and have a small change.The delta plain sub-facies developed in the study area,and five types of microfacies were identified:distributary channel,natural levee,crevasse splay,inter-distributary depression and swamp.The distribution of sedimentary microfacies showed that four to five distributary channels enter from the southwest to the middle during the Yan 7 depositional period and flow out from the northeast after confluence and bifurcation.Except for the Yan 711 distributary channel,the scale of the distributary channel was slightly reduced,and the other sub-layers of the distributary channel had no significant difference.A stage distributary channel single sand body was identified in each sublayer,which corresponded to the first,second,third,and fourth stages from bottom to top in the Yan 7 oil layer group.Vertically,the second and third stages were mainly separated.On the lateral side,the first and second-stage sand bodies were mostly butt-jointed and laterally cut,which increased the connectivity of the sand bodies.On the plane,the third-stage sand bodies were relatively well developed,thicker in the middle-northeast part,and the first and fourth-stage sand bodies were of the same size.The width and thickness of a single channel controlling the development of a single sand body in each stage had an exponential positive correlation.The width of the channel sand body on the plane could be predicted according to the thickness of the channel sand body based on the functional relationship,which had reference value for well placement.Taking the injection-production well group as the unit,according to the effectiveness of water injection,the connectivity of the identified single sand body was verified.Three key well groups were selected to analyze the relationship between injection and production,and adjustment measures were proposed that the water wells were refilled with 3 well times and the oil wells with 33 wells. |
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