Study On Flow Unit And Remaining Oil Distribution Of Chang 8₁ Reservoir In Baibao Area,Ordos Basin

The method based on flow unit was used to study the production demand of remaining oil for chang 8₁ reservoir in baibao area of ordos basin.The flow units are divided by using geological and mathematical methods.With the concept of reservoir architecture interface,the third and fourth order seepage barrier are identified by logging markers.Three parameters,namely porosity,permeability and oil saturation,were optimized from eight flow cell partition parameters by using R-type clustering and its correlation with initial production.By using Q-type clustering and Bayes discrimination,the study is divided into four types of flow units and the discriminant functions of each type of flow unit are established.Under the constraint of seepage barrier,the vertical and plane distribution of flow units are obtained according to the discriminant scheme.The distribution of throat radius and the homogeneity degree of pore throat were studied by means of high pressure mercury injection,the volume components of throat with different radii and the control space volume were explored by means of constant speed mercury injection,the spatial distribution frequency of pore throat with different radii was qualitatively analyzed by means of nuclear magnetic resonance experiment,and the pore structure of samples was divided into six categories according to the experimental results.The reservoir can be divided into three types according to the curve shape and displacement efficiency.The movable fluid saturation obtained by NMR experiments can be divided into five types of reservoirs.The results of classification correspond to the results of flow unit division,and the analysis shows that the flow unit is influenced by the comprehensive characteristics of pore throat and seepage flow,and the results of flow unit division by clustering and discrimination method correspond to the experimental results to a higher degree,which proves that the division results are reasonable and feasible.By analyzing the sequence of vertical superposition of water-absorbing profile data and flow units of different masses,the distribution of third-level and fourth-level seepage interfaces,the distribution of injection-production Wells in the well group and the position relationship of flow units,the internal characteristics of flow units are concluded as follows.Residual oil tends to concentrate around the barrier,in poor cells adjacent to better flow units,in the upper part of the same flow unit,in the area with uneven pore throat in the flow units of type one and second.Based on the comprehensive analysis of the distribution of flow units and residual oil distribution laws,the residual oil distribution locations of different causes are predicted.The remaining oil distribution in the B168 well area and B418 well area controlled by the combination of flow units is the largest,which is the main target for potential tapping.The results show that the methods of reservoir architecture,cluster analysis and discriminant analysis are reasonable and suitable for prediction of residual oil.