Logging Evaluation Of Water-flooded Zone Of Chang 4+5 Ultra-low Permeability Reservoir In Changqing Oilfield

After the long-term water injection development in the Baiyushan block,the Chang 4+5oil layer has entered the development stage of the medium and high water cut period.Although the development of the reservoir has experienced several time of adjustment,due to the anisotropic and heterogeneous nature of the reservoir in the longitudinal and lateral directions,the reservoir has fine lithology and complex pore structure,which makes the relationship between water and oil very complicated and increases the difficulty of logging interpretation in the flooded layer,resulting in poor interpretation of the logging interpretation of the flooded layer and actual production.The overall interpretation rate is low.Therefore,this paper proposes to establish a complete logging evaluation technique suitable for the Chang4+5interval of the encryption adjustment well in Baiyushan block.In this paper,the existing logging interpretation methods of water-flooded layers in the study block are investigated,and then the changes of rock electrical parameters and resistivity of freshwater flooded layers are studied.The variation characteristics of reservoir parameters such as shale content,reservoir physical property,oil content and formation water salinity before and after flooding in the Chang4+5 interval are compared and analyzed.At the same time,the logging response characteristics of natural potential logs,acoustic logs,natural gamma longs and resistivity logs after flooding are analyzed,which lays a foundation for qualitative identification and quantitative evaluation of water-flooded layers.In the qualitative identification of water-flooded layers,five methods for qualitatively identifying water-flooded layers are proposed in this paper: Natural potential curve change method,resistivity correlation analysis method,new and old well resistivity comparison method,resistivity reconstruction method and resistivity difference ratio method,And using the difference ratio between the measured resistivity and the reconstructed saturated oil-containing water-containing two resistivities,the intersection map of the freshwater flooding level is established,which can achieve better results in practical applications.In the quantitative evaluation of water-flooded layer,the shale content,porosity,permeability,irreducible water saturation,residual oil saturation,oil-water relative permeability model of the study block were established.Based on the principle of variable material balance,the three-parameter joint quantitative iterative method was used to solve the water saturation,water production rate and mixed formation water resistivity.At the same time,the quantitative classification criteria of freshwater flooding level are established by using two water-flooding level evaluation parameters,such as water production rate and oil displacement efficiency,which can effectively divide the flooding level of the study block and improve the accuracy of quantitative evaluation of water-flooded layers.Finally the combination of qualitative identification method and quantitative recognition method were applied to evaluate the freshwater flooded layer and the water flooded level finely in the Chang4+5 interval of the Baiyushan block.The actual logging data processing was carried out on the thirty-three encrypted adjustment wells in the study block.The interpretation rate of the water-flooded layer reached more than 85.56%,and achieved very satisfactory application results.