Chang4+5 Low-resistivity Oil Layers Logging Interpretation In North Of Yanchi

With the continuous exploitation of the Jiyuan oilfield,a large number of low-resistivity oil layers were found in the Yanchang section of the Chang4+5 layer.Due to the lack of systematic understanding of the low-resistivity oil layer,miscalculation of fluid properties may be caused in log interpretation.In this paper,a set of assessment procedures for low-resistivity reservoirs in the study area was formed using various data from the core,physical properties,logging,oil testing,and geology in the study area.The systematic comparison of low-resistivity reservoirs and conventional oil reservoirs in the study area explores the micro-mechanism of the low-resistivity reservoirs in the study area from differences in lithology,physical properties,shale,formation water salinity,and microscopic pore structure.Through the analysis of sedimentary,diagenetic,and tectonic effects in the study area,the macroscopic mechanism of the low-resistivity reservoir in the study area was explored.Regar as under the influence of sedimentary and structural macro-geological factors,resulting in fine rock particles,poor physical properties,complex pore structures causing high irreducible water saturation and mud invasionBased on the study of reservoir "four-properties" in the study area.In view of the incompleteness of logging data in the study area,the shale content was constructed by natural gamma curves and density and neutron logging,taking the tri-porosity multiple regression fitting porosity model and using porosity to model permeability model.The irreducible water saturation model is established by NMR experiments,and the variable parameter Archie formula to establish the saturation model and the core analysis data both have a good correspondence.According to the cause of low resistance,the curve overlap method,the NMR logging difference method,and the invasive factor map method are proposed.Combined with the lower limit of reservoir validity,the low resistivity oil layers can be well identified.By superimposing the reservoir parameters in the study area on the plane distribution and sand body thickness,the prediction of the favorable area is based on the test oil and production data.