The Research On Response Mechanism Of Sweep-Frequency Dielectric Logging And Interpretation Method

Due to low-contrast reservoir oil layer and water layer because of the low formation water salinity,or due to changeable or unknown flooding water salinity,it is difficult to combine conventional resistivity and Archie formula to evaluate water saturation accurately.In addition,the water saturation evaluation with fixed cemetation index m often lead to error in carbonate formation often with changeful m.As a logging technology,dielectric logging is gradually showing its advantages in evaluating the water saturation.According to the problems of imcomplete sweep-frequency dielectric logging response mechanis,lack of correction charts of sweep-frequency dielectric logging and improper dielctric logging interpretation mixing laws,the packed models are firstly researched in order to analyze the factors affecting the cemetation index.Based on the result,the artificial cores with changeful m are made to carry out the sweep-frequency dielectric experiment.At the same time,the research is done systemly though the numerical simulation method.Finally,based on the dielectric experiments,the noval dielectric logging interpretation mixing law is modified.Combined with the correction charts,the noval dielectric constant mixing law is verified by the field data processing.The resistivity experiment results show that the cementation index is affected by the surrounding pressure,porosity and salinity etc.The dielectric experiment results show that the dielectric constant of the matrix is approximately 5.4;dry samples and cores saturated distilled water were frequency independent;the dielectric constant increases linearly with the increase of water saturation,the lower the frequency,the higher the increasing amplitude and vice vise;the dielectric constant also increases with the increase of the salinity,porosity and cementation index.All the experiment results make the sweep-frequency dielectric logging response mechanism more clearly especially for the artificial cores with changeful m.The numerical simulation results show that the use of the saddle point method for solution of the mixed wave model in half space field with higher resolution is even better than the equivalent dipole model in homogeneous field.From the research of radial detection characteristics,the dielectric logging can reach up to 65 mm when the frequency is set to 20 MHz,while the shallowest is only 36 mm when the operation frequency is set to 1000 MHz.The vertical resolution of sweep-frequency dielectric logging is as low as 50 mm.When the thickness of the target formation is greater than this value,half point can be adopted to identify the bed boundaries.By researching the influence of mud cake,the larger the thickness of mud cake,the higher the relative dielectric constant and conductivity value.The less the formation dielectric constant and the less spacing between transmitting antenna to the receiving antenna,the larger the mud cake correction.The mud cake correction charts of sweep-frequency dielectric logging are then used to preprocess the dielectric logs.Finally,based on the dielectric experiments and comparision with the previous dielectric constant interpretation mixing laws,the noval dielectric logging interpretation mixing law is modified based on the Maxwell-Garnett effective media theory and Lichtenecker model.The cemetation index model is reformed according to the resistivity experiment and dielectric logging experiment result.Combined with the correction charts,a suit of dielectric logging interpretation workflow is built to cover all the frequency scope.The noval dielectric constant mixing law is verified by the field data processing and the test.