Numerical Modelling Study On The Relationship Of The Rock Resistivity And The Four-property In Constant Current Field

With the development of the oil-gas exploration, all kinds of complex reservoirlike the thin sand-shale interbeded formation, the sandy conglomerate and the pore orfractured carbonatite, are becoming exploration layers. Setting up the quatativerelation formula of the rock resistivity and the four-property has an importanttheoretical and practical significance for these complex reservoirs oil-gas evaluationand interpretation through logging. In this paper, the quatative relation formula of therock resistivity and the four-property in the constant current field is numericallycalculated and studied by the COMSOL Multiphysics to build the3D modeling. Theinfluences of lithology, petrophysical, waterborne and oil-bearing on the formationresistivity are analyzed. In addition, the resistivity variation characteristics of a thininterbed rock sample and a mirror image theory of three-layer-conductive-medium arestudied. Main research contents and results are concluded in the following fiveaspects.The first part mainly sums up the feasibility and advantages of using COMSOLMultiphysics to numerically calculate the conglomerate’s resistivity, and thecomputing process of using COMSOL Multiphysics to compute the conglomerateformation’s resistivity. Design conglomerate formation model which is based onCOMSOL Multiphysics’s numerically calculattion, study its computing method. Allthe these results are the foundation for the study on the complex conglomerateformation. Simply explain the Archie’s formula.The sesond part studies the influence of the conglomerate shape, size andarrangement on the formation resistivity. Firstly, design the single conglomerateformation model, calculate and analyze its conglomerate formation resistivity whenparameters (background resistivity, conglomerate resistivity, conglomerate size andposition) are changed. Secondly, by comparing the results of different complex modelwith different conglomerate shape and size, design a complex conglomerate formationmodel which is close to the actual formation. It is the base to study the relationship ofthe rock resistivity and the four-property. The third part studies the relation of the rock resistivity and porosity when theconglomerate formation’s pore contains only water. Design an isotropy and somekinds of anisotropy conglomerate formation models. Study quantitatively therelationship of the conglomerate formation’s formation factor and porosity. We findthe conglomerate formation’s formation factor is anisotropic, to describe it with tensorvariable.The fourth part studies the relation of the rock resistivity and oil saturation whenthe conglomerate formation’s pore contains both water and oil. Design the isotropyand anisotropy models which are oleophilic or hydrophilic. Study the quantitativerelation of conglomerate formation resistivity and pore fluid. We find the resistivityindex is anisotropic when the rock is hydrophilic. When the rock is oleophilic, theresistivity increase index reduces.The fifth part studies the resistivity of the thin interbed rock sample through thenumerical simulation. Design some kinds of thin interbed rock samples underdifferent conditions. Explain the influence of various factors on the resistivity of rockthrough the numerical calculation and analysis of the resistivity of the thin interbedrock sample. The results lay the foundation for researching complex rock samples’resistivity.The sixth part studies the mirror image theory of the three-layer-conductive-medium and its application in resistivity log. Study the mirror image theory ofthree-layer-conductive-medium using the mirror image principle of the constantcurrent field. Using this theory calculates the log response of a gradient electrodesystem in the three layers of conductive medium. The log response mechanism ofgradient electrode is revealed through the analysis of the relationship between thefeatures of the apparent resistivity and measuring electrodes’ potential and theelectrodes’ position.