Study On Conduction Mechanism And Resistivity Model For Matrix-conducting Clean Sands

Six matrix-conducting clean samples with different porosity have been designed andmanufactured for the first time in the paper. Core sample resistivity is measured in differentwater salinity and oil saturation. Few of resistivity models in current use can give a gooddescription of conductive laws of sands in which rock matrix contains a certain amount ofpyrite, therefore it is necessary to study the conductive laws and propose matrix-conductingresistivity model. First, the effect of water resistivity and conductive matrix grain content onthe conductive laws of matrix-conducting clean sands is analyzed by using resistivitymeasurement of six matrix-conducting clean samples manufactured in the paper andlaboratory resistivity measurements of artificial and field samples, in which rock matrix iscomposed partially or entirely of conductive grains. We come to a conclusion that thenonlinear relationship between formation resistivity factor and porosity appears in log-loggraph. Conductivity of matrix-conducting clean sands increases nonlinearly as waterconductivity increases and values of formation resistivity factor decreases as conductivematrix grain content increases. The nonlinear relationship between formation resistivity indexand water saturation appears in log-log graph. Values of formation resistivity index decreasesas water conductivity decreases or conductive matrix grain content increases. Second, basedon research results of conductance mechanism and the compositions of matrix-conductingclean sands, matrix-conducting clean sands are divided into non-conducting matrix grains,conductive matrix grains, oil and water. Three new matrix-conducting resistivity models forclean sands are proposed basing on connectivity conductance theory and HB equation, andsymmetrical effective medium conductance theory, and pore combination conductance theory.Finally the theoretical validation of three models is carried out by changing single parameter,and the result shows that the theoretical relationships between formation resistivity factor andporosity, and between formation resistivity index and water saturation predicted by theproposed models are consistent with the experimental rule, and the proposed models are incompliance with meaningful physical boundary. Also the accuracy of three proposed modelsis evaluated with measured data in this paper and laboratory resistivity measurements ofartificial and field samples and optimization method. It concludes that threematrix-conducting resistivity models for clean sands proposed in this paper can describe theconductive law of matrix-conducting clean sands in which rock matrix is composed entirelyor partially of conductive grains. Three proposed models can be applied to calculate saturation in matrix-conducting clean low resistivity reservoir quantitatively.