Study On The Effective Electrical Properties Of Shale Models Using 3D Finite Difference Method

Fully understand the physical properties of the parent shale that store unconventional oil and gas is of great significance for improving the quality of shale oil and gas exploitation,development efficiency and reducing development cost,its effective electrical properties research is an important foundation of unconventional oil and gas exploration and logging interpretation.This thesis establishes idealized shale physical models for shale reservoir with thin-layered structure and crack characteristics.An accelerated three-dimensional finite difference method(3D-FDM)is used to calculate the effective electrical parameters of the layered shale model,the shale model containing extra-thin layer,and the shale model containing ellipsoidal cracks.The effects on the effective electrical parameters and frequency dispersion of the electrical and geometrical parameters of each layer are investigated,and the variation of effective electrical properties in broadband frequency range are summarized for each model.In the meantime,the Debye dispersion analytical formula of two-layered model is derived using the idea of equivalent circuit.The numerical results obtained by the 3D-FDM are compared with the results of analytic formulas to verify each other.Some observations and conclusions are made: the lossy medium in the shale model dominates the electrical dispersion behavior of shale.There are quantitative relations between the effective electrical properties of the model and the frequencies,electrical parameters and geometric parameters of each component.The extra-thin layer existing in shale model results in an obvious dielectric enhancement phenomenon at low frequencies.The presence of ellipsoidal cracks brings anisotropic characteristics of the shale model.Variation of crack shape or arrangement shows impact on the effective electrical properties in three directions.These researches conducted for the effective electrical properties of shale model will provide valuable theoretical reference for the broadband electromagnetic logging method and potential benefit to the inversion of shale oil and gas.