Reservoir Rock Electrical Properties Study Based On Percolation Network Model And Upscaling

In order to resolve the problems facing in the well log fine interpretation and the evaluation of the complex reservoir, it is important to take the corresponding basic petrophysical researches. The rock resistivity is one of the important parameters in reservoir identification, saturation evaluation et al., but it is not perfection in the understanding of the influencing factors and laws of rock resistivity. Therefore, in this thesis the percolation network model that can describe the microcosmic pore structure of the reservoir rock, fluid properties and interaction between fluids and pores, is firstly built. Then the microcosmic influencing factors and laws of rock resistivity are discussed through numerical modeling. Upscaling methods are innovatively used to study the macroscopical influencing factors and laws of rock resistivity. At last, based on theoretical analysis, the MESPG conductivity model is built, which has physical meaning and is universal.The reservoirs rock microcosmic characteristics, such as pore size, uniformity, correlation, connectivity of the pores, wettability, fluid salinity, dispersed shale and so on, are considered in building percolation network model. Through microcosmic modeling, the effects of the characteristics mentioned above on rock resistivity are discussed in detail. Through optimal fitting, the influencing magnitude of several pore structure parameters on rock reisitivity is studied. Based on actual oilfield data, the influencing laws of the rock microcosmic characteristics on resisitivity in low porosity and permeability reservoir, high porosity and permeability reservoir and in low resistivity reservoir are discussed. During upscaling, the different methods are adopted for different macroscopical reservoir characteristics: the upscaling method based on mixture theory for the structure shale, the upscaling method based on the DBU for laminated shale, the upscaling method based on the capillary pressure for the reservoir with property gradual changing, the upscaling method based on the volume average for fractured reservoir.The modeling results indicate that there is not simple linear relation between saturation exponent and porosity described in some literatures. The relation between saturation exponent and porosity also depends on the wettability, pore-throat ratio and so on. The distribution of the pores has greater effect on rock resisitivity than the pore size. The fitting results show that pore connectivity and the micropores have great effect on rock resistivity and these factors easily lead to non-Archie phenomenon. However, the pore size and the pore shape have little effect. The formation water salinity and the shale have greater effect on rock resistivity in low porosity and low permeability reservoir than that in high porosity and high permeability reservoir. Both theoretical and modeling results show that the I-Sw curve in water wetting reservoir can represent convexity or concave shapes. The actual shape of the I-Sw curve depends on the pore connectivity, uniformity and so on. Throughing microcosmic modeling, we confirm the multi-role of the shale and gain the qualitative relation between the critical salinity in which shale pole changes from reducing resistivity to increasing resistivity role, and the reservoir characteristics such as porosity, permeability. Besides itself properties of the shale, the shale content and shale distribution form have great effect on rock resistivity. Different upscaling methods should been used for different shale distribution forms. For different reservoir rocks, the different I-Sw curve shapes can be appeared, but all shapes can be reduced to three representative types. The analysis results of experimental data show that the MESPG conductivity model is universal, has physical meaning and satisfies theoretical boundary.