Grain-Scale Modeling of Electrical Resistivity of 'Shaly Sands'

作者：Motealleh S^*; Gladkikh M; Bespalov A; Herrick D C; Bryant S L

来源：Petrophysics, 2010, 51(3): 199-207.

Several empirical and semi-empirical models are available to relate electrical resistivity to water saturation in "shaly sand" formations. The usual assumption in most of these models is that clay and bulk water in pores act as a system of parallel resistors. The goal of this work is to investigate the validity of this assumption.
For the investigation, we compute the DC electrical conductivity of model shaly sands at the pore level. The model porous medium is a random dense packing of equal size non-conductive spheres saturated with electrolyte (brine). The electrical conductivity of the model rock is computed on the discretized geometric domain using the finite element method for up-scaling DC electrical conductivity.
The results of our simulations clearly show the plot of the rock conductivity, C(0), versus electrolyte conductivity, C(w), exhibits a non-linear behavior at low values of C(w). This effect was observed in many experiments as well. The usual explanation invokes a dependence of specific surface conductivity of clay on C(w) at small values of C(w). However, our simulations show that this is not the only possible explanation. We observe the non-linear behavior of C(0)-C(w) plot as a result of a purely geometric effect, namely the arrangement of grain surfaces and grain-grain contacts in sandstones.

• 出版日期2010-6