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Very often, we need to scale things down

Geological porous media, even when homogeneous on a large scale, can present major heterogeneities on a microscopic scale (from the size of a pore to several thousand pores). And yet the behavior of fluids on a large scale is significantly dependent on this microscopic structure.

That is why the modeling and simulation of flow and transport in porous media require fine structural characterization of the rock.

To achieve this, IFPEN relies on the observation of samples using high-resolution imaging techniques: X-ray imaging techniques (micro-tomography), implemented both at IFPEN and at the Grenoble synchrotron (ESRF), reveal the structure of the porous medium, with a resolution ranging from 0.3 to 3 µ.

From these observations, two methods are used to simulate flow and transport in the porous medium:

  • the Lattice Boltzmann method, a direct method that uses a grid corresponding to discretization in space of the image obtained,
  • Pore Network Modeling (PNM), based on the resolution of linear equations, which describe transport within a network, itself obtained from a skeletonization algorithm applied to the images.

The importance of taking into account the structure of the porous space when modeling properties on a large scale was demonstrated in the case of a parameter widely used to estimate the oil saturation of a petroleum reservoir: the resistivity index, determination of which is based on an empirical law, known as Archie’s law, relating this property to saturation of the mediuma.

In fact, it has been observed experimentally1 that this law is not respected for certain types of carbonate rocks, when water saturation is low. PNM simulation has been used to explain this divergence and proposes a predictive model for the resistivity index.

Hence, it has been shown that the deviation from the empirical law increases when the water present in the medium is reduced to films covering the rock walls.

 

a - Rind = Sw2 (Rind being the resistivity index and Sw the fluid saturation)
   

 

Scientific contact:  daniela.bauer@ifpen.fr

Published in Science@ifpen n°26 - October 2016

Publication

  1. D. Bauer, S. Youssef, M. Han, S. Bekri, E. Rosenberg, M. Fleury, et O. Vizika, From computed microtomography images to resistivity index calculations of heterogeneous carbonates using a dual-porosity pore-network approach: Influence of percolation on the electrical transport properties, Physical Review, 2011.
    >> DOI: 10.1103/PhysRevE.84.011133

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