Effect of Structure on Petrophysical Properties of Porous Media

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1994-05

Authors

Gao, Yaming

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Abstract

The objective of this project is to relate the microscopic structure of porous media to macroscopic properties, such as porosity, permeability, dispersion coefficient, and chemical reactivity. In the first part of this study, fluid flow in porous media is simulated by a lattice gas automaton model. The fluid velocity profiles and pressure drops around obstacles of known-shape are calculated. Heterogeneous permeability fields at a macroscopic and megascopic length scale are created by distributing scatterers within the fluid flow field. These scatterers act as obstacles to flow. The loss in momentum of the fluid is directly related to the permeability of the lattice gas model. It is shown that by varying the probability of occurrence of solid nodes, the permeability of the porous medium can be changed over several orders of magnitude. To simulate fluid flow in heterogeneous permeability fields, isotropic, anisotropic, random, and correlated permeability fields are generated. The lattice gas model developed here is used to obtain the effective permeability as well as the local fluid flow field. The method presented here can be used to simulate fluid flow in arbitrarily complex, heterogeneous porous media. The lattice gas automaton model is also applied to the problem of simulating dispersion and mixing in heterogeneous porous media. We demonstrate here that tracer concentration profiles and longitudinal dispersion coefficients can be computed for heterogeneous porous media It is shown that some basic petrographic measurements such as pore perimeter, pore size, and grain surface area can be made from thin sections that can be used to obtain an order of magnitude estimate of flow properties, such as permeability. The reactivity of rock with acid in an acidizing process depends on the geometrical arrangement of various minerals with respect to each other. A model is developed where the minerals are located in accordance with thin section images. Since the rate of reaction of each mineral is known, an erosion process is used to obtain the reactivity of the rock as a function of time. It is shown that this model provides substantially different results than a simple model that is based only on the mineral abundance in the rock matrix. This result can have a significant impact on currently used acidizing simulators.

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