An efficient method for selecting representative elementary volume in digital representations of porous media

Abstract

The present invention relates a method to estimate representative elementary volume (REV) in a sample of porous media wherein the sub-volume selected is a better approximation of the elementary volume than existing methods. REV in a sample of porous media such as rock can be defined wherein the REV is selected with respect to the expected direction of fluid flow through the porous media. The method can quantify how good is the digital representation of a rock and how accurate a description of a fluid flow through Darcy's law will be, and allows the evaluation of different length scales in different directions for the REV and an assessment of the anisotropy of the pores structures when the method is applied in different directions. The method also can determine a robust criteria to understand when a trend of porosity-permeability breaks down due to an insufficient size of the subsample.

Description

[0001] This application claims priority under 35 U.S.C. §119(e) to earlier U.S. Patent Application 13 / 546,053, filed July 11, 2012, and U.S. Provisional Patent Application 61 / 618,265, filed March 30, 2012, hereby Its entire content is incorporated by reference. Background technique [0002] The present invention relates to methods and systems for predicting properties of fluid flow through porous media, such as porous rocks, and more particularly to methods and systems for selecting the most representative sub-samples from a numerical representation of heterogeneous porous media for use in predicting properties such as These methods and systems for properties such as porosity, permeability, and / or related properties. [0003] Digital representations of porous media such as rock, bone, soil, and other materials can be produced via x-ray computed tomography scanning, scanning electron microscopy, confocal microscopy, and other techniques. These digital representations are used ...

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Problems solved by technology

[0029] Where REV is selected using any of the above methods, there is the possibility that there will be porosity variations within the REV, making assumptions about Darcy flow invalid or prone to errors

Furthermore, pressure gradients can change rapidly along the flow direction, making it impossible to define the permeability associated with a particular subsample

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