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Multi-scale insights on the threshold pressure gradient in low-permeability porous media

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Wang, H, Wang, J, Wang, X ORCID: 0000-0003-4293-7523 and Chan, A ORCID: 0000-0003-0042-8448 2020 , 'Multi-scale insights on the threshold pressure gradient in low-permeability porous media' , Symmetry, vol. 12 , pp. 1-23 , doi: 10.3390/sym12030364.

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Abstract

Low‐permeability porous medium usually has asymmetric distributions of pore sizes andpore‐throat tortuosity, thus has a non‐linear flow behavior with an initial pressure gradientobserved in experiments. A threshold pressure gradient (TPG) has been proposed as a crucial parameter to describe this non‐linear flow behavior. However, the determination of this TPG is still unclear. This study provides multi‐scale insights on the TPG in low‐permeability porous media. First, a semi‐empirical formula of TPG was proposed based on a macroscopic relationship with permeability, water saturation, and pore pressure, and verified by three sets of experimental data. Second, a fractal model of capillary tubes was developed to link this TPG formula with structural parameters of porous media (pore‐size distribution fractal dimension and tortuosity fractal dimension), residual water saturation, and capillary pressure. The effect of pore structure complexity on the TPG is explicitly derived. It is found that the effects of water saturation and pore pressure on the TPG follow an exponential function and the TPG is a linear function of yield stress. These effects are also spatially asymmetric. Complex pore structures significantly affect the TPG only in the range of low porosity, but water saturation and yield stress have effects on a wider rangeof porosity. These results are meaningful to the understanding of non‐linear flow mechanism in low‐permeability reservoirs.

Item Type: Article
Authors/Creators:Wang, H and Wang, J and Wang, X and Chan, A
Keywords: threshold pressure gradient, non‐Darcy flow, fractal theory, residual water saturation
Journal or Publication Title: Symmetry
Publisher: MDPIAG
ISSN: 2073-8994
DOI / ID Number: 10.3390/sym12030364
Copyright Information:

Copyright 2020 The Authors. Licensed under Creative Commons Attribution 4.0 International (CC BY 4.0) https://creativecommons.org/licenses/by/4.0/

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