Evaluating Flow in Fractal-Fracture Networks: Effect of Variable Aperture

<p>While fractal models are often employed for describing the geometry of fracture networks, a constant aperture is mostly assigned to all the fractures when such models are flow simulated. In nature however, almost all fracture networks exhibit variable aperture values and it is this fracture...

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Autores principales:	A. K. Sahu, A. Roy
Formato:	article
Lenguaje:	EN
Publicado:	Copernicus Publications 2021
Materias:	Science Q Geology QE1-996.5 Dynamic and structural geology QE500-639.5
Acceso en línea:	https://doaj.org/article/79f53626aaf547b0a4e246d76bb02efa
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spelling	oai:doaj.org-article:79f53626aaf547b0a4e246d76bb02efa2021-11-16T09:46:19ZEvaluating Flow in Fractal-Fracture Networks: Effect of Variable Aperture10.5194/adgeo-56-117-20211680-73401680-7359https://doaj.org/article/79f53626aaf547b0a4e246d76bb02efa2021-11-01T00:00:00Zhttps://adgeo.copernicus.org/articles/56/117/2021/adgeo-56-117-2021.pdfhttps://doaj.org/toc/1680-7340https://doaj.org/toc/1680-7359<p>While fractal models are often employed for describing the geometry of fracture networks, a constant aperture is mostly assigned to all the fractures when such models are flow simulated. In nature however, almost all fracture networks exhibit variable aperture values and it is this fracture aperture that controls the conductivity of individual fractures as described by the well-known cubic-law. It would therefore be of practical interest to investigate flow patterns in a fractal-fracture network where the apertures scale in accordance to their position in the hierarchy of the fractal. A set of synthetic fractal-fracture networks and two well-connected natural fracture maps that belong to the same fractal system are used for this purpose. A set of dominant sub-networks are generated from a given fractal-fracture map by systematically removing the smaller fracture segments with narrow apertures. The connectivity values of the fractal-fracture networks and their respective dominant sub-networks are then computed. Although a large number of fractures with smaller aperture are eliminated, no significant decrease is seen in the connectivity of the dominant sub-networks. A streamline simulator based on Darcy's law is used for flow simulating the fracture networks, which are conceptualized as two-dimensional fracture continuum models. A single high porosity value is assigned to all the fractures. The permeability assigned to fractures within the continuum model is based on their aperture values and there is nearly no matrix porosity and permeability. The recovery profiles and time-of-flight plots for each network and its dominant sub-networks at different time steps are compared. The results from both the synthetic networks and the natural data show that there is no significant decrease in fluid recovery in the dominant sub-networks compared to their respective parent fractal-fracture networks. It may therefore be concluded that in the case of such hierarchical fractal-fracture systems with scaled aperture, the smaller fractures do not significantly contribute to connectivity or fluid flow. In terms of decision making, this result will aid geoscientists and engineers in identifying only those fractures that ultimately matter in evaluating the flow recovery, thus building models that are computationally less expensive while being geologically realistic.</p>A. K. SahuA. RoyCopernicus PublicationsarticleScienceQGeologyQE1-996.5Dynamic and structural geologyQE500-639.5ENAdvances in Geosciences, Vol 56, Pp 117-128 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	Science Q Geology QE1-996.5 Dynamic and structural geology QE500-639.5
spellingShingle	Science Q Geology QE1-996.5 Dynamic and structural geology QE500-639.5 A. K. Sahu A. Roy Evaluating Flow in Fractal-Fracture Networks: Effect of Variable Aperture
description	<p>While fractal models are often employed for describing the geometry of fracture networks, a constant aperture is mostly assigned to all the fractures when such models are flow simulated. In nature however, almost all fracture networks exhibit variable aperture values and it is this fracture aperture that controls the conductivity of individual fractures as described by the well-known cubic-law. It would therefore be of practical interest to investigate flow patterns in a fractal-fracture network where the apertures scale in accordance to their position in the hierarchy of the fractal. A set of synthetic fractal-fracture networks and two well-connected natural fracture maps that belong to the same fractal system are used for this purpose. A set of dominant sub-networks are generated from a given fractal-fracture map by systematically removing the smaller fracture segments with narrow apertures. The connectivity values of the fractal-fracture networks and their respective dominant sub-networks are then computed. Although a large number of fractures with smaller aperture are eliminated, no significant decrease is seen in the connectivity of the dominant sub-networks. A streamline simulator based on Darcy's law is used for flow simulating the fracture networks, which are conceptualized as two-dimensional fracture continuum models. A single high porosity value is assigned to all the fractures. The permeability assigned to fractures within the continuum model is based on their aperture values and there is nearly no matrix porosity and permeability. The recovery profiles and time-of-flight plots for each network and its dominant sub-networks at different time steps are compared. The results from both the synthetic networks and the natural data show that there is no significant decrease in fluid recovery in the dominant sub-networks compared to their respective parent fractal-fracture networks. It may therefore be concluded that in the case of such hierarchical fractal-fracture systems with scaled aperture, the smaller fractures do not significantly contribute to connectivity or fluid flow. In terms of decision making, this result will aid geoscientists and engineers in identifying only those fractures that ultimately matter in evaluating the flow recovery, thus building models that are computationally less expensive while being geologically realistic.</p>
format	article
author	A. K. Sahu A. Roy
author_facet	A. K. Sahu A. Roy
author_sort	A. K. Sahu
title	Evaluating Flow in Fractal-Fracture Networks: Effect of Variable Aperture
title_short	Evaluating Flow in Fractal-Fracture Networks: Effect of Variable Aperture
title_full	Evaluating Flow in Fractal-Fracture Networks: Effect of Variable Aperture
title_fullStr	Evaluating Flow in Fractal-Fracture Networks: Effect of Variable Aperture
title_full_unstemmed	Evaluating Flow in Fractal-Fracture Networks: Effect of Variable Aperture
title_sort	evaluating flow in fractal-fracture networks: effect of variable aperture
publisher	Copernicus Publications
publishDate	2021
url	https://doaj.org/article/79f53626aaf547b0a4e246d76bb02efa
work_keys_str_mv	AT aksahu evaluatingflowinfractalfracturenetworkseffectofvariableaperture AT aroy evaluatingflowinfractalfracturenetworkseffectofvariableaperture
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Evaluating Flow in Fractal-Fracture Networks: Effect of Variable Aperture

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