Modeling Coupled Fracture-Matrix Fluid Flow in Geomechanically Simulated Fracture Networks

Philip, Zeno; Jennings, James W.; Olson, Jon E.; Laubach, Stephen E.; Holder, Jon

doi:10.2118/77340-pa

Cited by 126 publications

(26 citation statements)

References 24 publications

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“…However, our aim is to compare relative aperture and permeability trends, for which we make the assumption that far-field stress is representative of local stress. As a result of this simplification, as well as the omission of the role of cement during fracture development [Philip et al, 2005;Laubach and Ward, 2006], the absolute aperture values presented are likely an overestimation of true 2-D aperture.…”

Section: Model Boundary Conditionsmentioning

confidence: 96%

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The impact of different aperture distribution models and critical stress criteria on equivalent permeability in fractured rocks

2016

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Predicting equivalent permeability in fractured reservoirs requires an understanding of the fracture network geometry and apertures. There are different methods for defining aperture, based on outcrop observations (power law scaling), fundamental mechanics (sublinear length‐aperture scaling), and experiments (Barton‐Bandis conductive shearing). Each method predicts heterogeneous apertures, even along single fractures (i.e., intrafracture variations), but most fractured reservoir models imply constant apertures for single fractures. We compare the relative differences in aperture and permeability predicted by three aperture methods, where permeability is modeled in explicit fracture networks with coupled fracture‐matrix flow. Aperture varies along single fractures, and geomechanical relations are used to identify which fractures are critically stressed. The aperture models are applied to real‐world large‐scale fracture networks. (Sub)linear length scaling predicts the largest average aperture and equivalent permeability. Barton‐Bandis aperture is smaller, predicting on average a sixfold increase compared to matrix permeability. Application of critical stress criteria results in a decrease in the fraction of open fractures. For the applied stress conditions, Coulomb predicts that 50% of the network is critically stressed, compared to 80% for Barton‐Bandis peak shear. The impact of the fracture network on equivalent permeability depends on the matrix hydraulic properties, as in a low‐permeable matrix, intrafracture connectivity, i.e., the opening along a single fracture, controls equivalent permeability, whereas for a more permeable matrix, absolute apertures have a larger impact. Quantification of fracture flow regimes using only the ratio of fracture versus matrix permeability is insufficient, as these regimes also depend on aperture variations within fractures.

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Section: Model Boundary Conditionsmentioning

confidence: 96%

“…We only consider the relation between stress and hydraulically open fractures; i.e., we do not consider the role of cement bridges in keeping fractures open [Laubach et al, 2004;Philip et al, 2005;Hooker et al, 2012].…”

Section: Models For Critically Stressed Fracturesmentioning

confidence: 99%

The impact of different aperture distribution models and critical stress criteria on equivalent permeability in fractured rocks

2016

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“…Mimicking internal pressures with effective stresses or effective strains on the boundaries of models is a widely used approach (Olson et al 2009;Philip et al 2005;Rijken and Cooke 2001), and concerning numerical modelling, results in far less complicated mesh geometries. This implies that, the results presented depict static solutions of the applied boundary conditions and implemented fractures.…”

Section: Model Setupmentioning

confidence: 99%

Mechanical Factors Controlling the Development of Orthogonal and Nested Fracture Network Geometries

et al. 2018

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Orthogonal fracture networks form an arrangement of open well-connected fractures which have perpendicular abutment angles and sometimes show topological relations by which fracture sets abut against each other, thus forming a nested network. Previous modelling studies have shown that orthogonal fractures may be caused by a local stress perturbation rather than a rotation in remote stresses. In this study, we expand on the implications of these local stress perturbations using a static finite element approach. The derived stress field is examined to assess the development of implemented microfractures. The results show that the continuous infill of fractures leads to a gradual decrease in the local tensile stresses and strain energies, and, therefore, results in the development of a saturated network, at which further fracture placement is inhibit. The geometry of this fully developed network is dependent on the remote effective stresses and partly on the material properties. Saturated networks range from: (1) a set of closely spaced parallel fractures; (2) a ladder-like geometry; and (3) an interconnected nested arrangement. Finally, we show that our modelling results at which we apply effective tension, are equivalent to having a uniformly distributed internal pore fluid pressure, when assuming static steady state conditions and no dynamic fluid behaviour.

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“…Networks with longer fracture lengths and lower densities exhibit higher connectivities and therefore higher permeabilities than those formed of shorter fracture lengths with higher densities. That permeabilities are more sensitive to fracture patterns and connectivity than aperture has been confirmed by Philip et al (2005). Park et al (2004) found a positive correlation between fracture density and hydraulic conductivity measured in single-hole hydraulic tests.…”

Section: Influence Of Fracture Characteristics On Flow and Permeabilimentioning

confidence: 71%

“…Fracture apertures cover a wide scale range as their variation is influenced by mechanical and chemical actions in the system (Bonnet et al, 2001). Philip et al (2005) numerically investigated the effect of diagenesis on the initial flow properties of fracture systems, especially with respect to diagenetic effects on the connectivity of the fracture network. The results indicated that fracture permeability is more sensitive to fracture patterns and connectivity than aperture.…”

Section: Cleat Aperturementioning

confidence: 99%

Multi-scale permeability of coal fractures and cleats

Busse¹

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Coal is characterised by its unique microstructure made up of a porous matrix intersected by a network of face and butt cleats. Together with mining-induced fractures and faults caused by geological activities, these small scale cleats provide the principal source of permeability for groundwater and gas flow within a coal seam. The coal seam permeability plays a crucial role in mine stability, minability, gas well performance, and seam drainage behaviour. Therefore, a fundamental understanding of the fracture and cleat characteristics is essential for safe and efficient coal mining and coal seam gas production.Due to the various structural parameters of coal varying widely in size, the permeability of coal is highly scale-dependent. This thesis investigates the permeability of coal fractures and cleats on the example of Bowen Basin coals over a range of scales. The investigation of permeability is carried out using field studies, laboratory work, and numerical modelling.The relationship between permeability results gathered across scales is investigated to determine the Representative Element Volume and thus the smallest volume over which a measurement can be made that will yield a value representative of the whole.Field work has been undertaken at the Hail Creek Coal Mine in Central Queensland, Australia. A Heat Pulse Flow Meter, a downhole wireline tool, was utilised to test for permeability of macro-scale (metres to kilometres) fractures frequently associated with fault structures intersecting the coal measures at the mine site. Coal samples were taken for subsequent laboratory work. Laboratory investigations of permeabilities cover the meso-scale (centimetres to decimetres). The coal samples taken at two coal seams, the Elphinstone and the Hynds seam, were tested for permeability in a triaxial cell using the constant head test method. Based on Computer Tomography scans of the coal, the samples were numerically reconstructed to allow for investigations on the micro-scale The University of Queensland has provided me with a well-equipped work environment to conduct my PhD studies using a wide range of techniques and instruments.

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Modeling Coupled Fracture-Matrix Fluid Flow in Geomechanically Simulated Fracture Networks

Cited by 126 publications

References 24 publications

The impact of different aperture distribution models and critical stress criteria on equivalent permeability in fractured rocks

The impact of different aperture distribution models and critical stress criteria on equivalent permeability in fractured rocks

Mechanical Factors Controlling the Development of Orthogonal and Nested Fracture Network Geometries

Multi-scale permeability of coal fractures and cleats

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