Natural fracture characterization in tight gas sandstones: Integrating mechanics and diagenesis

Olson, Jon E.; Laubach, Stephen E.; Lander, Robert H.

doi:10.1306/08110909100

Cited by 294 publications

(166 citation statements)

References 61 publications

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“…The third sample that is presented (H1) shows parallel face cleats only. The different networks of butt and face cleats found in the examples look similar to those fracture networks in tight gas sandstones explained by Olson et al (2009) where systematic effects of fracture blockage and length changes are noted and their effects on permeability are investigated.…”

Section: 1supporting

confidence: 56%

Image processing based characterisation of coal cleat networks

Busse

Dreuzy

Galindo‐Torres

et al. 2017

International Journal of Coal Geology

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Characterisation of the cleat network serves as the basis for estimating the hydraulic and mechanical seam properties which in turn are fundamental for flow and geomechanical modelling in the context of underground coal mining. Cleat and cleat network geometry can be described as a function of frequency, aperture, size, orientation relative to in situ stresses, connectivity and porosity, with mineralised and un-mineralised cleats occurring. To describe these properties, CTscans of core samples of a Bowen Basin coal in central Queensland, Australia, are analysed.A unique image processing workflow method is introduced to extract the key statistical parameters of perpendicular butt and face cleats present in a two-dimensional image. As face and butt cleats have different characteristics, the presented method distinguishes face cleats and butt cleats by direction and present detailed data for both cleat types. The results comprise cleat length, apertures, sizes, intensities, densities, shape parameter, spacing, orientation and connectivity and are therefore more comprehensive than previous cleat descriptions. Three generally different cleat geometries are considered within this study, one sample shows perpendicular face and butt cleats, the second two sets of face cleats intersected by butt cleats and the third parallel face cleats only.

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Section: 1supporting

confidence: 56%

Image processing based characterisation of coal cleat networks

Busse

Dreuzy

Galindo‐Torres

et al. 2017

International Journal of Coal Geology

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“…The subcritical toughness is generally defined as K Ã C ≅K C =10 [Atkinson, 1984;Segall, 1984;Olson et al, 2009]. The behavior of fracture toughness with respect to length defined by equation (2) is matter of debate, as K c is either considered to scale linearly with length on all scales, or only for small fractures [Olson, 2003;Scholz, 2010Scholz, , 2011Olson and Schultz, 2011;Anders et al, 2014].…”

Section: Models For Aperture Predictionmentioning

confidence: 99%

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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“…Some porosity controlled models [Boone and Ingraffea, 1990;Flekkøy et al, 2002; Mourgues 16 and Cobbold, 2003;Olson et al, 2009;Wangen, 2002] revealed that the potential response of 17 inherent poroelastic mechanics is an important parameter in hydro-driven rock failure, where the 18 seepage forces caused by pore pressure gradients [Engelder and Lacazette, 1990;Rozhko, 2010; 19 Rozhko et al, 2007] in porous rocks affect the driving stress for fracture initiation and growth.…”

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Dynamic Development of Hydrofracture

Ghani

Koehn

Toussaint

et al. 2013

Pure Appl. Geophys.

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23Many natural examples of complex joint and vein networks in layered sedimentary rocks are 1 hydro-fractures that form by a combination of pore fluid overpressure and tectonic stresses. In 2 this paper, a two-dimensional hybrid hydro-mechanical formulation is proposed to model the Darcy based pore-pressure diffusion as continuum description for the fluid. This combination 6 yields a porosity controlled coupling between an evolving fracture network and the associated 7 hydraulic field. The model is tested on some basic cases of hydro-driven fracturing commonly 8 found in nature i.e., fracturing due to local fluid overpressure in rocks subjected to hydrostatic 9 and nonhydrostatic tectonic loadings. In our models we find that seepage forces created by 10 hydraulic pressure gradients together with poroelastic feedback upon discrete fracturing play a 11 significant role in subsurface rock deformation. These forces manipulate the growth and [Fyfe et al., 1978]. A number of fluid expansion mechanisms e.g., The mechanism of hydrofracturing has great implications in the interpretation of field 21 observations and for the prediction of natural or industrial problems in a broad range of research 22 disciplines. After pioneering work of [Hubbert and Willis, 1957;Hubbert and Rubey, 1959] 23 which explored pore fluid pressure as an important factor for small scale hydrofracturing in 1 tectonic processes, significant efforts have been made in the development of theoretical 2 fundamentals [Biot et al., 1986; J M Cleary and Illinois State Geological Survey., 1958; 3 Daneshy, 1973;Secor, 1965;Valkó and Economides, 1995]. Apart from theoretical aspects, a 4 significant amount of analytical and numerical solutions have also been put forward by many 5 investigators to address this coupled process in a qualitative and quantitative manner [M P 6 Cleary and Wong, 1985;Flekkøy et al., 2002;Gordeyev and Zazovsky, 1992;Meyer, 1986; 7 Tzschichholz et al., 1994;Yu.N, 1993]. 15Some porosity controlled models [Boone and Ingraffea, 1990;Flekkøy et al., 2002; Mourgues 16 and Cobbold, 2003;Olson et al., 2009;Wangen, 2002] revealed that the potential response of 17 inherent poroelastic mechanics is an important parameter in hydro-driven rock failure, where the 18 seepage forces caused by pore pressure gradients [Engelder and Lacazette, 1990;Rozhko, 2010; 19 Rozhko et al., 2007] in porous rocks affect the driving stress for fracture initiation and growth. 20Regardless of the underlying driving agent hydrofracturing is a complex process which 21 incorporates the dynamic coupling of at least three sub-processes [Adachi et al., 2007]; 1) 22Restructuring of rock skeleton upon elastic/in-elastic strain. 2) Corresponding alteration of both 23

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Natural fracture characterization in tight gas sandstones: Integrating mechanics and diagenesis

Cited by 294 publications

References 61 publications

Image processing based characterisation of coal cleat networks

Image processing based characterisation of coal cleat networks

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

Dynamic Development of Hydrofracture

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