A review of the formation of tectonic veins and their microstructures

Bons, Paul D.; Elburg, Marlina; Gomez‐Rivas, Enrique

doi:10.1016/j.jsg.2012.07.005

Cited by 574 publications

(442 citation statements)

References 240 publications

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“…With a tensile strength of 1 MPa [44] the fluid pressure is very close to the lithostatic pressure if hydraulic fracturing is initiated. If we assume a volumetric flux of 1 m/s, which has been suggested for Mount Painter, a necessary minimum conductivity of approximately 6 × 10 −5 m/s for the conducting material follows from Equation (1). The conductivity of non-fractured crustal material is approximately in the range of 10 −9 -10 −12 ms/s [43], several orders of magnitude too small to allow the necessary fluid flow from the source zone to the surface.…”

Section: Fluid Flow and Hydraulic Fracturing In The Earth's Crustmentioning

confidence: 99%

“…This has the additional effect that the fluid pressure gradient in the vicinity of a fluid source is often higher at large depth than it is at shallower crustal levels, resulting in larger flow velocities on fractures at depth (Equation 1). Another effect of the different fluid and solid pressure gradients is the potential formation of mobile hydraulic fractures ( Figure 2B, [1]). …”

Section: Fluid Flow and Hydraulic Fracturing In The Earth's Crustmentioning

confidence: 99%

“…Veins are dilatant structures, typically fractures, filled with minerals that precipitated from fluid (see review of [1], and references therein). Hydraulic breccias are fragmented rocks where the fragmentation is mainly caused by chaotic fracturing due to fluid overpressure [2][3][4][5], as opposed to tectonic breccias where the diminution is due to tectonic stresses, typically along faults [6][7][8].…”

Section: Introductionmentioning

confidence: 99%

“…Such convective flow requires a fluid pressure that is close to hydrostatic, which is incompatible with the high, supra-lithostatic fluid pressures required to fracture rocks to produce veins and breccias [1].…”

Section: Introductionmentioning

confidence: 99%

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Transport efficiency and dynamics of hydraulic fracture networks

2015

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Intermittent fluid pulses in the Earth's crust can explain a variety of geological phenomena, for instance the occurrence of hydraulic breccia. Fluid transport in the crust is usually modeled as continuous Darcian flow, ignoring that sufficient fluid overpressure can cause hydraulic fractures as fluid pathways with very dynamic behavior. Resulting hydraulic fracture networks are largely self-organized: opening and healing of hydraulic fractures depends on local fluid pressure, which is, in turn, largely controlled by the fracture network. We develop a crustal-scale 2D computer model designed to simulate this process. To focus on the dynamics of the process we chose a setup as simple as possible. Control factors are constant overpressure at a basal fluid source and a constant "viscous" parameter controlling fracture-healing. Our results indicate that at large healing rates hydraulic fractures are mobile, transporting fluid in intermittent pulses to the surface and displaying a 1/f α behavior. Low healing rates result in stable networks and constant flow. The efficiency of the fluid transport is independent from the closure dynamics of veins or fractures. More important than preexisting fracture networks is the distribution of fluid pressure. A key requirement for dynamic fracture networks is the presence of a fluid pressure gradient.

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Section: Fluid Flow and Hydraulic Fracturing In The Earth's Crustmentioning

confidence: 99%

Section: Fluid Flow and Hydraulic Fracturing In The Earth's Crustmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Transport efficiency and dynamics of hydraulic fracture networks

2015

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“…The term "hydrofracture" is well-established for fluid-driven rock fractures, including mineral veins and (igneous and clastic) dykes, as well as many joints (e.g., Davis, 1983;Rummel, 1987;Sleep and Fujita, 1997;Rijsdijk et al, 1999;Bons, 2001;Gudmundsson, 2011a;Gundersen et al, 2011;Bons et al, 2012). Hydraulic fractures that is, man-made fractures generated by fluid overpressure and injected into reservoir rocks to increase their permeabilities (e.g., Hubbert and Willis, 1957;Charlez, 1997;Yew, 1997;Mahrer, 1999;Economides and Nolte, 2000), are also considered hydrofractures.…”

Section: Introductionmentioning

confidence: 99%

Effects of mechanical layering on hydrofracture emplacement and fluid transport in reservoirs

2013

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Fractures generated by internal fluid pressure, for example, dykes, mineral veins, many joints and man-made hydraulic fractures, are referred to as hydrofractures. Together with shear fractures, they contribute significantly to the permeability of fluid reservoirs such as those of petroleum, geothermal water, and groundwater. Analytical and numerical models show that-in homogeneous host rocks-any significant overpressure in hydrofractures theoretically generates very high crack tip tensile stresses. Consequently, overpressured hydrofractures should propagate and help to form interconnected fracture systems that would then contribute to the permeability of fluid reservoirs. Field observations, however, show that in heterogeneous and anisotropic, e.g., layered, rocks many hydrofractures become arrested or offset at layer contacts and do not form vertically interconnected networks. The most important factors that contribute to hydrofracture arrest are discontinuities (including contacts), stiffness changes between layers, and stress barriers, where the local stress field is unfavorable to hydrofracture propagation. A necessary condition for a hydrofracture to propagate to the surface is that the stress field along its potential path is everywhere favorable to extension-fracture formation so that the probability of hydrofracture arrest is minimized. Mechanical layering and the resulting heterogeneous stress field largely control whether evolving hydrofractures become confined to single layers (stratabound fractures) or not (non-stratabound fractures) and, therefore, if a vertically interconnected fracture system forms. Non-stratabound hydrofractures may propagate through many layers and generate interconnected fracture systems. Such systems commonly reach the percolation threshold and largely control the overall permeability of the fluid reservoirs within which they develop.

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Extension fracture propagation in rocks with veins: Insight into the crack‐seal process using Discrete Element Method modeling

2013

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[1] We investigate how existing veins interact with extension fractures in rocks using 3-D Discrete Element Method models with a geometry inspired by tension tests with notched samples. In a sensitivity study, we varied (a) the angle between the vein and the bulk extension direction and (b) the strength ratio between host rock and vein material. Results show a range of vein-fracture interactions, which fall into different, robust, "structural styles." Veins, which are weaker than the host rock, tend to localize fracturing into the vein, even at high-misorientation angles. Veins, which are stronger than the host rock, cause deflection of the fracture tip along the vein-host rock interface. Fractures are arrested at the interface from weak to stronger material. When propagating from a stronger to a weaker material, macroscopic bifurcation of the fracture is common. Complex interactions are favored by a low angle between the vein and the fracture and by high-strength contrast. The structural styles in the models show good agreement with microstructures and mesostructures of crack-seal veins found in natural systems. We propose that these structural styles form the basis for criteria to recognize strength contrasts and stress of crack-seal systems in nature.Citation: Virgo, S., S. Abe, and J. L. Urai (2013), Extension fracture propagation in rocks with veins: Insight into the crack-seal process using Discrete Element Method modeling,

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A review of the formation of tectonic veins and their microstructures

Cited by 574 publications

References 240 publications

Transport efficiency and dynamics of hydraulic fracture networks

Transport efficiency and dynamics of hydraulic fracture networks

Effects of mechanical layering on hydrofracture emplacement and fluid transport in reservoirs

Extension fracture propagation in rocks with veins: Insight into the crack‐seal process using Discrete Element Method modeling

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