Formation and growth of extensional fracture sets

Segall, P.

doi:10.1130/0016-7606(1984)95<454:fagoef>2.0.co;2

Cited by 148 publications

(93 citation statements)

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“…Small variations of the size of the process zone and the correlated width of the vein (see Section 6.3; Rubin, 1995) observed in one fracture event are explained by small variations of the crack propagation velocity, which accordingly result in somewhat different values of the crack propagation fracture toughness. These interdependent relationships are supported by observations made by Segall (1984b). The author shows a photograph of a vein and alteration halo for a crack that apparently has slowed down and finally come to arrest, resulting in a continuously decreasing size of both the width of the alteration zone and the width of the vein itself.…”

Section: A Mechanical Model For the Development Of The Damage Zone Ansupporting

confidence: 52%

Magma-driven hydraulic fracturing and infiltration of fluids into the damaged host rock, an example from Dronning Maud Land, Antarctica

Engvik

Bertram

Kalthoff

et al. 2005

Journal of Structural Geology

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Excellent outcrops in Dronning Maud Land, Antarctica, provide unique insight into the mode and extent of fluid infiltration into metamorphic and plutonic rocks in the middle crust. The fluids are liberated from pegmatitic veins and give rise to alteration halos. In the alteration halos, the conspicuous change in colour is correlated with (1) hydration mineral reactions, and (2) high density of microcracks in quartz and feldspar exceeding that observed in the unaltered host rock by an order of magnitude. The field relations indicate that the veins originated as melt-driven hydraulic fractures, sealed by pegmatite and aplite crystallising from volatile-rich melts, with the alteration halo being the wake of the process zone formed at the tip of the propagating fractures. It is proposed that (1) the size of the alteration zone and the width of the vein are correlated, resulting in higher values of both these quantities for cracks propagating at higher velocities and consequently higher crack propagation toughnesses; (2) the damage zone is characterised by a transient state of high permeability which was short-lived due to rapid healing and sealing of microcracks; (3) the infiltration and retrogression of the high-grade rocks can be considered as a quasi-instantaneous process on geologic time scales with a duration of hours to weeks. q

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Section: A Mechanical Model For the Development Of The Damage Zone Ansupporting

confidence: 52%

Magma-driven hydraulic fracturing and infiltration of fluids into the damaged host rock, an example from Dronning Maud Land, Antarctica

Engvik

Bertram

Kalthoff

et al. 2005

Journal of Structural Geology

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“…Critical crack growth occurs when P f > σ n , i.e., when hydraulic fracturing takes place [Segall, 1984;Engelder and Lacazette, 1990]. This stress condition is, however, relatively rare in most subsurface rocks and does not explain the abundance of open natural fractures [Atkinson, 1984;Segall, 1984;Lorenz et al, 1991;Swarbrick et al, 2002].…”

Section: Models For Aperture Predictionmentioning

confidence: 99%

“…Δσ I is the driving stress (in Pa), which is the difference between fluid pressure P f within the fracture and normal stress σ n acting on the fracture [Lawn and Wilshaw, 1975;Pollard and Segall, 1987;Vermilye and Scholz, 1995;Olson, 2003;Anders et al, 2014]. Critical crack growth occurs when P f > σ n , i.e., when hydraulic fracturing takes place [Segall, 1984;Engelder and Lacazette, 1990]. This stress condition is, however, relatively rare in most subsurface rocks and does not explain the abundance of open natural fractures [Atkinson, 1984;Segall, 1984;Lorenz et al, 1991;Swarbrick et al, 2002].…”

Section: Models For Aperture Predictionmentioning

confidence: 99%

“…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%

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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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“…Two dimensional, plane strain modeling of the development of fracture networks utilizing subcritical crack growth conditions has shown that the value of the subcritical index, n, exerts a strong influence on the spatial arrangement and length distribution of fractures (Segall, 1984;Olson, 1993;Renshaw and Pollard, 1994). Results in Olson (1993) demonstrated how subcritical index controls fracture spacing to bed thickness ratio when modeling vertical fracture propagation across a bed under plane strain conditions.…”

Section: Fracture Propagation Modelmentioning

confidence: 93%

Advanced Technology for Predicting the Fluid Flow Attributes of Naturally Fractured Reservoirs From Quantitative Geologic Data and Modeling

Olson

Lake

Laubach

2003

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Abstract:This report summarizes the work carried out during the period of September 29, 2000 to September 28, 2001. Our goal is to establish an integrated methodology of fractured reservoir characterization and show how that can be incorporated into fluid flow simulation. We have made progress in the characterization of mineral infilling of natural fractures. The main advancement in this regard was to recognize the strong interplay between diagenetic and mechanical processes. We accomplished several firsts in documenting and quantifying these processes, including documenting the range of emergent threshold in several formations and quantifying the internal structures of crack-seal bridges in fractures. These results will be the basis for an appreciation of fracture opening and filling rates that go well beyond our original goals. Looking at geochemical modeling of fracture infilling, our theoretical analysis addressed the problem of calcite precipitation in a fracture. We have built a model for the deposition of calcite within a fracture. The diagenetic processes of dissolution and partial cementation are key controls on the creation and distribution of natural fractures within hydrocarbon reservoirs. Even with extensive data collection, fracture permeability still creates uncertainty in reservoir description and the prediction of well performance. Data on the timing and stages of diagenetic events can provide explanation as to why, when and where natural fractures will be open and permeable. We have been pursuing the fracture mechanics testing of a wide range of rocks, particularly sandstone using a key rock property test that has hitherto not been widely applied to sedimentary rocks. A major accomplishment in this first year has been to identify sample suites available in the core repository at the University of Texas that represent a wide range of diagenetic alteration and to begin to test these samples. The basis for the fluid flow simulations to be carried out in this part of the project is the adequate spatial characterization of fracture networks. Our initial focus has been on the tendency of fracture sets to cluster into highly fracture zones that are often widely separated. Our preliminary modeling work shows the extent of this clustering to be controlled by the subcritical fracture index of the material. With continued progress, we move toward an integrated fracture characterization methodology that will ultimately be applied through detailed reservoir simulation.iv Fig. 3.1. Features associated with the crack-seal mechanism. Fig. 3.2. Evidence of fracture opening mechanics. Fig. 3.3. Demonstrations of how new imaging techniques reveal mechanically significant microstructures. Fig. 3.4. Internal structure of synkinematic cement bridges. Fig. 3.5. Complex crack-seal texture within an almost completely quartz-filled macrofracture. Fig. 3.6. Limited wavelength (UV-blue) gray-scale CL image showing crack-seal texture at the bases of euhedral quartz crystals growing into a macrofracture. Fig. 3.7. Compari...

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Formation and growth of extensional fracture sets

Cited by 148 publications

References 0 publications

Magma-driven hydraulic fracturing and infiltration of fluids into the damaged host rock, an example from Dronning Maud Land, Antarctica

Magma-driven hydraulic fracturing and infiltration of fluids into the damaged host rock, an example from Dronning Maud Land, Antarctica

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

Advanced Technology for Predicting the Fluid Flow Attributes of Naturally Fractured Reservoirs From Quantitative Geologic Data and Modeling

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