Effects of internal structure and local stresses on fracture propagation, deflection, and arrest in fault zones

Guðmundsson, Ágúst; Simmenes, T. H.; Larsen, Belinda; Philipp, Sonja L.

doi:10.1016/j.jsg.2009.08.013

Cited by 222 publications

(114 citation statements)

References 48 publications

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“…since the latter constitutes an unconformity between the rotliegende sediment and the weathered upper part of the granite, a contrast in mechanical properties between the sediment and intact granite can be expected which extends across the weathered zone. stiffness contrast between beds subject to strain can produce bed-tobed changes in stress magnitude and direction as shown by the field observations and modelling results of bruno and Winterstein (1994) and Gudmundsson (2006Gudmundsson ( , 2009. However, if the deformation is uniform horizontal straining, then the development of changes in horizontal stress orientation between beds of different elastic stiffness requires some obliquity of the beds to the horizontal plane (bruno and Winterstein, 1994), or the presence of elastic anisotropy in the horizontal plane.…”

Section: Discussionmentioning

confidence: 89%

Stress orientation to 5 km depth in the basement below Basel (Switzerland) from borehole failure analysis

Valley

Evans

2009

Swiss J. Geosci.

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A vertical profile of maximum horizontal principal stress, sHmax, orientation to 5 km depth was obtained beneath the swiss city of basel from observations of wellbore failure derived from ultrasonic televiewer images obtained in two 1 km distant near-vertical boreholes: a 2755 m exploration well (Ot2) imaged from 2550 m to 2753 m across the granitic basement-sediment interface at 2649 m; and a 5 km deep borehole (bs1) imaged entirely within the granite from 2569 m to 4992 m. stress-related wellbore failure in the form of breakouts or drilling-induced tension fractures (DItFs) occurs throughout the depth range of the logs with breakouts predominant. Within the granite, DItFs are intermittently present, and breakouts more or less continuously present over all but the uppermost 100 m where they are sparse. the mean sHmax orientations from DItFs is 151 ± 13° whereas breakouts yield 143 ± 14°, the combined value weighted for frequency of occurrence being N144°E ± 14°. No marked depth dependence in mean sHmax orientation averaged over several hundred meters depth intervals is evident. this mean sHmax orientation for the granite is consistent with the results of the inversion of populations of focal mechanism solutions of earthquakes occurring between depths of 10-15 km within regions immediately to the north and south of basel, and with the t-axis of events occurring within the reservoir (Deichmann and Ernst, this volume). DItFs and breakouts identified in Ot2 above and below the sediment-basement interface suggest that a change in sHmax orientation to N115°E ± 12° within the rotliegendes sandstone occurs near its interface with the basement. the origin of the 20-30° change is uncertain, as is its lateral extent. the logs do not extend higher than 80 m above the interface, and so the data do not define whether a further change in stress orientation occurs at the evaporites. Near-surface measurements taken within 50 km of basel suggest a mean orientation of N-s, albeit with large variability, as do the orientation of hydrofractures at depths up to 850 m within and above the evaporite layers and an active salt diapir, also within 50 km of basel. thus, the available evidence supports the notion that the orientation of sHmax above the evaporites is on average more N-s oriented and thus differs from the NW-sE inferred for the basement from the bs1/Os2 wellbore failure data and the earthquake data. changes in stress orientation with depth can have significant practical consequences for the development of an EGs reservoir, and serve to emphasise the importance of obtaining estimates from within the target rock mass.

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Section: Discussionmentioning

confidence: 89%

Stress orientation to 5 km depth in the basement below Basel (Switzerland) from borehole failure analysis

Valley

Evans

2009

Swiss J. Geosci.

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“…These include normal fault initiation from tension fractures and en echelon linking of faults Frontiers in Earth Science | www.frontiersin.org (Gudmundsson et al, 2010;Gudmundsson, 2011b, chapter 14). At mid-ocean ridges, the motion between segments is taken up on transform faults, but during rift development, there may be complex zones of mixed normal, strike-slip (e.g., Spacapan et al, 2016) and even compressional tectonics (e.g., Sachau et al, 2015).…”

Section: Complexities In Rift Geometrymentioning

confidence: 99%

Historical Volcanism and the State of Stress in the East African Rift System

et al. 2016

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Crustal extension at the East African Rift System (EARS) should, as a tectonic ideal, involve a stress field in which the direction of minimum horizontal stress is perpendicular to the rift. A volcano in such a setting should produce dykes and fissures parallel to the rift. How closely do the volcanoes of the EARS follow this? We answer this question by studying the 21 volcanoes that have erupted historically (since about 1800) and find that 7 match the (approximate) geometrical ideal. At the other 14 volcanoes the orientation of the eruptive fissures/dykes and/or the axes of the host rift segments are oblique to the ideal values. To explain the eruptions at these volcanoes we invoke local (non-plate tectonic) variations of the stress field caused by: crustal heterogeneities and anisotropies (dominated by NW structures in the Protoerozoic basement), transfer zone tectonics at the ends of offset rift segments, gravitational loading by the volcanic edifice (typically those with 1-2 km relief) and magmatic pressure in central reservoirs. We find that the more oblique volcanoes tend to have large edifices, large eruptive volumes, and evolved and mixed magmas capable of explosive behavior. Nine of the volcanoes have calderas of varying ellipticity, 6 of which are large, reservoir-collapse types mainly elongated across rift (e.g., Kone) and 3 are smaller, elongated parallel to the rift and contain active lava lakes (e.g., Erta Ale), suggesting different mechanisms of formation and stress fields. Nyamuragira is the only EARS volcano with enough sufficiently well-documented eruptions to infer its long-term dynamic behavior. Eruptions within 7 km of the volcano are of relatively short duration (<100 days), but eruptions with more distal fissures tend to have lesser obliquity and longer durations, indicating a changing stress field away from the volcano. There were major changes in long-term magma extrusion rates in 1977 (and perhaps in 2002) due to major along-rift dyking events that effectively changed the Nyamuragira stress field and the intrusion/extrusion ratios of eruptions.

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“…For example, in a Liassic limestone-shale succession in England, calcite veins occur almost exclusively in the damage zones and the cores of normal faults, indicating that the fault planes transported the fluids that formed the veins (Figure 8). Some veins were clearly injected into the limestone layers of the damage zone directly from the fault plane (Brenner, 2003;Brenner and Gudmundsson, 2004a;Gudmundsson et al, 2010). Many inactive faults are of low permeability and even act as seals for fluids, particularly if they develop clay smear along their planes.…”

Section: Fluid Transport In Faultsmentioning

confidence: 99%

“…More specifically, if there is no Young's modulus (stiffness) mismatch (no difference in Young's modulus) across the interface, then fracture deflection occurs only if contact toughness is about 25% of the toughness of the material (here the rock) on the other side of the contact (He and Hutchinson, 1989;Hutchinson and Suo, 1992;Kim et al, 2006;Lee et al, 2007; cf. Gudmundsson et al, 2010;Gudmundsson, 2011a,b). However, when the Young's modulus mismatch increases, deflection will still occur even if the material toughness of the interface/contact becomes equal to or higher than the bulk material toughness.…”

Section: Field Observations and Numerical Model On Hydrofracture Emplmentioning

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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Effects of internal structure and local stresses on fracture propagation, deflection, and arrest in fault zones

Cited by 222 publications

References 48 publications

Stress orientation to 5 km depth in the basement below Basel (Switzerland) from borehole failure analysis

Stress orientation to 5 km depth in the basement below Basel (Switzerland) from borehole failure analysis

Historical Volcanism and the State of Stress in the East African Rift System

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

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