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1

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Small faults formed as deformation bands in sandstone (1978)

Aydin, Atilla

Springer

Pure and applied geophysics 116 (1978), S. 913-930

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ISSN: 1420-9136

Keywords: Fault structures ; Deformation bands ; Entrada and Navajo Sandstores

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract Small faults with displacements of a few millimeters or centimeters are abundant in the Entrada and Navajo Sandstones, in the San Rafael Desert, Utah, where they are important primary structures, preceding the development of large faults with displacements of several meters or tens of meters. The small faults contain no surfaces of discontinuity, rather they occur asdeformation bands about one millimeter and tens or hundreds of meters long, and across which the displacements are distributed. Two zones with different modes of deformation can be distinguished within a deformation band: an outer zone where the matrix, including pores and matrix material, deforms; and an inner zone, about 0.5 mm thick, where the sand grains fracture and further consolidation takes place. Fracturing of the grains is controlled by contact geometry; the grains tend to split into subgrains along lines connecting contact points between the grains. Then the angular subgrains, which are readily fractured, are further granulated and mixed with the matrix. The final product is the deformation band, with much smaller grain size, poorer sorting, and lower porosity than the original parent sandstone. The sandstone on either side of a deformation band is almost undisturbed-fractures are rare there — so that deformation is highly localized within the band. The material within a deformation band apparently strain hardens as a result of the deformation; perhaps this is why the shear displacement across a deformation band is at most a few centimeters.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00876546

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2

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Development of faults as zones of deformation bands and as slip surfaces in sandstone (1978)

Aydin, Atilla ; Johnson, Arvid M.

Springer

Pure and applied geophysics 116 (1978), S. 931-942

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ISSN: 1420-9136

Keywords: Fault structures ; Deformation bands ; Entrada and Navajo Sandstones

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract Three forms of fault are recognized in Entrada and Navajo Sandstones in the San Rafael Desert, southeastern Utah; deformation bands, zones of deformation bands, and slip surfaces. Small faults occur asdeformation bands, about one millimeter thick, in which pores collapse and sand grains fracture, and along which there are shear displacements on the order of a few millimeters or centimeters. Two or more deformation bands adjacent to each other, which share the same average strike and dip, form azone of deformation bands. A zone becomes thicker by addition of new bands, side by side. Displacement across a zone is the sum of displacements on each individual band. The thickest zones are about 0.5 m and total displacement across a thick zone rarely exceeds 30 cm. Finally,slip surfaces, which are through-going surfaces of discontinuity in displacement, form at either edge of zones of highly concentrated deformation bands. In contrast with individual deformation bands and zones of deformation bands, slip surfaces accommodate large displacements, on the order of several meters in the San Rafael Desert. The sequence of development is from individual deformation bands, to zones, to slip surfaces, and each type of faulting apparently is controlled by somewhat different processes. The formation of zones apparently involves strain hardening, whereas the formation of slip surfaces probably involves strain softening of crushed sandstone.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00876547

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3

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Interaction of multiple cracks and formation of echelon crack arrays (1991)

Du, Yijun ; Aydin, Atilla

New York, NY [u.a.] : Wiley-Blackwell

International Journal for Numerical and Analytical Methods in Geomechanics 15 (1991), S. 205-218

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ISSN: 0363-9061

Keywords: Engineering ; Engineering General

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Architecture, Civil Engineering, Surveying , Geosciences

Notes: Fracturing of rock under compression is a product of a series of processes, including nucleation, growth, interaction and coalescence of multiple microcracks. The formation of echelon arrays of microcracks and macrocracks is one of the crucial rings in the processes. We use a superposition and asymptotic approximation technique to analyse the interaction of multiple cracks with various geometrical configurations. It is shown that crack geometry has a strong influence on crack interaction. Echelon crack arrays produce the strongest interaction and are the preferred geometrical configuration for multiple cracks prior to the formation of through-going shear fractures. This technique provides parameter-dependent global behaviour, and is more efficient and easier to use.

Additional Material: 10 Ill.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/nag.1610150305

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Using an elastic dislocation model to investigate static Coulomb stress change scenarios for earthquake ruptures in the eastern Marmara Sea region, Turkey (2007)

Muller, Jordan R. ; Aydin, Atilla ; Wright, Tim J.

In: Geological Society Special Publication 253: 397-414.

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Publication Date: 2007-10-08

Description: Using an elastic dislocation model, we incorporate a historical earthquake catalog, mapped Marmara Sea fault traces, and fault slip distributions for the 1999 Izmit earthquake inferred from InSAR and GPS data to determine various stress change scenarios crucial for evaluating future earthquake potential in the eastern Marmara Sea. We have tested six plausible past rupture configurations arising from the uncertainty in the location of the western termination of 1999 Izmit earthquake rupture and the location of the 1963 Yalova earthquake rupture. Coulomb stresses calculated are increased on the Princes' Islands, Cinarcik, and Armutlu fault segments in each case. In four of the six plausible configurations of previous ruptures, the Cinarcik fault receives the greatest average stress change. In one other configuration, the average stress increase on the Princes' Islands fault is greatest. In another, the stress changes on the Cinarcik and Princes' Islands faults are comparable. Moreover, we show that rupture initiating on either the Princes' Islands or Armutlu faults would be favoured to propagate onto the Central Marmara, or Imrali fault, respectively, based on the favourable geometries of the respective fault intersections. Rupture initiating on the Cinarcik fault, however would be limited to a much shorter length based on its mapped western termination. Therefore, while the earthquake-induced stress changes may, in most cases, be greatest on the Cinarcik fault, an earthquake initiating on this fault segment may produce a shorter cumulative rupture compared to rupture initiated on the two other major eastern Marmara Sea fault segments. These results are encouraging for the use of geomechanical modelling tools in addressing uncertainties inherent in most geological and geophysical data applied to earthquake-related problems.

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From outcrop to flow simulation: Constructing discrete fracture models from a LIDAR survey (2011)

Wilson, Christopher E. ; Aydin, Atilla ; Karimi-Fard, Mohammad ; Durlofsky, Louis J. ; Amir, Sagy ; Brodsky, Emily E. ; Kreylos, Oliver ; Kellogg, Louise H.

American Association of Petroleum Geologists (AAPG)

In: AAPG Bulletin 95: 1883-1905.

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Publication Date: 2011-11-01

Description: Terrestrial light detection and ranging (LIDAR) surveys offer potential enrichment of outcrop-based research efforts to characterize fracture networks and assess their impact on subsurface fluid flow. Here, we explore two methods to extract the three-dimensional (3-D) positions of natural fractures from a LIDAR survey collected at a roadcut through the Cretaceous Austin Chalk: (1) a manual method using the University of California, Davis, Keck Center for Active Visualization in the Earth Sciences and (2) a semiautomated method based on mean normal and Gaussian curvature surface classification. Each extraction method captures the characteristic frequencies and orientations of the primary fracture sets that we identified in the field, yet they extract secondary fracture sets with varying ability. After making assumptions regarding fracture lengths and apertures, the extracted fractures served as a basis to construct a discrete fracture network (DFN) that agrees with field observations and a priori knowledge of fracture network systems. Using this DFN, we performed flow simulations for two hypothetical scenarios: with and without secondary fracture sets. The results of these two scenarios indicate that for this particular fracture network, secondary fracture sets marginally impact ([~]10% change) the breakthrough time of water injected into an oil-filled reservoir. Our work provides a prototype workflow that links outcrop fracture observations to 3-D DFN model flow simulations using LIDAR data, an approach that offers some improvement over traditional field-based DFN constructions. In addition, the techniques we used to extract fractures may prove applicable to other outcrop studies with different research goals.

Print ISSN: 0149-1423

Electronic ISSN: 0149-1423

Topics: Geosciences

Published by American Association of Petroleum Geologists (AAPG)

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Use of outcrop observations, geostatistical analysis, and flow simulation to investigate structural controls on secondary hydrocarbon migration in the Anacacho Limestone, Uvalde, Texas (2011)

Wilson, Christopher E. ; Aydin, Atilla ; Durlofsky, Louis J. ; Boucher, Alexandre ; Brownlow, Darrell T.

American Association of Petroleum Geologists (AAPG)

In: AAPG Bulletin 95: 1181-1206.

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Publication Date: 2011-07-01

Description: We undertake a multidisciplinary investigation into the distribution of asphalt in the Anacacho Limestone in an effort to decipher the potential roles of fractures and faults on secondary hydrocarbon migration. Field relationships between fractures, faults, and asphalt are evaluated at an asphaltic limestone mine near Uvalde, Texas. Based on their distributions, geometries, and structural relationships, we infer that normal faults provided vertical flow paths through the Anacacho Limestone, whereas strata-bound fractures enhanced lateral permeability. Variograms calculated from 75 subsurface measurements indicate that the asphalt concentration is anisotropically correlated and that the longest correlation length points in the mean strike direction of fractures and faults. A globally positioned laser rangefinder is used to measure faults and stratigraphic contacts within the mine. That data are then combined with lithologic descriptions from surrounding subsurface wells to construct a three-dimensional (3-D) model of the Anacacho Limestone. When an ordinary block-kriging algorithm populates the model with asphalt concentration estimates, the high values align along a trend that connects the two largest normal fault zones at the mine. The 3-D model provides a framework to numerically simulate secondary hydrocarbon migration. We test numerous hydrocarbon migration scenarios by adjusting simulation parameters within physically realistic ranges until producing an oil saturation field that agrees with asphalt concentration estimates. Our best match simulation indicates that oil entered the Anacacho Limestone through normal faults, that regional aquifer flow impacted oil flow, and that fractures increased the horizontal permeability of the formation by an order of magnitude along their strike direction.

Print ISSN: 0149-1423

Electronic ISSN: 0149-1423

Topics: Geosciences