Brittle–ductile transition, shear failure and leakage in shales and mudrocks

Nygård, Runar; Gutierrez, Marte; Bratli, Rolf K.; Höeg, Kaare

doi:10.1016/j.marpetgeo.2005.10.001

Cited by 231 publications

(115 citation statements)

References 38 publications

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“…Shear strain effects, which can be important for fracture-induced porosity (Table 1), are neglected in our model. Initial rock property values in the DEM are taken from the literature for sandstone (Hoek and Brown, 1997;Mavko et al, 2009) and shale (Horsrud et al, 1998;Nygård et al, 2006). We use the computed volumetric strain from the DEM to modify these initial rock properties.…”

Section: Changes Of Properties Due To Strainmentioning

confidence: 99%

“…These values are averages from the literature adapted to the scale, depth and stress conditions of the simulations. In the models of Section 3, they correspond to sandstone (Hoek and Brown, 1997;Mavko et al, 2009) and shale (Horsrud et al, 1998;Nygård et al, 2006). At any stage of the DEM simulation, incremental and total particle displacements are known.…”

Section: Change Of Seismic Properties Due To Finite Strainmentioning

confidence: 99%

“…To compute the seismic properties in the fault, we assign elastic properties to the sandstone and shale before faulting (Table 3). These properties are average values from the literature for intact sandstone (Hoek and Brown, 1997;Mavko et al, 2009) and shale (Horsrud et al, 1998;Nygård et al, 2006) at~1.5 km depth and at the scale of the DEM. The computed finite volumetric strain (section 2.2) at 60 m of fault displacement (Fig.…”

Section: Application: Large Normal Faultmentioning

confidence: 99%

See 2 more Smart Citations

From mechanical modeling to seismic imaging of faults: A synthetic workflow to study the impact of faults on seismic

Botter

Cardozo

Hardy

et al. 2014

Marine and Petroleum Geology

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Section: Changes Of Properties Due To Strainmentioning

confidence: 99%

Section: Change Of Seismic Properties Due To Finite Strainmentioning

confidence: 99%

Section: Application: Large Normal Faultmentioning

confidence: 99%

See 1 more Smart Citation

From mechanical modeling to seismic imaging of faults: A synthetic workflow to study the impact of faults on seismic

Botter

Cardozo

Hardy

et al. 2014

Marine and Petroleum Geology

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“…Therefore, using Equations (3-8), (3-10) and (3-11), the brittleness index in Equation (3-9) may be computed. Nygård et al (2006) proposed that the brittleness index could be related to the overconsolidation ratio by the following:…”

Section: Linking the Overconsolidation Ratio To Seismic Velocitymentioning

confidence: 99%

Inventory of Shale Formations in the US, Including Geologic, Hydrological, and Mechanical Characteristics

Dobson¹

2013

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SUMMARY Inventory of Shale Formations in the USThis section provides a summary of the distribution, thickness, and depth of selected shale formations found within many of the sedimentary basins in the contiguous US. Clay-rich shale formations have a number of properties, such as low permeability, high cation exchange potential, and the ability to self seal, which make them candidates for a geologic repository for high-level radioactive waste. The United States has an abundance of thick shale deposits that span a wide range of geologic ages, mineralogic compositions, and geologic environments, some of which might be suitable for hosting repositories to safeguard radioactive waste. The objective of this report is to build upon previous compilations of shale formations within many of the major sedimentary basins in the US by developing GIS data delineating isopach and structural depth maps for many of these units. These data are being incorporated into the LANL digital GIS database being developed for determining host rock distribution and depth/thickness parameters consistent with repository design. Rock Properties and In-Situ Conditions for Shale Estimated from Sonic Velocity MeasurementsThis section presents the development of methods to assess hydrological and geomechanical properties and conditions for shale formations based on sonic velocity measurements. Publically available data sets have been identified for shales under investigation for nuclear waste disposal in Europe and from shales of interest for oil exploration and production in the North Sea. These data have been used in the development of several correlations which link properties to sonic compressional velocity. The advantage of using correlations based on sonic velocity is that properties can be estimated from geophysical logs. This information is often more readily available than direct property measurements on core that would otherwise be required. Furthermore, geophysical logs typically provide a continuous readout along wells that can be more readily used to characterize spatial variability in properties. The correlations developed are then used to assess properties and conditions in several shale formations of interest within the United States which have publically available data on sonic velocity. Some of the proposed correlations have been previously investigated by others and comparisons between correlations are reasonably consistent. The approach has been extended here to other properties as well as insitu conditions, in particular, a method to estimate pore-fluid pressure. A method is also developed and used to account for anisotropy for properties where sufficient information is available to assess directional dependence. Some of the correlations, in particular estimation of sonic velocity parallel to bedding from normal to bedding sonic velocity measurements, and estimation of clay content from sonic velocity were found to be weak, indicating that additional independent measurements are desirable to supplement such estimates. Several ...

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“…Pre-existing fractures have been identified in these formations in core studies (Gabrielsen and Kloevjan 1997 (Nygaard et al 2006). When fractures are hydraulically open, losses may occur if the mud weight is higher than the pore pressure gradient.…”

Section: Introductionmentioning

confidence: 99%

Experimental investigation of fracture width limitations of granular lost circulation treatments

Alsaba

Nygaard

Saasen

et al. 2016

J Petrol Explor Prod Technol

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Drilling fluid losses into fractured shales is a major challenge. Lost circulation treatments are widely applied to mitigate the losses; however, the effectiveness of these treatments is affected by different physical properties of the used lost circulation materials (LCM). This paper presents an experimental investigation to study the effect of LCM type, concentration, particle size distribution, temperature, and LCM shape on the formed seal integrity, with respect to differential pressure, at different fracture widths. The overall objective of this study is to address the effectiveness of LCM treatments in sealing fractured shales, with specific application to the over consolidated Barents Sea overburden. Three commonly used LCMs that vary in size were used to formulate and evaluate the effectiveness of nine LCM blends. Nutshell blends effectively sealed different fracture widths with high seal integrities. Examination of the formed seal under an optical microscope and a scanning electron microscope revealed that this performance is due to the irregular shapes of these materials as well as their ability to deform under elevated pressure. Based on the results, it has been found that to effectively seal fractures using granular LCM treatments, the D90 value should be equal or slightly larger than the anticipated fracture width. However, due to both the increased risk of plugging downhole tools and the availability of larger LCM, granular LCM treatments can only be used to seal fractures up to 2000 microns. With the current limitations, other unconventional treatments are required to seal fractures wider than 2000 microns.

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Brittle–ductile transition, shear failure and leakage in shales and mudrocks

Cited by 231 publications

References 38 publications

From mechanical modeling to seismic imaging of faults: A synthetic workflow to study the impact of faults on seismic

From mechanical modeling to seismic imaging of faults: A synthetic workflow to study the impact of faults on seismic

Inventory of Shale Formations in the US, Including Geologic, Hydrological, and Mechanical Characteristics

Experimental investigation of fracture width limitations of granular lost circulation treatments

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