Azimuthal anisotropy from the Valhall 4C 3D survey

Olofsson, Björn; Probert, T.; Kommedal, Jan H.; Barkved, O. I.

doi:10.1190/1.1641375

Cited by 69 publications

(25 citation statements)

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“…In producing oilfields, changes in the travel time above the reservoir have been used to infer stress transfer into the overburden (31,32). Similarly, azimuthal variations in seismic attributes (59) and/or S-wave splitting (60) have been used to image the creation and reactivation of fracture networks due to reservoir deformation.…”

Section: Discussionmentioning

confidence: 99%

Comparison of geomechanical deformation induced by megatonne-scale CO ₂ storage at Sleipner, Weyburn, and In Salah

Verdon

Kendall

Stork

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

195

101

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Geological storage of CO 2 that has been captured at large, point source emitters represents a key potential method for reduction of anthropogenic greenhouse gas emissions. However, this technology will only be viable if it can be guaranteed that injected CO 2 will remain trapped in the subsurface for thousands of years or more. A significant issue for storage security is the geomechanical response of the reservoir. Concerns have been raised that geomechanical deformation induced by CO 2 injection will create or reactivate fracture networks in the sealing caprocks, providing a pathway for CO 2 leakage. In this paper, we examine three large-scale sites where CO 2 is injected at rates of ∼1 megatonne/y or more: Sleipner, Weyburn, and In Salah. We compare and contrast the observed geomechanical behavior of each site, with particular focus on the risks to storage security posed by geomechanical deformation. At Sleipner, the large, high-permeability storage aquifer has experienced little pore pressure increase over 15 y of injection, implying little possibility of geomechanical deformation. At Weyburn, 45 y of oil production has depleted pore pressures before increases associated with CO 2 injection. The long history of the field has led to complicated, sometimes nonintuitive geomechanical deformation. At In Salah, injection into the water leg of a gas reservoir has increased pore pressures, leading to uplift and substantial microseismic activity. The differences in the geomechanical responses of these sites emphasize the need for systematic geomechanical appraisal before injection in any potential storage site.carbon sequestration | geomechanics | InSAR | microseismic monitoring C arbon capture and storage (CCS)-where CO 2 is captured at large point source emitters (such as coal-fired power stations) and stored in suitable geological repositories-has been touted as a technology with the potential to achieve dramatic reductions in anthropogenic greenhouse gas emissions (1, 2). However, its success is dependent on the ability of reservoirs to retain CO 2 over long timescales (a minimum of several thousand years). If CCS is to make a significant impact on global emissions, more than 3.5 billion tons of CO 2 per year must be stored (3), which at reservoir conditions will have a volume of ∼30 billion barrels (4).Secure storage of such large volumes of CO 2 requires more than just the availability of the appropriate volumes of pore space. CO 2 is buoyant in comparison with the saline brines that fill the majority of putative storage sites. Therefore, injected CO 2 will rise through porous rocks and return to the surface, unless trapped by impermeable sealing layers (such as shales and evaporites). Preliminary estimates have tended to indicate that, from a volumetric perspective at least, sufficient storage capacity exists for many decades of CO 2 emissions in deep-lying saline aquifers that have suitable sealing capability (5).It is equally important that the integrity of the seal is not compromised by injection activitie...

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Section: Discussionmentioning

confidence: 99%

Comparison of geomechanical deformation induced by megatonne-scale CO ₂ storage at Sleipner, Weyburn, and In Salah

Verdon

Kendall

Stork

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

195

101

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“…This contribution could be due to the development of damage around the subsidence zones or perhaps a non-linear stress/strain effect associated with preferential opening of existing cracks or grain contacts, in any case it indicates the sensitivity of the anisotropy measures to an underlying geomechanical process (although the story is inevitably much more complex). In the same context it is worth mentioning the results of [55], in which shear-wave splitting results indicate anisotropy in the overburden of this field with orientations of anisotropy axes that follow the outline of the main subsidence bowl.…”

Section: Time-lapse Seismic and Monitoring Of Fluid-extraction Inducementioning

confidence: 94%

When geophysics met geomechanics: Imaging of geomechanical properties and processes using elastic waves

Hall

2009

Mechanics of Natural Solids

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Geophysics measurement techniques can be considered as non-destructive, remote methods to analyse the physical properties of geologic materials hidden at depth in the earth, within geotechnical structures or within laboratory test specimens. The objective of this paper is to highlight at least some of the potential to use geophysics methods to aid geomechanical investigations, both at the laboratory and the real-world scales, by characterising property distributions and their changes plus, eventually, the mechanisms by which they change. The focus is primarily on geophysical imaging using elastic waves, whose propagation is controlled by a material's elastic properties and density. The former can be thought of as the summation of contributions over a range of length scales: grains, discontinuities (including cemented or uncemented grain contacts), inter-or intra-granular cracks, fractures and layers, which can all be anisotropic or can produce an anisotropic aggregate material. Examples are provided, at the laboratory and hydrocarbon reservoir scales, of geophysical characterisation of these different geomechanical attributes through anisotropy analyses, time-lapse measures of deformation and "full-field" velocity imaging.

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“…Consequently, S-or PS-wave data can be used to detect and quantify subtle properties of subsurface rocks that are of interest to geoscientists and engineers. For example, Mueller (1991) reports spatial changes in crack-related hydraulic conductivity detected through processing of S-waves, Angerer et al (2002) discuss the S-wave expression of zones with increased pore-fluid pressure, and Olofsson et al (2003) use PS-wave data to map strain around a zone of seabed subsidence. It has also been shown in numerous examples that long shear wavetrains generated by interference of split PS-waves can dramatically degrade the quality of PS-wave images.…”

Section: Introductionmentioning

confidence: 99%

High-precision estimation of split PS-wave time delays and polarization directions

Haacke¹

2013

GEOPHYSICS

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The measurement of split PS-wave time delays and polarization directions is notoriously difficult in field data, partly because the signals are small and overprinted by competing mechanisms. This contribution describes a new processing method that suppresses many of the overprinted traveltime and amplitude anomalies, allowing depth-averaged split PSwave time delays and polarization directions to be measured simply and precisely. These depth-averaged properties are then inverted using a simple forward model, allowing an earth model of split PS-wave time delays and polarization azimuths to be estimated without the need for layer stripping. In the field data used as an example, the processing and inversion methods are used to estimate split PS-wave time delays and polarization directions for ten layers spanning about 500 m depth from the seabed downward. Inversions using data-error covariances estimated from prestack data show model uncertainties less than 0.3 ms of time delay and 3°of polarization azimuth. However, it is clear that if the data-error covariances cannot be estimated from prestack data, due to low fold for example, model uncertainties would rise considerably. Repeating the inversions using data-error covariances of a postulated form leads to a range of maximum-likelihood models. When the data-error covariances cannot be estimated from prestack data, it seems reasonable to report precision levels implied by the spread of maximum-likelihood models, which in this case is up to 0.5 ms of time delay and 20°of polarization azimuth. The principal achievement of this processing and inversion scheme is to constrain a relatively large number of depth layers with similar levels of model uncertainty. The depth resolution available to this new method may have important implications for the development of tight-gas and shale-gas plays, in which variations of stress, strain, and fracture properties in discrete layers are important.

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Azimuthal anisotropy from the Valhall 4C 3D survey

Cited by 69 publications

References 0 publications

Comparison of geomechanical deformation induced by megatonne-scale CO ₂ storage at Sleipner, Weyburn, and In Salah

Comparison of geomechanical deformation induced by megatonne-scale CO ₂ storage at Sleipner, Weyburn, and In Salah

When geophysics met geomechanics: Imaging of geomechanical properties and processes using elastic waves

High-precision estimation of split PS-wave time delays and polarization directions

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Azimuthal anisotropy from the Valhall 4C 3D survey

Cited by 69 publications

References 0 publications

Comparison of geomechanical deformation induced by megatonne-scale CO 2 storage at Sleipner, Weyburn, and In Salah

Comparison of geomechanical deformation induced by megatonne-scale CO 2 storage at Sleipner, Weyburn, and In Salah

When geophysics met geomechanics: Imaging of geomechanical properties and processes using elastic waves

High-precision estimation of split PS-wave time delays and polarization directions

Contact Info

Product

Resources

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Comparison of geomechanical deformation induced by megatonne-scale CO ₂ storage at Sleipner, Weyburn, and In Salah

Comparison of geomechanical deformation induced by megatonne-scale CO ₂ storage at Sleipner, Weyburn, and In Salah