Seismic imaging of massive sulfide deposits; Part III, Borehole seismic imaging of near-vertical structures

Eaton, David W.; Guest, Sean; Milkereit, B.; Bleeker, Wouter; Crick, Dean; Schmitt, Douglas R.; Salisbury, Matthew H.

doi:10.2113/gsecongeo.91.5.835

Cited by 17 publications

(7 citation statements)

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“…[9] Imaging basalts in the field has been performed with P and S wave passive seismic tomography of volcanoes [Zandomeneghi et al, 2009;Vanorio et al, 2005] and with vertical seismic profiles [Pujol and Smithson, 1991;Eaton et al, 1996] or cross-well geometries [Daley et al, 2004], but seismic monitoring in basalt environments is rare, as are laboratory data to monitor fluid substitution in basalts [Johnston and Christensen, 1997;Vanorio et al, 2002;Adelinet et al, 2010;Adam and Otheim, 2013]. Elastic waves have been used to quantify fluid substitution in sedimentary basins [Arts et al, 2004;Landrø, 2001;Tura and Lumley, 1998] and rock-CO 2 reactions in carbonates and sandstones [Vialle and Vanorio, 2011;Joy et al, 2011], but an integrated laboratory experiment to monitor CO 2 -basalt reactivity with ultrasonic waves is a first and necessary step toward field-scale monitoring of these rock-fluid interactions.…”

Section: Introductionmentioning

confidence: 99%

Changes in elastic wave velocity and rock microstructure due to basalt‐CO₂‐water reactions

et al. 2013

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[1] The chemical interaction between carbon dioxide, water, and basalt is a common process in the earth, which results in the dissolution of primary minerals that later precipitate as alteration minerals. This occurs naturally in volcanic settings, but more recently basalts have been suggested as reservoirs for sequestration of anthropogenic CO 2 . In both the natural and man-made cases, rock-fluid reactions lead to the precipitation of carbonates. Here, we quantify changes in ultrasonic wave speeds, associated with changes in the frame of whole-rock basalts, as CO 2 and basalt react. After 30 weeks of reactions and carbonate precipitation, the ultrasonic wave speed in dry basalt samples increases between 4% and 20% and permeability is reduced by up to an order of magnitude. However, porosity decreases only by 2% to 3%. The correlation between significant changes in wave speed and permeability indicates that a precipitate is developing in fractures and compliant pores. Thin sections, XRF-loss on ignition, and water chemistry confirm this observation. This means time-lapse seismic monitoring of a CO 2 -water-basalt system cannot assume invariance of the rock frame, as typically done in fluid substitution models. We conclude that secondary mineral precipitation causes a measurable change in the velocities of elastic waves in basalt-water-CO 2 systems, suggesting that seismic waves could be used to remotely monitor future CO 2 injection sites. Although monitoring these reactions in the field with seismic waves might be complicated due to the heterogeneous nature of basalt, quantifying the elastic velocity changes associated with rock alteration in a controlled laboratory experiment forms an important step toward field-scale seismic monitoring.Citation: Adam, L., K. van Wijk, T. Otheim, and M. Batzle (2013), Changes in elastic wave velocity and rock microstructure due to basalt-CO 2 -water reactions,

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Section: Introductionmentioning

confidence: 99%

Changes in elastic wave velocity and rock microstructure due to basalt‐CO₂‐water reactions

et al. 2013

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“…Interest in hardrock seismic exploration has increased dramatically in recent years following major advances in the acquisition and processing of seismic data (e.g., Enachescu, 1993); the successful multichannel seismic (MCS) imaging of deep crustal structure by programs such as DEKORP, COCORP, BIRPS, and LITHOPROBE (e.g., Barazangi and Brown, 1986;Matthews and Smith, 1987); and recent declines in base metal reserves caused by the depletion of known shallow deposits (Debicki, 1996). Redistribution subject to SEG license or copyright; see Terms of Use at http://library.seg.org/ surveys have been used to delineate steeply dipping ore bodies (Eaton et al, 1996;Adam et al, this volume) and to identify fracture zones in potential nuclear waste disposal sites (Cosma et al, this volume). Similarly, VSP (vertical seismic profiling) Downloaded 08/21/15 to 155.69.4.4.…”

Section: Introductionmentioning

confidence: 99%

1. The Acoustic Properties of Ores and Host Rocks in Hardrock Terranes

Salisbury¹,

Harvey²,

Matthews³

2003

Hardrock Seismic Exploration

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Compiled laboratory measurements of the densities (p) and compressional (V•) and shear (V s) wave ve-locities of common rocks demonstrate that the velocities of silicate rocks increase with density along the Nafe-Drake curve as the rocks become more mafic and increase in metamorphic grade. Reflection coefficients calculated from impedance contrasts between felsic and mafic rocks and other common lithologies in hardrock terranes often exceed 6%, the estimated minimum value required to give strong reflections. This finding is consistent with observations of deep structure and stratigraphy in high-grade terranes using seismic reflection. Sulfides lie far to the right of the Nafe-Drake curve in a large velocity-density field controlled by mixing lines connecting individual sulfide minerals and their hosts. The elastic properties and acoustic impedances of massive sulfides differ significantly from those of most common host rocks, suggesting that large massive sulfide deposits should be detectable as reflectors or scatterers using high-resolution seismic reflection techniques, a prediction confirmed by recent VSP, 2D and 3D MCS surveys in Canada. Laboratory measurements of acoustic velocities under in-situ conditions provide the basis for the interpretation of seismic refraction and stacking velocities in terms of lithology.

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“…A weaker event arriving at near infinite apparent velocity on the vertical component and appearing to intersect the borehole at -2500 m (X27 in the Z component of Figure 9) could correspond to a P to S converted wave reflection from this interface. Steeply dipping (70-85 ø ) reflectors have also been observed on VSP data from the Canadian Shield when testing seismic methods for mineral exploration [Eaton et al, 1996]. Reflection A in the vertical component of the VSP94 (Figure 9) and parallel ones below it can also be modeled as P to S converted waves generated on the east dipping set of reflectivity.…”

Section: Modeling Resultsmentioning

confidence: 93%

Integrated geological and geophysical studies in the SG4 borehole area, Tagil Volcanic Arc, Middle Urals: Location of seismic reflectors and source of the reflectivity

Ayarza¹,

Juhlin²,

Brown³

et al. 2000

J. Geophys. Res.

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Abstract. Near-vertical incidence reflection seismic data acquired in the Tagil Volcanic Arc (Middle Urals) show the upper crust to be highly reflective. Two intersecting seismic lines located near the ongoing -5400 m deep SG4 borehole show that the main reflectivity strikes approximately N-S and dips -350-55 ø to the east. Prominent reflections intercept the borehole at -1000, -1500, 2800-2900, -3400, and between -4000 and 5400 m, which correspond to intervals of low velocity/low density/low resistivity. The surface projections of these reflections lie parallel to the strike of magnetic anomaly trends. Multioffset vertical seismic profile (VSP) data acquired in the SG4 borehole show a seismic response dominated by P to S reflected converted waves from the moderately east dipping reflectivity and from a set of very steep east dipping reflectors not imaged by the surface data. Modeling of the VSP data constrains the depth at which reflectors intercept the borehole and suggests that the P to S conversions are best explained by low-velocity porous intervals rather than higher-velocity mafic material. The most prominent east dipping reflection on the surface seismic data is only imaged on VSP shots that sample the crust closer to the E-W seismic line. This discrepancy between the VSP and the surface seismic data is attributed to rapid lateral changes in the physical properties of the reflector. Surface and borehole data suggest that the low-velocity/low-density/low-resistivity intervals are the most important source of reflectivity in the SG4 borehole area, although lithological contrasts may also play a role. Drill cores from the these zones contain hydrothermal alteration minerals indicating interaction with fluids. Tectonic criteria suggest that they might represent imbricated fracture zones often bounding different lithologies and/or intrusions. Some of them might also represent high-porosity lava flows or pyroclastic units, common in island arc environments.

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Seismic imaging of massive sulfide deposits; Part III, Borehole seismic imaging of near-vertical structures

Cited by 17 publications

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Changes in elastic wave velocity and rock microstructure due to basalt‐CO₂‐water reactions

Changes in elastic wave velocity and rock microstructure due to basalt‐CO₂‐water reactions

1. The Acoustic Properties of Ores and Host Rocks in Hardrock Terranes

Integrated geological and geophysical studies in the SG4 borehole area, Tagil Volcanic Arc, Middle Urals: Location of seismic reflectors and source of the reflectivity

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Seismic imaging of massive sulfide deposits; Part III, Borehole seismic imaging of near-vertical structures

Cited by 17 publications

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Changes in elastic wave velocity and rock microstructure due to basalt‐CO2‐water reactions

Changes in elastic wave velocity and rock microstructure due to basalt‐CO2‐water reactions

1. The Acoustic Properties of Ores and Host Rocks in Hardrock Terranes

Integrated geological and geophysical studies in the SG4 borehole area, Tagil Volcanic Arc, Middle Urals: Location of seismic reflectors and source of the reflectivity

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Changes in elastic wave velocity and rock microstructure due to basalt‐CO₂‐water reactions

Changes in elastic wave velocity and rock microstructure due to basalt‐CO₂‐water reactions