scholarly journals Seismic anisotropy in deforming halite: evidence from the Mahogany salt body

2020 ◽  
Vol 223 (3) ◽  
pp. 1672-1687
Author(s):  
Philipp Prasse ◽  
James Wookey ◽  
J-Michael Kendall ◽  
Daniel Roberts ◽  
Martin Dutko
Keyword(s):  
Shear Wave ◽  
Rock Salt ◽  
Seismic Anisotropy ◽  
Seismic Profile ◽  
Wave Form ◽  
Deformation Model ◽  
Data Set ◽  
Salt Layer ◽  
Combining Data ◽  
Zero Offset

SUMMARY We present unambiguous evidence that the Mahogany salt body, located in the Northern part of the Gulf of Mexico, is seismically anisotropic. Evidence of anisotropy comes from shear wave splitting data obtained from a vertical seismic profile VSP. The data set consists of 48 vertically aligned receivers in a borehole drilled through the salt body. Splitting analysis is performed on shear wave phases that are converted from compressional waves at the top and bottom of the salt body. The phase converted at the top of the salt layer shows a clear signature of seismic anisotropy, while the phase at the base of the salt layer shows negligible splitting. We investigate the possibility of rock salt halite LPO as a cause of the observed anisotropy. A finite element geomechanical salt deformation model of the Mahogany salt body is developed, where deformation history is used as an input to the texture plasticity simulation program VPSC. Assuming a halite salt body, a full elasticity model is then calculated and used to create a synthetic VSP splitting data set. The comparison between the synthetic and real VSP data set shows that LPO of rock salt can explain the observed anisotropy remarkably well. This is the strongest evidence to date of seismic anisotropy in a deforming salt structure. Furthermore, for the first time, we are able to demonstrate clear evidence that deforming halite is the most likely cause of this anisotropy, combining data set analysis and synthetic full wave form modelling based on calculated rock salt elasticities. Neglecting anisotropy in seismic processing in salt settings could lead to potential imaging errors, for example the deformation models show an averaged delta parameter of δ = –0.06, which would lead in a zero offset reflection setting to a depth mismatch of 6.2 per cent. Our work also show how observations of salt anisotropy can be used to probe characteristics of salt deformation.

The 1998 Valhall microseismic data set: An integrated study of relocated sources, seismic multiplets, and S-wave splitting

Geophysics ◽  
2009 ◽  
Vol 74 (5) ◽  
pp. B183-B195 ◽  
Author(s):  
K. De Meersman ◽  
J.-M. Kendall ◽  
M. van der Baan
Keyword(s):  
Seismic Anisotropy ◽  
Amplitude Ratio ◽  
Temporal Variations ◽  
Oil Field ◽  
P Wave ◽  
Wave Form ◽  
S Wave ◽  
Data Set ◽  
Wave Splitting ◽  
Source Mechanisms

We relocate 303 microseismic events recorded in 1998 by sensors in a single borehole in the North Sea Valhall oil field. A semiautomated array analysis method repicks the P- and S-wave arrival times and P-wave polarizations, which are needed to locate these events. The relocated sources are confined predominantly to a [Formula: see text]-thick zone just above the reservoir, and location uncertainties are half those of previous efforts. Multiplet analysis identifies 40 multiplet groups, which include 208 of the 303 events. The largest group contains 24 events, and five groups contain 10 or more events. Within each multiplet group, we further improve arrival-time picking through crosscorrelation, which enhances the relative accuracy of the relocated events and reveals that more than 99% of the seismic activity lies spatially in three distinct clusters. The spatial distribution of events and wave-form similarities reveal two faultlike structures that match well with north-northwest–south-southeast-trending fault planes interpreted from 3D surface seismic data. Most waveform differences between multiplet groups located on these faults can be attributed to S-wave phase content and polarity or P-to-S amplitude ratio. The range in P-to-S amplitude ratios observed on the faults is explained best in terms of varying source mechanisms. We also find a correlation between multiplet groups and temporal variations in seismic anisotropy, as revealed by S-wave splitting analysis. We explain these findings in the context of a cyclic recharge and dissipation of cap-rock stresses in response to production-driven compaction of the underlying oil reservoir. The cyclic nature of this mechanism drives the short-term variations in seismic anisotropy and the reactivation of microseismic source mechanisms over time.

Linear‐transform techniques for processing shear‐wave anisotropy in four‐component seismic data

Geophysics ◽  
1993 ◽  
Vol 58 (2) ◽  
pp. 240-256 ◽  
Author(s):  
Xiang‐Yang Li ◽  
Stuart Crampin
Keyword(s):  
Time Series ◽  
Shear Wave ◽  
Seismic Data ◽  
Shear Waves ◽  
Shear Wave Splitting ◽  
Data Set ◽  
Reflection Data ◽  
Wave Splitting ◽  
Linear Transform ◽  
Zero Offset

Most published techniques for analyzing shear‐wave splitting tend to be computing intensive, and make assumptions, such as the orthogonality of the two split shear waves, which are not necessarily correct. We present a fast linear‐transform technique for analyzing shear‐wave splitting in four‐component (two sources/ two receivers) seismic data, which is flexible and widely applicable. We transform the four‐component data by simple linear transforms so that the complicated shear‐wave motion is linearized in a wide variety of circumstances. This allows various attributes to be measured, including the polarizations of faster split shear waves and the time delays between faster and slower split shear waves, as well as allowing the time series of the faster and slower split shear waves to be separated deterministically. In addition, with minimal assumptions, the geophone orientations can be estimated for zero‐offset verticle seismic profiles (VSPs), and the polarizations of the slower split shear waves can be measured for offset VSPs. The time series of the split shear‐waves can be separated before stack for reflection surveys. The technique has been successfully applied to a number of field VSPs and reflection data sets. Applications to a zero‐offset VSP, an offset VSP, and a reflection data set will be presented to illustrate the technique.

Inferring rock fracture evolution during reservoir stimulation from seismic anisotropy

Geophysics ◽  
2011 ◽  
Vol 76 (6) ◽  
pp. WC157-WC166 ◽  
Author(s):  
Andreas Wuestefeld ◽  
James P. Verdon ◽  
J-Michael Kendall ◽  
James Rutledge ◽  
Huw Clarke ◽  
...  
Keyword(s):  
Rock Mass ◽  
Shear Wave ◽  
Hydraulic Fracture ◽  
Seismic Anisotropy ◽  
Rock Fracture ◽  
Shear Wave Splitting ◽  
Data Set ◽  
Tight Gas Reservoir ◽  
Wave Splitting ◽  
Microseismic Events

We have analyzed seismic anisotropy using shear-wave-splitting measurements made on microseismic events recorded during a hydraulic fracture experiment in a tight gas reservoir in Carthage, east Texas. Microseismic events were recorded on two downhole arrays of three-component sensors, the geometry of which provided good ray coverage for anisotropy analysis. A total of 16,633 seismograms from 888 located events yielded 1545 well-constrained shear-wave-splitting measurements. Manual analysis of splitting from a subset of this data set reveals temporal changes in splitting during fracturing. Inversion using the full data set allows the identification of fracture strike and density, which is observed to vary during fracturing. The recovered fracture strike in the rock mass is parallel to directions of regional borehole breakout, but oblique to the hydraulic fracture corridor as mapped by the microseismic event. We relate this to en-echelon fracturing of preexisting cracks. The magnitude of shear-wave splitting shows a clear temporal increase during each pumping stage, indicating the generation of cracks and fissures in a halo around the fracture corridor, which thus increase the overall permeability of the rock mass. Our results show that shear-wave-splitting analysis can provide a useful tool for monitoring spatial and temporal variations in fracture networks generated by hydraulic stimulation.

Walk‐away VSP using drill noise as a source

Geophysics ◽  
1995 ◽  
Vol 60 (4) ◽  
pp. 978-997 ◽  
Author(s):  
Jacob B. U. Haldorsen ◽  
Douglas E. Miller ◽  
John J. Walsh
Keyword(s):  
Seismic Profile ◽  
Drill String ◽  
Seismic Survey ◽  
Effective Bandwidth ◽  
Walk Away ◽  
Data Set ◽  
Deconvolution Technique ◽  
Noise Data ◽  
Zero Offset ◽  
Noise Signature

We describe a method for extracting and deconvolving a signal generated by a drill bit and collected by an array of surface geophones. The drill‐noise signature is reduced to an effective impulse by means of a multichannel Wiener deconvolution technique, producing a walk‐away reverse vertical seismic profile (VSP) sampled almost continuously in depth. We show how the multichannel technique accounts for noise and for internal drill‐string reflections, automatically limiting the deconvolved data to frequencies containing significant energy. We have acquired and processed a data set from a well in Germany while drilling at a depth of almost 4000 m. The subsurface image derived from these data compares well with corresponding images from a 3-D surface seismic survey, a zero‐offset VSP survey, and a walk‐away VSP survey acquired using conventional wireline techniques. The effective bandwidth of the deconvolved drill‐noise data is comparable to the bandwidth of surface seismic data but significantly smaller than what can be achieved with wireline VSP techniques. Although the processing algorithm does not require the use of sensors mounted on the drill string, these sensors provide a very economic way to compress the data. The sensors on the drill string were also used for accurate timing of the deconvolved drill‐noise data.

Seismic anisotropy and natural fractures from VSP and borehole sonic tools—A field study

Geophysics ◽  
1996 ◽  
Vol 61 (2) ◽  
pp. 456-466 ◽  
Author(s):  
Wallace E. Beckham
Keyword(s):  
Field Study ◽  
Shear Wave ◽  
Seismic Data ◽  
Seismic Anisotropy ◽  
Seismic Profile ◽  
Azimuthal Anisotropy ◽  
Small Scale ◽  
Natural Fractures ◽  
Vertical Seismic Profile ◽  
The Cross

A multicomponent vertical seismic profile (VSP), cross‐dipole shear‐wave log, formation micro imaging (FMI) log, and oriented core were obtained in the Brady Ranch 1–5 well, Carter County, Oklahoma in November 1992. The intent was to study the properties of fractured intervals and the response of the seismic data with respect to fracture orientation. The primary zones of interest were the Sycamore and Hunton carbonates. A full nine‐component VSP was obtained from 152 to 3010 m. Data from a cross‐dipole shear‐wave log were obtained primarily in the deep carbonates at 2600–2900 m. The VSP and cross‐dipole data gave estimates of the orientation of azimuthal anisotropy in the section, and indicate three changes in the orientation of azimuthal anisotropy with depth. An east‐northeast orientation was obtained in the deepest zone, which includes the carbonate interval. The cross‐dipole data indicate anisotropy having east‐northeast, east‐south‐east, and approximately north‐south orientations in this zone. The cross‐dipole tool may be responding to small scale microcracks, which may have more random orientations than the larger scale macrofractures. FMI log data and oriented core, also obtained in the deep carbonate section, indicate macrofractures oriented in east‐northeast and east‐southeast directions.

A proposed polarity standard for multicomponent seismic data

Geophysics ◽  
2002 ◽  
Vol 67 (4) ◽  
pp. 1028-1037 ◽  
Author(s):  
R. James Brown ◽  
Robert R. Stewart ◽  
Don C. Lawton
Keyword(s):  
Ground Motion ◽  
Pressure Change ◽  
Seismic Profile ◽  
Primary Objective ◽  
Data Sets ◽  
Ocean Bottom ◽  
Data Set ◽  
Field Recording ◽  
Sea Bottom ◽  
Cable Lines

This paper proposes a multicomponent acquisition and preprocessing polarity standard that will apply generally to the three Cartesian geophone components and the hydrophone or microphone components of a 2‐D or 3‐D multicomponent survey on land, at the sea bottom, acquired as a vertical seismic profile, vertical‐cable, or marine streamer survey. We use a four‐component ocean‐bottom data set for purposes of illustration and example. A primary objective is a consistent system of polarity specifications to facilitate consistent horizon correlation among multicomponent data sets and enable determination of correct reflectivity polarity. The basis of this standard is the current SEG polarity standard, first enunciated as a field‐recording standard for vertical geophone data and hydrophone streamer data. It is founded on a right‐handed coordinate system: z positive downward; x positive in the forward line direction in a 2‐D survey, or a specified direction in a 3‐D survey, usually that of the receiver‐cable lines; and y positive in the direction 90° clockwise from x. The polarities of these axes determine the polarity of ground motion in any component direction (e.g., downward ground motion recording as positive values on the vertical‐geophone trace). According also to this SEG standard, a pressure decrease is to be recorded as positive output on the hydrophone trace. We also recommend a cyclic indexing convention, [W, X, Y, Z] or [0, 1, 2, 3], to denote hydrophone or microphone (pressure), inline (radial) geophone, crossline (transverse) geophone, and vertical geophone, respectively. We distinguish among three kinds of polarity standard: acquisition, preprocessing, and final‐display standards. The acquisition standard (summarized in the preceding paragraph) relates instrument output solely to sense of ground motion (geophones) and of pressure change (hydrophones). Polarity considerations beyond this [involving, e.g., source type, wave type (P or S), direction of arrival, anisotropy, tap‐test adjustments, etc.] fall under preprocessing polarity standards. We largely defer any consideration of a display standard.

Seismic anisotropy and mantle flow constrained by shear wave splitting in central Myanmar

2021 ◽  
Author(s):  
Enbo Fan ◽  
Yumei He ◽  
Yinshuang Ai ◽  
Stephen S. Gao ◽  
Kelly H. Liu ◽  
...  
Keyword(s):  
Shear Wave ◽  
Seismic Anisotropy ◽  
Shear Wave Splitting ◽  
Mantle Flow ◽  
Wave Splitting

Similarities between the Madeira and Canary Hotspots Revealed by Seismic Anisotropy from Teleseismic and Local Shear-Wave Splitting with the SIGHT Project

2021 ◽  
Author(s):  
David Schlaphorst ◽  
Graça Silveira ◽  
João Mata ◽  
Frank Krüger ◽  
Torsten Dahm ◽  
...  
Keyword(s):  
Shear Wave ◽  
Canary Islands ◽  
Delay Time ◽  
Seismic Anisotropy ◽  
Vertical Component ◽  
Mantle Flow ◽  
Crust And Upper Mantle ◽  
Length Scales ◽  
Flow Models ◽  
Using Data

<p>The Madeira and Canary archipelagos, located in the eastern North Atlantic, are two of many examples of hotspot surface expressions, but a better understanding of the crust and upper mantle structure beneath these regions is needed to investigate their structure in more detail. With the study of seismic anisotropy, it is possible to assess the rheology and structure of asthenosphere and lithosphere that can reflect a combination of mantle and crustal contributions.</p><p>Here, as part of the SIGHT project (SeIsmic and Geochemical constraints on the Madeira HoTspot), we present the first detailed study of seismic anisotropy beneath both archipelagos, using data collected from over 60 local three-component seismic land stations. Basing our observations on both teleseismic SKS and local S splitting, we are able to distinguish between multiple layers of anisotropy. We observe significant changes in delay time and fast shear-wave orientation patterns on short length-scales on the order of tens of kilometres beneath the western Canary Islands and Madeira Island. In contrast, the eastern Canary Islands and Porto Santo the pattern is much more uniform. The detected delay time increase and more complex orientation patterns beneath the western Canary Islands and Madeira can be attributed to mantle flow disturbed and diverted on small-length scales by a strong vertical component. This is a clear indication of the existence of a plume at each of those archipelagos, nowadays exerting a strong influence on the western and younger islands. We therefore conclude that a plume-like feature beneath Madeira exists in a similar way to the Canary Island hotspot and that regional mantle flow models for the region should be reassessed.</p><p>This is a contribution to project SIGHT (Ref. PTDC/CTA-GEF/30264/2017). The authors would like to acknowledge the financial support FCT through project UIDB/50019/2020 – IDL.</p>

Abstract 964: Effect of Volume Overload on Left Ventricular Torsion and Extra Cellular Matrix

Circulation ◽  
2007 ◽  
Vol 116 (suppl_16) ◽  
Author(s):  
Hosakote M Nagaraj ◽  
Thomas S Denney ◽  
Steven G Lloyd ◽  
David Calhoun ◽  
Inmaculada Aban ◽  
...  
Keyword(s):  
Picric Acid ◽  
Three Dimensional ◽  
Volume Overload ◽  
Left Ventricular ◽  
Deformation Model ◽  
Data Set ◽  
Left Ventricular Torsion ◽  
Tissue Tagging ◽  
Ventricular Torsion ◽  
Longitudinal Strains

Background: Muscle fibers are arranged in a spiral network and are connected by extracellular matrix (ECM). LV torsion is increased in the pressure overloaded heart where there is an increase in ECM. However, torsion and its relation to ECM have not been systematically studied in the volume overloaded heart. Hypothesis: The volume overloaded heart has a decrease in LV torsion due a loss of ECM. Methods: Primary mitral regurgitation (MR) (n=29), resistant hypertension (HTN) (n=77) and normal volunteers (NL) (n±37) were studied. Comprehensive cardiac magnetic resonance imaging (MRI) with tissue tagging was performed and analyzed using three-dimensional data set. Torsion was computed by fitting a B-spline deformation model in prolate-spheroidal coordinates to the tag line data. A subset of MR subjects had LV collagen assessed by picric acid Sirius red from biopsy samples taken at the time of surgery. Results: LV ejection fraction was 65% in MR and 70% in HTN. MR demonstrated eccentric remodeling and HTN demonstrated concentric remodeling. HTN had significantly higher torsion angle and systolic twist compared to NL and MR. This was associated with a simultaneous decrease in longitudinal strain. In contrast, MR patients had similar torsion indices, circumferential and longitudinal strains compared to NL. LV biopsy in MR demonstrated a decrease in interstitial collagen compared to NL. Conclusions: As opposed to the pure volume overloaded heart, LV torsional forces are increased in the pressure overloaded heart. This difference may be related to a rearrangement of the laminar structure due to a differential effect on ECM in the volume overloaded versus the pressure overloaded heart.

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