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- Volume 37, Issue 1, 2019
First Break - Volume 37, Issue 1, 2019
Volume 37, Issue 1, 2019
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Measured sound levels in ice-covered shallow water caused by seismic shooting on top of and below floating ice, reviewed for possible impacts on true seals
More LessAbstractSeismic surveying of the Arctic is important for several reasons, but also introduces some challenges. One is the concern that seismic data may affect the hearing of marine mammals living there, including true seals. We performed two seismic experiments on floating ice on Svalbard in the Norwegian Arctic in early March 2016 and late May 2017, just before and right after the ringed seal breeding period. We used a single airgun below ice and detonating cord on ice, measured sound levels in the water column, compared these with hearing capabilities of true seals found from previous studies, and observed the animals’ reactions when exposed to seismic waves in the field. We found that these actual seismic experiments have little potential to cause physical hearing damage, but temporary behavioural change may occur. We also observed a difference in measured sound levels, frequency content, and animal reactions, depending on the type of source used.
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The enigma of arrays
By Jason CrissAbstractThe debate over arrays vs. single-point recording continues. In college (in the 1980s) we learnt that arrays can suppress certain forms of seismic noise and that the array itself acted as a multiplier to our stacking fold with regard to random noise. To understand the impact of arrays on our seismic data we need to challenge these fundamental truths about array behaviour and look more closely at what is taking place when we sum sensor responses from multiple receivers spread over an area. There is a great wealth of published material available on this topic with many experimental results from the field. However, the materials derived from these works never seem to result in an industry-wide conclusion which answers the question ‘is an array better or worse than a single point sensor?’. The default is often to continue on with arrays in acquisition since it has always been done that way in the past. With the introduction of very high channel count systems and very dense acquisition geometries it seems apparent that continued use of arrays must be under threat. This article hopes to challenge some of the fundamental assumptions about array behaviour.
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Low-frequency Vibroseis: current achievements and the road ahead?
Authors Nicolas Tellier and Gilles OllivrinAbstractExtending the seismic signal frequency towards low frequencies has become almost standard on seismic projects, owing to the benefits it provides in terms of vertical resolution, signal penetration, inversion workflow results or ease of interpretation. Vibroseis is preferred to explosives not only for its productivity, but also for the control it allows over frequencies generated. While Vibroseis equipment has been improved in recent years, discrepancies are observed in the equipment and methods used, in particular in the design of low-frequency sweeps. A desire for lower frequencies seems also to guide the development of some vibrators, at the expense of technical complexity, higher cost and reduced performance at higher frequencies. However, if the need for broader frequencies is not questioned, the right level of low-frequency energy necessary for imaging and interpretation purposes is still not clearly defined by the industry, at the risk that the current focus for more powerful lower frequencies could be a temporary trend. This paper discusses achievements in equipment and methods, and speculates on the future of low-frequency Vibroseis.
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The use of nodal seismic acquisition systems to acquire limited-scale surveys
Authors Tim Dean and Denis SweeneyAbstractNumerous new nodal seismic acquisition systems have been recently introduced that are significantly more advanced than those previously available (Dean et al. 2018). These new generation nodes are not only lightweight (the lightest currently commercially available is the Inova Quantum, being only 650 g) but also have significant battery lives, with 50 days not being unusual. Other than the Geometrics Atom, they have mostly been developed for large channel count surveys — thousands to tens of thousands. Often, however, surveys are acquired on a reduced scale, i.e. employing relatively small channel counts (from 24 to several hundred) and/or having a limited duration (four weeks or less). Examples of such ‘limited-scale’ surveys involve geotechnical work (refraction, Multi-Channel Analysis of Surface Wave (MASW), etc.), passive monitoring, and reflection surveys over small areas, such as mine sites. In this paper, we will look at the suitability of these recently introduced nodal systems for use in such limited-scale surveys. We begin by describing the acquisition systems that are currently used for such surveys before addressing positioning, an essential part of any survey. We then look at the influence of geophone selection, including 3-component recording and other recording parameters. We will then address the operational use of nodal systems and seismic sources. We finish with a brief data example followed by a discussion.
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High-resolution land seismic acquisition with Broadsweep
Authors Tagir Galikeev, Alexander Zhukov and Ilya KorotkovAbstractSeismic acquisition techniques have steadily progressed over time to achieve higher productivity and greater data bandwidth. Vibroseis sources with new hydraulics and plate and chassis design (Bagaini, 2008; Wei, 2017) are able to generate sweeps between 1–2 Hz to 300–400 Hz (Wei, 2015). Receivers have graduated from complicated patterns to the single-point omnidirectional receiver. Trace density of surveys has increased to provide higher signal-to-noise ratio and homogeneous azimuthal and offset coverage.
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Applying full-azimuth depth processing in the Local Angle Domain for Frequency Absorption versus Azimuth) (FAVAz) analysis to predict permeable, oil-saturated fractures
Authors Alexander Inozemtsev, Gali Dekel, Zvi Koren and Alexander GalkinAbstractPredicting the permeability of fractured reservoirs is valuable for both reservoir assessment and drilling planning. Characterization of such systems requires advanced amplitude analysis, mainly based on seismic imaging results of the recorded wavefield. A significant amount of work has been done on the subject over the past few decades.
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High-frequency acoustic land full-waveform inversion: a case study from the Sultanate of Oman
Authors A. Sedova, G. Royle, T. Allemand, G. Lambaré and O. HermantAbstractApplications of full-waveform inversion (FWI) to land seismic data exhibit specific challenges, largely associated with elastic effects and near-surface heterogeneities. This explains why only a few land FWI case studies have been published to date (Mothi et al., 2012; Mei et al., 2014). In recent years, the acquisition design of land surveys has improved dramatically and now offers ideal conditions for FWI: dense sampling, long offsets and full azimuths (FAZ), and very low frequencies down to 1.5 Hz (Mahrooqi et al., 2012). The first published application of 3D land FWI to this new, ultra-low frequency, data set was encouraging (Stopin et al., 2014). The authors demonstrated the capability to recover the long spatial wavelength components of the velocity model, robustly and efficiently, using diving wave FWI and basic data pre-processing. It was proposed that the resulting velocity model be used as a starting model for reflection-based tomography. Limitations in obtaining a high-resolution velocity model (> 6 Hz) from FWI were identified, and attributed to the acoustic assumption and a weak signal-to-noise ratio.
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Safer seismic energy source for complex geological imaging
Authors David Vidal, Juan Ledezma, Jose Luis Calle, Bladimir Ballesteros and Juan MirandaAbstractSeismic data acquisition operations continuously demand new methodologies and safer procedures. One of the riskiest activities in the operation is the handling and charging of seismic shot holes with explosives as an energy source. The development of electronic detonators in the seismic industry has significantly reduced the risk of an accidental detonation. The Oseis initiation system demonstrated excellent performance and provided enough energy for good signal-to-noise-ratio seismic data. Additionally, the full-wave sampling survey design approach effectively attenuated different kinds of noises and obtained a high level of repeatability to reinforce the reflected seismic signal from complex geological imaging targets.
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Volumes & issues
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Volume 42 (2024)
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Volume 41 (2023)
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Volume 40 (2022)
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Volume 39 (2021)
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Volume 38 (2020)
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Volume 37 (2019)
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Volume 36 (2018)
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Volume 35 (2017)
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Volume 34 (2016)
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Volume 33 (2015)
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Volume 32 (2014)
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Volume 31 (2013)
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Volume 30 (2012)
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Volume 29 (2011)
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Volume 28 (2010)
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Volume 27 (2009)
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Volume 26 (2008)
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Volume 25 (2007)
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Volume 24 (2006)
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Volume 23 (2005)
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Volume 22 (2004)
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Volume 21 (2003)
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Volume 20 (2002)
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Volume 19 (2001)
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Volume 18 (2000)
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Volume 17 (1999)
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Volume 16 (1998)
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Volume 15 (1997)
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Volume 14 (1996)
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Volume 13 (1995)
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Volume 12 (1994)
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Volume 11 (1993)
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Volume 10 (1992)
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Volume 9 (1991)
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Volume 8 (1990)
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Volume 7 (1989)
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Volume 6 (1988)
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Volume 5 (1987)
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Volume 4 (1986)
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Volume 3 (1985)
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Volume 2 (1984)
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Volume 1 (1983)