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- Volume 37, Issue 5, 2019
First Break - Volume 37, Issue 5, 2019
Volume 37, Issue 5, 2019
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Tutorial: the mechanics of waveform inversion
By Ian F. JonesAbstractUnresolved velocity anomalies lead to distortion in images: consequently, much effort has gone into developing model-building techniques to identify such anomalies. Historically, the industry has relied on ray-based tomography to achieve this, but ray methods are limited to detecting features that are typically larger than about five times the dominant wavelength of the recorded seismic data. More recently, model building based on wavefield tomography has been introduced (full waveform inversion). Waveform inversion methods are more costly than ray methods, but have the potential to resolve features smaller than the recorded seismic wavelengths.
Using waveform inversion to update a parameter field comprises two main steps: firstly, determine the spatial location of where an observed error came from, and then, determine the magnitude of that error, so as to update the parameter model. The first step uses the same principles as reverse-time migration to construct an ‘image’ of the parameter error, and the second step employs gradient descent methods to estimate the magnitude of the required parameter update. In this tutorial, I will describe both steps of the waveform inversion procedure, and also discuss differing methods of characterizing the error in a given parameter model.
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Joint inversion of gravity gradiometry and magnetic data using Gramian structural constraints: A case study from the McFaulds Lake survey, Ontario
Authors Michael S. Zhdanov and Martin ČumaAbstractPotential field data form an important frontline exploration tool thanks to the modern-day airborne platforms capable of collecting large amounts of data over large areas. Interpretation of these data using a 3D inversion is still a challenging problem due to the large amount of data and the need to discretize the inversion volume into a huge number of elements.
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A full wavefield approach to marine survey planning
Authors Chloé Lazizi, Stefan Jetschny, Morten W. Pedersen and Alba OrdoñezAbstractConventional processing of 3D marine seismic data based on primary reflections can suffer from strong acquisition related footprint. The problem manifests as gaps in the data because the water bottom and shallow features lack full illumination in shallow water data. The phenomenon is most obvious at the water bottom and gradually heals with increasing depth. This degradation of the shallow image is particularly problematic for surveys that target geohazard evaluation. Furthermore, accurate and continuous water bottom information can be crucial for multiple removal techniques that are required for successful imaging of deeper targets (Brittan et al., 2011).
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K18-Golf Field seismic and reservoir modelling challenges
Authors J.C.P. Pipping, A. Wever, R. Bachmann, V. Smirnov and S. DeneuvillersAbstractThe Wintershall Noordzee operated K18 Golf field is located ca. 50 km WNW of Den Helder in the middle of a restricted military area (Figure 1). The gas field was discovered by well K18-7x in 2005 and subsequently appraised by well K18-8. The reservoir consists of a 270-m thick Rotliegend (Permian) sandstone reservoir with average porosities of less than 10%. The reservoir quality is very heterogeneous and of a tight nature with average permeabilities of 0.6 mD. The well K18-8 showed a maximum gas rate of 200,000 Nm3/d at 25 bar FWHP before hydraulic fracking while K18-7x was tested at 56,000 Nm3/d at a 12 bar FWHP. A hydraulic frac in the K18-7x top interval increased the production to 370,000 Nm3/d at 128 bar FWHP.
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Impact of grey level transformation and chosen amplitude range on GLCM-based anisotropy estimation
Authors Christoph Georg Eichkitz and Johannes AmtmannAbstractThe relative influence of parameters used for seismic anisotropy estimation based on the grey level co-occurrence matrix (GLCM) was examined in a previous article (Eichkitz and Amtmann, 2018) whose objective was a general understanding of the parameters, including the number of grey levels, type of grey level transformation, size of the analysis window, and type of GLCM-based attribute. We now examine the influence of the type of grey level transformation and amplitude range chosen for the transformation.
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Addressing uncertainty during early stage frontier exploration: bringing regional context to basin modelling
Authors Natasha Dowey and Christine YallupAbstractDuring the early stages of exploration, uncertainties regarding the nature and presence of a petroleum system are significant. The potential risk on charge conditions is typically a key factor in frontier exploration; charge has been a common cause of wildcat well failure in recent years (e.g., Rabat Deep, Morocco and Maria-1, Black Sea). The ability to assess charge risk when even basic geological conditions are poorly understood is therefore a crucial first step in increasing exploration success. Basin modelling is an essential tool for evaluating and quantifying charge timing, phase and volume, and allows the impact of uncertainty to be investigated through sensitivity analysis. However, during the early stages of frontier exploration, there is typically little data available to unequivocally constrain stratigraphic predictions and thermal conditions in subsurface models.
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3D fault imaging using windowed Radon transforms: an example from the North Sea
More LessAbstractThe interpretation of fault surfaces is key to understanding the subsurface geology represented in 3D seismic volumes. The geologic structure represented by seismic reflections can be auto-tracked in the volume. Faults, however, are imaged as discontinuities or changes in curvature in the seismic data. For many years, fault interpretation involved manually picking fault cuts on orthogonal slices through the seismic volume. These fault cuts were grouped into conceptual faults, and 3D fault surfaces were created from the fault cuts.
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Spectral Decomposition AVO attributes for identifying potential hydrocarbon-related frequency anomalies
By Chris HanAbstractLow-frequency seismic anomalies have long been a subject of interest to geoscientists involved in hydrocarbon exploration since such ‘gas-shadows’ can be a direct hydrocarbon indicator (DHI). Published studies have demonstrated evidence for them potentially resulting from increased seismic attenuation and velocity dispersion, as a result of hydrocarbon saturation. The topic gained wide interest during the 2000s with well-cited publications by Castagna et al. (2003), Ebrom (2004), Chapman et al. (2005, 2006) and Odebeatu et al. (2006), to name a few. The consensus of these studies was that hydrocarbon related frequency effects are predicted to be detectable on stacked seismic data. Furthermore, it has been suggested that low frequencies tend to show the highest sensitivity to fluid changes. (e.g. Korneev et al., 2004). The effect has been shown not only from seismic data; studies involving laboratory tests and borehole data provide similar conclusions. Overall there is general agreement that the effect exists. However the physical cause remains inconclusive. Several studies have also shown evidence that hydrocarbon reservoirs have an amplitude-versus-offset (AVO) frequency dependence (e.g. Chapman et al. (2005, 2006), Odebeatu et al. (2006), Liu et al. (2006), Ren et al. (2007), Zhang et al. (2007), Chen et al. (2008), Wu et al. (2014)). In the modelled case of gas-saturated sands, low frequencies have tended to show the greatest change in amplitude with offset (Figure 1a).
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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)