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- Volume 35, Issue 6, 2017
First Break - Volume 35, Issue 6, 2017
Volume 35, Issue 6, 2017
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Full-fold, multi-source acquisition through shot isolation technology and its implications on productivity gains
Authors K. Eggenberger, J.O.A. Robertsson, F. Andersson, D.J. van Manen, R. Walker and L. AmundsenShot isolation enabled full-fold, multi-source acquisition is achieved by applying the novel technology of signal apparition to the encoding and decoding of fully superimposed shot records from non-distance separated sources. The introduction of periodically varying shot-to-shot modulation functions for encoding injects energy at predetermined positions within distinct wavenumber ranges, which then enables a deterministic decoding of individual shots in data processing. We demonstrate the method for single vessel operations, first on a dual source configuration for seabed acquisition, extracted from the SEG Advanced Modeling Program (SEAM) Phase I dataset, and then extend the methodology to triple-sources through the use of an emulated marine real data example from the North Sea. With shot isolation enabled multi-source acquisition being successfully applied in a marine and seabed seismic context, scope for significant productivity gains is created. Compared to established acquisition techniques, gains arise from the ability to acquire full-fold data in a shorter time frame without compromising the subsurface bin size. For marine seismic acquisition, this also implies that the number of towed streamers can be reduced, giving leeway to additional strategic considerations on subjects such as capital expenditures and the optimization of vessel deployment plans.
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Petroleum systems of the deepwater Mozambique Basin
The Mozambique margin is relatively under explored with a small number of wells both onshore and offshore. Nine major gas fields have been identified to date (Brownfield et al., 2012), which are believed to contain a combined more than 150 trillion ft3 of natural gas. The discovery of large natural gas fields in the Rovuma basin represents one of the most exciting exploration successes of recent years and Mozambique is now considered to be a prolific hydrocarbon province (Hollebeek et al., 2015). This exploration study utilizes a modern, regional 2D seismic grid that was acquired in 2013 and processed to depth in 2015. It covers a large proportion of the Mozambique offshore province (Figure 1) and was used to assess hydrocarbon prospectivity in the region. Seven mega-sequences were identified based on stratigraphy from well ties (Uzcategui et al., 2014), the regional geology and seismic character and were interpreted throughout the study area. This interpretation provided a basin-scale, structural framework in which to model the petroleum systems. Structural and stratigraphic plays were mapped, assessed and built into a 3D model that assesses the viability and quality of petroleum systems offshore Mozambique.
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Digital Geology and the upstream business — using virtual and augmented reality technologies for subsurface capability building and collaboration
Authors H.J. Kloosterman, J. Grötsch, Y.K. Yong and E. Zeeland‘Digital Geology’ has recently been developed at Shell’s Subsurface Learning Faculty where geological outcrops are brought into the office environment and augmented reality techniques are used with real geological exhibits (rock slabs, cores, fossils) to provide the experience of hands-on reservoir characterization work combined with digital overlays. Five geological exhibits, representing different scales of geological analysis and investigation (ranging from ‘basin-scale’ to ‘grain-scale’), have been constructed and integrated through interactive exercises in the existing learning programmes in Shell. The success of complex upstream projects is critically influenced by the ability of geoscientists to understand: 1 Regional basin architecture and petroleum systems in exploration 2 Subsurface reservoir architecture, impact on fluid flow and related uncertainties in production Such success depends on how the above knowledge is communicated among various expertise holders involved in upstream projects. Good collaboration is based on the subsurface complexity being shared effectively among all stakeholders. This is often a significant challenge owing to the lack of adequate means to build required integration capabilities within project or technology teams. Shell has identified novel ways of learning to address such challenges but has also realized the opportunities digitalisation can offer nowadays. Digital Geology is Shell’s approach to address this in a structured and comprehensive way by introducing innovative ways of learning, collaboration and communication aimed at improved integration within the upstream business.
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Rayleigh wave phase velocity models for gravitational wave detectors using an array of nodal sensors
Authors Soumen Koley, Henk Jan Bulten, Jo van den Brand, Maria Bader, Xander Campman and Mark BekerArray studies of ambient seismic noise have gained much importance in recent years for the purpose of classifying noise sources corresponding to different frequency bands. Stehly et al. (2006), Snieder et al. (2009), Wapenaar et al. (2010), have also demonstrated useful applications of using ambient noise recordings for surface wave tomography. Seismic motions generated by natural and artificial sources propagate through the subsurface both in the form of body and shear waves. But the major contribution to the seismic noise field is in the form of Rayleigh and Love waves (Haubrich et al., 1963), especially at shallow depths. In the context of gravitational wave detectors, such displacement of the subsurface couples with the suspended elements of the detector through gravitational forces of attraction and is referred to as Newtonian noise. In order to subtract this noise, it is necessary to understand the sources of seismic noise near the detectors and the propagation characteristics. Hence, an optimal seismic array was designed and a passive seismic survey was carried out at the Advanced Virgo gravitational wave detector in Italy. Easily deployable 5 Hz vertical component wireless geophones were used for continuous acquisition of the seismic noise.
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A bigger picture view of separated wavefields and marine broadband seismic
By Andrew LongThe advent of dual-sensor recording for towed seismic streamers enabled the true separation of the up-going and down-going pressure wavefields (Carlson et al., 2007), and heralded the ‘broadband’ seismic revolution seen in marine seismic exploration over the past decade (Widmaier et al., 2015). In reality, ‘broadband’ typically means deghosting accompanied by some additional forms of spectral conditioning. In most cases, the post-stack interpretation of deghosted data is enhanced by improved geological texture, improved event coherence and deeper signal penetration. Recent attention has focused on the benefits of low frequencies in broadband seismic data (ten Kroode et al., 2013), and indeed where ultra-low frequency phase integrity is preserved as a complement to accurate amplitude-versus-angle fidelity, deghosted data also enables more accurate pre-stack quantitative interpretation (Reiser et al., 2015a, 2015b). However, it has also become clear that some long-standing imperfections in the seismic method remain. The rapid decay in air gun output below about 7 Hz (Parkes and Hegna, 2011) is not satisfactorily addressed by deghosting, compensation for high-frequency attenuation remains a fundamental challenge, and traditional challenges to wavelet processing, denoise, multiple removal, velocity estimation and imaging may in fact be more complicated for some broadband methods, or unaffected for others. The key benefit of dual-sensor methods are accurate access to the various separated wavefields, in addition to enhanced recoverable frequency bandwidth. Reservoir monitoring is enhanced by the elimination of the down-going pressure wavefield from 4D differencing, reservoir illumination can be enhanced by the incorporation of the down-going pressure wavefield into wave theoretic imaging, reflectivity inversion can be enhanced by isolating the up-going pressure wavefield in imaging, and overall we expect to see ‘complete wavefield’ reservoir imaging and characterization solutions mature rapidly. Furthermore, increased focus on spatial frequency content courtesy of ‘wave equation inversion’ imaging solutions is also taking broadband seismic past the historical focus upon only temporal frequency content.
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Thermal extraction for organic-matter containing materials to answer questions both on Earth and in Space
By M.A. SephtonThe role of heat in the generation of petroleum has led to the study of organic matter-containing rocks by laboratory heating techniques. In particular, heat is used for the thermal extraction of organic matter in preparation for characterization by a range of detectors. Recently, thermal extraction has been used to answer certain planetary science questions such as the history of habitability for planets in the solar system and the search for evidence of life outside the Earth. The development of new thermal extraction protocols for challenging planetary science objectives provides methods that are readily translatable back to petroleum activities and include new shale screening and assessment techniques.
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Shooting over the seismic spread
Conventional marine seismic surveys typically mobilize a single vessel towing two airgun source arrays in front of a spread of ten or more streamers. The data acquired in this way are narrow-azimuth and lack near offsets owing to the distance between the sources and the streamers which can be in the range of 100 to 200 m for the inner cables and up to 500 m for the outer cables. Several solutions, such as coil shooting (French, 1984; Ross, 2008) or advanced multi-vessel operations (Mandroux et al., 2013), have been proposed and deployed to improve azimuth coverage and fold. Although these are excellent solutions for achieving wide-azimuth data, they are generally expensive and/ or time-consuming, and none of them record zero-offset data. Near- and zero-offset data are, however, especially critical for imaging shallow geological targets and of great benefit for multiple attenuation. In this paper, we present a tailored solution to this challenge that allows the recording of both zero-offset data and dual azimuths in an effective and safe way. We call this acquisition solution TopSeis. This solution was created in close co-operation between Lundin Norway and CGG and is designed to deliver excellent broadband (2.5-200 Hz) imaging of shallow to intermediate targets at depths of up to 3000 m or more.
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The vibrator-ground model and the vibroseis source wavelet
By Zhouhong WeiMiller and Pursey (1954) have shown that for an isotropic-homogeneous-elastic half-space, the far-field particle displacement is proportional to the surface stress if the surface stress is uniformly applied over a small disc. This relationship of force and far-field particle displacement establishes the theory of the vibroseis method. It implies that the vibrator ground force is proportional to the far field particle displacement if the ground is assumed to be an isotropic-homogeneous-elastic body and the vibrator baseplate is small enough comparing with the wavelength of interest. The true ground force is the integration of the pressures beneath the baseplate. However, this true ground force is not directly measured, and it is often estimated by a weighted sum of outputs from two accelerometers placed on the reaction mass and baseplate assemblies (Sallas and Weber, 1982; Sallas, 1984). The weighted sum estimation of the ground force, often referred as the weighted-sum ground force, has been widely used as the phase locking feedback signal on the vibrator force control since 1984. Initially, the vibroseis source wavelet embedded in correlated vibroseis data is assumed to be the autocorrelation of the pilot sweep (zero-phase with a flat spectrum).
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Effects of igneous intrusions on the petroleum system: a review
Igneous intrusions feature in many sedimentary basins where hydrocarbon exploration and production is continuing. Owing to distinct geophysical property contrasts with siliciclastic host rocks (e.g., higher Vp, density and resistivity than host rocks), intrusions can be easily delineated within data sets including seismic and CSEM profiles, provided igneous bodies are larger than the detection limit of the geophysical methods. On the other hand, igneous bodies affect geophysical imaging in volcanic basins. Recent analyses of 3D seismic data, supported by field observations and lab-based experiments, have provided valuable insights into the prevailing geometries of intrusions, i.e. (1) layerdiscordant dykes, (2) layer-parallel sills and (3) saucer-shaped intrusions. Where emplaced, intrusive bodies affect all five principal components of a given petroleum system: (1) charge, (2) migration, (3) reservoir, (4) trap and (5) seal. Magmatic activity may positively or adversely affect any of these individual components, for instance by locally enhancing maturation within regionally immature source rocks, typically 30-250% of the intrusion thickness, or by causing compartmentalization of source and reservoir rocks. Site-specific evaluations, including the timing and duration of the magmatic event are needed to evaluate the overall effect of intrusions on a given sedimentary basin’s petroleum system, and these are highlighted by case studies from different volcanic basins.
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Taking seismic acquisition artefacts beyond mitigation
More LessSeismic acquisition footprint is a problematic noise artefact in seismic data which if left un-attenuated distorts recorded primary data in pre- and post-stack datasets and so comprises processing and interpretation quality. A conventional method of attenuating this orthogonal geometry acquisition footprint is the application of a 3D Kx-Ky frequency-slice, wavenumber notch filter on pre-stack offset vector tiles (OVT) and post-stack data. However, this approach may leave residual unfiltered acquisition footprint noise. This is because any discontinuities in seismic amplitudes have the potential to be interpreted as a fracture network or faults. The attenuation of an acquisition footprint is a compromise between successfully removing these amplitude discontinuities while preserving geologically-related ones. This paper attempts to address seismic acquisition footprint attenuation via a cascaded processing flow which aims to remove this noise completely without affecting primary amplitude.
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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)