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[PDF] A practical crosstalk attenuation method for separated wavefield imaging
Author: Shaoping Lu, Dan Whitmore, Alejandro Valenciano, Nizar Chemingui, Grunde Rønholt
SEG - 1 October 2016Images of primaries and multiples can be contaminated by erroneous phantom images caused by the crosstalk of multiply scattered events. Using a causality property of the events in separated up- and down-going wavefields, we present a practical crosstalk prediction and attenuation method when imaging using surface reflected wavefields. Our method does not explicitly separate multiples of any specified order. Through both synthetic and field data examples, we show how the proposed method reliably predicts the crosstalk in separated wavefield imaging. Consequently, it provides higher quality images with balanced amplitudes and improved illumination.
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[PDF] Taking an integrated approach to seismic exploration
Author: Patrick Coole
Hart E&P - 1 April 2015In 2014 Petroleum Geo-Services (PGS) began a large,integrated 2-D geosciences project with the aim of increasing the geological understanding of the Angolan and Namibian offshore margins. The project employed an integrated approach using regional 2-D interpretation, gravity and magnetics, and quantitative seismic interpretation to achieve this aim.
Seismic acquisition took place offshore Angola in 2011 and offshore Namibia in 2013. Both datasets were acquired using PGS' dual-source GeoStreamer and GeoStreamer with GeoSource, respectively. The true broadband nature of this type of acquisition system allows a superior seismic image, providing broader frequencies across the amplitude spectrum and making it ideal for reservoir characterization/quantitative interpretation and geological interpretation.
While shooting the seismic data, PGS also acquired gravity and magnetics data along the same lines. As such, the PGS Access project combines regional 2-D geological interpretation, quantitative interpretation, and gravity and magnetics. It also ties to important pre- and post-salt wells and discoveries, providing an integrated geoscience project targeted specifically at exploration and aiding geoscientists in understanding this prolific yet geologically complex margin.
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[PDF] Towed streamer EM - Resistivity in context
Author: Joshua May
PESA News - 31 August 2015Controlled Source Electromagnetic (CSEM) data acquisition systems have historically been based on the seafloor node method. Receiver nodes are deployed on the seabed and record data generated from an EM dipole source towed behind a vessel. Such a method is inherently inefficient and in order to improve the cost-effectiveness of acquisition, a sparse grid of nodes is generally used. This lack of data density can adversely affect the quality and resolution of the final data. It was these challenges, alongside PGS' pioneering attitude and expertise in high tech marine engineering which inspired the development of a Towed Streamer EM system.
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[PDF] Towed Streamer EM
Author: Joshua May
Seismic Profile - 1 July 2015A Step Change in acquisition efficiency, data density and seismic and EM integration.
A case study: High density 3D EM in the Barents Sea Southeast.
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[PDF] Illuminating Challenging Areas
Author: Gregg Parker
GEO ExPro - 1 March 2014PGS's new full azimuth survey design can illuminate challenging deepwater areas of the Gulf of Mexico like never before.
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[PDF] Unlocking Offshore Greece: New Regional GeoStreamer Dataset Provides Key Answers
Author: Mari Schjeldsøe Berg, Øystein Lie, Spyridon Bellas, Antonis Angelopoulos
GEO ExPro - 1 September 2014In preparation for the 2014 licensing round that opens in September, PGS have, on behalf of YPEKA, acquired 12,500 km of 2D seismic data offshore western and southern Greece. The exceptional quality of the new seismic data has allowed a confident delineation of the stratigraphic record and the various play types. The exploration blocks are now defined and, with the regulatory framework in place, the region is ready to be further explored.
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[PDF] Full waveform inversion with steerable variation
Author: Lingyun Qiu, Kathy Zou, Alejandro Valenciano, Nizar Chemingui
SEG - 1 October 2016We propose a new regularization scheme for Full Waveform Inversion (FWI). The new method makes use of a priori information on the spatial variability of the earth model to overcome the limitations of the inversion in the presence of high velocity contrast geobodies and cycle skipping. It comprises two additional regularization terms to the FWI objective function. The first term evaluates the L1 norm of total variation (TV) of the model, while the second term steers the solution based on local prior information of the model spatial variability. Both regularization terms can be made spatially variant to accommodate different geological features in the model, i.e. sediments (smooth changes), salt bodies (piecewise constant). Our procedure makes use of the split Bregman iterations, an effective algorithm for solving the L1 optimization problems. The result is a computationally efficient and accurate implementation. We show the potential of the method by using the BP 2004 velocity benchmark model. There, our regularization scheme allows the inversion to start from a simple velocity model and delivers a high-quality reconstruction of salt bodies.
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[PDF] Advances in broadband quantitative interpretation
Author: Cyrille Reiser, Tim Bird
SEG - 1 October 2016For almost 10 years now marine broadband seismic has provided the industry access to seismic data with a significant increase of seismic frequency bandwidth on both the low side of the frequency spectra and also on the high side. Seismic analysis and case studies in recent years using broadband seismic have revealed several benefits of broader seismic bandwidth for reservoir geoscientists - both for structural-stratigraphic interpretation and for quantitative seismic reservoir characterization and properties estimation. Pre-stack seismic inversion has been an excellent means to derive the full benefits and the value of acquired broadband pre-stack seismic for seismic reservoir characterisation and reservoir imaging.
This paper presents case studies of recent analysis at various stages of the exploration-production asset life as well as some potential pitfalls to be aware of when using pre-stack broadband seismic data for improved target delineation, estimation of reservoir properties and ultimately de-risking of a prospect or well positioning. A case study for a shallow reservoir in a frontier exploration setting will also demonstrate some recent developments in the integration of Full Waveform Inversion and imaging using multiples for an improved low frequency model and more reliable pre-stack seismic inversion.
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[PDF] Krauklis wave in a trilayer
Author: Valeri Korneev, Ludmila Danilovskaya, Seiji Nakagawa, George Moridis
Geophysics - 31 July 2014The Krauklis wave is a slow dispersive wave mode that propagates in a fluid layer bounded by elastic media. The guided properties of this wave and its ability to generate very short wavelengths at seismic frequency range predict possibility
of resonances in fluid-filled rock fractures. Study of Krauklis wave properties at laboratory scales requires evaluation of its propagation velocities in models with finite and thin elastic walls. Analysis of an exact solution for a fluid-filled trilayer
with equal thickness plates reveals existence of the Krauklis waves in such a model, as well as another mode which propagates mostly in the solid part. Both propagation modes exist at all frequencies.We derived and verified various asymptotic solutions by comparing their dependencies on layer thicknesses and frequency with the exact numerical solution. Analytical and computational results demonstrate that in a 60-cm long model, the first resonant frequency can be below 10 Hz.
This result suggests that the Krauklis-wave effects can be studied in a laboratory at seismic range of frequencies avoiding a notorious problem of frequency downscaling. Strong dispersive properties of Krauklis waves and their dominant
behavior in fluid-fracture systems are likely phenomena explaining the observed frequency-dependent seismic effects in natural underground reservoirs. -
[PDF] Beneath the Labrador Sea
Author: Kai Floistad, Jerry Witney, Ron Borsato, James Carter, Richard Wright, Thomas Neugebauer
GEO ExPro - 1 April 2013A new seismic dataset helps clarify the deepwater hydrocarbon potential offshore Newfoundland and Labrador in Canada