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[PDF] Making the Transition from Discrete Shot Records to Continuous Wavefields – Real Data Application
Author: Tilman Klüver, Stian Hegna, Jostein Lima
EAGE - 4 June 2018In this paper, we present real data applications of the acquisition and processing method outlined in the companion paper (Hegna, S., Klüver, T., and Lima J., 2018, Making the transition from discrete shot records to continuous
wavefields – Methodology: Expanded abstract submitted to the EAGE annual meeting). We discuss the design of sources that emit continuous wavefields approaching the properties of white noise using air-guns. The design
minimizes correlation between sources and allows a six-source configuration with a vessel towing six strings of airguns, thereby increasing efficiency or cross-line sampling. The environmental benefit of spreading source energy in time will be demonstrated. We illustrate the processing method based on continuous source and receiver wavefields on seismic data acquired on top of data acquired previously based on discrete shot records. Both data sets will be compared at image level. -
[PDF] Intra-Chalk Porosity Variations in Norway-Danish Central Graben: Integrated Mapping Using Broadband Elastic Attributes
Author: Noémie Pernin, Tim Bird, Cyrille Reiser
EAGE - 4 June 2018Understanding the influence of porosity on elastic properties through rock physics analysis is essential in seismic reservoir characterisation and key in the context of the chalk play. It is known that acoustic impedance is strongly correlated with porosity in carbonates but also that the chalk properties can vary widely creating intra-chalk layers of varying reservoir quality. This integrated study shows how reliable broadband relative elastic attributes tie at the wells and are able to map lateral and vertical changes of porosity within the Chalk interval in the Norwegian and Danish North Sea Central Graben.
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[PDF] Shot to Shot Source Signature Variation Correction
Author: Hocine Tabti, Jens Fredrik Wisløff, Torben Høy, Martin Widmaier
EAGE - 4 June 2018In this paper we discuss the ability to correct for shot to shot source signature variations and show how this could impact current survey source specifications. Contractual survey specifications define acceptability limits as to which
changes can be tolerated based on source wavelet attribute changes. Parts of two acquisition sequences have been acquired with deliberate survey source out-of-spec configurations. The out-of-spec tests included both source dropouts and pressure drop in separate sequences. Shot by shot source signatures have been generated from near field measurements. These were used to correct the seismic data for source wavelet changes including those caused by the out-ofspec pressure and source dropouts. We have demonstrated in this work that changes in the source signature, including changes beyond out-of-spec limits, can be estimated at every shot point and can efficiently be corrected for in processing. Current source out-of-spec limits are possibly too rigid if source variations
can be estimated at each shot point and corrected for in processing. -
[PDF] 4D Broadband Towed-Streamer Assessment, West Africa Deep Water Case Study
Author: Didier Lecerf, David Raistrick, Bertrand Caselitz, M. Wingham, J. Bradley, B. Moseley
EAGE - 4 June 2018A 4D broadband assessment has been performed in a deep offshore West Africa environment using repeated dualsensor streamer acquisitions. Three sail lines have been re-acquired only a few weeks after the original acquisition with standard 4D acquisition consideration. The study has compared the data repeatability metric NRMS along the processing sequences using, on one side, a reconstructed band limited 4D data corresponding to a single hydrophone and on the other side an extended bandwidth 4D data using the up-going wavefield only. Because the datasets have been recorded using the same acquisition, the main differences come from the bandwidth discrepancy and the variable sea-state. The 4D “Up-going on Up-going” preserves, for all processing steps, around 1% NRMS benefit against the 4D hydrophone-only. Because the NRMS comparison is biased by the dominant frequency discrepancy, the 1% gain does not fully reflect the detectability advantage of the 4D broadband. The NRMS analysis on the low frequency part has demonstrated the clear improvement on 4D broadband and a
qualitative evaluation on the 4D differences has highlighted the negative effect of the sea-state on the hydrophoneonly 4D results. -
[PDF] A Method to Suppress Salt-related Converted Wave Using 3D Acoustic Modelling
Author: Jyoti Kumar, Mamdouh Salem, D.E. Cegani
EAGE - 4 June 2018Converted waves can be recorded in a marine environment in the presence of large velocity contrasts, like a salt body. Salt-related converted waves can significantly contaminate P-wave image. The most noteworthy converted wave recorded in a salt province is generated from the base of salt. In this paper a method has been proposed to attenuate this energy before migration to improve sub-salt imaging. A clean converted wave model is generated using 3D acoustic forward modelling. This is then adaptively subtracted from the input dataset. Application of the proposed method is demonstrated in a complex deep water salt environment data set from the Mediterranean Sea.
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[PDF] A new approach to compensate for illumination differences in 4D surveys with different individual acquisition geometries
Author: Didier Lecerf, Martin Besselievre
First Break - 1 February 2018The authors demonstrate how the concept of Point Spread Functions can be successfully applied to time-lapse seismic when the respective acquisition geometries are very different and cannot be closely repeated.
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[PDF] Source and streamer towing strategies for improved efficiency, spatial sampling and near offset coverage
Author: Andrew Long
First Break - 1 November 2017The author presents a study of the fundamental relationships between cross-line source configurations and towed streamer survey efficiency and spatial sampling using a set of robust geometric relationships.
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[PDF] Enhanced subsurface illumination from separated wavefield imaging
Author: Shaoping Lu, Dan Whitmore, Alejandro Valenciano, Nizar Chemingui
First Break - 1 November 2014The authors present applications of separated wavefield imaging to a deepwater wide-azimuth survey in the Gulf of Mexico and to a narrow azimuth data set from offshore Malaysia.
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[PDF] Exploring Greece With a New Subsurface Perspective
Author: Mari Schjeldsøe Berg, Jörn Fürstenau, Spyridon Bellas
Offshore - 1 July 2014Exploring Greece with a new subsurface perspective.
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[PDF] Streaming ahead - examining best practice 4D streamer survey lessons.
Author: Andrew Long
Oilfield Technology - 10 May 2018The author examines best practice 4D streamer survey lessons, principally repeated acquisition and increased 4D signal detection.