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[PDF] Seismic Noise Attenuation Using Curvelet Transform and Dip Map Data Structure
12 June 2017
The curvelet transform is a known tool used in the attenuation of coherent and incoherent noise in seismic data. It utilizes the fact that signal and noise are usually better separated in the curvelet domain than in the time-space (TX) domain. Coefficients of the transform are not independent and neighboring coefficients are strongly correlated, which existing curvelet-based noise attenuation algorithms do not fully utilize. In this work, we propose to use a data structure called a ‘dip map’ to describe dip information in seismic data. This information links local curvelet coefficients together in adaptive thresholding or subtraction of curvelet coefficients in seismic denoising algorithms. We used the dip map to improve the curvelet multiple subtraction algorithm and the results show significant improvement over traditional methods with real data.
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[PDF] A New Look at the Geology and Prospectivity of a North Sea Frontier Area with Modern Seismic - The East Shetland Platform
12 June 2017
The greater East Shetland Platform (ESP) area is characterized by numerous proven Devonian-Eocene fields, but is still one of the few remaining underexplored regions of the UK Continental Shelf. In particular, Permo-Carboniferous carbonates and sandstones, Devonian sandstones and fractured basement in prominent structural traps have been successful, proving these units to be viable reservoirs. Some of these are large producing fields in nearby areas (e.g., Buchan, Clair, Auk, with >100 MMboe).
The improved imaging of the 3D broadband dual-sensor towed streamer data has allowed the interpretation of the Paleozoic horizons over the entire outer ESP region (17,500 km2), enabling interpreters to spread new light on its evolution.
Possible Paleozoic structural traps are often sealed by the overlying Cretaceous strata. Source rocks could be provided by the ‘classical’ upper Jurassic Kimmeridge Clay (lateral migration from the basin depocenters lying further east). Potential additional oil-prone sources may be provided by middle Devonian shales (c.f., Beatrice Field).
Burial history modelling indicates that the best case scenario (late generation) did occur over parts of the study area. This supports previous geochemical analyses in analogue areas, which suggested a contribution from the Devonian source for the oils of large fields (e.g., Claymore and Clair fields). -
[PDF] Intelligent Adaptive Subtraction for Multiple Attenuation
12 June 2017
A lot of improvements have been seen in the last decade in 3D multiple modelling techniques, such as 3D Surface Related Multiple Elimination (SRME) and 3D wavefield modelling. These processes create accurate multiple models in terms of kinematics and amplitude. The main challenge now is to improve the subtraction of multiples, with a reduction in both residual multiple and primary leakage. This paper describes a new approach for multiple adaptive subtraction, which combines different techniques (least squares filtering in the time-space domain and
curvelet-based subtraction) and improves primary preservation by using true multiple adaptive subtraction. The ultimate aim is to automatically get the best subtraction according to the complexity of the geology with minimum testing for the geophysicist. -
[PDF] Shot by Shot Source Wave Field Estimation
12 June 2017
In this paper we discuss the behavior of air gun source arrays in marine seismic acquisition. We comment the fact that the source configuration and depth are changing continually with the combined actions of surface waves, sea currents and general towing conditions. This has a direct effect on the emitted source pressure wave field and thus on the signature in the seismic data. We describe the method of backpropagation with relative motion that allows an efficient and robust estimation of notional and far-field signatures from near-field measurements at every shot point. The derived shot by shot signatures show very good correlation with seastate and sea-currents, as we would expect. We show that the variation of the signature can affect the quality of seismic data. We demonstrate that the estimated far-field signatures describe the real variation of the signature in the data and we show how the estimated shot by shot signatures can be used to mitigate the effect of signature variations and thereby improve the quality of the seismic data.
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[PDF] Utilizing a novel quantitative interpretation workflow to derisk shallow hydrocarbon prospects — a Barents Sea case study
Author: Laurent Feuilleaubois, Valerie Charoing, Andrea Maioli, Cyrille Reiser
First Break - 1 March 2017The authors demonstrate that combining separated wavefield imaging with high-resolution velocity computations improves the pre-stack amplitude analysis of shallow water hydrocarbon targets in the Barents Sea.
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[PDF] New technique corrects distortions
Author: Volker Dirks, Senira Kattah
Hart E&P - 1 November 2016WEI leads to improved amplitude fidelity and image resolution in the Jequitinhonha Basin offshore Brazil.
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[PDF] The East Shetland Platform and Mid North Sea High
Author: Stefano Patruno, William Reid
GEO ExPro - 1 June 2016An introduction to the Devonian-Paleogene prospectivity of the key areas of interest for the UKCS 29th Frontier Licensing Round.
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[PDF] Full Waveform Inversion and Ambiguities Related to Strong Anisotropy in Exploration Areas – Case Study Barents Sea
30 May 2016
In this case study from the Barents Sea, we have used refraction based Full Waveform Inversion (FWI) in an extreme anisotropy regime without the support from well information. We reveal our observations for decoupling the vertical and horizontal velocity, which enables us to achieve good data matching as well as flat gathers, focused images and a geological consistent model. Our frequency cascaded FWI flow results in a high resolution velocity model to the depth of interest, following the faulted crest in great detail, as well as low velocity zones correlating with the bright spots in the seismic image.
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[PDF] On Broadband Data and Rough Sea Surface Receiver Deghosting
30 May 2016
Efficient removal of the ghosts is key to achieving broadband seismic data. Accurate deghosting on the receiver-side can only be performed when both pressure and vertical particle velocity information is available. We use acoustic reciprocity to derive a relationship that defines the total pressure wavefield as a function of the up-going pressure wavefield and the ghost function. Utilizing this relationship, and assuming the shape of the sea surface is known, we propose a pre-stack deghosting method based on integral inversion for a pressure-only dataset. Deghosting by spectral division with a flat sea surface or a statistical ghost function is shown to be special cases of this new inversion based method. The behavior of the pressure ghost function under rough sea condition is analysed in comparison to the flat and the statistical pressure ghost functions. The error of deghosting rough sea pressure-only data with a flat sea surface or a statistical ghost function is quantified using both synthetic and real seismic data.
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[PDF] Modelling Seismic Data for Time-varying Rough Sea Surfaces
30 May 2016
The impact of moving rough sea surfaces on seismic data can only be assessed through proper modelling. Existing seismic data modelling tools assume either flat or frozen sea surfaces. We present a tool for modelling seismic data from a time-varying rough sea surfaces. This is achieved by coupling the up-going subsurface reflection data with the time-varying sea surface reflectivity on a plane interface below the sea surface using integral technique. The algorithm was verified with known analytical solutions for both frozen and moving sea surfaces. Our data examples show that time varying sea surfaces affect reflection signals significantly in comparison to the static counterpart.