iSIMM Experience with Peak- and Bubble-Tuned Sources for Generating Low Frequencies

Christie, P. A. F.; Lunnon, Z.; White, R. S.; Kusznir, Nick; Roberts, A. W.; Parkin, C. J.; Smith, L. K.; Eccles, J. D.; Healy, D.; Hurst, N.; Tymms, V.; Chappell, A.; Fletcher, Richard

doi:10.3997/2214-4609.201402143

Cited by 6 publications

(4 citation statements)

References 6 publications

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“…The peak output of the iSIMM air-gun source array was at frequencies of 9-11 Hz (Lunnon et al 2003). Both conventional peak tuning and bubble tuning (Avedik et al 1996;Lunnon et al 2003) were tested; the peak tuned source signature was found to be more stable with varying angle while the bubble tuning provided a slight improvement in the low frequency bandwidth (Christie et al 2006b). …”

Section: Introductionmentioning

confidence: 98%

Identification and inversion of converted shear waves: case studies from the European North Atlantic continental margins

Eccles

White²,

Christie

2009

Geophysical Journal International

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S U M M A R YWide-angle shear wave arrivals, converted from compressional to shear waves at crustal interfaces, enable crustal Vp/Vs ratios to be determined which provide valuable constraint on geological interpretations. Analysis of the converted shear wave phases represents the next logical step in characterizing the crustal structure and composition following multichannel seismic structural imaging and tomographic inversion of the wide-angle compressional wave phases. In this offshore study across two passive margins extending from stretched continental to fully oceanic crust, the high-data density (2-10 km ocean bottom seismometer, OBS, spacing) and a consistent, efficient conversion interface produced shear wave data sets suitable for traveltime inversion. The shear waves were recorded by three orthogonal geophones in each OBS. Arrival phases, visible to 180 km offset, were identified using their arrival times, moveout velocities and particle motions. Across the North Atlantic volcanic rifted continental margins studied, breakup was accompanied by the eruption of large volumes of basalts of the North Atlantic Igneous Province. The interface between post-volcanic sediments and the top of the basalts provides the dominant conversion boundary across the oceanic crust and the continent-ocean transition. However, the shear wave data quality was significantly diminished at the continental ends of the profiles where the thick basalt flows and hence this conversion interface feathers out and crustal attenuation increases. Initial modelling of the converted shear wave phases was carried out using a layer-based approach with arrivals converted on the way up used to constrain the Vp/Vs ratio of the post-volcanic sedimentary sequence beneath each OBS. To produce a model with continuous crustal S-wave velocities, the compressional wave velocities beneath the sediment-top basalt interface were transformed into starting shear wave velocities using a constant value of Vp/Vs and the inversion carried out by specifying the appropriate ray path. Once the data set had been fully interpreted, correction of the traveltimes to effective symmetric ray paths enabled us to apply a regularized grid inversion. Such inversions are less subjective than the layer-based approach and yield more robust minimum structure results with quantifiable errors, except in the vicinity of a known subbasalt low-velocity zone encountered on the Faroes margin. Monte Carlo analyses were performed for this approach; the average model from multiple inversions using randomized starting models and traveltimes shows the structure required by the traveltimes and the model standard deviation gives an estimate of uncertainty. Model and inversion parametrizations were fully tested and optimum parameters chosen for compressional and shear wave inversions. This allows, after appropriate model smoothing, an estimate to be made of the spatial variation of the Vp/Vs ratio within the crust. There are marked gradients in Vp, Vs and Vp/Vs ratio across the continent-ocean ...

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Section: Introductionmentioning

confidence: 98%

Identification and inversion of converted shear waves: case studies from the European North Atlantic continental margins

Eccles

White²,

Christie

2009

Geophysical Journal International

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“…Furthermore, according to the work of Christie et al . (); and Hegna and Parkes (), this deficiency is practically unaffected by the source depth.…”

Section: Discussion and Resultsmentioning

confidence: 90%

Theoretical study on multi‐level source design

Shen

Elboth

Tian

et al. 2014

Geophysical Prospecting

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A B S T R A C TThis paper studies aspects that influence the de-ghosting performance of marine multi-level sources based on a modified Johnson model. The normalized squared error between actual signature and its corresponding ghost-free signature is introduced to evaluate the multi-level source design. The results show that optimum depth combinations and volume combinations exist in the design. However, there is also some flexibility in the volume combination which makes it possible to optimize with respect to residual bubble oscillation. By considering both operational aspects and performance, we propose that three or four levels in a multi-level source are reasonable. Compared to a horizontal source, a multi-level source can be designed to reduce the notch effect, strengthen the down-going energy and improve the energy transmission directivity. Studies of the influence of depth and firing time deviations indicate that a multi-level source is more stable than a normal horizontal source in an operational environment.

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“…The first part of this section refers to inversion tests done on a synthetic data set, while the second reports on inversions done on a shot-gather from the integrated seismic imaging and modeling of margins (iSIMM) project (Christie et al, 2006b).…”

Section: Resultsmentioning

confidence: 99%

Wide-angle AVO waveform inversion with WKBJ modeling

Fuck

Chapman

Thomson

2011

12th International Congress of the Brazilian Geophysical Society &Amp; EXPOGEF, Rio De Janeiro, Brazil, 15–18 August 2011

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We propose a new target-oriented inversion workflow aimed at extending AVO-type inversions to long-offset seismic data. Such an ability improves reservoir parameter estimation, allowing sharper discrimination of velocity and density changes across an interface in comparison with estimations done with AVO inversion based on plane-wave reflection coefficients. The forward modeling used during the inversion is the WKBJ seismogram algorithm, a fast and robust way to compute seismograms from pre-critical partial reflections, through transitional waveforms, which include the interference with head waves, to totalreflection signals. The inversion fits a target reflection in raw shot or CMP gathers by direct comparison of either the waveforms of the observed data and modeled WKBJ seismograms or of their respective envelopes. In addition, to avoid local minima the workflow has been divided into two stages: first, a global random search of the parameter space provides the initial model, which is then fed into the second stage, a local gradient-based optimization. Inversions of a synthetic model and a raw shot gather from a 2D point-receiver survey demonstrate that the inclusion of wider-angle, near-critical and post-critical data in the proposed inversion improves the resolution of both velocity and density contrasts.

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iSIMM Experience with Peak- and Bubble-Tuned Sources for Generating Low Frequencies

Cited by 6 publications

References 6 publications

Identification and inversion of converted shear waves: case studies from the European North Atlantic continental margins

Identification and inversion of converted shear waves: case studies from the European North Atlantic continental margins

Theoretical study on multi‐level source design

Wide-angle AVO waveform inversion with WKBJ modeling

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