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75th EAGE Conference & Exhibition incorporating SPE EUROPEC 2013
- Conference date: 10 Jun 2013 - 13 Jun 2013
- Location: London, UK
- ISBN: 978-90-73834-48-4
- Published: 10 June 2013
81 - 100 of 1113 results
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Simultaneous-source Acquisition and Environmental Noise - Good or Bad?
More LessThe promise of simultaneous-source acquisition in improving acquisition efficiency and/or sampling has been studied by a number of authors, especially over the last few years. However, most of these studies focussed on processing the signal associated with the known shots, rather than on the impact of environmental noise. The presence of environmental noise will clearly degrade the processed product from a simultaneous-source dataset, much as it does a conventional (sequential) dataset. In addition, the impact of the noise on the separation process is a concern for simultaneous-source data. The story is not all bad, however. Simultaneous-source acquisition generally involves increased source effort compared to an equivalent sequential data set, and, therefore, the signal-to-noise ratio of the acquired data is improved. This observation raises the possibility that simultaneous-source data could be acquired in higher-noise environments than the equivalent sequential data. We study this possibility using real simultaneous-source data acquired with varying environmental noise levels. Comparisons between simulated sequential and simultaneous-source products with varying noise levels indicate that simultaneous-source acquisition can indeed produce equivalent results in a significantly noisier environment.
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Deblending of Simulated Simultaneous Sources Using an Iterative Approach - an Experiment with Variable-depth Streamer Data
More LessWe have simulated a simultaneous source experiment with a real variable-depth streamer NAZ survey acquired in Brazil and applied an iterative separation flow using a hybrid of median and f-x projection filters for deblending. The results show little leakage after deblending in both near and far offsets while preserving the AVO characteristics. We have also performed Kirchhoff migration in order to examine the residual cross-talk in common image gathers after deblending. The results reveal little leakage, and the quality of the common image gathers is adequate for velocity model building. We also study how the existence of spatial aliasing when shots are coarsely sampled degrades the deblending quality. Lastly, the impact of firing multiple sources simultaneously to improve shot sampling is investigated.
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Simultaneous Shooting for Marine Acquisition - Could We Catch Up with Land?
Authors N. Moldoveanu, J. Quigley and C. BeasleySampling of sources and receiver is at the core of any seismic survey design as the quality of seismic data, as well the cost of the survey, depend on this. Simultaneous shooting was used successfully for land acquisition to improve the source sampling and acquisition efficiency, and is fully accepted commercially. In this paper we look at the evolution of simultaneous shooting for land and marine acquisition and discuss a survey design for multivessel coil shooting that could improve the source sampling without additional source vessels.
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Decentralized Blended Acquisition - Are Networks the Next Big Step in Seismic Data Collection?
More LessUntil today, seismic acquisition is carried out with a centralized architecture, the collected information being linear in the number of detectors (N). In the last decades N has been continuously increased, making seismic acquisition systems very complex. It is proposed to break this trend by abandoning the traditional centralized acquisition concept. Instead, it is proposed to concentrate future developments on the promises offered by the network architecture, showing a quadratic behavior in seismic information (N^2). By moving from a single complex, centralized system to a network of simple, decentralized subsystems, robotization becomes a very attractive proposition.
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High Productivity Cable Less Acquisition in Libya with the ISSN™ Technique - From Field Trial to a Production Survey
Authors M. Dvorak, D. Howe, T. Allen, D. Buddery, M. Foster, T. Manning and M. PfisterThe ISSN™ technique, the use of a cable-less nodal system deployed on a sparse regular gird in conjunction with the ISS® method of acquisition is introduced. The development of the technique from initial field trial using static spreads of nodes acquired in parallel with a production cabled survey through to a production test of the technique with a dedicated crew and 5 Vibrator trucks is presented. An overview is given of the assurance process followed to introduce this new technology during a Seismic exploration program. We then review the implementation of the technique at a full scale production survey in the BP Ghadames concession. The development of the processing strategy for the ISSN technique is reviewed and compared with the ISS method. We show that in moderate desert conditions where Vibroseis acquisition is possible, using a autonomous cable-less recording system with the ISS method allows for a step change reduction in HSSE exposure for land seismic vibrator crews while still acquiring good quality data at very high production rates.
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The Impact of ISS(R) Blending on Amplitude Fidelity for AVO Analysis
Authors M. Dvorak, K. Ahmad, T. Manning and J. BradleyThe ISS® and ISSN™ techniques are high efficiency simultaneous source acquisition technologies. The high productivity of these techniques allows for the acquisition of high fold, wide azimuth datasets. The improvement in the quality of the stack image achieved with high fold, wide azimuth acquisition design has been well documented. However in order to evaluate the impact on pre stack data quality from blending data with the ISS and ISSN acquisition techniques, a study has been conducted using a non simultaneous source dataset acquired with the same high fold and wide azimuth geometry as an ISSN dataset. In this paper we review the acquisition of the control dataset, during a Libya ISSN survey. The artificial blending of the dataset to create different models of the ISSN acquisition, each with varying numbers of active sources and source separations is described. The processing of the ISSN models and control dataset and the subsequent AVO and pre stack amplitude analysis of the datasets are presented. We show that for the level of blending noise (2 to 3 simultaneous source events per record) typically encountered with BP ISS and ISSN surveys the results of the AVO analysis are consistent with the control dataset.
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3D High-Resolution Imaging Using Separated Wavefields
Authors S. Lu, N.D. Whitmore, H. LeGleut and A. LongConventional wave equation migration extrapolates upcoming boundary data generated from primary reflections to image the subsurface. In marine seismic data processing, sea surface related multiples are a major challenge. Particularly, when the water bottom is shallow, short period multiples are difficult to deal with. Acquisition footprint of seismic imaging is another issue for shallow water bottom geology, where the primary reflections do not have the complete illumination coverage to the shallow targets, including the water bottom. In this paper, we review a method of separated wavefield imaging using sea surface related multiples. We present a data processing work flow of separated wavefield imaging including up and down-going wavefield separation using dual-sensor data, wave equation migration of wavefield extrapolation and imaging condition, and a post processing step of amplitude balancing. A shallow water example from Asia-Pacific is tested, where the separated wavefield imaging generates remarkable high resolution 3D images. The separated wavefield image has greater area of subsurface illumination, which mitigates the strong acquisition footprint. The method and results can be useful to reduce well drilling geohazards.
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Channel Modelling Using Full Waveform Inversion Applied to Variable-depth Streamer Data
Authors A. Ratcliffe, R. Jupp and R. WombellFull Waveform Inversion (FWI) aims to estimate high resolution velocity models by minimizing the difference between observed and modelled seismic waveforms. Good low frequency data play an important role in the successful application of FWI. Variable-depth streamer acquisition delivers high signal-to-noise (S/N) seismic data over a significantly wider frequency bandwidth than standard streamer acquisition. We show that FWI adapts naturally to the variable-depth acquisition geometry and so benefits from the improved low frequencies recorded in this configuration. Application to data from the Central North Sea reveals detailed velocity features associated with shallow channels in the near surface geology. Migration with this updated velocity model improves the subsequent imaging.
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Broadband Extended Images by Joint Deconvolution of Multiple Blended Wavefields
Authors I. Vasconcelos and J.E. RickettWe propose a method for inversion of subsurface reflectivity image gathers that jointly relies on the broadband nature of combining multiple wavefields with diverse temporal and spatial spectra. Our inversion retrieves depth-domain extended images (EIs), which represent the full reflectivity operators within the subsurface. Based on interferometry by multidimensional deconvolution (MDD), we present MDD-based imaging conditions for an extended-image inversion. Our method consists of deconvolving correlation-based EIs with the so-called joint point-spread function (JPSF). This method can account for imaging primaries as well as internal and free-surface multiples. Because it is based on MDD, our JPSF approach can account for blended/simultaneous-source data in imaging with no need to separate the simultaneous-source data prior to imaging. With the example dual-source vector-acoustic seismic data the extended-image JPSF system is constructed by separating source and receiver wavefields from upgoing and ghost data, from both pressure and gradient sources. We demonstrate how the method inverts for EIs representing subsurface reflectivity, while benefiting from the increase in temporal and spatial bandwidth brought on by dual-source multimeasurement data. In addition, our joint wavefield approach provides a framework for jointly imaging data from multiple experiments of any kind (e.g., surface and borehole, active and passive).
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Wave Equation Receiver Deghosting
Authors C. Beasley, R. Coates and Y. JiCurrent solutions to receiver deghosting generally involve making complementary measurements of the wavefield or, alternatively, involve estimation of data not recorded due to ghost interference. Both solutions offer challenges in practice today. For marine streamer data, although multimeasurement streamers are commercially available, it is still on a somewhat limited basis and existing p-wave data and conventional acquisition could benefit from accurate single-measurement deghosting. In the second case, statistical estimates of the unrecorded frequencies near the ghost notches can be confounded by a variety of factors. Our approach to up/down wavefield separation does not require complementary measurements – we demonstrate the method on pressure-only data – nor does it rely on statistical estimation of the missing spectral components. Instead, we use the wave equation to compute directly the up and downgoing wavefields between the receiver and the surface. This migration-like approach only assumes that the upcoming wavefield is causal with respect to the downgoing wavefield, a good assumption if certain types of noise such as the direct arrivals are removed from the recorded wavefield. Moreover, our method exposes the underlying physics of the problem and thereby allows for complexities such as variable water velocity, variable sea surface and complex wavefields.
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Premigration Deghosting for Marine Streamer Data Using a Bootstrap Approach in Tau-P Domain
More LessRemoving the receiver ghost before migration provides better low and high frequency response as well as a higher signal-to-noise ratio. We recognize these benefits for preprocessing steps like multiple suppression and velocity analysis. In this paper, we modify a previously published bootstrap approach that self-determines its own parameters for receiver deghosting in a t-x window. Similarly to the t-x bootstrap method, the recorded data in the shot domain are first used to create mirror data through a 1D ray-tracing-based normal moveout correction method. The recorded and mirror data are then transformed into tau-p domain and used to jointly invert for the receiver-ghost-free data. We apply this new algorithm to a field data set with a streamer depth of 27 m. Our deghosting method effectively removes the receiver ghost and the resulting image has broader bandwidth and a higher signal-to-noise ratio.
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Broadband Processing of Conventional Streamer Data - Optimized De-Ghosting in the Tau-P Domain
Authors H. Masoomzadeh and N. WoodburnConventional marine seismic data is affected by the interference from ghosts in both source and receiver sides. The natural diversity provided by propagation directions, depths variations and imperfect reflections at the sea surface means the notches are not as deep as they often appear after stack. Since the apparent time delay between the main signal and its ghost is angle dependent, a deterministic de-ghosting process in the tau-p domain can reduce the effect of ghosts and retrieve the original wavelet spectrum. The amplitude and phase discrepancies around the notch frequencies caused by the variations in depths and effective refection coefficients can be reduced by using a stochastic search for the optimum set of de-ghosting parameters. A deconvolution process stabilized by averaging over a large number of traces in common–slowness panels may be used to address the remaining spectral defects.
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Crossline Wavefield Reconstruction from Multimeasurement, Towed Marine Seismic Data and Its Implications for Imaging
Authors K. Eggenberger, M. Vassallo, P. Kitchenside, N. El Yadari and D.J. van ManenMeasurements of particle motion bring significant benefits to towed marine seismic data when processed in conjunction with pressure data. We describe how horizontal particle velocity (Vy) measurements can enable dealiased crossline wavefield interpolation and, hence, improve the final image. For this purpose, 3D synthetic data, representative of the Barents Sea area and consisting of a single shot line, are used to simulate two different, realistic acquisition geometries. For each acquisition scenario we focus on those features and areas where enhancement through interpolation is expected. We then apply novel interpolation techniques, based on both single- and multimeasurement seismic data, to reconstruct the seismic wavefield between the streamer positions on a shot-by-shot basis prior to imaging. Finally, for both acquisition geometries, we assess the impact of denser crossline sampling on the wavefield-extrapolated migration image and we show that the multichannel crossline wavefield reconstruction prior to imaging provides better protection against aliasing-related noise in the image. This finding is further corroborated by trials on the SEG advance modeling (SEAM) I model where we use modeled multiple shot lines to investigate the contribution of 3D stacking to the attenuation of migration noise originating in spatial aliasing.
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Ricker-Compliant and Pseudo-Unitary Decon
Authors J.F. Claerbout and A. GuittonPredictive deconvolution does not yield Ricker wavelets as source wavelets. Analytic theory here tells how to fix it. The theory is not inverse theory. It is computable in N.log(N) time. Results here confirm better seismogram polarities.
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Under-Explored Palaeozoic and Mesozoic Petroleum Systems
By P.A. CarterThe possible existence of Palaeozoic oil source rocks in the Barakan Graben is based on analogues from the Goulburn Graben and the Petrel Sub-basin. Such sources could charge either interbedded Palaeozoic reservoirs or overlying and updip Jurassic and younger reservoirs.
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A Global Evaluation of Source Rock Potential Since the Ediacaran
Authors J.C. Wrobel-Daveau, G. Baines and J. EtienneKey factors influencing source rock potential are the extent and nature of primary deposition and post-depositional thermal, tectonic and geodynamic history, which will affect the subsequent preservation and maturity of the source rock. We present a global evaluation of source rock potential and risk from the Ediacaran and Phanerozoic. This evaluation is made by combining 52 palinspastically restored gross depositional environment maps with a global plate model for the Phanerozoic and Ediacaran taken from the Neftex Global Earth Model product suite. The 52 palinspastic gross depositional environment maps were produced by taking reconstructed observations and interpreting them regionally based on both the tectonic setting and a predictive sequence stratigraphic framework. When combined with predictions of paleoclimate and paleo-ocean circulation, this framework allows us to predict zones of organic enrichment and source rock deposition through time. Once deposited, the global plate model allows us to identify regions where geodynamic processes (e.g. collision zones, large igneous provinces, rifts) are likely to have influenced source rock preservation and maturity. By combining these data with the observed geology and sediment thickness at the present day, we generate a global risk map of source rock potential that can be used to identify new exploration opportunities,
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Fracture Patterns in Organic Rich Mudstones - Implications for Primary Petroleum Migration
Authors J. Jahren, B.G. Haile, H. Hellevang, K. Bjřrlykke and S.E. OhmScanning Electron Microscopy (SEM) of thin sections taken from organic rich Jurassic shale core samples from the Norwegian Continental Shelf reveal the existence of what appear to be fine scale fracture patterns filled with migrated petroleum oriented normal to depositional bedding. The suggested fracture patterns forms in shales rich in fine grained clays (smectite, kaolinite) at temperatures around 90 şC (2500m burial depth). Coarser grained shales appear not to be fractured on a thin section scale. Fewer and less extensive micro fractures are found in samples intermediate between the fine and coarse grained samples investigated. The mechanism responsible for the fractures is suggested to be pressure build up during initial maturation around isolated patches of organic material before a functioning migration network has been formed. This indicate that a certain amount of petroleum must be produced before an effective long range organic network functioning as a migration pathway is established in source rocks. The absence of fracture networks in coarser grained source rocks indicate that functioning migration networks are establish in such rocks before local fracture pressure is reached. This is probably due to higher permeability resulting in a more effective displacement of the continuous porewater phase.
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The Phanerozoic Evolution of the South-Tethys Domain from Morocco to Iran - Vertical Movements and Main Geodynamic Events
With the aim of giving an integrated tectonic scenario for the Northern African and Arabian plates, we revisit six key areas, namely, the Anti-Atlas Belt (Morocco), the Bechar Basin (west Algeria), the Hassi R’Mel High (central Algeria), the Talemezane Arch (south Tunisia), the Western Desert (Egypt), and the High Zagros Belt (Iran). Below the so-called “Hercynian unconformity,” which is in reality a highly composite discontinuity, surface and subsurface data display a well-known arch-and-basin geometry, with basement highs and intervening Paleozoic basins. We show that this major feature results mainly from a Late Devonian event and can no longer be interpreted as a far effect of the Variscan Orogeny. From the Jurassic, Pangea breakup has been diachronic and the Alpine-Tethys propagated through the development of two branches which will finally connect at the end of Jurassic times, achieving the development of Africa northern plate boundary. By the Late Cretaceous, convergence between Africa and Eurasia led to the progressive closure of the Tethys realm. Two major geodynamic events appear synchronous and occured during the Campanian-Santonian and the Middle-Late Eocene. These two synchronous events coincides either with a change in plate kinematics or with a period of strong lithospheric coupling.
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Timing and Distribution of Biogenic Gas Generation in the Shallow Gas Play in the Dutch Offshore
Authors J.M. Verweij, S. Nelskamp and M.A. Guaipo SarmientoShallow gas accumulations in the Plio-Pleistocene Eridanos Delta deposits in the Dutch offshore are a valuable additional hydrocarbon source. Ongoing studies focus on better understanding the shallow gas play. The focus of this paper is on increasing the understanding of the origin of the shallow gas. For that purpose we used integrated modeling approaches to assess the timing and spatial distribution of biogenic gas generation. It was found that intra-Eridanos Delta deposits are the most probable source of biogenic gas and that these biogenic sources are at maximum depth and temperature today. Detailed glacial-interglacial temperature fluctuations do not have a large influence on the history of the optimum window for biogenic gas generation, i.e. on start of biogenic gas generation. In the oldest and deepest buried units of the Delta, biogenic gas generation started already at the beginning of the Pleistocene, while the youngest units have not yet reached the optimum window for biogenic gas generation.
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Improving Hydrocarbon Exploration through Mantle Circulation Modelling
Authors J.H. Davies and H. van HeckThe nature of the mantle underlying prospective hydrocarbon basins during their critical history is poorly known. This mantle can affect the basin dynamically and thermally. Knowing these effects through Earth history would be invaluable for assessing basin prospectivity. Mantle geodynamic modelling has advanced dramatically over the past decade such that the outputs are starting to become of interest in assessing the palaeo-environments of frontier regions. We focus on outlining the elements of the basic mantle circulation modelling (MCM) method, including the input plate motion histories, the equations solved, and the boundary and initial conditions. The method can predict dynamic topography and mantle flow back to the Jurassic. We introduce an extension of the method to allow tracing of the flow of magmatic source regions. This could be realised in the data from geochemical signatures of magmatic outputs over time. We also introduce how MCM can be used to test plate motion histories by comparing present day predictions with seismic tomography.
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