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EAGE Seabed Seismic Today: from Acquisition to Application
- Conference date: September 8-10, 2020
- Location: Online
- Published: 08 September 2020
20 results
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Multi-component seismic data processing of a 3D 4C OBC dataset for lithological identification
By B. KamelSummaryIn this case history we present the advantages and improvements in lithological discrimination and identification by implementing a robust seismic data processing workflow of vertical component (PP) and converted wave (PS), for a 3D 4C dual sensor OBC dataset.
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4D gravity and subsidence monitoring as cost-effective alternatives to 4D seismic
Authors H. Ruiz, M. Lien and J.E. LindgårdSummarySummary not available
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Elastic full-waveform inversion using all components of 4C data
More LessSummaryRecent computer computational improvements have allowed us to simulate elastic data in a 3D manner and undertake the challenge to execute elastic full waveform inversion (EFWI). The field data experiment to demonstrate the technologies, we elected to use a Gulf of Mexico (GOM) ocean bottom cable (OBC) data-set which allowed us to take advantage of relatively large offsets along with the four-component acquisition. The input data was minimally processed mostly through noise removal and the initial model was built via tomography with a strong smooth version of the tomographic update from a pre-stack migrated gather flattening process. During the EFWI, a multiscale approach was followed to ensure the convergence and the early stages of the / ratio was constrained by the mud rock-line ratio. The velocity fields were validated via imaging algorithm of the elastic reverse time migration and the imaging shows clear structural improvements when inputting the inverted velocities in conjunction with the measurements.
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Robust Full Waveform Inversion for sparse ultra-long offset OBN data
Authors H. Aghamiry, A. Gholami and S. OpertoSummaryUltra-long offset node acquisition are beneficial for full waveform inversion (FWI) because the wide variety of wave types recorded by these geometries are suitable for broadband velocity model building. However, long propagation distances induced by long offsets exacerbate cycle skipping and the sparsity of the acquisition can inject wraparound artefacts in the velocity model. To mitigate these issues, we develop the wavefield reconstruction inversion (WRI) method with sparsity-promoting regularization. WRI first reconstructs wavefields such that they match the data, hence preventing cycle skipping at receivers, at the expense of the accuracy with which they satisfy the wave equation. Then, the velocity model is updated by minimizing the wave equation errors (source residuals). This workflow is iterated until wavefields jointly fit the data and satisfy the wave equation. Solving these two optimization subproblems with the alternating-direction method of multiplier (ADMM) breaks down FWI in two linear subproblems for wavefields and velocity model thanks to the bilinearity of the wave equation. This provides a suitable framework to implement sparsity-promoting regularizations in WRI. The capacity of our method to exploit sparse long-offset acquisition to build broadband velocity model without cycle skipping is illustrated with a toy synthetic example and the BP salt model.
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Multiple Source Towed Streamer and Seabed “Hybrid” Seismic Acquisition in The Middle East
Authors J. Wallace, M. Adnan and D. SturkoSummaryThe Arabian Basin contains some of the world’s largest fields and has a long and successful track record of exploration and production. The offshore waters have numerous legacy datasets, both towed streamer and ocean bottom seismic of varying vintages. To maximize existing field potential, E&P companies are embracing new innovations, leveraging new technology to improve sub-surface knowledge through advanced seismic acquisition and/or reprocessing techniques. For the last 50 years there has been oil and gas production offshore Dubai. Around and within the case study, outlined in this abstract, there are four active fields that contain seventy-five platforms. Until 2019, the area was covered by 2D seismic exploration lines and a number of focused 3D surveys acquired in the 1990s: OBC data was acquired over “Field One” and towed streamer over “Field Three”. Both datasets had been reprocessed, with the most recent performed approximately 10 years after acquisition. The inherent limitations in the legacy data had now been reached and this meant there was a requirement for new seismic over the area.
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Improved reservoir monitoring with PP & PS time-lapse imaging utilising up/down deconvolution: Edvard Grieg field
Authors F. Twynam, R. Ford, P. Caprioli, M. Hooke, R. Whitebread, P.E. Dhelie, V. Danielsen and K.R. StraithSummaryAdditional insight into the interaction between pressure and fluid saturation changes within the reservoir can be extracted through discrimination of time-lapse (4D) signal from both PP and PS data. Previous processing of the 4D PP data set over the Edvard Grieg field in the Norwegian North Sea from a 2016 baseline to the 2018 monitor survey yielded interpretive saturation-related 4D changes due to production and injection. The PS radial data followed, centred on a co-processed up/down deconvolution (UDD) workflow in alignment with the PP route. This PS result provided additional insight into pressure changes across the field due to the nature of converted-wave propagation. The UDD workflow involved spectral division of the radial with the downgoing wavefield in the 3D tau-p-q domain. The output was shaped to a user-defined wavelet and, thereby, 3D deghosted. Performing joint PP-PS tomography provided an uplift in depth-domain event alignment, which helped correlate structural boundaries with the extracted 4D attributes. The 4D PS result correlates well with the predicted model and the low-frequency response was observed to be significantly improved over the legacy processing route.
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Seabed Seismic Application in Malaysian Basins: Unlocking the Subsurface Complexities
Authors S. Kumar, S. Chandola, A.A. Khalil, W.H. Tang and A.A.B. MuhamadSummaryMarine towed streamer acquisition has witnessed major technological advancement during the past few decades but suffers from certain operational and geophysical limitations e.g. imaging below the gas cloud due to attenuation of the P-waves. The advent of seabed seismic technology coupled with advancement in processing techniques has allowed the industry to overcome some of these limitations enabling broadband-full wave imaging of the sub-surface. The journey of seabed seismic in Malaysia goes back to 1990’s when few 2D-OBC lines were acquired by an operator on test basis. PETRONAS conducted its first 3D-2C Ocean Bottom Cable (OBC) survey in east Malaysia in 2004 where towed streamer acquisition was not possible due to shallow water depths and the presence of surface facilities. Ever since, PETRONAS has emerged as one of the front runners in leveraging seabed seismic technology primarily to address the issue of poor seismic imaging below shallow gas clouds affecting majority of its producing fields. Since 2009, PETRONAS and its partners have carried out more than a dozen seabed seismic surveys (2C & 4C) in Malaysian basins to address both exploration and development challenges.
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An Overview of OBN Processing Challenges and Technologies Development
Authors D. Zhang, C. Tsingas, A.A. Ghamdi, M. Huang, K.K. Sliz and W. JeongSummaryIn the oil industry, ocean bottom node acquisition (OBN) is one of the technologies utilized to help in deep marine exploration and development. It has also allowed us to acquire data over areas with more complex shallow bathymetry. Like many new techniques, it has its advantages and limitations. In this abstract, we will discuss some of them by showing examples from a recently acquired large, high density and full azimuth OBN survey.
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A denoising workflow of seafloor vertical geophone using 4-C data
Authors W. Jeong, C. Tsingas and M. MubarakSummaryOne of the key advantage of multicomponent seafloor seismic acquisition is to suppress receiver side ghost and water-layer multiples by PZ processing. It is well known that the success of PZ processing is heavily rely on the processing/pre-conditioning of the vertical geophone component. In this study, we propose a pre-conditioning workflow for applying a vertical geophone de-noise process to enhance compressional wave signal free from shear energy contamination. The proposed workflow is a fully automated process and is comprised by three steps: 1) Masking filter, 2) Adaptive subtraction and 3) Envelope matching. Numerical examples show that the proposed methodology highly enhances signal-to-noise ratio of the vertical geophone component exhibiting high coherency with the hydrophone. The denoising result indicates the effectiveness of the proposed workflow, which will serve as a pre-conditioning step prior to the subsequent application of PZ processing as well as conventional data processing.
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The largest 3D seabed seismic survey in the world is under way offshore Abu Dhabi
Authors G. Cambois, S. Al Mesaabi, G.A. Casson, J. Cowell, D. Arnold, M. Mahgoub, M. Al Hammadi and K. ObaidSummaryADNOC has launched a survey aimed at imaging the entire acreage offshore Abu Dhabi with high-resolution full-azimuth seismic data. Due to the shallow waters, everything will be acquired with either nodes or cables. Covering about 30,000km2, this will be the largest seabed seismic survey ever recorded. An aggressive timeline of just over three years means that five crews will be acquiring simultaneously, with full source blending. The survey started early 2019 and has already ramped up to three crews. The data is showing broad bandwidth and intriguing new azimuthal features that could lead to improved near-surface imaging.
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Surface-related multiples help image the overburden in shallow waters offshore Abu Dhabi
Authors A. Almessabi, G. Cambois, M. Mahgoub, J. Oukili, S. Naumann and A. PankovSummaryUsing up- and down-going waves separated at the seabed and invoking reciprocity, we can apply separated wavefield imaging to ocean-bottom data and generate a virtual acquisition spread where every source becomes a secondary receiver. This technique provides an improved broadband and zero-phase image of the near-surface, and combines with refraction FWI to generate a high-resolution anisotropic velocity model. We applied this workflow to an old OBC survey offshore Abu Dhabi in ultra-shallow waters, and managed to obtain an improved image of the near-surface and the overburden, which can be used to identify drilling hazards.
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Up-down deconvolution in complex geological scenarios
Authors D. Boiero and C. BagainiSummaryThe interferometric approach often referred to as up-down deconvolution is well known and applied to attenuate free-surface related multiples in seabed surveys. In a horizontally layered medium, the up-going wavefield can be expressed as the convolution of the down-going wavefield with the Earth’s reflectivity for each plane-wave component in which the wavefields are decomposed. Consequently, deconvolving the down-going wavefield from the up-going wavefield, gives us the Earth’s reflectivity response for a certain plane-wave component. It has been experimentally observed that deconvolution carried out one plane-wave component at a time gives reasonable results even in the presence of complex subsurface structures, provided that the seabed is relatively flat. When these conditions are not satisfied, the same problem can be formulated in terms of interferometric redatuming using multi-dimensional deconvolution. The inverse problem that performs the deconvolution is usually ill-conditioned and hence must be regularized. We mitigate numerical instability by adding a regularization term on the solution norm and by introducing lateral weighted regularization to exploit the similarity across different receiver/source locations.
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Down/down deconvolution
Authors G. Hampson and G. SzumskiSummaryImages constructed from up-coming wavefields can be very effectively deconvolved using up/down deconvolution, however, they have geometry related drawbacks that reduce the quality of the shallower zones. In contrast, the down-going wavefield, which is imaged using mirror imaging, does not suffer from such geometry related disadvantages, however, it lacks a powerful deconvolution technique akin to up/down deconvolution. We use a modified Delft feedback model to describe the up- and down-going scattered wavefields. Using these results, we illustrate how up/down deconvolution works and then go on to introduce a new idea called down/down deconvolution. This new technique inverts the down-going wavefield for the Earth’s response in the absence of a free-surface. The free-surface multiples are removed and the 3D source wavefield is deconvolved to produce a result that is theoretically the same as up/down deconvolution. As a result we can combine the geometrical advantages of the down-going wavefield and the benefits of a powerful deconvolution technique. We illustrate this new idea using a synthetic dataset and a real 3D OBN dataset from the North Sea.
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Processing and imaging of a multi-petabyte OBN survey in the North Sea
Authors T. Rayment, G. Hampson and L. LetkiSummaryAn ocean-bottom node (OBN) survey was acquired during 2018/19 covering 1510 km2 in an area 90 nautical miles west of Stavanger. As it was acquired using several asynchronous triple-source vessels, deblending was an essential step to recover signal at target depths. Deblending also removed very strong nearby seismic interference, by using the interfering survey’s shot times, with as many as 14 active sources firing. Up-down deconvolution is a key step to address the challenges observed in the area as it achieves both free-surface multiple elimination and 3D signature deconvolution. A similar approach was developed to tackle the same issues for the down-going wavefield resulting in a more effective and efficient processing flow for imaging shallow targets than conventional techniques. The long offsets and rich azimuthal sampling of the wavefield meant FWI could solve model building and imaging challenges over a range of depths. Such challenges included shallow channels and deeper cemented sand injectites. This survey illustrates how advances in acquisition and processing technologies enable large-scale, high-density OBN surveys to be acquired and processed in accelerated time frames leading to new insights even in relatively well-explored areas.
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OBN 3D/4D imaging: Reducing radically the number of seabed sensor for Full Wavefield Migration and FWI
By D. LecerfSummaryThis paper analyzes the potential of using Full Wavefield Migration (FWM) algorithms for breaking the constraint of density, geometry and location of the seabed OBN layout. Using data from deep-water surveys, we simulate and investigate the impact of various alternative sensor geometries on the resolution of the seismic image. Radical OBN acquisition parametrization such as limited aperture, extensive separation distance and original “donut” layout designs have been tested.
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The Evolution of the OBN Acquisition Solution
By T. BuntingSummaryThe productivity of an ocean bottom node (OBN) survey is dependent on a number of inter-connected factors. Historically OBN surveys were limited by node deployment and recovery speed. Seismic acquisition contractors have made heavy investment in sub-sea node deployment technology with the sole goal of improving ocean bottom node project efficiency and consequently reducing project cost. This effort has resulted in the more wide spread use of OBN technology in the recent past. As sampling demands increase and the industry becomes more comfortable with efficient SimSource schemes we can expect further demands on the node deployment resources and we can expect further improvements; both incremental improvements to the current solutions and step changes in sub-sea technology.
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Sparse Node survey in GoM, first results and further experiments
Authors H. Roende, C. Udengaard, R. Malik, Y. Huang and D. BateSummaryThe quest for reducing risk for carbohydrate explorations is an ongoing task the latest advances in Full wave from inversion has increased the need for longer offsets and preservation of low frequencies. We present a large scale ultra-long offset full azimuth sparse node survey from the Gulf of Mexico. We show that we can achieve a dual-purpose objective, both model building and illimitation. offset from 0–20 km for imaging and offset from 0–40 km for FWI. To compliment a dual waz 8 km offset underlaying survey.
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Improving quality control and data understanding of a large OBN survey through unsupervised machine learning
Authors F. Damianus, M. Al Sarmi, A. Roubaud, G. Cambois and M. MahgoubSummaryGiven the nature of operational complexity, raw OBN field data received from the acquisition crew often comes with quality problems such as noisy nodes, abnormal instrument response, and positioning errors. Even in relatively small amounts, these problems can become an issue in processing work if they are not detected and corrected at an early stage. In standard target-oriented OBN surveys, manual inspection of amplitude maps measured from the field records is often used to identify anomalously bad nodes for rejection, but this approach becomes impractical on large, regional-scale OBN surveys, such as the multi-year OBN acquisition campaign at offshore Abu Dhabi with hundreds of thousands of receiver gathers. Machine learning approaches can provide practical alternative quality control (QC) tools for identifying problems in field data. By combining the multivariate Gaussian distribution method, principal component analysis (PCA) and K-means clustering, we were able to identify bad nodes using receiver amplitude maps generated from field records. We also demonstrate the application of such tools for removing bad first-break (FB) picks to improve the first-break tomography result.
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Strategies to increase cost efficiency of node surveys
More LessSummaryNode based surveys have attractive features such ability acquire long offset data and low S/N recordings. The relative higher cost of a node survey compared to a streamer survey can be significantly reduced by using a relatively sparse node coverage. A sparse lends itself very well to velocity surveys where the new data are used generate a highly accurate velocity model through FWI. The sparseness results in a lower fold, which can be compensated by using a properly calibrated source.
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