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Second EAGE Seabed Seismic Today Workshop
- Conference date: September 18 - 20, 2023
- Location: Milan, Italy
- Published: 18 September 2023
1 - 20 of 35 results
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Applications of Coherent Laser Interferometry over the Optical Fiber Network for Seismic Monitoring
By D. CalonicoSummaryThis paper discusses a field trial conducted over the Sleipner carbon capture and storage (CCS) field, which aimed to explore the capabilities of using Ocean Bottom Nodes (OBN) in CCS monitoring. To achieve this, OBN data was acquired in combination with short-offset streamer (XHR) data. The geophysical advantages of the 4 components acquisition allow to derive improved velocity and imaging using low frequencies and long-offset sparse geometries to measure refracted and diving waves at target depth. The potential of using advanced imaging techniques such as Full Waveform Inversion (FWI) is explored. Current and initial FWI results are shown in this paper.
In addition, an innovative node operation is also presented. A set of nodes was successfully deployed using a free-fall deployment and a proprietary auto-recovery system. This node handling technique eliminates the need for a ROV vessel, which is an important step toward a more cost-efficient OBN acquisition.
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Temperature Compensated Clock Correction for Autonomous Ocean Bottom Nodes
Authors T. Bunting, J. Jurok and J. WallaceSummaryThe Ocean Bottom Node (OBN) seismic method is unique in the seismic industry in that the recorder is not fed a highly accurate GPS timing measurement while measuring the earth reflections. Instead the method relies on an internal clock which will drift over the dive time of the node. Initially the standard for OBN’s was the Cip Scale Atomic Clock (CSAC) which uses a quantum feedback loop to discipline the clock during the dive. More recently contractors have adopted crystal oscillators for practical reasons. This paper will compare the benefits of the two clock types and propose a method to correct for the main deficiency of the crystal oscillator.
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Use of Hovering AUV’s to Deliver a Step Change in Ocean Bottom Node Deployment and Recovery
Authors T. Bunting, M. Hartland, N. Ragoonanan and J. WallaceSummaryIn this paper we describe a new method to deploy and recover ocean bottom nodes with the advantages of ROV deployment but at a lower cost and faster speed. The technology integrates a number of well-established marine technologies including hovering AUV’s. With a change in the efficiency of the node resource, survey design geophysicists will need to decide how to utilize this resource and maintain source and receiver balance.
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Third Generation Seabed Survey Design
Authors D.J. Monk, D. Hite, B. Hollings, D. Ridyard and F. ManciniSummaryIn this paper we first examine the operational benefits of Autonomous self-relocating receivers (ASSR) technology for traditional survey designs in two very different applications. The first example is a sparse OBN survey acquired for FWI typical of multiclient acquisition in the Gulf of Mexico. The second is a much smaller dense OBN project more typical of a North Sea 4D project. We then suggest a new survey design paradigm enabled by ASRR technology to deliver acquisition time (and cost) reductions in excess of 50%. Survey simulation software was used to estimate time to acquire for each scenario, and scenario efficiency was evaluated based on the minimum theoretical time to acquire (MTTA) measured in vessel-days. MTTA is a good proxy for cost, personnel risk and greenhouse gas emissions.
ASSRs offer the potential to reduce MTTA on conventional survey designs by 25–40%.
Survey designs that break the mould of linear deployment could further reduce MTTA.
With source as the limiting factor in MTTA, additional benefits could accrue from wider multi-source towing capability, increased compressor capacity as well as enhanced compressive sensing and deblending technology.
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Observations and Learnings from a Trio of Concurrent Deepwater ROV OBN Projects
Authors J. Southgate, A. Dingler and M. SolimanSummaryIn 2022, bp had three proprietary deepwater ROV deployed OBN projects being acquired concurrently in different areas, with two different contractors, using different technology to solve different challenges and achieve different goals. These three concurrent projects provided an opportunity for making comparisons and gaining insights to inform future OBN surveys from design and operational perspectives.
The three main areas for comparison covers 1) node availability and inventory including the increasing demand for larger deployed node spreads, 2) ROV design and operations including further improvements to enhance nodal seismic acquisition and 3) personnel including the size and depth of the personnel pool as well as application of innovative technologies to enable alternative solution.
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Spectral Gap-Based Regular or Irregular Seismic Survey Design with Random Time Dithers
Authors R. Kumar, M. Vassallo, A. Zarkhidze, F. Le Diagon, G. Poole, R. Bloor and L. Arechiga SalinasSummaryWe propose generating an optimal irregular survey design with time or space dithers using the spectral-gap-based rank-minimization technique. The work is first of its kind where a computationally efficient practical seismic survey with random time dithers can be designed using spectral gap based technique.
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A Reciprocal Rayleigh-Marchenko Method for Full-Wavefield Redatuming of Sparse Seabed Data
More LessSummaryThe seabed seismic industry is heading towards an acquisition paradigm shift where dense ocean-bottom systems are becoming less and less attractive in favour of sparse node geometries. It is therefore important to adapt technologies that previously relied on the availability of regular (and possibly dense) receiver carpets to this new sparse standard. In this work, we present a reciprocal version of the Rayleigh-Marchenko method that, whilst preserving all of the features of the original method, can handle irregular and sparse receiver geometries, provided availability of multi-component receivers and either dual-sensor sources or a pre-processing step of model-based source deghosting. A synthetic example is presented to validate the effectiveness of the proposed method and evaluate its robustness to sparse receiver geometries.
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OBS Receiver Geometry - An Arabian Gulf Pilot Study
Authors A. Mathieson and B. AlqarniSummaryAppropriate receiver sampling was determined using an ultra-high density pilot survey in the Arabian Gulf. The high density geometry permitted a range of acquisition scenarios to be evaluated using processing decimation tests. Receiver density was found to be critical in improving seismic data quality for reservoir characterization purposes. Future acquisition planning in this area will be supported through the decimation test findings.
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Benefits of FWI Imaging and 4D FWI in the Culzean Field
More LessSummaryDeriving an impedance image from a velocity model obtained by full waveform inversion is shown to provide a great uplift compared to conventional migration. By using the full wave-field and a least-square fitting process, FWI Imaging gives better continuity of complex structures and greatly improves the signal to noise ratio, revealing subtle impedance contrasts. This technology has been successfully applied on the Culzean OBN dataset, allowing a better understanding of the reservoir. Pushing the FWI maximum frequency to 40Hz enabled to image thin sediment layers and faults, easing the identification of possible reservoir compartments. In terms of monitoring, velocity variations (dv) related to the reservoir evolution, can be detected when running two parallel FWI on base and monitor seismic datasets and analysing the difference between the obtained velocity fields. This dv highlights the hardening and softening layers as well as the compartmentalization in the reservoir. Moreover, in the shallow surface, the resulting dv could also be of great interest to prevent possible hazards during production.
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Unmanned Mapping of Ultra-Shallow Water Environment in The Framework of CCS Project in Liverpool Bay
Authors S. Lamuraglia, T. Ciccarone, D. Calcagni, B. Ulivieri, S. Baudo and C. NiniSummaryBetween March and June 2022, Eni S.p.A and Eni UK Limited undertook the acquisition of a 500 km² bathy-morphological survey in the CS004 license in the framework of the HyNet Project, where Eni UK will develop and operate the onshore to offshore transportation and storage of CO2 in three depleted gas fields in the Liverpool Bay.
The main aim of the survey was the collection of seabed and sub-seabed data with sufficient penetration and resolution to set a baseline for monitoring activities and to de-risk subsequent seismic operations and engineering design in the area.
The articulated context of Liverpool Bay is mainly affected by ultra-shallow bathymetry, strong tidal excursions (up to 8 m) with their related currents, presence of surface infrastructure (O&G platforms and wind farms among the others) and heavy marine traffic.
This required a careful analysis in terms of acquisition feasibility, survey strategy and safety of operations. In particular, the paper focuses on the successful use of a fleet of Unmanned Surface Vehicles (USV) as a valuable approach for bathy-morphological data collection, highlighting the good-quality results against the local constraints and the repeatability of this acquisition method in other similar challenging environments.
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Source-Side Multi-Dimensional Deconvolution Using a Downgoing Annihilation Filter Approach
More LessSummaryWavefield deconvolution of seabed seismic data presents a powerful method for attenuating multiple arrivals and removing the source signature from its output reflectivity. However, although Up/Down wavefield deconvolution is widely found to be useful in practice, the accuracy of the method degrades with dipping near surface reflectivity. Furthermore, extensions to deconvolution of the downgoing wavefield to access the improved illumination of mirror migration suffer practical problems where removal of the water wave is challenging (e.g. in shallow water). An alternative approach is therefore described, in which the deconvolution proceeds by annihilation of the downgoing wavefield to produce an estimate of the isolated water wave. The resultant reflectivity includes all events below the surface source array, and is positioned at two way time. Implementation of this Annihilation Filter Deconvolution (AFD) inside a 3D Source-side Multi-Dimensional Deconvolution (S-MDD) framework allows the S-AFMDD method to work well with sparse receivers and dense shots. This avoids the problem of aliasing across widely-spaced receiver lines that is suffered by the more standard receiver-side MDD. Results from a sparse OBC dataset in the Caspian Sea show good quality, dense, reflectivity and multiple models produced by the S-AFMDD with strongly dipping near surface reflectivity.
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Sparse Node Acquisition Aided Velocity Modeling
Authors D. Vigh, X. Cheng and K. GlaccumSummarySparse node acquisition has become a standard approach to improve the earth model by the addition of ultra-long offsets. The new designs of node data collections coupled with simultaneous shooting can be deployed on a regional basis covering thousands of square kilometers in a cost-effective manner. In complex geological settings including irregular salt geometry, the salt interpretation has a direct impact on subsalt imaging, however salt interpretation can be quite time-intensive and challenging. Full-waveform inversion (FWI), as a data-driven optimization algorithm with full wavefield modeling, has become one of the essential tools for earth model building.
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Time-Lapse Full-Wavefield Migration for Sparse Ocean-Bottom Node Surveys
Authors M. Farshad, F. Papillon, G. Poole, A. Roodaki, A. Grandi and R. SalamiSummaryOcean bottom node (OBN) acquisition is recognized to offer excellent subsurface illumination as well as providing the possibility for accurate repeatability for time-lapse surveys. In order to keep acquisition effort down as much as possible, there is a push to acquire OBN data with sparser receiver geometries. Using an OBN acquisition from offshore West Africa, we compare 3D imaging from primary migration, multiple migration, and full-wavefield migration. We examine how the 3D subsurface images degrade with OBN node decimation and assess how the decimation affects the 4D difference for each of these imaging options. Our results highlight that full-wavefield migration may provide the flexibility to design a sparse survey with a limited pool of nodes without significantly degrading 3D and 4D image quality, even after reducing nodes by a factor of 16. This can lead to not only substantial savings in future acquisition costs but also 4D processing turnaround time, by eliminating de-ghosting and de-multiple processing steps. Although crosstalk continues to be a challenge when imaging using multiples, in this deep-water case the crosstalk noise did not interfere with the 4D signal.
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A Purpose Built Ocean Bottom Seismic Node for Sparse Receiver Surveys
Authors T. Bunting, J. Jurok, J. Wallace and N. RagoonananSummaryIt is generally accepted, by the industry, that seabed receivers deliver superior seismic reflection measurements and that ROV deployed seabed receivers are the optimum methodology to ensure position repeatability and seafloor coupling consistency.
Recently, the industry has benefitted from the geometry flexibility of the seafloor node method to deliver ultra-long offset / full azimuth measurements, as an input to a velocity inversion. This velocity inversion solution has looser requirements in terms of receiver sampling, positioning to pre-plot and measurement type; and is consequently open to different, and more efficient, deployment and recovery solutions.
In this paper we review the design and some early testing of a prototype seafloor node, currently referred to as “Manta FreeDive”, that was designed primarily for collection of diving waves for velocity modelling. The driver for this effort is to understand the optimum combination of deployment method, coupling solution and sensor package for a node designed for sparse node acquisition.
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Improving the 4D Signal Inside the SOA at Eldfisk Using RTM Pseudo-Offset Gathers
Authors L. Bencherif-Soerensen, Z. Li, K. McCluskey and A. RatcliffeSummarySeismically obscured areas are observed in the P-wave imaging of ocean bottom node data acquired over the Eldfisk area of the Norwegian North Sea. These are mainly caused by gas chimneys that overlie the anticlinal structures of the reservoir. Due to its ability to better handle complex velocity models, reverse time migration (RTM) produces better structural imaging of these obscured areas than Kirchhoff pre-stack depth migration. Further, RTM can be modified to output ‘pseudo-offset-gathers’ that offer a post-imaging domain for subsequent processing before final stacking. This work presents a time-lapse imaging case study using a recent, state-of-the-art, velocity model build, involving complex velocity, anisotropy and attenuation updates, and applies the ‘pseudo-offset-gather-based’ RTM concept to two vintages of Eldfisk data. The results show an improved 3D image and 4D response from the final stack of the RTM ‘pseudo-offset-gather-based’ data, both in structural aspects and signal-to-noise, compared to an equivalent Kirchhoff or ‘stack-based’ RTM product.
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Multi-Parameter FWI Imaging of an OBN Dataset in the Gulf of Mexico
Authors T. Rayment, K. Dancer, T. Ooi, J. Penwarden and G. HampsonSummaryMulti-parameter FWI (MP-FWI) imaging is a novel approach to seismic processing and imaging that, through the use of the full-wavefield, can deliver superior imaging in complex environments compared to conventional processing and imaging workflows. Here, it is applied to a deep-water OBN data set in the Gulf of Mexico where complex salt bodies impede the imaging of sub-salt targets. Comparisons to the conventional approaches of RTM, image-domain least-squares RTM and data-domain least-squares RTM show that MP-FWI imaging delivers improved sub-surface illumination and resolution. In addition, this simultaneous inversion also provides an updated, high-resolution velocity model. Comparisons are also made to an RTM of the raw field data to demonstrate how MP-FWI imaging is resolving issues that traditionally require extensive pre-processing steps. This demonstrates that all scattered parts of the wavefield are automatically used to form a single reflectivity volume that extends the imaging of OBN data well beyond the extent of the receiver carpet.
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Unlocking the Full Potential of Shallow Water OBN Data: An Integrated Acquisition, Processing & Interpretation Solution
SummaryNowadays, with the improvement in seismic data needed for oilfield development, the problems existing in the legacy data are gradually emerging, which brings sharply into focus the higher requirements for new seismic acquisition and corresponding challenges for data processing and imaging. As the number and complexity of facilities in a producing oilfield increases with its maturity of development this increases the difficulty of acquiring the improved quality seismic data required for optimised field development. The Ocean Bottom Node (OBN) solution is an effective means to solve these problems in highly congested producing field areas. In this paper we will describe the techniques for working in congested shallow water, explain the comprehensive OBN data quality control techniques needed for such high channel count acquisition, such as the node positioning accuracy QC and geophone tilt accuracy QC. Additionally, the paper will present distinctive marine processing technologies: the latest development in AI-based first-break picking, as well as a robust tomo-statics inversion package for seismic acquisition in shallow water areas. With the support of fault AI detection, the resulting fault distribution maps are clearer and more geologically reasonable. BGP’s proprietary technologies have been proven to be a successful solution for shallow water seismic acquisition.
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Leveraging Ocean Bottom Nodes (OBN) Technology for Carbon Capture and Storage Monitoring, Sleipner Field Case Study
Authors S. David, S. Baldock, E. Cho, S. Stockes and G. StockSummaryThis paper discusses a field trial conducted over the Sleipner carbon capture and storage (CCS) field, which aimed to explore the capabilities of using Ocean Bottom Nodes (OBN) in CCS monitoring. To achieve this, OBN data was acquired in combination with short-offset streamer (XHR) data. The geophysical advantages of the 4 components acquisition allow to derive improved velocity and imaging using low frequencies and long-offset sparse geometries to measure refracted and diving waves at target depth. The potential of using advanced imaging techniques such as Full Waveform Inversion (FWI) is explored. Current and initial FWI results are shown in this paper.
In addition, an innovative node operation is also presented. A set of nodes was successfully deployed using a free-fall deployment and a proprietary auto-recovery system. This node handling technique eliminates the need for a ROV vessel, which is an important step toward a more cost-efficient OBN acquisition.
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Improving Seismic Processing and Measuring Seabed Subsidence through Accurate Node Depths
Authors A. Libak, E. Bergfjord, H. Ruiz and J.E. LindgårdSummaryIn deepwater OBN, uncertainties in sensor positions lead to errors in the static solutions and deteriorate imaging capabilities. In particular, node depths are generally measured with an accuracy of a few meters. Corrections can be applied, but they are complicated by changes in tides and water velocities that couple with positioning errors.
The patented DepthWatch technology has been used for decades to monitor the vertical deformation of the seafloor over hydrocarbon-producing fields with an accuracy of a few millimeters. The technology has recently been incorporated into OBN surveys, providing an accuracy of a few centimeters in node depths in deep waters.
These new accurate node depths are used in seismic data processing to update the statics solutions. With accurate node depths, timing error corrections are fully decoupled from the bathymetry errors.
In 4D applications, the subtraction of accurate node depths at the baseline and repeat surveys provides a measurement of seabed subsidence in the area covered by the node grid. This information is useful for updating and calibrating geomechanical and reservoir models.
In 4D seismic workflows, precise node-based subsidence measurements ensure that the corrections related to water velocity are not coupled with those related to changes in node depths.
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An Integrated OBN Solution for a Complex Multi-Terrain Project, from Shallow Water to Transition Zone
SummaryThe complex terrain project currently being acquired in Persian Gulf is a large-scale seismic acquisition project in water depths from zero to 30m. Differing seabed conditions and bathymetries introduce enormous challenges for seismic survey design, large volume data handling, operational organization and HSEQ, not least because of the Covid-19 pandemic. This paper focuses on how to develop an integrated solution to address the challenges such a large project presents in terms of equipment, key acquisition techniques, and including HSE measurement and control.
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