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Marine Acquisition Workshop 2018
- Conference date: 22 Aug 2018 - 24 Aug 2018
- Location: Oslo, Norway
- ISBN: 978-94-6282-259-7
- Published: 22 August 2018
1 - 20 of 25 results
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Acquisition And Application Of Aero-Magnetometry In Norway And On The Norwegian Shelf
Magnetometry is one of the oldest geophysical methods and it is probably the first one which was applied to exploration. Significant technologically achievements in instrumentation and positioning made the application a fast and effective method to map geological and tectonic settings over large areas. Strong interaction of the Earth's magnetic field in the Arctic with external fields, mostly deriving from the sun, can disturb the magnetic signal from the crust and makes the acquisition at such high latitude extremely challenging. The Geological survey of Norway has more than 60 years of experience with airborne magnetic acquisition and together with TGS has acquired aeromagnetic data over Norway and almost the entire Norwegian shelf. The data contribute to characterize the underlying basement lithology on the Norwegian shelf, understanding better the tectonic processes of the sedimentary basins and the crustal heat flow. In the oceanic domain, seafloor spreading anomalies are predominant to identify the limit of the oceanic crust and allow plate reconstruction to better understand the opening of the North Atlantic.
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Marine 4D Gravity And Seafloor Subsidence Monitoring: Recent Development And Prospects
Authors M. Lien, L.T. Hille, H. Ruiz and M. VathshelleGravity changes measured at the seafloor are sensitive to fluid redistribution in hydrocarbon reservoirs. As an example, vertical movements of water-gas contacts smaller than a meter can be detected under some circumstances. Seafloor subsidence monitoring uses water pressure measurements at the seafloor as a starting point. Once the required tide corrections are applied, the method reaches accuracies as low as 2 mm, depending on the field conditions. Subsidence is a required correction for the interpretation of gravity results, and it is by itself a valuable monitoring tool, sensitive to important reservoir and overburden properties. It is directly related to pressure depletion and lateral compartmentalization, and in some cases, it is a key factor for the safety of the installations. In this abstract, we review the principles of the 4D gravity and subsidence monitoring technology. We then discuss some field cases from the Norwegian Continental Shelf that illustrate the value that this type of data provides for reservoir management. Finally, we discuss what are the drivers of the cost of the technology and what steps are taken by the industry to reduce cost, and hence to make it feasible in more fields.
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High Resolution Imaging And Mapping Of The Seabed Using Synthetic Aperture Sonar
By R.E. HansenDetailed information of the seabed at large depths is increasingly important in many fields such as marine biology, marine geology, offshore constructions and installations, and military applications. With the advent of unmanned autonomous underwater vehicles (AUV) capable of operating at large depths, there is a need for high performance imaging sensors. Synthetic aperture sonar (SAS) is becoming a tool of choice for very high resolution imaging and mapping of the seabed. The Norwegian Defence Research Establishment (FFI) has an ongoing long-term collaboration in research and development of the HUGIN AUV and the HISAS interferometric SAS with Norwegian company Kongsberg Maritime. The specified image resolution is better than 5 x 5 cm and the mapping rate is 2 km2/hour. In this paper, we give an overview of the SAS technology including the challenges involved. We show example images to illustrate the achievable performance.
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Advancements In 3D CSEM Hardware And Processing For Quantitative Earth Parameter Estimation
Authors M.A. Drage, J.P. Morten and P.T. GabrielsenThis presentation will review the latest developments for 3D CSEM acquisition and inversion. The recently introduced high-power, deep-towed EM source increases the dipole moment with up to 10 times compared to the conventional source. It can output 10 kA current and realizes enhanced accuracy and current control to improve detection of deep reservoir targets. The new source enables transmission of broad-band waveforms to resolve the subsurface resistivity with increased resolution including imaging of small reservoirs. This will be demonstrated with examples from large field datasets processed using 3D Gauss-Newton inversion. The inversion achieves exceptionally good data fit which implies that detailed information have been extracted from the measurements, and quantitatively represented in the 3D resistivity subsurface model.
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Prediction Of Sonic Log Data Using Machine Learning Regression Methods
Authors S. Pandey and R. SaraiyaThis study aims to predict sonic log data using density log, gamma log and porosity. For the purpose Random Forest Regression methods, Support Vector Regression (SVR) algorithm with kernels such as linear, gaussian and polynomial and K Nearest Neighbors algorithm has been applied. SVR linear kernel turns out to be the best algorithm for prediction of sonic data using gamma log, density log and porosity. The training time for SVR linear method is much less than neural networks. In neural networks whereby number nodes in input layer and hidden layers, number of hidden layers required , the functional form in the node responsible for mapping from one node to other node has to be chosen while in SVR linear method only box constraint and margin has to be chosen. One does not have to bother with the order of the model as in case of auto regressive models. Presence of other log data such as resistivity etc could have helped in improving the predictability of sonic log using SVR linear method.
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How Repeatable 4D Csem Surveys Need To Be?
Authors D.V. Shantsev, A. Babakhani, L.J. Gelius and E.A. NerlandRepeatability of acquisition parameters for the base and monitor surveys is an important consideration for time-lapse studies of hydrocarbon reservoirs using controlled-source electromagnetics (CSEM). Variations in parameters such as source and receivers positions, conductivity and depth of seawater, etc lead to differences in the recorded EM fields that are often comparable to or exceed EM response due to production-induced changes in the reservoir resistivity. In that case, 4D CSEM is not feasible as long as 4D effects are analysed in the data domain. In the present study, we demonstrate the feasibility of 4D CSEM even for large differences in the acquisition parameters if the analysis is performed in the model domain. Using the “canonical” model considered by Orange et al. [Geophysics, 2009], we show that the repeatability requirements for water conductivity and receiver positions are relaxed approximately by an order of magnitude if the conventional sensitivity analysis is replaced by examination of inverted resistivity volumes.
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Considerations About Multi-Sensor Solid Streamer Design
Authors G. Mellier and N. TellierMulti-component recording of seismic data with two components and four components has been in use in shallow water environments for nearly three decades. The use of motion sensors for streamer marine acquisition has a much shorter history. The earliest system introduced by PGS in 2007 used a combination of hydrophones and gimbaled vertical geophones, but in recent years two additional systems have been deployed that also record the horizontal motion of the streamers in the crossline direction. The motivation for the introduction of the vertical sensor was to improve the spectral content of the data, while for the horizontal sensor it is to enable sensor rotation when gimbals are not being utilized. This paper describes the design considerations and characteristics of one of these systems, and compares seismic data acquired on a recent production survey and produced with either hydrophone-only or joint deghosting.
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The Autonomous Midwater Stationary Cable (Freecable): A Totally Flexible Acquisition Technology
Authors E. Bathellier and L. HaumontéHaumonté et al. (2016a) recently introduced a new marine seismic acquisition method named midwater stationary cable (MSC). This technique uses recording autonomous vessels (RAV) to command and control independent seismic four-component cables. It is demonstrated in this paper that the high number of degrees of freedom of the FreeCable system enables to record full-azimuth, full-offset, low-noise and full-band data which materializes in geophysical advantages and productivity gains.
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Using Finite-Difference Modelling To Understand And Optimise Time-Lapse Acquisition And Processing Strategies
Authors R. Whitebread, M. Branston, M. Paydayesh and P. KristiensenThroughout the recent challenges in the marine seismic industry, both time-lapse and ocean-bottom acquisition programs have remained robust. As the industry requirement for these techniques increases, it is important that we fully understand if the survey we acquire will overcome the specific challenges for the given field and provide the data and insight required by the end users. Recent advances in model building, forward-modeling algorithms, and compute architecture, coupled with the depth of knowledge and information available on the areas being considered for time-lapse acquisition programs, allow us to run efficient and accurate forward simulations to answer these design questions and benchmark our time-lapse processing workflows. Here, we present results from a forward-looking finite-difference modelling exercise that uses a synthetic visco-elastic model. As we learn what changes occur within the reservoir and overburden, we can assess the impact of likely acquisition variables on our ability to resolve the true 4D signal. Furthermore, we can look at implications of acquisition geometry variations on seismic processing steps in isolation, which is simply not possible with real data.
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Preparing For Large Scale Ocean Bottom Seismic Surveys In Norway
Authors B.A. King, N. Moyle, E. Sadikhov, G.W. Simensen and T. NilsenOcean bottom seismic (OBS) surveys have been acquired on the Norwegian continental shelf since the 1990s, almost exclusively for the aim of field development or reservoir monitoring. Due to high acquisition cost, OBS surveys were traditionally small compared to towed streamer surveys, although they have yielded superior reservoir images especially beneath overburden anomalies, beneath gas clouds or in the presence of complex faulting. As OBS becomes cheaper, the prospect of acquiring high quality OBS surveys for exploration on a large scale is a realistic goal. Further efficiencies are sought through designing sparse receiver arrays, counter balanced by dense source carpets. This study examines the relationship between receiver sampling and data quality, in a typical North Sea setting. By decimating dense recorded data and performing modelling studies, we demonstrate that receiver sampling can be greatly reduced without compromising image quality at expected reservoir depths. We examine the inevitable compromise to image quality in the overburden and discuss possible mitigating actions.
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Advances In OBN Technology: New Designs For Reservoir Monitoring And Large Scale Surveys
Authors J. Smythe, D. Hays, P. Docherty and C. UdengaardTwo new designs are introduced that demonstrate the flexibility and scalability of node technology from reservoir monitoring to large-scale OBN surveys. ZLoF is a nodal alternative for reservoir monitoring. The system features a 5 year deployment life and an optical communication system for high-speed data download. In deep water, ZLoF will provide frequently repeated, high quality 4D seismic data at a lower cost than cable based permanent reservoir monitoring systems. ZXPLR is a new node capable of dual mode deployment with either a passive rope, in shallow water, or by ROV, in deep water. In the first deepwater deployment, overall survey duration was reduced by 50% from similar deployments using older systems. The entire deployment /retrieval system has been redesigned and made safer and more efficient by powered and piloted thrusters on the all subsea systems.
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Cost-Efficient Full-Azimuth Exploration With Next Generation OBN Technology
By R. BohnThis paper is a revised and updated version of an abstract titled "Seabed seismic: from reservoir management to full-azimuth exploration", first presented at the SEG OBS/OBN work shop in Beijing, China, in September 2017. The paper considers the high cost and operational inefficiencies traditionally associated with ocean bottom seismic (OBS) acquisition that have deterred wider industry adoption of this compelling technology. A case study is presented on how the main challenges are being overcome in the development of a next generation ocean bottom node (OBN) system focused on lower cost and more efficient, faster operation with scope for exploration projects as well as reservoir characterization and monitoring.
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Developing A Fully Autonomous Marine Seismic Acquisition System For Low-Cost On-Demand Reservoir Monitoring
Authors J.L. Lopez, D.A. Chalenski and S. GrandiWith more demand for seismic monitoring, especially in areas with small, rapid, and complex changes, seismic acquisition needs to be cheaper and available on demand. This is currently not the case anywhere in the world, mainly because of the need to contract, permit, and mobilize scarce, high-specification vessels over long distances. Using a semi-permanent Ocean Bottom Node (OBN) system removes the complexity of mobilizing node handling vessels for each monitor survey. Harvesting the data from the nodes in-situ using a field-resident AUV removes all remaining activity on the surface regarding node operations, thus providing an On Demand OBN system. Coupling this autonomous seismic recording system with an Unmanned Surface Vessel (USV) for autonomous source operations (RAM4D), would enable the whole operation to take place by remote control. If the USV is multi-purposed and stationed in-country, then the seismic operations could take place on short notice. Shell is developing and field testing the elements of such a fully autonomous, completely unmanned marine seismic acquisition system to provide on-demand reservoir monitoring data at much lower cost and environmental exposure.
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Real Time Seismic Monitoring Of Drilling Operations
Authors J.E. Lindgard, T. Thiem, E.V. Bergfjord and R.S. AgersborgWe present a new monitoring concept for more effective and safer drilling operations. The underlaying concept is to monitor the drilling operation with a network of seismic sensors on the seafloor listening to acoustic signals emitted from the subsurface. The acoustic subsurface sources used for the analysis include both microseismic sources and acoustic energy emitted from the drill bit. The system developed allows for real-time processing and visualization of the results passing on demand information for decision support during operation. The analysis of microseismicity around the well provides location of fracturing caused by the drilling operation, allowing for mitigation actions of unwanted well integrity events. Acoustic positioning of the drill bit eliminates the time-depth uncertainty introduced when drilling for subsurface targets since both the drill target and the drill bit position is acquired in the acoustic domain from seismic data. In a more elaborate application, the signal from the drill bit is used as a source to image formation boundaries ahead of the drill bit. Furthermore this data is used to identify interval velocity and pore pressure in the formations.
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A Novel Marine Seismic Method Making Use Of Continuous Wavefields
More LessA method that extracts the response of the earth from continuous wavefields on both the source and the receiver side is presented. Seismic data recorded continuously are treated over the entire time length at once. The source(s) can emit signals continuously while moving. The entire source wavefield contributing to each stationary receiver position is derived and used to extract common receiver gathers with the response of the earth. The trace spacing in the resulting gathers can be chosen in processing and corresponding anti-aliasing protection is applied. Real data examples are presented including a comparison between the method based on continuous source and receiver wavefields and a seismic data set acquired and processed based on discrete shot records.
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A Novel Source-Over-Cable Solution To Address The Barents Sea Imaging Challenges
Authors J.E. Lie, V. Danielsen, P.E. Dhelie, R. Sablon, R. Siliqi, C. Grubb, V. Vinje, C.I. Nilsen and R. SoubarasThe Barents Sea is an important petroleum province for Norway. Several oil and gas fields have been found and some of them are already in production, such as Snøhvit, Goliat and soon Johan Castberg. However, seismic imaging in the area is problematic. The large Tertiary uplift and erosion of the area has brought rocks with high seismic velocities up shallow and the seabed is often irregular due to iceberg plough marks. Lundin set themselves the challenge of fundamentally improving the seismic imaging across the Barents sea. This resulted in a new way of acquiring seismic data, which was developed through close technical cooperation with CGG. The solution involves two vessels, one streamer vessel and one source vessel towing its sources with a wide crossline separation on top of the seismic spread. A series of modelling, field tests, risk assessments led to the decision of acquiring a full-scale source-over-cables acquisition in the Barents Sea during the summer of 2017. This paper describes the geological and geophysical arguments that led to this new acquisition geometry. It also presents the large scale 2017 seismic acquisition as well as the processing and imaging results from this unique slit-spread marine geometry.
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Reduced Volume And Hexa-Source Marine Acquisition In The Barents Sea
Authors T. Elboth, V. Vinje, C. Walters, P.-E. Dhelie and V. DanielsenIn this paper we present results from a reduced volume and a hexa-source test recently conducted in the Barents Sea offshore Norway. In this relatively shallow water environment with 200-300m water depth, we show that good quality seismic imaging can be obtained with significantly smaller air-gun source volumes than what the marine seismic industry have traditionally deployed. Furthermore, we present data results from, to the best of our knowledge, an industry first wide source tow hexa-source acquisition, with very high resolution and quality down to the reservoir level of 1-2sec seismic two-way travel time.
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Source Isolation: A Seismic Shift For Seabed Seismic Productivity
Authors J.O.A. Robertsson, F. Andersson, D.J. van Manen, K. Eggenberger, R. Walker, F. van den Broek, E. Frømyr and I. GimseSeabed seismic data have proven critical for addressing long-standing challenges in seismic imaging both for exploration and especially optimizing reservoir development and management, including broadband data acquisition, full azimuth acquisition, gas clouds or removal of multiples to name a few. Historically, OBS acquisition has been expensive and an increased focus on receiver efficiency and source efficiency is essential to bring the cost down. The Marine Autonomous Seismic System (MASS) is a miniaturized long-battery life 4-component node designed for efficient OBS acquisition (Steen-Hansen, 2017). The compact size allows for handling large numbers of receivers during operations in an automated manner. With such significant advances on the receiver side, a step change is needed for source side technology where little has happened since the advent of flip/flop acquisition in the early 1980’s.
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More And Smaller Sources In Deep Water Exploration
Authors J. Langhammer, S. Baldock, H. Bondeson and B. KjølhamarIn this paper we present experiences of using triple source configurations in connection with deep water marine streamer exploration campaigns. Going from dual- to triple source configuration will increase the sampling in between the streamers, or can allow for a wider streamer spread given the same crossline bin-size. Careful planning of the streamer spread dimensions, together with an increased number of sources, will provide better spatial sampling and increased efficiency. The effect of going from three sub-array sources to two sub-arrays sources will inevitably lead to reduction in the sound pressure level from each fired source. However, despite the reduction in sound pressure levels, sufficient acoustic energy is still available for maintaining a good signal-to-noise ratio. It has been shown that even in exploration areas where water depth is more than 1000 m, there is still sufficient sound pressure level from the lower volume seismic sources to also image deeper structures. The application of triple sources is not only good for increased resolution and cost saving, but also in the context of complying to more strict environmental regulations.
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Exploiting Phase Control Of A Marine Seismic Vibrator For High-Multiplicity Simultaneous Source Acquisition
Authors D.F. Halliday, R.M. Laws, J-F Hopperstad and M. SupawalaA high-fidelity marine seismic vibrator would allow control of the phase of the seismic source wavefield. Phase control can be used to encode high-multiplicity simultaneous-source data. By changing the phase of the source wavefield from shot-to-shot following a prescribed sequence of phase delays, energy from selected sources can be coherently shifted into different parts of the frequency-wavenumber spectrum in the common-receiver domain. Results of this approach are demonstrated using realistic synthetic examples. A comparison with the more conventional time-dithered air-gun approach indicates that the phase sequencing approach gives an improved result, with a lower separation error. The phase sequencing approach cannot be used as effectively with air guns because they only allow changes to the overall time delay of the source.
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