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3rd Applied Shallow Marine Geophysics Conference
- Conference date: September 9-12, 2018
- Location: Porto, Portugal
- Published: 09 September 2018
1 - 20 of 29 results
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The Use of VHR 2D and 3D Sub-Surface Data for Shallow Boulder Detection and Detailed Stratigraphical Mapping for Renewable Energy Developments
By M. KingstonSummaryCurrently there are not many options on the market for multi-channel Ultra High Resolution (UHRS). As a result of this Gardline, in collaboration with Applied Acoustics, have been working on a new streamer system and bespoke source to go with it. The newly developed recording system and streamer is called μSeis, and consist of 1m group interval mini streamers.
When designing and building the equipment, there were a series of objectives. Firstly, the idea was to develop a tool to provide cost effective ultra-high-resolution sub seabed seismic data to detect high reflectivity targets (for example boulders). Secondly the system needed to have a penetration capability of up to 75m. Thirdly a depth of burial measurement accuracy of less than 0.3m was required, and lastly the system should be capable of a 16m swath with a resolution capable of the detection of objects <1m in size.
The applications of the system include geohazard boulder detection in shallow soils and the development of geomodels in Offshore Windfarms and Oil and Gas developments.
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Cognitive Techniques in Seismic Interpretation - See and Understand More of Your Data
Authors P. Szafian and G. PatonSummarySeismic data offer an abstract, incomplete and ambiguous representation of the subsurface. The interpreters’ task is to use these data and identify and classify objects they have never seen before. During interpretation they rely on context and association: seismic data are analysed as part of a larger scene and certain fragments of information are associated to geological features that are not necessarily obvious in the data set. Experience and knowledge of the interpreters are of paramount importance, the less complete and more abstract the representation, the greater level of expertise is required to extract information from the data.
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Seismic Attenuation - Friend or Foe
More LessSummarySeismic attenuation is an important parameter to understand and parameterise, with implications for survey design, processing, interpretation, and inversion. Here we present a brief summary of the physical theory underpinning our understanding of attenuation and illustrate how this can be used to compensate for the loss of energy within a data processing workflow, preserving vertical resolution down-trace. Furthermore, we discuss the potential uses of attenuation as a parameter for characterising the nature of the subsurface, suggesting that attenuation should be perceived in a more positive light and seen as another parameter (alongside amplitude, phase, and move-out) that provides valuable quantitative information.
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High-Resolution Quantitative Ground-Model for Shallow Subsurface
Authors G. Sauvin, M. Vanneste and C. MadshusSummaryIntegrated ground models are a requirement for proper site characterization, for offshore renewables, coastal activities and O&G projects.
Here we propose a workflow to build quantitative ground model based on rock/soil physical model developed in-house. We then apply it to a set of data from the Borssele wind farm site.
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Pipeline and Cable Detection Using Automated Contact Recognition in Seismic Data
By J. KweeSummaryWith the presence of more and more pipelines and cables in the coastal waters, the need to determine the exact location increases. This extended abstract will focus on sub-bottom detections of cables and pipelines using single channel shallow seismic data and describes the automated contact detection of SILAS. Vital information with regards to cables is the depth of burial of cables and pipelines. A changing bathymetry can create free span of cables, which could lead to potential dangers of an interrupted power or communication grid. If the location and depth is known, risks can be mitigated before mayor problems arise. Methods using an active signal on pipeline or the cable may detect this properly, but result in a shutdown of the cable for the time of monitoring. A passive method to detect these cables and pipelines is sub bottom profiling and will be discussed in this extended abstract.
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Combined Electric Resistivity Tomography and Seismic Refraction Tomography in Brackish Water in Saltsjön in Stockholm
More LessSummaryElectrical resistivity tomography (ERT) combined with seismic refraction tomography (SRT) were performed in brackish water in Saltsjön in Stockholm. Results from a test survey with measurements along two lines are presented, whereas a larger survey is in progress at the moment of writing. Geological interpretation of the obtained models fits well with the documentation from drilling, and show that the method works well in practice. As for geophysical surveys on land, the advantage is that you get continuous models that can be linked to variation in soil depth, structures in the rock and hydrogeological conditions. ERT is also a possibility where it is inappropriate to blast or drill because of occurrence of cables, pipelines or archaeological remains on the seabed. The electrical and seismic models from the combined survey complement each other and provide a more reliable overall picture of the variations in sediment depth and rock conditions.
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The Development of Time Domain Ocean Bottom EM System Capable of Measuring Magnetic, IP and SP Anomalies
Authors K. Nakayama and A. SaitoSummaryAs a practical exploration method for seafloor hydrothermal mineral deposits, we developed a time-domain EM system towed with a ROV. We included a magneto- impedance (MI) seafloor magnetometer with high sensitivity and wide-band MI elements, and a three-component fluxgate seafloor magnetometer functioned as the receiving magnetic sensors. Furthermore, we used three pairs of electrodes, measuring three components of the electrical potential differences to measure SP (spontaneous electrical potential), and a coincident-type receiver loop for resistivity and IP (induced polarization) measurement. Around known deposits in the Okinawa area, conductive anomalies caused by hydrothermal mineral deposits were clearly observed, and we showed that the existence of these hydrothermal deposits below the seafloor can be measured by this method. The current investigated depth is 25–35 m from the seafloor. SP anomalies measured after the electromagnetic induction phenomenon was completed at each measurement point were present at the conductive anomaly captured by this electromagnetic method,showing downward current flow on the mineral body.
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Calculating Time-Domain Controlled Source Electromagnetic Signals with MARE2DEM
More LessSummaryThe time-domain controlled source electromagnetic (TD-CSEM) method is commonly used to map shallow regions of the seafloor from several metres up to a couple hundred metres penetration depth. The method is effective in detecting shallow conductivity anomalies within the seafloor. Compared to the commonly applied frequency-domain controlled source electromagnetic method, the time-domain application is particularly effective in shallow marine environments, where the signal is less susceptible to the masking issue of the well-known airwave effect. However, the current interpretation of TD-CSEM data is mainly based on one-dimensional inversion, which creates problems in accurately mapping the true bathymetry. Here we present results of a 2D goal-orientated, adaptive finite-element modelling based on the MARE2DEM software that is freely available to academia for frequency-domain applications. A comparative modelling study using semi-analytical solutions for a simple 1D conductivity model shows that the time-domain developments can accurately calculate the main components of a horizontal dipole source in both the inline and broadside components. Merely, the vertical electric field is inaccurate at late times of the step-off current excitation and may need a more accurate discretisation approach.
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Integration and Validation of Land, Shipborne and Satellite Gravity Data for Studying a Sector of the Continental Margin of Asturias (N-Spain)
More LessSummarythe Asturian margin has been investigated in terms of the gravity signatures derived from all gravity data available. As the area of interest comprises a land/sea transition that has underwent successive tectonic regimes of rifting, passive margin, and compression from Mesozoic to Tertiary times. Then the integration of all gravity data available could help to elucidate the extension of the tectonic structures beyond the area covered by seawaters. Three databases have been used in this study: land gravity, shipborne gravity and satellite altimetry gravity data. From the structural point of view, the residual gravity anomaly map reflects the large tectonic accidents in the basin that coincide, at a general level, with accidents in direction NW-parallel to the fault of Ventaniella and their conjugates of direction SW-NE parallel to the faults of Caldones, Villaviciosa and Lastres.
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Evaluation of GPR Data for the Determination of Peat Properties and Bathymetry in Lake Danamandira, Istanbul, Turkey
SummaryThis project covers the investigation of the formation process of two peatlands in the Marmara Region in terms of humic substances and to identify the palaeoclimatic process through the pollen analysis and mineral magnetic studies. Ground penetrating radar survey (GPR) is applied on one of the lake, called Danamandira and characteristics of inner parts of the lake was determined and bathymetry map was created during the first phase.
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Post-Stack AVO Techniques for Shallow Gas Detection in 3DHR Data
By D. VaughanSummaryDetection and characterisation of shallow gas in the marine environment is a principle reason for carrying out geohazard site surveys prior to commencing rig installation and drilling operations (OGP, 2011). In order to achieve this, 2D or 3D high-resolution multichannel seismic data, or a combination thereof, is acquired throughout the area of interest and subsequently interpreted using a combination of manual and automatic techniques.
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The Challenges of Acquiring 2D High Resolution Seismic Data in a Shallow Marine Environment
By S. GriffithsSummaryAcquiring 2D high resolution multichannel seismic data in shallow marine environments presents challenges that do not occur within the deeper marine environments. Changing the source and streamer array configuration so that the near streamer groups are arranged in a cross-line configuration helps the recording of the highest possible frequencies. This is in conjunction with reducing the direct offset to a practical distance as possible. Overall these techniques will aim to improve the resolution in the top section of the seismic record.
Other implications, such as removing undesirable bubble pulse energy recorded from airgun array and the careful creation of a suitable mute prior to stacking the seismic data must also be considered to visualise the data as best as possible for quality control purposes in the offshore environment.
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The Comparison between Two Methods for Chirp Seismic Data Processing
More LessSummaryHigh-resolution Chirp (2–8 kHz) seismic profiles are collected from the northern Marmara Sea in Turkey. The aim of the study is to enhance the chirp seismic data quality by using different processing methods. Using two different processing methods, we have obtained different results by having improved S/N ratio Chirp data.
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Modern Techniques of Near Surface High-Resolution Marine Seismic Data Processing
Authors S. Vakulenko and S. BuryakSummaryNear surface high resolution marine seismic data is widely used for geohazard seismic assessments, pipeline routs and platform site surveys, sub-bottom site characterization, as well as 4D reservoir monitoring.
Over the past few years, marine engineering seismic has experienced significant development in both acquisition and processing techniques. Complexity and variability of state-of-the-art shallow seismic data acquisition requires adequate processing approaches. Nowadays processing of marine shallow seismic data is a combination of graphs, used for oil and gas seismic exploration and processing techniques, developed inside the companies, adjusted to the data they acquire.
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Joint Inversion and Hyperbolic Median Filtering for Simultaneous Source Data Separation
Authors A. Tarasov, A. Shuvalov, V. Ignatev, A. Konkov, B. Kashtan and A. OshkinSummaryThe simultaneous source technique allows one to improve efficiency and quality of seismic acquisition by using several independent sources that overlap with small time delay. The main problem in working with simultaneous source is deblending. Different methods of separating simultaneous source data use features of a complex wave filed. Our approach offers an iterative scheme with inversion that allows using information about time delays between sources activation and hyperbolic median filtering, that is using kinematic properties of reflected waves. The operation of this algorithm is demonstrated for the simultaneous long offset technique. Synthetic data examples demonstrate capabilities of the proposed approach.
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A Seismic Beamforming Approach for the Detection Of Boulders in the Shallow Sub-Seafloor
More LessSummaryDetailed knowledge of the seafloor and the shallow sub-seafloor is required to plan and construct offshore infrastructure such as windfarms. A considerable effort is made for such pre-construction surveys in the form of geophysical measurements (mostly seismic/acoustic and magnetic), coring activity and geotechnical testing. Modern wind turbines are installed on foundations that penetrate ∼60 m into the seafloor, depending on the encountered geotechnical parameters of the sediments. A significant obstruction to such foundation work are boulders on the seafloor and within the sediments ( Holeyman et al., 2015 ).
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Optimisation of Source and Receiver Geometry for Ultra High Frequency Seismic Data
More LessSummaryUltra-High Frequency (UHF) seismic data, with vertical resolutions at decimetric scales, is more commonly being implemented in industry after being used in academia on a frequent basis. Adoption of multichannel arrays rather than single channel configurations leads to improved signal to noise ratios and subsurface imaging. This allows for a wider suite of advanced processing techniques to be applied requiring constraints on the way data is positioned and processed.
In conventional UHF processing the geometry allocation consists of a basic and crude setup, where databases containing lateral and layback offsets are populated assuming straight streamer configurations. In fact, streamer shapes vary from the idealised straight model during acquisition leading to issues understanding the streamer geometry in 3-Dimensions.
Casting the problem of geometry as an inversion allows us to overcome the deviations from a straight streamer model in data acquisition. Understanding the influence of geometry on travel-times for direct, primary and ghost arrivals enables the optimisation of a model using a Genetic Algorithm. The results of this model can then be applied to UHF data supergathers showing that the inverted geometry has significantly improved accuracy of reflection flattening using a best-case velocity model when compared against the conventional processing.
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3D Seismic Data Acquired in Shallow Waters in Denmark by Use of the P-Cable System
Authors E. Nørmark, K.J. Andresen, O.R. Clausen and J.B. JensenSummaryResult from two 3D seismic surveys acquired in inner Danish shallow water in May 2017 are presented. One survey was acquired south of the island of Anholt in cooperation with the Geological Survey of Denmark and Greenland (GEUS) and the other survey was acquired in Limfjorden (Visby Bredning).
Both survey areas are located in shallow waters (< 30 m) and acquisition was carried out from Aarhus University’s research vessel Aurora. The P-cable 3D seismic acquisition system has been applied in both surveys. This system was recently introduced at the Department of Geoscience, Aarhus University and is presently being adapted to our survey capabilities.
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High-Resolution 3D Site Characterization
SummaryWe present the results of a novel method for high-resolution 3D site characterization. The strategy is based on using 3D seismic data as the framework for integrating geochemical, geophysical and geotechnical data. The end-results are 3D volumes with various attributes relevant for improved site characterization and ultimately geohazard assessment (i.e. identification of shallow gas, boulders, faults and fractures, leakage, spatial variability, soil strength …). We further show that geochemical data integrated with current high-resolution 3D seismic data can be used to constrain fluid migration pathways to the seafloor. In addition, re-processing focusing on the higher frequencies of 3D seismic data increases the resolution, resulting in a data volume displaying more details on the geology and geomorphology of the sub-surface when compared to data processed for deeper imaging. Finally, we configured an optimized 3D seismic acquisition system, which is fine-tuned for imaging the top 150 m of overburden with a meter-scale lateral and vertical resolution. Such a high-resolution 3D seismic system would provide data volumes that allow well-constrained integration of various type of data.
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Industrial 2D and 3D Ultra High Resolution Seismic (UHRS) Marine Surveying
By H. DuarteSummaryIndustrial 2D and 3D Ultra High Resolution Seismic (UHRS) marine surveying involves the acquisition of increasingly larger volumes of seismic data (∼ 500 Gb /day) at very high shot rates of up to 5 Hz ( Monrigal et al, 2017 ). Near continuous acquisition at such high shot rates, i.e. millions of traces per hour, present serious Quality Control (QC) and Quality Assurance (QA) challenges. This cannot be overstated, specially given the traditionally weak signal to noise rations of UHRS data (when compared with high resolution or exploration seismics) and the necessity of reliable signal quality to adequately resolve source and receiver heave, critical to successful data processing ( Wardell et al, 2002 ; Duarte et al, 2017 ). Furthermore, the desired broadband imaging requires the ability to continuously monitor the cable slant and its effect on the recorded frequency spectrum ( Soubara et al, 2011 ; Sablon et al; 2012 , Reilly, 2016 ).
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