New insights into North Sea tunnel valley infill and genesis from high-resolution 3D seismic data

2020 ◽  
Author(s):  
James Kirkham ◽  
Kelly Hogan ◽  
Robert Larter ◽  
Ed Self ◽  
Ken Games ◽  
...  
Keyword(s):  
High Resolution ◽  
North Sea ◽  
Seismic Data ◽  
3D Seismic ◽  
Seismic Reflection Data ◽  
North West ◽  
The North ◽  
Reflection Data ◽  
Order Of Magnitude ◽  
Subglacial Meltwater

<p>Tunnel valleys are large (kilometres wide, hundreds of metres deep) channels incised into bedrock and soft sediments by the action of pressurised subglacial meltwater. Discovered over a century ago, they are common across large swathes of North-West Europe and North America. However, many aspects of tunnel valley formation, and the processes by which they are infilled, remain poorly understood. Here, we use new high-resolution 3D seismic reflection data, collected by the geohazard assessment industry, to examine the infill lithology and architecture of buried tunnel valleys located in the central North Sea. The spatial resolution of our seismic data (3.125-6.25 m bin size) represents an order of magnitude improvement in the data resolution that has previously been used to study tunnel valleys in this region, allowing us to examine their infill in unprecedented detail. Inside the tunnel valleys, we identify a suite of buried subglacial landforms, some of which have rarely been reported inside tunnel valleys before. These landforms include a 14-km-long system of segmented eskers, crevasse-squeeze ridges, subsidiary meltwater channels and retreat moraines. Their presence suggests that, in some cases, tunnel valleys in the North Sea were reoccupied by ice following their initial formation, casting doubt on hypotheses which invoke catastrophic releases of water to explain tunnel valley creation.</p>

DEMETER HIGH RESOLUTION 3D SEISMIC SURVEY—REVITALISED DEVELOPMENT AND EXPLORATION ON THE NORTH WEST SHELF, AUSTRALIA

2006 ◽  
Vol 46 (1) ◽  
pp. 101 ◽  
Author(s):  
K.J. Bennett ◽  
M.R. Bussell
Keyword(s):  
High Resolution ◽  
Seismic Data ◽  
New Technologies ◽  
Seismic Survey ◽  
Future Application ◽  
3D Seismic ◽  
Gas Field ◽  
North West ◽  
The North ◽  
Exploration And Development

The newly acquired 3,590 km2 Demeter 3D high resolution seismic survey covers most of the North West Shelf Venture (NWSV) area; a prolific hydrocarbon province with ultimate recoverable reserves of greater than 30 Tcf gas and 1.5 billion bbls of oil and natural gas liquids. The exploration and development of this area has evolved in parallel with the advent of new technologies, maturing into the present phase of revitalised development and exploration based on the Demeter 3D.The NWSV is entering a period of growing gas market demand and infrastructure expansion, combined with a more diverse and mature supply portfolio of offshore fields. A sequence of satellite fields will require optimised development over the next 5–10 years, with a large number of wells to be drilled.The NWSV area is acknowledged to be a complex seismic environment that, until recently, was imaged by a patchwork of eight vintage (1981–98) 3D seismic surveys, each acquired with different parameters. With most of the clearly defined structural highs drilled, exploration success in recent years has been modest. This is due primarily to severe seismic multiple contamination masking the more subtle and deeper exploration prospects. The poor quality and low resolution of vintage seismic data has also impeded reservoir characterisation and sub-surface modelling. These sub-surface uncertainties, together with the large planned expenditure associated with forthcoming development, justified the need for the Demeter leading edge 3D seismic acquisition and processing techniques to underpin field development planning and reserves evaluations.The objective of the Demeter 3D survey was to re-image the NWSV area with a single acquisition and processing sequence to reduce multiple contamination and improve imaging of intra-reservoir architecture. Single source (133 nominal fold), shallow solid streamer acquisition combined with five stages of demultiple and detailed velocity analysis are considered key components of Demeter.The final Demeter volumes were delivered early 2005 and already some benefits of the higher resolution data have been realised, exemplified in the following:Successful drilling of development wells on the Wanaea, Lambert and Hermes oil fields and identification of further opportunities on Wanaea-Cossack and Lambert- Hermes;Dramatic improvements in seismic data quality observed at the giant Perseus gas field helping define seven development well locations;Considerably improved definition of fluvial channel architecture in the south of the Goodwyn gas field allowing for improved well placement and understanding of reservoir distribution;Identification of new exploration prospects and reevaluation of the existing prospect portfolio. Although the Demeter data set has given significant bandwidth needed for this revitalised phase of exploration and development, there remain areas that still suffer from poor seismic imaging, providing challenges for the future application of new technologies.

scholarly journals Geohazard detection using 3D seismic data to enhance offshore scientific drilling site selection

2020 ◽  
Vol 28 ◽  
pp. 1-27 ◽  
Author(s):  
David R. Cox ◽  
Paul C. Knutz ◽  
D. Calvin Campbell ◽  
John R. Hopper ◽  
Andrew M. W. Newton ◽  
...  
Keyword(s):  
Site Selection ◽  
Seismic Data ◽  
Seismic Survey ◽  
3D Seismic ◽  
Seismic Reflection Data ◽  
Scientific Drilling ◽  
The North ◽  
Reflection Data ◽  
3D Seismic Data ◽  
Geohazard Assessment

Abstract. A geohazard assessment workflow is presented that maximizes the use of 3D seismic reflection data to improve the safety and success of offshore scientific drilling. This workflow has been implemented for International Ocean Discovery Program (IODP) Proposal 909 that aims to core seven sites with targets between 300 and 1000 m below seabed across the north-western Greenland continental shelf. This glaciated margin is a frontier petroleum province containing potential drilling hazards that must be avoided during drilling. Modern seismic interpretation techniques are used to identify, map and spatially analyse seismic features that may represent subsurface drilling hazards, such as seabed structures, faults, fluids and challenging lithologies. These hazards are compared against the spatial distribution of stratigraphic targets to guide site selection and minimize risk. The 3D seismic geohazard assessment specifically advanced the proposal by providing a more detailed and spatially extensive understanding of hazard distribution that was used to confidently select eight new site locations, abandon four others and fine-tune sites originally selected using 2D seismic data. Had several of the more challenging areas targeted by this proposal only been covered by 2D seismic data, it is likely that they would have been abandoned, restricting access to stratigraphic targets. The results informed the targeted location of an ultra-high-resolution 2D seismic survey by minimizing acquisition in unnecessary areas, saving valuable resources. With future IODP missions targeting similarly challenging frontier environments where 3D seismic data are available, this workflow provides a template for geohazard assessments that will enhance the success of future scientific drilling.

Exploring mechanisms and rates of tunnel valley formation beneath deglaciating mid-latitude ice sheets using high-resolution 3D seismic data and numerical modelling

2021 ◽  
Author(s):  
James Kirkham ◽  
Kelly Hogan ◽  
Robert Larter ◽  
Ed Self ◽  
Ken Games ◽  
...  
Keyword(s):  
High Resolution ◽  
North Sea ◽  
Seismic Data ◽  
Ice Sheets ◽  
3D Seismic ◽  
Ice Dynamics ◽  
The North ◽  
The North Sea ◽  
State Water ◽  
3D Seismic Data

<p>The geological record of landforms produced beneath deglaciating ice sheets offers insights into otherwise inaccessible subglacial processes. Large subglacial channels formed by meltwater erosion of sediments (tunnel valleys) are widespread in formerly glaciated regions such as the North Sea. These features have the potential to inform basal melt rate parameterisations, realistic water routing and the interplay between basal hydrology and ice dynamics in numerical ice‑sheet models; however, the mechanisms and timescales over which tunnel valleys form remain poorly understood. Here, we present a series of modelling experiments, informed by geophysical observations from novel high-resolution 3D seismic data (6.25 m bin size, ~3.5 m vertical resolution), which test different hypotheses of tunnel valley formation and calculate the rates at which these features likely form beneath deglaciating ice sheets. Reconstructions of the former British-Irish and Fennoscandian ice sheets from a 3D thermomechanical ice‑sheet model (BRITICE CHRONO version 2) are used to calculate subglacial water routing and steady-state water discharges as these ice sheets retreated across the North Sea Basin during the last glaciation. Using these simulations, we calculate potential meltwater channel erosion rates and estimate how quickly tunnel  valleys are formed beneath deglaciating ice sheets in warmer than present-day climates. We find little evidence for widespread water ponding which may have led to channel formation through outburst floods. Instead, our results demonstrate that seasonal surface melt delivered to the bed could incise large channels of comparable dimensions to tunnel valleys over timescales of several hundred years as these ice sheets deglaciated.  </p>

Late Cretaceous – Cenozoic history of the transition zone between the East European Craton and the Paleozoic Platform, Polish sector of the Baltic Sea, revealed by new offshore regional seismic reflection data (BALTEC project)

2021 ◽  
Author(s):  
Piotr Krzywiec ◽  
Łukasz Słonka ◽  
Quang Nguyen ◽  
Michał Malinowski ◽  
Mateusz Kufrasa ◽  
...  
Keyword(s):  
High Resolution ◽  
Late Cretaceous ◽  
Seismic Data ◽  
Seismic Reflection ◽  
Upper Cretaceous ◽  
Seismic Reflection Data ◽  
East European ◽  
Reflection Data ◽  
Multichannel Seismic Reflection ◽  
Multichannel Seismic Reflection Data

<p>In 2016, approximately 850 km of high-resolution multichannel seismic reflection data of the BALTEC survey have been acquired offshore Poland within the transition zone between the East European Craton and the Paleozoic Platform. Data processing, focused on removal of multiples, strongly overprinting geological information at shallower intervals, included SRME, TAU-P domain deconvolution, high resolution parabolic Radon demultiple and SWDM (Shallow Water De-Multiple). Entire dataset was Kirchhoff pre-stack time migrated. Additionally, legacy shallow high-resolution multichannel seismic reflection data acquired in this zone in 1997 was also used. All this data provided new information on various aspects of the Phanerozoic evolution of this area, including Late Cretaceous to Cenozoic tectonics and sedimentation. This phase of geological evolution could be until now hardly resolved by analysis of industry seismic data as, due to limited shallow seismic imaging and very strong overprint of multiples, essentially no information could have been retrieved from this data for first 200-300 m. Western part of the BALTEC dataset is located above the offshore segment of the Mid-Polish Swell (MPS) – large anticlinorium formed due to inversion of the axial part of the Polish Basin. BALTEC seismic data proved that Late Cretaceous inversion of the Koszalin – Chojnice fault zone located along the NE border of the MPS was thick-skinned in nature and was associated with substantial syn-inversion sedimentation. Subtle thickness variations and progressive unconformities imaged by BALTEC seismic data within the Upper Cretaceous succession in vicinity of the Kamień-Adler and the Trzebiatów fault zones located within the MPS documented complex interplay of Late Cretaceous basin inversion, erosion and re-deposition. Precambrian basement of the Eastern, cratonic part of the study area is overlain by Cambro-Silurian sedimentary cover. It is dissected by a system of steep, mostly reverse faults rooted in most cases in the deep basement. This fault system has been regarded so far as having been formed mostly in Paleozoic times, due to the Caledonian orogeny. As a consequence, Upper Cretaceous succession, locally present in this area, has been vaguely defined as a post-tectonic cover, locally onlapping uplifted Paleozoic blocks. New seismic data, because of its reliable imaging of the shallowest substratum, confirmed that at least some of these deeply-rooted faults were active as a reverse faults in latest Cretaceous – earliest Paleogene. Consequently, it can be unequivocally proved that large offshore blocks of Silurian and older rocks presently located directly beneath the Cenozoic veneer must have been at least partly covered by the Upper Cretaceous succession; then, they were uplifted during the widespread inversion that affected most of Europe. Ensuing regional erosion might have at least partly provided sediments that formed Upper Cretaceous progradational wedges recently imaged within the onshore Baltic Basin by high-end PolandSPAN regional seismic data. New seismic data imaged also Paleogene and younger post-inversion cover. All these results prove that Late Cretaceous tectonics substantially affected large areas located much farther towards the East than previously assumed.</p><p>This study was funded by the Polish National Science Centre (NCN) grant no UMO-2017/27/B/ST10/02316.</p>

Quaternary evolution of the northern North Sea

2020 ◽  
Author(s):  
Christine Batchelor ◽  
Dag Ottesen ◽  
Benjamin Bellwald ◽  
Sverre Planke ◽  
Helge Løseth ◽  
...  
Keyword(s):  
North Sea ◽  
Seismic Data ◽  
3D Seismic ◽  
Quaternary Sediments ◽  
The North ◽  
The North Sea ◽  
Data Coverage ◽  
Northern North Sea ◽  
2D And 3D ◽  
3D Seismic Data

<p>The North Sea has arguably the most extensive geophysical data coverage of any glacier-influenced sedimentary regime on Earth, enabling detailed investigation of the thick (up to 1 km) sequence of Quaternary sediments that is preserved within the North Sea Basin. At the start of the Quaternary, the bathymetry of the northern North Sea was dominated by a deep depression that provided accommodation for sediment input from the Norwegian mainland and the East Shetland Platform. Here we use an extensive database of 2D and 3D seismic data to investigate the geological development of the northern North Sea through the Quaternary.</p><p>Three main sedimentary processes were dominant within the northern North Sea during the early Quaternary: 1) the delivery and associated basinward transfer of glacier-derived sediments from an ice mass centred over mainland Norway; 2) the delivery of fluvio-deltaic sediments from the East Shetland Platform; and 3) contourite deposition and the reworking of sediments by contour currents. The infilling of the North Sea Basin during the early Quaternary increased the width and reduced the water depth of the continental shelf, facilitating the initiation of the Norwegian Channel Ice Stream.</p>

Extensive, Gas-charged Quaternary Sand Accumulations of the Northern North Sea and North Sea Fan

2020 ◽  
Author(s):  
Benjamin Bellwald ◽  
Sverre Planke ◽  
Sunil Vadakkepuliyambatta ◽  
Stefan Buenz ◽  
Christine Batchelor ◽  
...  
Keyword(s):  
North Sea ◽  
Seismic Data ◽  
Data Sets ◽  
3D Seismic ◽  
Fine Grained ◽  
The North ◽  
Northern North Sea ◽  
Well Data ◽  
Sea Fan ◽  
3D Seismic Data

<p>Sediments deposited by marine-based ice sheets are dominantly fine-grained glacial muds, which are commonly known for their sealing properties for migrating fluids. However, the Peon and Aviat hydrocarbon discoveries in the North Sea show that coarse-grained glacial sands can occur over large areas in formerly glaciated continental shelves. In this study, we use conventional and high-resolution 2D and 3D seismic data combined with well information to present new models for large-scale fluid accumulations within the shallow subsurface of the Norwegian Continental Shelf. The data include 48,000 km<sup>2</sup> of high-quality 3D seismic data and 150 km<sup>2</sup> of high-resolution P-Cable 3D seismic data, with a vertical resolution of 2 m and a horizontal resolution of 6 to 10 m in these data sets. We conducted horizon picking, gridding and attribute extractions as well as seismic geomorphological interpretation, and integrated the results obtained from the seismic interpretation with existing well data.</p><p>The thicknesses of the Quaternary deposits vary from hundreds of meters of subglacial till in the Northern North Sea to several kilometers of glacigenic sediments in the North Sea Fan. Gas-charged, sandy accumulations are characterized by phase-reserved reflections with anomalously high amplitudes in the seismic data as well as density and velocity decreases in the well data. Extensive (>10 km<sup>2</sup>) Quaternary sand accumulations within this package include (i) glacial sands in an ice-marginal outwash fan, sealed by stiff glacial tills deposited by repeated glaciations (the Peon discovery in the Northern North Sea), (ii) sandy channel-levee systems sealed by fine-grained mud within sequences of glacigenic debris flows, formed during shelf-edge glaciations, (iii) fine-grained glacimarine sands of contouritic origin sealed by gas hydrates, and (iv) remobilized oozes above large evacuation craters and sealed by megaslides and glacial muds. The development of the Fennoscandian Ice Sheet resulted in a rich variety of depositional environments with frequently changing types and patterns of glacial sedimentation. Extensive new 3D seismic data sets are crucial to correctly interpret glacial processes and to analyze the grain sizes of the related deposits. Furthermore, these data sets allow the identification of localized extensive fluid accumulations within the Quaternary succession and distinguish stratigraphic levels favorable for fluid accumulations from layers acting as fluid barriers.</p>

Shear margin moraine, mass transport deposits and soft beds revealed by high-resolution P-Cable three-dimensional seismic data in the Hoop area, Barents Sea

2018 ◽  
Vol 477 (1) ◽  
pp. 537-548 ◽  
Author(s):  
Benjamin Bellwald ◽  
Sverre Planke
Keyword(s):  
High Resolution ◽  
Mass Transport ◽  
Seismic Data ◽  
Slope Failure ◽  
Barents Sea ◽  
3D Seismic ◽  
Seismic Reflection Data ◽  
Shallow Subsurface ◽  
Mass Transport Deposits ◽  
Amplitude Reflection

AbstractHigh-resolution seismic data are powerful tools that can help the offshore industries to better understand the nature of the shallow subsurface and plan the development of vulnerable infrastructure. Submarine mass movements and shallow gas are among the most significant geohazards in petroleum prospecting areas. A variety of high-resolution geophysical datasets collected in the Barents Sea have significantly improved our knowledge of the shallow subsurface in recent decades. Here we use a c. 200 km2 high-resolution P-Cable 3D seismic cube from the Hoop area, SW Barents Sea, to study a 20–65 m thick glacial package between the seabed and the Upper Regional Unconformity (URU) horizons. Intra-glacial reflections, not visible in conventional seismic reflection data, are well imaged. These reflections have been mapped in detail to better understand the glacial deposits and to assess their impact on seabed installations. A shear margin moraine, mass transport deposits and thin soft beds are examples of distinct units only resolvable in the P-Cable 3D seismic data. The top of the shear margin moraine is characterized by a positive amplitude reflection incised by glacial ploughmarks. Sedimentary slide wedges and shear bands are characteristic sedimentary features of the moraine. A soft reflection locally draping the URU is interpreted as a coarser grained turbidite bed related to slope failure along the moraine. The bed is possibly filled with gas. Alternatively, this negative amplitude reflection represents a thin, soft bed above the URU. This study shows that P-Cable 3D data can be used successfully to identify and map the external and internal structures of ice stream shear margin moraines and that this knowledge is useful for site-survey investigations.

Rift processes in the Westralian Superbasin, North West Shelf, Australia: insights from 2D deep reflection seismic interpretation and potential fields modelling

2015 ◽  
Vol 55 (2) ◽  
pp. 400 ◽  
Author(s):  
Catherine Belgarde ◽  
Gianreto Manatschal ◽  
Nick Kusznir ◽  
Sonia Scarselli ◽  
Michal Ruder
Keyword(s):  
Seismic Reflection ◽  
Potential Fields ◽  
Moho Depth ◽  
Late Permian ◽  
Forward Modelling ◽  
Seismic Reflection Data ◽  
North West ◽  
Reflection Seismic ◽  
The North ◽  
Reflection Data

Acquisition of long-offset (8–10 km), long-record length (12–18 sec), 2D reflection seismic and ship-borne potential fields data (WestraliaSpan by Ion/GXT and New Dawn by PGS) on the North West Shelf of Australia provide the opportunity to study rift processes in the context of modern models for rifted margins (Manatschal, 2004). Basement and Moho surfaces were interpreted on seismic reflection data. Refraction models from Geoscience Australia constrain Moho depth and initial densities for gravity modelling through standard velocity-density transformation. 2D joint inversion of seismic reflection and gravity data for Moho depth and basement density constrain depth to basement on seismic. 2D gravity and magnetic intensity forward modelling of key seismic lines constrain basement thickness, type and density. Late Permian and Jurassic-Early Cretaceous rift zones were mapped on seismic reflection data and constrained further by inversion and forward modelling of potential fields data. The Westralian Superbasin formed as a marginal basin in Eastern Gondwana during the Late Permian rifting of the Sibumasu terrane. Crustal necking was localised along mechanically-weak Proterozoic suture belts or Early Paleozoic sedimentary basins (such as Paterson and Canning). Mechanically-strong cratons (such as Pilbara and Kimberley) remained intact, resulting in necking and hyper-extension at their edges. Late Permian hyper-extended areas (such as Exmouth Plateau) behaved as mechanically-strong blocks during the Jurassic to Early Cretaceous continental break-up. Late Permian necking zones were reactivated as failed-rift basins and localised the deposition of the Jurassic oil-prone source rocks that have generated much of the oil discovered on the North West Shelf.

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