Seismic-Stratigraphical Analysis of Large-Scale Ridge–Trough Sedimentary Structures in the Late Miocene to Early Pliocene of the Central North Sea

AbstractThe Triassic of the Central North Sea is a continental succession that contains prolific hydrocarbon-bearing fluvial sandstone reservoirs stratigraphically partitioned by mudstones. Within the Skagerrak Formation of the UK sector, hydrocarbon accumulations in the Judy, Joanne and Josephine Sandstone members are top sealed by the Julius, Jonathan and Joshua Mudstone members, respectively. However, UK and Norwegian stratigraphic correlations have been problematical for decades, largely due to biostratigraphic challenges but also due to the non-uniqueness of the lithotypes and because the cross-border stratigraphic nomenclature differs and has yet to be rationalized. This study focuses on mudstones rather than sandstones to unify cross-border correlation efforts at a regional scale. The mudstone members have been characterized by integrating sedimentological, petrophysical and geophysical data. The facies are indicative of playa lakes that frequently desiccated and preserved minor anhydrite. These conditions alternated with periods of marshy, palustrine conditions favourable for the formation of dolostones. Regional correlations have detected lateral facies changes in the mudstones which are important for their seismically mappable extents, resulting palaeogeographies and, ultimately, their competency as intraformational top seals. Significant diachroneity is associated with the lithological transitions at sandstone–mudstone member boundaries and although lithostratigraphic surfaces can be used as timelines over short distances (e.g. within a field), they should not be assumed to represent timelines over longer correlation lengths. Palaeoclimatic trends are interpreted and compared to those of adjacent regions to test the extent and impact of climate change as a predictive allogenic forcing factor on sedimentation. Mudstone member deposition occurred as a result of the retreat of large-scale terminal fluvial systems during a return to more arid ‘background’ climatic conditions. The cause of the member-scale climatic cyclicity observed within the Skagerrak Formation may be related to volcanic activity in large igneous provinces which triggered the episodic progradation of fluvial systems.

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Diagenesis of the shallow marine Fulmar Formation in the Central North Sea

Clay Minerals ◽

10.1180/claymin.1986.021.4.08 ◽

1986 ◽

Vol 21 (4) ◽

pp. 537-564 ◽

Cited By ~ 28

Author(s):

D. J. Stewart

Keyword(s):

Clay Mineral ◽

North Sea ◽

Large Scale ◽

Shear Zones ◽

Upper Jurassic ◽

Burial Diagenesis ◽

Secondary Porosity ◽

Shallow Marine ◽

History Of ◽

Central North Sea

AbstractThe diagenetic history of the Upper Jurassic Fulmar Formation of the Central North Sea is described with emphasis on the Fulmar Field. The Fulmar Formation was deposited on a variably subsiding shallow-marine shelf under the influence of halokinetic and fault movements. The sediments are extensively bio-destratified although large-scale cross-bedding is locally preserved. The dominant mechanism of deposition is thought to have been storm-generated currents. Soft-sediment deformation structures are common and are attributed to syn- and post-depositional dewatering of the sandstones. The dewatering was associated with fractures and shear zones which reflect tectonic instability resulting from periodic salt withdrawal and/or graben fault movements. The dewatering may have been initiated by repacking of the sediments during earth movements or by the gradual build-up and sudden release of overpressures due to compaction and/or clay mineral dehydration during rapid burial at the end of the Cretaceous. The formation is composed of arkosic sandstone of similar composition to Triassic sandstones from which it was probably derived. The sandstones also contain limited amounts of marine biogenic debris including sponge solenasters, bivalve shells, rare ammonites and belemnites. Initial diagenesis began with an environment-related phase during which quartz and feldspar overgrowths and chalcedony and calcite cements were precipitated. These cements appear to form concretions adjacent to local concentrations of sponge debris and shell debris, respectively, and were disturbed after their formation by fracturing and dewatering. This was followed by an early burial stage of diagenesis which resulted in extensive dolomite cementation and minor clay mineral authigenesis (illite and chlorite). The last phase of mineral growth was probably pyrite. During early burial diagenesis, secondary porosity after feldspar and/or carbonate was produced, although the exact timing is not clear. The lack of both stylolitic developments and extensive illitization indicates that the late burial diagenesis stage was never reached, although sufficient clay diagenesis occurred to destroy all traces of mixed-layer illite-smectite (present in some shallower wells). The main control on reservoir behaviour is primary depositional fabric. Diagenesis only overprints these controls. Locally-cemented fracture sets act as baffles to fluid flow, but they are not extensive and the reservoir acts as one unit.

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The Catcher, Varadero and Burgman fields, Block 28/9a, UK North Sea

Geological Society London Memoirs ◽

10.1144/m52-2019-24 ◽

2020 ◽

Vol 52 (1) ◽

pp. 399-412 ◽

Cited By ~ 1

Author(s):

Matthew Gibson ◽

Dominic Riley ◽

Stephen Kenyon-Roberts ◽

Jacob Opata ◽

Andy Beck ◽

...

Keyword(s):

Data Acquisition ◽

North Sea ◽

Large Scale ◽

Injection Wells ◽

Field Development ◽

Development Plans ◽

Turbidite System ◽

Central North Sea ◽

Further Development ◽

Area Development

AbstractThe Catcher area fields – Catcher, Varadero and Burgman – were discovered in the Central North Sea between 2010 and 2011. The three fields are found in Block 28/9a. Oil is produced from Eocene sandstones stratigraphically equivalent to the Cromarty and Tay Sandstone members of the Sele and Horda formations, respectively. The reservoir for the Catcher area fields was formed by the large-scale injection of sand from the Eocene Cromarty turbidite system into shallower Sele and Horda Formation mudstones to form the Greater Catcher area injectite complex. The Catcher area development is a floating production, storage and offloading (FPSO) based development, with 18 production and injection wells drilled from two drilling templates per field, tied back to the centrally located BW Offshore Catcher FPSO. A further development well will be drilled in 2020 to complete the base development. A phased approach to development drilling, with focused data acquisition, allowed the well layout and count to be optimized as the fields were being developed. Excellent well results have meant that the well count has been reduced relative to the development plans at sanction while delivering an increase in predicted reserves. Further infill wells and satellite field development drilling is planned for the future.

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LATE-MIOCENE TO EARLY-PLIOCENE TIDAL SEAWAY ALONG THE LOWER COLORADO RIVER VALLEY: EVIDENCE FROM LARGE-SCALE TIDAL BEDFORMS IN THE SOUTHERN BOUSE FORMATION BASAL CARBONATE MEMBER

10.1130/abs/2019am-337093 ◽

2019 ◽

Author(s):

Kevin Gardner ◽

◽

Rebecca J. Dorsey

Keyword(s):

Late Miocene ◽

Large Scale ◽

Colorado River ◽

River Valley ◽

Early Pliocene ◽

Lower Colorado River

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Enigmatic large-scale furrows of Miocene to Pliocene age from the central North Sea: current-scoured pockmarks?

Geo-Marine Letters ◽

10.1007/s00367-011-0235-1 ◽

2011 ◽

Vol 31 (5-6) ◽

pp. 437-449 ◽

Cited By ~ 18

Author(s):

Ben Kilhams ◽

Adam McArthur ◽

Mads Huuse ◽

Eyita Ita ◽

Adrian Hartley

Keyword(s):

North Sea ◽

Large Scale ◽

Sea Current ◽

Central North Sea

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Regional Cenozoic uplift and subsidence events in the southeastern North Sea

Danmarks Geologiske Undersøgelse Serie C ◽

10.34194/seriec.v12.7109 ◽

1995 ◽

Vol 12 ◽

pp. 53-67

Author(s):

Henrik Jordt

Keyword(s):

North Sea ◽

Fennoscandian Shield ◽

Vertical Movements ◽

Early Pliocene ◽

The North ◽

Central Trough ◽

The North Sea ◽

Central North Sea ◽

East West ◽

Basin Margin

The Paleocene topography of the Fennoscandian Shield is indicated by outbuilding towards the Central Trough and the Ringkøbing-Fyn High. From Eocene until Pliocene time three events of relative vertical movements are indicated by changes in outbuilding directions and reflection termination patterns in the central North Sea. The first event of uplift was in the Eocene and resulted in relative uplift of the Mid North Sea High and contemporary subsidence east of it, indicated by a change in outbuilding from north to west. A second event of uplift is indicated to the north of the study area at the Eocene-Oligocene boundary by renewed southward outbuilding in the Norwegian-Danish Basin. In Miocene until Early Pliocene time a relatively stationary, almost east-west striking, basin margin was probably located to the north along the Tornquist Zone as indicated by the continued outbuilding towards the Ringk0bing Fyn High. A third event of relative uplift is indicated east of the study area by changes in the Pliocene outbuilding pattern. After the first event of uplift it appears that the deepest parts of the Eocene North Sea Basin were located more easterly than the deepest parts are today. Apparently the two latest uplift events north and east of the study area were related to movements of, or along the Tornquist Zone or to regional uplift of the Fennoscandian Shield finally resulting in the presentday configuration of the North Sea.

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