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NARROW
GeoRef Subject
-
all geography including DSDP/ODP Sites and Legs
-
Africa
-
North Africa
-
Atlas Mountains
-
Moroccan Atlas Mountains
-
High Atlas (1)
-
-
-
Morocco
-
Moroccan Atlas Mountains
-
High Atlas (1)
-
-
-
-
-
Antarctica (1)
-
Arctic Ocean
-
Norwegian Sea
-
More Basin (1)
-
-
-
Arctic region
-
Greenland (2)
-
-
Asia
-
Far East
-
China
-
Bohaiwan Basin (1)
-
North China Platform (1)
-
Ordos Basin (1)
-
Xinjiang China
-
Kuqa Depression (1)
-
Tarim Basin (1)
-
-
-
-
Indian Peninsula
-
India (1)
-
-
Middle East
-
Iran (1)
-
Zagros (1)
-
-
-
Atlantic Ocean
-
North Atlantic
-
Bay of Fundy (1)
-
Celtic Sea (3)
-
English Channel (1)
-
Faeroe-Shetland Basin (5)
-
Goban Spur (1)
-
Irish Sea (8)
-
North Sea
-
East Shetland Basin (3)
-
Viking Graben (2)
-
-
Northeast Atlantic
-
Porcupine Bank (2)
-
Porcupine Seabight (1)
-
-
Northwest Atlantic (2)
-
Porcupine Basin (10)
-
Rockall Bank (1)
-
Rockall Trough (10)
-
-
-
Atlantic Ocean Islands
-
Faeroe Islands (3)
-
-
Atlantic region (1)
-
Australasia
-
Australia
-
Otway Basin (1)
-
Queensland Australia (1)
-
-
-
Bowen Basin (1)
-
Caledonides (2)
-
Canada
-
Eastern Canada
-
Maritime Provinces
-
Nova Scotia
-
Minas Basin (2)
-
-
-
Meguma Terrane (1)
-
Newfoundland and Labrador
-
Labrador (1)
-
Newfoundland (1)
-
-
-
-
Central Graben (1)
-
Europe
-
Pyrenees (1)
-
Southern Europe
-
Iberian Peninsula
-
Portugal (1)
-
Spain (1)
-
-
-
Western Europe
-
Iceland (1)
-
Ireland
-
Cork Ireland (1)
-
Donegal Ireland (4)
-
Galway Ireland (2)
-
Kerry Ireland (1)
-
Mayo Ireland (2)
-
Sligo Ireland (2)
-
Wicklow Mountains (1)
-
-
Netherlands (1)
-
Scandinavia
-
Denmark (4)
-
Norway (2)
-
-
United Kingdom
-
Great Britain
-
Bristol Channel (1)
-
England
-
Gloucestershire England (1)
-
Morecambe Bay (1)
-
Wessex Basin (2)
-
Yorkshire England (1)
-
-
Scotland
-
Great Glen Fault (2)
-
Hebrides
-
Inner Hebrides
-
Isle of Skye (2)
-
Raasay (1)
-
-
Outer Hebrides (1)
-
-
Highland region Scotland
-
Inverness-shire Scotland
-
Isle of Skye (2)
-
Raasay (1)
-
-
-
Moray Firth (1)
-
Scottish Highlands
-
Grampian Highlands (1)
-
-
-
Wales (1)
-
-
Northern Ireland (2)
-
-
-
-
Lusitanian Basin (2)
-
Mediterranean region (1)
-
Mediterranean Sea (1)
-
Meseta (1)
-
North America
-
Williston Basin (1)
-
-
North Sea region (7)
-
Northern Highlands (1)
-
Pacific Ocean
-
North Pacific
-
Northwest Pacific
-
Yellow Sea
-
Bohai Sea
-
Bohai Bay (1)
-
-
-
-
-
West Pacific
-
Northwest Pacific
-
Yellow Sea
-
Bohai Sea
-
Bohai Bay (1)
-
-
-
-
-
-
polar regions (1)
-
United States
-
Illinois Basin (1)
-
North Dakota
-
McKenzie County North Dakota (1)
-
Mountrail County North Dakota (1)
-
-
Texas
-
East Texas Basin (1)
-
-
-
-
commodities
-
coal deposits (1)
-
energy sources (5)
-
geothermal energy (1)
-
metal ores
-
lead ores (1)
-
-
mineral deposits, genesis (1)
-
oil and gas fields (9)
-
petroleum
-
natural gas
-
coalbed methane (1)
-
-
-
tight sands (2)
-
-
elements, isotopes
-
carbon
-
C-13/C-12 (1)
-
-
hydrogen
-
D/H (1)
-
deuterium (1)
-
-
isotope ratios (6)
-
isotopes
-
radioactive isotopes
-
Pb-206/Pb-204 (3)
-
Pb-207/Pb-204 (1)
-
Pb-208/Pb-204 (1)
-
-
stable isotopes
-
C-13/C-12 (1)
-
D/H (1)
-
deuterium (1)
-
Nd-144/Nd-143 (1)
-
O-18/O-16 (4)
-
Pb-206/Pb-204 (3)
-
Pb-207/Pb-204 (1)
-
Pb-208/Pb-204 (1)
-
Sr-87/Sr-86 (1)
-
-
-
metals
-
alkaline earth metals
-
calcium (1)
-
magnesium (1)
-
strontium
-
Sr-87/Sr-86 (1)
-
-
-
iron (1)
-
lead
-
Pb-206/Pb-204 (3)
-
Pb-207/Pb-204 (1)
-
Pb-208/Pb-204 (1)
-
-
rare earths
-
neodymium
-
Nd-144/Nd-143 (1)
-
-
-
-
oxygen
-
O-18/O-16 (4)
-
-
-
fossils
-
Invertebrata
-
Arthropoda
-
Mandibulata
-
Crustacea
-
Ostracoda (1)
-
-
-
-
Protista
-
Foraminifera (1)
-
-
-
microfossils (3)
-
palynomorphs
-
Dinoflagellata (2)
-
miospores
-
pollen (1)
-
-
-
Plantae
-
Pteridophyta
-
Lycopsida
-
Lycopodium (1)
-
-
-
-
-
geochronology methods
-
(U-Th)/He (1)
-
Ar/Ar (3)
-
fission-track dating (4)
-
He/He (1)
-
K/Ar (1)
-
paleomagnetism (2)
-
thermochronology (2)
-
U/Pb (5)
-
-
geologic age
-
Cenozoic
-
Quaternary
-
Holocene (1)
-
Pleistocene
-
upper Pleistocene
-
Devensian (1)
-
-
-
-
Tertiary
-
Neogene
-
Miocene
-
lower Miocene (1)
-
middle Miocene (1)
-
-
Pliocene
-
Cimmerian (2)
-
-
-
Paleogene
-
Eocene
-
lower Eocene (1)
-
middle Eocene (1)
-
-
Paleocene (2)
-
-
-
-
Mesozoic
-
Cretaceous
-
Comanchean
-
Travis Peak Formation (1)
-
-
Lower Cretaceous
-
Aptian (1)
-
Berriasian (2)
-
Missisauga Formation (1)
-
Travis Peak Formation (1)
-
-
Middle Cretaceous (1)
-
Upper Cretaceous (4)
-
-
Jurassic
-
Heather Formation (1)
-
Lower Jurassic
-
Dunlin Group (1)
-
Hettangian (3)
-
Pliensbachian (1)
-
Sinemurian (1)
-
Toarcian (3)
-
upper Liassic (1)
-
-
Middle Jurassic
-
Aalenian (1)
-
Bajocian
-
Brent Group (1)
-
Ness Formation (1)
-
Tarbert Formation (1)
-
-
Bathonian
-
Great Oolite Group (1)
-
-
Callovian (2)
-
-
Upper Jurassic
-
Kimmeridgian (1)
-
Oxfordian
-
middle Oxfordian (1)
-
-
Tithonian (1)
-
-
-
Newark Supergroup (1)
-
Triassic
-
Middle Triassic
-
Anisian (1)
-
-
Sherwood Sandstone (4)
-
Upper Triassic
-
Mercia Mudstone (2)
-
Rhaetian (1)
-
Yanchang Formation (1)
-
-
-
-
Paleozoic
-
Cambrian
-
Upper Cambrian
-
Eau Claire Formation (1)
-
-
-
Carboniferous
-
Lower Carboniferous (1)
-
Mississippian
-
Middle Mississippian
-
Visean (1)
-
-
-
-
Devonian
-
Lower Devonian (1)
-
Upper Devonian (1)
-
-
Ordovician (1)
-
Permian (6)
-
Silurian
-
Middle Silurian (1)
-
-
upper Paleozoic
-
Bakken Formation (1)
-
-
-
Precambrian
-
Archean (2)
-
Lewisian Complex (2)
-
upper Precambrian
-
Proterozoic
-
Lewisian (1)
-
Paleoproterozoic (2)
-
-
-
-
-
igneous rocks
-
igneous rocks
-
plutonic rocks
-
granites (1)
-
lamprophyres
-
monchiquite (1)
-
-
-
volcanic rocks
-
basalts
-
mid-ocean ridge basalts (2)
-
-
-
-
-
metamorphic rocks
-
metamorphic rocks
-
gneisses
-
orthogneiss (1)
-
paragneiss (1)
-
-
metaigneous rocks
-
metagabbro (1)
-
-
metasedimentary rocks
-
paragneiss (1)
-
-
-
turbidite (1)
-
-
minerals
-
carbonates
-
ankerite (1)
-
calcite (2)
-
dolomite (1)
-
-
oxides
-
rutile (1)
-
-
phosphates
-
apatite (7)
-
-
silicates
-
framework silicates
-
feldspar group
-
alkali feldspar
-
K-feldspar (4)
-
-
-
silica minerals
-
quartz (1)
-
-
-
orthosilicates
-
nesosilicates
-
garnet group (1)
-
olivine group
-
olivine (1)
-
-
zircon group
-
zircon (4)
-
-
-
-
sheet silicates
-
clay minerals (1)
-
mica group
-
muscovite (1)
-
phlogopite (1)
-
-
-
-
sulfides
-
galena (1)
-
-
-
Primary terms
-
absolute age (9)
-
Africa
-
North Africa
-
Atlas Mountains
-
Moroccan Atlas Mountains
-
High Atlas (1)
-
-
-
Morocco
-
Moroccan Atlas Mountains
-
High Atlas (1)
-
-
-
-
-
Antarctica (1)
-
Arctic Ocean
-
Norwegian Sea
-
More Basin (1)
-
-
-
Arctic region
-
Greenland (2)
-
-
Asia
-
Far East
-
China
-
Bohaiwan Basin (1)
-
North China Platform (1)
-
Ordos Basin (1)
-
Xinjiang China
-
Kuqa Depression (1)
-
Tarim Basin (1)
-
-
-
-
Indian Peninsula
-
India (1)
-
-
Middle East
-
Iran (1)
-
Zagros (1)
-
-
-
Atlantic Ocean
-
North Atlantic
-
Bay of Fundy (1)
-
Celtic Sea (3)
-
English Channel (1)
-
Faeroe-Shetland Basin (5)
-
Goban Spur (1)
-
Irish Sea (8)
-
North Sea
-
East Shetland Basin (3)
-
Viking Graben (2)
-
-
Northeast Atlantic
-
Porcupine Bank (2)
-
Porcupine Seabight (1)
-
-
Northwest Atlantic (2)
-
Porcupine Basin (10)
-
Rockall Bank (1)
-
Rockall Trough (10)
-
-
-
Atlantic Ocean Islands
-
Faeroe Islands (3)
-
-
Atlantic region (1)
-
Australasia
-
Australia
-
Otway Basin (1)
-
Queensland Australia (1)
-
-
-
Canada
-
Eastern Canada
-
Maritime Provinces
-
Nova Scotia
-
Minas Basin (2)
-
-
-
Meguma Terrane (1)
-
Newfoundland and Labrador
-
Labrador (1)
-
Newfoundland (1)
-
-
-
-
carbon
-
C-13/C-12 (1)
-
-
Cenozoic
-
Quaternary
-
Holocene (1)
-
Pleistocene
-
upper Pleistocene
-
Devensian (1)
-
-
-
-
Tertiary
-
Neogene
-
Miocene
-
lower Miocene (1)
-
middle Miocene (1)
-
-
Pliocene
-
Cimmerian (2)
-
-
-
Paleogene
-
Eocene
-
lower Eocene (1)
-
middle Eocene (1)
-
-
Paleocene (2)
-
-
-
-
coal deposits (1)
-
continental drift (1)
-
continental shelf (6)
-
continental slope (3)
-
crust (3)
-
data processing (2)
-
deformation (7)
-
diagenesis (10)
-
earthquakes (1)
-
economic geology (3)
-
energy sources (5)
-
Europe
-
Pyrenees (1)
-
Southern Europe
-
Iberian Peninsula
-
Portugal (1)
-
Spain (1)
-
-
-
Western Europe
-
Iceland (1)
-
Ireland
-
Cork Ireland (1)
-
Donegal Ireland (4)
-
Galway Ireland (2)
-
Kerry Ireland (1)
-
Mayo Ireland (2)
-
Sligo Ireland (2)
-
Wicklow Mountains (1)
-
-
Netherlands (1)
-
Scandinavia
-
Denmark (4)
-
Norway (2)
-
-
United Kingdom
-
Great Britain
-
Bristol Channel (1)
-
England
-
Gloucestershire England (1)
-
Morecambe Bay (1)
-
Wessex Basin (2)
-
Yorkshire England (1)
-
-
Scotland
-
Great Glen Fault (2)
-
Hebrides
-
Inner Hebrides
-
Isle of Skye (2)
-
Raasay (1)
-
-
Outer Hebrides (1)
-
-
Highland region Scotland
-
Inverness-shire Scotland
-
Isle of Skye (2)
-
Raasay (1)
-
-
-
Moray Firth (1)
-
Scottish Highlands
-
Grampian Highlands (1)
-
-
-
Wales (1)
-
-
Northern Ireland (2)
-
-
-
-
faults (14)
-
folds (4)
-
fractures (1)
-
geochemistry (4)
-
geochronology (4)
-
geophysical methods (25)
-
geothermal energy (1)
-
heat flow (2)
-
hydrogen
-
D/H (1)
-
deuterium (1)
-
-
igneous rocks
-
plutonic rocks
-
granites (1)
-
lamprophyres
-
monchiquite (1)
-
-
-
volcanic rocks
-
basalts
-
mid-ocean ridge basalts (2)
-
-
-
-
inclusions
-
fluid inclusions (3)
-
-
Integrated Ocean Drilling Program
-
Expedition 307
-
IODP Site U1318 (1)
-
-
-
intrusions (3)
-
Invertebrata
-
Arthropoda
-
Mandibulata
-
Crustacea
-
Ostracoda (1)
-
-
-
-
Protista
-
Foraminifera (1)
-
-
-
isostasy (1)
-
isotopes
-
radioactive isotopes
-
Pb-206/Pb-204 (3)
-
Pb-207/Pb-204 (1)
-
Pb-208/Pb-204 (1)
-
-
stable isotopes
-
C-13/C-12 (1)
-
D/H (1)
-
deuterium (1)
-
Nd-144/Nd-143 (1)
-
O-18/O-16 (4)
-
Pb-206/Pb-204 (3)
-
Pb-207/Pb-204 (1)
-
Pb-208/Pb-204 (1)
-
Sr-87/Sr-86 (1)
-
-
-
lava (1)
-
mantle (3)
-
maps (1)
-
marine geology (1)
-
Mediterranean region (1)
-
Mediterranean Sea (1)
-
Mesozoic
-
Cretaceous
-
Comanchean
-
Travis Peak Formation (1)
-
-
Lower Cretaceous
-
Aptian (1)
-
Berriasian (2)
-
Missisauga Formation (1)
-
Travis Peak Formation (1)
-
-
Middle Cretaceous (1)
-
Upper Cretaceous (4)
-
-
Jurassic
-
Heather Formation (1)
-
Lower Jurassic
-
Dunlin Group (1)
-
Hettangian (3)
-
Pliensbachian (1)
-
Sinemurian (1)
-
Toarcian (3)
-
upper Liassic (1)
-
-
Middle Jurassic
-
Aalenian (1)
-
Bajocian
-
Brent Group (1)
-
Ness Formation (1)
-
Tarbert Formation (1)
-
-
Bathonian
-
Great Oolite Group (1)
-
-
Callovian (2)
-
-
Upper Jurassic
-
Kimmeridgian (1)
-
Oxfordian
-
middle Oxfordian (1)
-
-
Tithonian (1)
-
-
-
Newark Supergroup (1)
-
Triassic
-
Middle Triassic
-
Anisian (1)
-
-
Sherwood Sandstone (4)
-
Upper Triassic
-
Mercia Mudstone (2)
-
Rhaetian (1)
-
Yanchang Formation (1)
-
-
-
-
metal ores
-
lead ores (1)
-
-
metals
-
alkaline earth metals
-
calcium (1)
-
magnesium (1)
-
strontium
-
Sr-87/Sr-86 (1)
-
-
-
iron (1)
-
lead
-
Pb-206/Pb-204 (3)
-
Pb-207/Pb-204 (1)
-
Pb-208/Pb-204 (1)
-
-
rare earths
-
neodymium
-
Nd-144/Nd-143 (1)
-
-
-
-
metamorphic rocks
-
gneisses
-
orthogneiss (1)
-
paragneiss (1)
-
-
metaigneous rocks
-
metagabbro (1)
-
-
metasedimentary rocks
-
paragneiss (1)
-
-
-
micropaleontology (1)
-
mineral deposits, genesis (1)
-
Mohorovicic discontinuity (1)
-
North America
-
Williston Basin (1)
-
-
ocean basins (2)
-
ocean floors (2)
-
oceanography (4)
-
oil and gas fields (9)
-
oxygen
-
O-18/O-16 (4)
-
-
Pacific Ocean
-
North Pacific
-
Northwest Pacific
-
Yellow Sea
-
Bohai Sea
-
Bohai Bay (1)
-
-
-
-
-
West Pacific
-
Northwest Pacific
-
Yellow Sea
-
Bohai Sea
-
Bohai Bay (1)
-
-
-
-
-
-
paleoclimatology (1)
-
paleoecology (2)
-
paleogeography (9)
-
paleomagnetism (2)
-
Paleozoic
-
Cambrian
-
Upper Cambrian
-
Eau Claire Formation (1)
-
-
-
Carboniferous
-
Lower Carboniferous (1)
-
Mississippian
-
Middle Mississippian
-
Visean (1)
-
-
-
-
Devonian
-
Lower Devonian (1)
-
Upper Devonian (1)
-
-
Ordovician (1)
-
Permian (6)
-
Silurian
-
Middle Silurian (1)
-
-
upper Paleozoic
-
Bakken Formation (1)
-
-
-
palynology (1)
-
palynomorphs
-
Dinoflagellata (2)
-
miospores
-
pollen (1)
-
-
-
paragenesis (1)
-
petroleum
-
natural gas
-
coalbed methane (1)
-
-
-
petrology (1)
-
Plantae
-
Pteridophyta
-
Lycopsida
-
Lycopodium (1)
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Slyne Basin
Triassic sand supply to the Slyne Basin, offshore western Ireland – new insights from a multi-proxy provenance approach
Exhumation of the Corrib Gas Field, Slyne Basin, offshore Ireland
Abstract The Slyne Basin lies c. 60 km offshore west of Ireland, in water depths of 200–500 m. It consists of three asymmetric half-graben that are separated by complex structural transfer zones. Sporadic exploration in the basin over the last 20 years has resulted in the drilling of four exploration wells, which have yielded one gas discovery. Well 18/20-1 (Corrib) successfully tested a faulted anticlinal structure and encountered gas in the Triassic Sherwood Sandstone Formation. Although a number of other potential hydrocarbon traps have been identified in the Slyne Basin, the poor quality of the seismic data, plus the presence of complex transfer zones, has generated considerable uncertainty with respect to the correlation of seismic markers. A primary control on the seismic data quality is the presence of near-sea-bed, high-velocity, Tertiary volcanic and Cretaceous chalk layers. These result in very strong and long multiple trains, energy scattering, mode conversion and attenuation. Studies suggest that improved signal penetration can be achieved when the seismic acquisition is focused on the low-frequency end of the spectrum. However, predictive multiple attenuation has proved ineffective because of the complex nature of the multiple generators. An approach based on detailed velocity analysis and the judicious parameterization of more than one pass of Radon demultiple has yielded good results. This approach, coupled with 3D acquisition and processing with its inherent increase in signal-to-noise ratio, has led to a dramatic improvement in the seismic data quality in the Corrib area.
Comparative sequence stratigraphy and structural styles of the Slyne Trough and Hebrides Basin
Schematic palaeodrainage block model for the Slyne Basin; coloured arrows r...
Petroleum geochemistry of the Lower and Middle Jurassic in Atlantic margin basins of Ireland and the UK
Abstract Potential hydrocarbon source rocks of Lower and Middle Jurassic age have been reported from outcrop, shallow boreholes and exploration wells in Atlantic margin basins of the UK (Hebrides, West of Shetlands and flanking the NE Rockall Trough) and, recently, in the continuation of this trend offshore Ireland (Slyne, Erris and Porcupine basins). Previously these organic-rich mudrocks were considered to be of little economic importance, due largely to their perceived limited areal distribution and low maturity. However, recent geochemical studies of oils and shales from exploration drilling of thèse basins shows the Lower and Middle Jurassic to have considerable potential as effective hydrocarbon source rocks, supplanting the Late Jurassic-Early Cretaceous Kimmeridge Clay Formation equivalents as the only viable oil source rock in the region. Flanking the Atlantic margin in the Irish and UK sectors, rich oil source potential occurs in two transgressive mudrock cycles of Lower Jurassic age. These are the Sinemurian-Pliensbachian interval and the overlying Toarcian section, present in basins such as the Solan, Minch, Hebrides, Slyne, North Celtic Sea, St George’s Channel and Central English Channel. The Middle Jurassic source rocks have a more limited areal distribution and occur in the Faroe-Shetland, Solan, West Lewis, West Flannan, Hebrides, Slyne and North Porcupine basins with oil source potential in regressive marginal marine to lacustrine facies mudrocks. Geochemical studies were undertaken on mudrocks from the Lower and Middle Jurassic sections in Atlantic margin basins (outcrop, shallow borehole core and exploration well cores and cuttings samples) and on oils from drill stem test and shows (core and cuttings extracts). Detailed analyses using GC, GC-MS and carbon isotopes allowed both characterization of the source rocks and oil-to-source correlation. Biomarker and carbon isotope studies of oils from the Faroe-Shetland Basin (Foinaven and Schiehallion fields), the Porcupine Basin (Connemara accumulation), the Wessex Basin (Wytch Farm and Kimmeridge oil fields) and wells in the Slyne Basin show strong correlations to the various source rock developments in the Lower and Middle Jurassic. The mixed biodegraded Foinaven and Schiehallion oils have a major waxy component and correlate with lacustrine Middle Jurassic source rocks in the Solan and West Lewis/West Flannan basins. Middle Jurassic sourcing of the Connemara oils is also suggested, while oils in the Slyne Basin appear to have been largely sourced by the Lower Jurassic Pabba Shale Formation. Oils in the Wessex Basin (Wytch Farm and Kimmeridge) appear to have been sourced by Hettangian-Sinemurian mudrocks and those in the North Celtic Sea Basin by Toarcian source rocks. The results from this study, in combination with previously published data, show that rich, effective oil-prone source rocks occur in both the Lower and Middle Jurassic of the Atlantic margin basins offshore Ireland and the UK. These source rocks can be correlated with indigenous oils, indicating the existence of a previously under-evaluated petroleum system.
The Corrib gas field, offshore west of Ireland
Abstract The Corrib Gas Field in the Slyne Basin lies about 70 km west of Co. Mayo, offshore Ireland. The basin is a narrow Triassic/Jurassic half-graben and is one of a series of structurally linked basins that are present along the west coast of Ireland and the British Isles. The field was discovered in 1996 by well 18/20-1, encountering a 61 m gas column in low-porosity Triassic fluvial sandstones at a subsea depth of 3539.6 m. Using extremely poor 2D seismic data, it was originally mapped as a tilted fault block, with an associated rollover structure to the east. The data quality was particularly poor due to the near-surface Palaeogene volcanics that contribute to energy dispersion and extreme multiple generation. A 3D seismic survey was acquired in 1997 and resulted in a major improvement in data quality, allowing improved structural interpretation that showed the Corrib Field to be a faulted anticline. The subsequent appraisal well, 18/20-2z, drilled approximately 1 km from the subsurface location of 18/20-1, penetrated a 185 m gas column in fair to good quality sandstone. It tested dry gas at a stabilized rate of 62.87 × 10 6 SCF/d on a 2″ choke. Reprocessing of the seismic data, along with the successful drilling of the following well 18/25-1, confirmed the field to be a relatively simple anticlinal trap, with a complex faulted overburden that is structurally detached from the reservoir by the Mercia Halite. The source rock is assumed to be the Westphalian Coal Measures, similar to that encountered by well 27/5-1. The dry gas is consistent with a Type-III humic source rock. The reservoir is biostratigraphically barren, consisting of fluvial red bed sandstone, and is assumed to be of Triassic Sherwood Sandstone Group equivalent age. The unit is approximately 400 m thick, consisting of a high net-to-gross sequence of low-sinuosity braided fluvial channel sandstones with subordinate sand-flat and playa mudstone deposits. On a macro scale, it is a remarkably uniform sandstone with only subtle facies variations, but on a micro scale there is a significant variation in grainsize and cementation, which affects reservoir productivity. Mineralogically, there are distinct differences from the Sherwood Sandstone Group of the East Irish Sea, indicating that the Slyne Early Triassic system was depositionally similar to, but distinct and separate from, that to the east of Ireland. Dipmeter data indicated that the river system flowed from the SW to NE, essentially along the direction of the present-day Slyne Basin, suggesting that it was largely sourced from the south in the Variscan hinterland, but with evidence of sediment input from local highs such as the Connemara Massif.
Abstract Analysis of the results of regional mapping, integrated with new regional subcrop maps, has yielded significant regional concepts regarding the development of the frontier sedimentary basins west of Ireland. Five provinces of basement and Devono-Carboniferous rocks are mapped across the region. The nature of the basement successions, together with their inherent lineaments and structural fabrics, exerted a major influence on the location and structural segmentation of the basins and in acting as a conduit for Early Cretaceous and Early Cenozoic igneous activity. The major structures in the Porcupine region were N–S throughout its Late Palaeozoic to Cenozoic history, while those in the Slyne, Erris, Rockall and probably Hatton basins were predominantly NNE–SSW to NE–SW. The main structural controls in the Goban region were orientated ENE–WSW and NNW–SSE. The Porcupine Basin is shown to have a more pronounced N–S orientation than has hitherto been proposed. In particular, the basement core of the Porcupine High is shown to extend southwards to the Goban province, thereby isolating the basin for most of its history from the Atlantic region to the west. Separate Permo-Triassic to Jurassic basins occur on the flanks of the main, younger Rockall Basin and their location and orientation were influenced by NE–SW to ENE–WSW structural fabrics. Permo-Triassic sedimentation took place in a series of rift basins in the Porcupine, Rockall, Slyne–Erris and Goban regions. Jurassic rifting was widespread in most of the basins, commencing in Middle Jurassic time in the Slyne Basin but later (Late Jurassic) in the Porcupine and Rockall basins. Early Cretaceous sedimentation was more pronounced in the Porcupine and Rockall basins and shows less control by deep-seated structures. Late Jurassic to Early Cretaceous basin margin uplift on the flanks of the Rockall Basin in particular, is likely to explain the thin to absent nature of such strata in some of the adjacent smaller basins.
Axial stratigraphic cross-section through the Slyne/Erris Basin. The datum ...
Abstract The exploratory drilling of 200 wildcat wells along the NE Atlantic margin has yielded 30 finds with total discovered resources of c. 4.1×10 9 barrels of oil equivalent (BOE). Exploration has been highly concentrated in specific regions. Only 32 of 144 quadrants have been drilled, with only one prolific province discovered – the Faroe–Shetland Basin, where 23 finds have resources totalling c. 3.7×10 9 BOE. Along the margin, the pattern of discoveries can best be assessed in terms of petroleum systems. The Faroe–Shetland finds belong to an Upper Jurassic petroleum system. On the east flank of the Rockall Basin, the Benbecula gas and the Dooish condensate/gas discoveries have proven the existence of a petroleum system of unknown source – probably Upper Jurassic. The Corrib gas field in the Slyne Basin is evidence of a Carboniferous petroleum system. The three finds in the northern Porcupine Basin are from Upper Jurassic source rocks; in the south, the Dunquin well (44/23-1) suggests the presence of a petroleum system there, but of unknown source. This pattern of petroleum systems can be explained by considering the distribution of Jurassic source rocks related to the break-up of Pangaea and marine inundations of the resulting basins. The prolific synrift marine Upper Jurassic source rock (of the Northern North Sea) was not developed throughout the pre-Atlantic Ocean break-up basin system west of Britain and Ireland. Instead, lacustrine–fluvio-deltaic–marginal marine shales of predominantly Late Jurassic age are the main source rocks and have generated oils throughout the region. The structural position, in particular relating to the subsequent Early Cretaceous hyperextension adjacent to the continental margin, is critical in determining where this Upper Jurassic petroleum system will be most effective.
Interpretation of vitrinite reflectance profiles in sedimentary basins, onshore and offshore Ireland
Abstract Vitrinite reflectance (VR) data (R m %) have been compiled from 77 Irish offshore wells and 17 onshore boreholes. This database has facilitated the analysis of vitrinite reflectance v. depth relationships by both basin and stratigraphic interval. In general, VR gradients from the Carboniferous sections are defined by less scattered trends than those from Mesozoic and Cenozoic sections, reflecting the less complex vitrinite populations within Carboniferous coals and shales. A composite approach (display of profiles from a number of wells together) to the interpretation of vitrinite reflectance profiles has been utilized to characterize the thermal history and the prevalent heat transfer mechanisms within the various basins. Calculated peak palaeotemperatures from the wells are used to compute palaeogeothermal gradients and to estimate the magnitude of net exhumation at selected locations. Average palaeogeothermal gradients in the onshore Carboniferous basins range from less than 3 °C km −1 at well IIP-2 in the Clare Basin to 119 °C km −1 at well N998 in the Navan area of the Dublin Basin. Lateral variations in palaeogeothermal gradients recorded in the Carboniferous sections are consistent with a gravity-driven hydrothermal System discharging heated fluids, along fault systems, in a foreland platform area. In general, palaeogeothermal gradients are substantially higher in the Carboniferous sections (mean 60 °C km −1 ) than in the Mesozoic or Cenozoic sections (mean 32 °C km” 1 ). Maturation levels in many of the Carboniferous sections are considered to be the consequence of burial, elevated heat flows and a regional advective System during late Carboniferous to early Permian times rather than Mesozoic or Cenozoic processes. Empirically derived methods of calculating peak palaeotemperature from VR are compared with kinetic models and, although differing in detall, within the resolution of this dataset are shown to produce similar trends. There is a considerable body of evidence to suggest that the extensional evolution of Ireland’s Late Palaeozoic to Cenozoic sedimentary basins has been punctuated by a multiphase inversion history. Regional stratigraphic evidence, combined with VR and apatite fission-track data, suggests at least two periods of pervasive exhumation occurred; one during Late Carboniferous-Late Permian time and another during Tertiary time. Both of these phases are characterized by a component of compressional inversion and the widespread occurrence of extrusive and intrusive igneous rocks. However, the contrasting thermal signature of these regional uplift events suggests that both the basin setting and the mechanism of regional exhumation exerted a fundamental control on processes that determined heat flow distribution within a basin. In terms of the hydrocarbon exploration of Ireland’s sedimentary basins the model presented here has important implications for the timing of maturation of Carboniferous source rocks in these basins. Where Carboniferous source rocks are present, they will make a significant contribution to the hydrocarbon budget only in those basins that experienced relatively low heat flow during Late Carboniferous–Early Permian time and where sufficient Mesozoic burial has occurred to subsequently expose the kerogen to higher temperatures. This observation is consistent with the presence of gas accumulations, which are postulated to have been derived from Carboniferous source rocks, in both the Slyne Basin and the Northwest Carboniferous Basin.