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Offshore Ireland has nearly 50 years of exploration history. The
last licensing round held in 2015 saw a significant increase in the
interest of the exploration potential in the Irish offshore.
Licences were picked up by majors including ExxonMobil, ENI, CNOOC,
Equinor and Woodside and smaller independents including Europa,
AzEire and Predator.
To date, a total of 26 discoveries have been made from the
drilling of 189 E&A wells offshore Ireland. Drilling commenced
in the 1970's and a total of 65 E&A wells were drilled during
the decade. The first discovery, Kinsale Head, was made in 1971.
Drilling activity decreased slightly in the 1980`s with 59 wells
drilled. The 1990's and 2000's saw the drilling of 30 wells and 28
wells respectively and since 2010 a total of 7 wells have been
drilled offshore. Most of the drilling activity to date has focused
on the Celtic Sea area. More recently companies have started
exploring further offshore in the deep waters of the Porcupine
Basin. However, success has been limited so what does the future
hold for Ireland`s offshore?
Figure 1: Offshore Ireland Fields and Prospects
Map.
Regional Geology
The five main offshore basins of Ireland comprise the Celtic Sea
Graben System, Central Irish Sea, Rockall, Porcupine and Northwest
Ireland Offshore. These extensive Mesozoic basins are subdivided
into several smaller rift basins: Slyne-Erris, Goban Spur, Kish
Bank and the North and South Celtic Sea basins. This article will
discuss the Porcupine, Northwest Offshore Basin and Celtic Sea
Graben System. These basins evolved in response to three phases of
basin development occurring in the Permian-Triassic, Mid-Late
Jurassic and Cretaceous to Cenozoic ages.
Field History of the Porcupine Basin
Several plays have been identified within the Porcupine Basin,
ranging from Jurassic through to Cretaceous and Cenozoic in age,
with a focus on both structural and stratigraphic plays. Three
discoveries - Burren (1978), Connemara (1979) and Spanish Point
(1981) have been made in the northern part of the Porcupine Basin.
The Burren exploration well targeted an Upper Cretaceous reef and
Upper Jurassic sandstone play and was drilled by Phillips
Petroleum. Connemara and Spanish Point have reservoirs of the
Steerdagh submarine fan sandstones and fluvial sandstones of the
Minard Formation. The hydrocarbons are trapped in tilted fault
blocks and capped by Lower Cretaceous Shales. Over the years, the
ownership of these discoveries has changed, however, to date all
three discoveries are yet to be developed.
Impact of 2015 Atlantic Margin Licensing Round in the
Porcupine Basin
Recent exploration in Ireland has focused on the Porcupine
Basin. Even before the 2015 Atlantic Margin licensing round big
companies were entering the Irish offshore with the likes of
Woodside, Cairn and Kosmos picking up acreage in the basin. But, it
was during the 2015 Licensing Round that interest increased. A
total of 28 Licensing Options were awarded across the Porcupine
Basin (and further north) to majors ENI, BP, ExxonMobil, Equinor,
Woodside and CNOOC and smaller independents including Europa,
AzEire and Providence. This was the largest number of awards in any
Irish round to date (PAD 2016).
The surge in interest was driven by a combination of new seismic
data, technological improvements and new thinking. Early
exploration activity was focused on large Jurassic and Triassic
fault blocks. However, improvements in seismic technology and
improved coverage have allowed shallower and far more subtle
features to be identified. Therefore, potential exists in both
large traditional structural targets and also stratigraphic plays.
Discoveries in other parts of the Atlantic Margin in West Africa
and Canada have also shown the potential that exists in different
plays in the Irish offshore.
The success of the round is an indication of the potential of
the frontier Irish Atlantic Margin, particularly the prospective
Porcupine Basin. Seismic acquisition has already commenced but
drilling is not required to take place on the new acreage before
2021. To date 6 seismic surveys have been shot across 2016, 2017
and 2018 within the Porcupine Basin.
In the Southern Porcupine Basin (SPB), three high impact wells
have been drilled over the last 6 years: Dunquin North in 2013
(ExxonMobil), Druid/Drombeg in 2017 (Providence Resources) and
Iolar in 2019 (CNOOC). All three wells failed to encounter
hydrocarbons.
The Dunquin North well targeted a Lower Cretaceous isolated
carbonate build up. The well was spudded in April 2013 and
encountered a porous carbonate reservoir ~245m thick but it was
water bearing. Providence thought the presence of gas chimneys
associated with the targeted structure is evidence of trap failure.
The Druid/Drombeg 2017 well targeted two separate stratigraphic
objectives within a single vertical well. The Druid prospect
comprised two Paleocene deep-water sandstone fans located at
~4,000m. The fans were thought to be 85m thick with porosities of
30%. Drombeg was interpreted as a Lower Cretaceous sandstone
deep-water fan, located at 5,000m thought to be 45m thick with 20%
porosity. Both targets were dry. Seismic analysis and spectral
decomposition identified an erosive channel cutting the Druid fans
suggesting the channel was backfilled with mudstone, thus providing
an effective trap and seal. However, Providence thought that the
failure of this backfilling mudstone led to the reservoir being
water wet. Further upside at the well location exists in the Diablo
target however this wasn't tagged by the exploration well. The
third and most recent well drilled in the SPB was CNOOC's Iolar
well in May 2019. Iolar was interpreted as a pre-syn rift Jurassic
structural closure on the western flank of the basin. The main
objective was the Middle Jurassic (Kenmare Formation) with
secondary targets in the Upper Jurassic (Bantry Group) and
Cretaceous submarine channel complex (Greensand Formation). These
targets were predicted to be sourced and sealed by the Kimmeridge
Clay Formation. However, in August 2019 it was confirmed that the
well was a dry hole.
Even though recent drilling activity has yielded disappointing
results, potential remains in this significantly underexplored
basin, with several high impact wells scheduled in the coming
years.
Woodside is potentially looking to drill the Beaufort prospect
in FEL 5/13. Beaufort is a stratigraphic trap with an Upper
Jurassic reservoir charged by the Kimmeridgian-Tithonian aged
source rocks. The overpressured Upper Jurassic and Lower Cretaceous
Shales provide ideal conditions for the stratigraphic trapping and
sealing of the reservoirs. Upside in the acreage consists of the
underlying Walton prospect. Woodside may look to drill a well in
2020 and has been actively farming out the prospect.
Following the unsuccessful Dunquin North well, attention has
turned toward the southern structure. ENI plans to drill an
exploration well on Dunquin South in FEL 3/04 in 2020. Dunquin
South has a similar Cretaceous carbonate reservoir to that of
Dunquin North, but the fluid escape features seen above Dunquin
North are absent at this location. Dunquin South has a resource
estimate of 1.4 Bboe.
Further prospects identified within the basin include Avalon.
Avalon, an analogue prospect to Druid and adjacent to Dunquin
North, is interpreted to be a Paleocene north-south orientated
basin floor channel sand system. Providence predicted that the
system is sourced from the north with shales becoming localised
towards the south.
Kiely, Kiely West and Kiely East are three large tilted fault
block structures with Middle Jurassic marine sandstone reservoirs,
located within the FEL 2/13 licence. These prospects are sourced
and sealed by Kimmeridge Clay formation. The 43/13-1 well located
within FEL 2/13 proved that the source rock was oil-mature
down-dip. Europa have a site survey planned for 2020 and are
seeking a farm in partner.
Field history of the Celtic Sea
The North Celtic Sea Basin hosts three producing fields (Kinsale
Head, Seven Heads and Ballycotton) and several discoveries. Kinsale
Head was discovered in 1971. Marathon Oil drilled and successfully
tested the seismically defined shallow anticlinal Lower Cretaceous
feature. This was a surprising discovery as the first well was
drilled slightly off structure but encountered oil and gas shows
within the Greensand and Wealden reservoirs. The field came
onstream in 1978 and has been a key domestic gas producer for
Ireland. Operator, Kinsale Energy confirmed that production will
cease in 2020/21. It is expected that well abandonment and
decommissioning operations will commence in 2021. The operator has
estimated that Kinsale Head has produced in the region of just
under 2 Tcf of gas, making it the largest Cretaceous gas discovery
offshore Ireland to date.
The Seven Heads gas field was discovered in 1974 by Marathon's
wildcat 48/24-1, which encountered gas within the Lower Cretaceous
and Wealden reservoirs. At the time of discovery, it was not
considered to be commercial and therefore did not come onstream
until 2003. The field was tied-back to the Kinsale Head
facilities.
Ballycotton, a field also analogous to Kinsale Head was
discovered by Marathon in 1989 and has a Lower Cretaceous reservoir
with a shallow anticline. It was brought onstream in 1991 and
continues to produce.
In 1995 Kinsale Head Southwest was discovered and subsequently
tied into the Kinsale Head development, coming onstream in 1999. In
2001 the field was redeveloped as a gas storage facility. Further
development in 2006 enabled the storage facility to receive gas
from the onshore network.
Looking forward in the Celtic Sea
Beneath the Kinsale Head Southwest field in the Lower Cretaceous
stacked Lower Wealden and Purbeckian sandstones lies the Barryroe
oil field. Barryroe has remained undeveloped since its discovery in
1973. However, current operator Providence Resources has been
attempting to mature the development. In 2018 it signed a farm-out
agreement with APEC Energy Enterprise to develop the field. In
September 2019 a site survey for development drilling was
undertaken.
Another discovery, Ram Head, was made in 1984 by Marathon with
well 49/19-1. The discovery is now operated by Predator and the
company has announced a potential appraisal programme on the
discovery. The company is looking to re-enter 49/19-1 to test the
discovered gas to understand the scope of a potential development.
Predator state that a reservoir engineering study shows development
potential of 10 wells with a recovery of 1 Tcf of gas over an
11-year period.
Field History of the Northwest Offshore Ireland
Basin
The Northwest Offshore Ireland Basin is subdivided into the
Slyne and Erris sub-basins. The Slyne sub-basin hosts the Corrib
gas field. First discovered in 1996 by Enterprise Energy it is the
largest gas discovery since Kinsale Head. The successful discovery
proved the highly porous and permeable nature of the Triassic
Sherwood sandstone reservoir. The Carboniferous coals charged the
Triassic reservoir and the halite Merica Mudstone group sealed the
Corrib anticline, creating a four-way dip closure. Shell acquired
Enterprise in 2001. The Dutch major encountered issues developing
Corrib but finally bought the field onstream in December 2015. At
peak production Corrib has produced approximately 96% of Ireland's
gas demand. Subsequently Shell exited Corrib in 2016 and Vermillion
became operator.
Corrib's success led to further exploration interest within the
Slyne sub-basin (Figure 2), and several prospects have been
identified. The Corrib South prospect owned by Predator is located
20 km south of Corrib and has the same Triassic Sherwood sandstone
reservoir. Corrib South is estimated to hold resources of 424 Bcf
and could be tied into the Corrib infrastructure. Key risks include
the seal effectiveness and hydrocarbon migration. A potential well
is planned for 2020.
Europa has a number of prospects in the area. In FEL 4/19 lies
the Inishkea prospect. Inishkea is a large fault-bounded, pre-rift
Triassic prospect mapped on 3D data. Its located 11 km northwest of
Corrib and also has a Triassic Sherwood sandstone reservoir. The
prospect has best resource estimates of 968 Bcf and is understood
to be sourced from the Carboniferous and sealed by a combination of
the Triassic Uilleann halite and also fault seal. The key risk with
Inishkea is seal effectiveness due to Mid-Cretaceous inversion
causing shortening and salt movement throughout the area, leading
to the removal of approximately 1 km of overburden. The absence of
a gas chimney associated with Inishkea compared to Corrib is likely
to de-risk this prospect. Europa has been attempting to farm out
the prospect with a view to drill a well in 2020. Inishkea West and
Northwest provide exploration upside in the licence. GIIP for all
prospects in FEL 4/19 is estimated to be 2,363 Bcf. Further
exploration upside exists within Europa's acreage in the form of
Corrib North, another Triassic Sherwood sandstone structure.
Figure 2- Petroleum Play of Inishkea and Corrib.
Outlook
Further exploration activity is required to unlock the
hydrocarbon potential of offshore Ireland. With many of the
Licensing Options being converted in to Frontier Exploration
Licences from the 2015 licence round, it is hoped that further
exploration activity is on the horizon. More exploration is
required to prevent Ireland's energy security from becoming
increasingly strained as producing fields such as Kinsale Head
approach abandonment. As Corrib begins to decline Ireland will need
to either replace this domestic gas supply or become increasingly
reliant on imports. This coupled with the Climate Energy Emergency
Bill which was put forward through Dáil Eireann has put the future
of the oil and gas industry under scrutiny. The Taoiseach Leo
Varadkar, recently put forward his proposal at the UN Climate
Action Summit to phase out oil exploration in Irish waters, in
order to achieve carbon neutrality by 2050. The Government
confirmed that companies can continue to explore for natural gas as
it sees gas playing a role in Ireland's Energy security for years
to come. The Irish Offshore Operator Association has announced:
"that existing exploration licenses will be unaffected and the
Government announcement only relates to future licenses not those
granted in the 2015 Licence Round". Thus it is clear that the
Government's proposals "will relate to future
applications" and that "existing licences will remain
valid". IOOA, Chief Executive Officer, Mandy Johnston said:
"It is important that further clarity is given on how the
Government's proposal for future licencing rounds will be
implemented as a representative body investing considerably in
offshore Ireland we are seeking a meeting with Minister Canney at
the earliest possible opportunity".
With drilling activity planned for 2020 and companies working up
their 2015 licence round acreage, there is the potential for
future discoveries to address Ireland's falling gas production.
Despite the optimism, the Irish operating environment comes with
its challenges, such as a lack of transport infrastructure and high
deep-water drilling costs. Although more than half of the Licensing
Options awarded during the 2015 round have been progressed to
Frontier Exploration Licences it will be drilling results that
ultimately determine its success. Ireland now needs proven
commercial discoveries.
Gain additional insight into offshore basins, licensing
rounds, exploration history and more with
Upstream Intelligence Solutions from IHS Markit.