Exploration for oil and gas in Northern Ireland began in 1965 and whilst both have been detected in wells, this has not yet led to commercial production. Despite this initial lack of success many areas remain relatively little explored and the rocks beneath Northern Ireland are still considered to have significant hydrocarbons potential.
The geology of Northern Ireland divides into four main regions: the Dalradian rocks of the Sperrin Mountains and surrounding areas; the Lower Palaeozoic rocks of Down and Armagh; the Devonian and Carboniferous sedimentary rocks of Fermanagh, Tyrone and parts of Armagh; and the Antrim Plateau with its cover of basalts and underlying Mesozoic and Palaeozoic sedimentary rocks. In terms of oil and gas prospectivity the first of these regions is not of interest.
The two most prospective areas are in the Lower Carboniferous rocks of Co Fermanagh and south Co Tyrone and the Carboniferous to Triassic rocks beneath the Antrim Plateau. The former has a history of gas shows from a small number of exploration wells but the prospectivity is reduced by the poor quality of the low permeability tight gas sandstone reservoir rocks. Similar unconventional gas resources are exploited in North America by hydraulically fracturing the reservoir to stimulate gas production. Following the recent boom in shale gas production in North America the focus of interest in Fermanagh has shifted to the shale gas potential of the Lower Carboniferous marine shales.
The Antrim Plateau is even less well explored because of the technical difficulties in imaging the geological structure beneath the thick cover of Palaeogene basalt lava. Consequently only six exploration boreholes have been drilled there since 1971, the most recent in 2008. The underlying geology has many similarities to that of the East Irish Sea Basin which hosts the ‘giant’ Morecambe Bay Gas Field and several producing oilfields.
Early Carboniferous basins in Co Fermanagh and south Co Tyrone
This area covers the Carboniferous outcrop that extends from Co Fermanagh eastwards through south Co Tyrone to Co Armagh.
Westwards it extends to Counties Cavan, Leitrim, Sligo, Monaghan and south Co Donegal in the Republic of Ireland. In counties Fermanagh and Cavan, the early Carboniferous section comprises 3,500 metres of marine sedimentary rocks that include organic-rich mudstone and sandstone which are potential hydrocarbon source and reservoir rocks respectively. Late Carboniferous rocks of the Fintona Block and in the Coalisland area of east Co Tyrone contribute to a cumulative maximum thickness of c.7,000metres of Carboniferous strata.
Five wells were drilled in 1965-1966, resulting in gas shows at Dowra and McNean in Co Cavan and at Big Dog and Owengarr in Co Fermanagh while the Glenoo No.1 well, in the SlieveBeagh area of Co Tyrone, was dry. Interest in the area lapsed when testing of the wells produced non-commercial gas flows. Dowra No.1 was re-entered in 1981 and the reservoir interval was hydraulically fractured producing a tenfold increase in flow-rates to 250,000 cubic feet of gas per day (250 mscfg/day) from the Dowra Sandstone Member of the Bundoran Shale Formation. This led to further exploration comprising a 2D seismic reflection survey in 1982 followed by drilling of wells at Slisgarrow and Kilcoo Cross in Co Fermanagh, and Macnean No.2 and Drumkeeran in Co Cavan in 1984-1985. Gas shows were again encountered but the wells did not flow to surface when tested.
In 1996, licences were awarded for the area between Co Fermanagh and the west shore of Lough Neagh. Six wells were drilled in 2001, four in Co Fermanagh and two in the Republic of Ireland. The Mullaghmore Sandstone Formation reservoir intervals were hydraulically fractured and extended well tests performed. Unfortunately, the fractures did not propagate as well as had been hoped and this, combined with low formation pressures, led to low gas flow rates of <100 mscfg/day. The wells were considered non-commercial given the high drilling costs and lack of infrastructure in the area.
The development of shale gas resources has the potential to provide economic benefits and to help reduce the continuing dependence on imported fossil fuels to meet Northern Ireland’s energy needs but ultimately, it will fall to the Northern Ireland Executive to determine whether or not to approve the use of high volume hydraulic fracturing in Northern Ireland. Moreover, the shale gas industry and, in particular, the use of hydraulic fracturing are controversial topics which can lead to polarised public opinion. Consequently the ability of a company to engage with the local community and obtain a ‘social licence’ to operate in an area is likely to be as necessary as obtaining all the regulatory permits required for shale gas exploration and production.
In Northern Ireland, two main areas of thick Permian and Triassic sedimentary rocks are located in the Rathlin and Foyle basins, north of the Highland Border Ridge, and in the Lough Neagh and Larne basins, to the south. The succession comprises up to 3,000 metres of Permian and Triassic volcanic and sedimentary rocks and includes rock units that are good potential reservoirs and seals, similar to those in the Morecambe Bay Gas Field and in oilfields in the East Irish Sea Basin. Lower and Upper Carboniferous mudstones and coals are known from outcrop west of Lough Neagh and in the Ballycastle coalfield and these oil- and gas-prone potential source rocks are predicted to have reached maturity beneath the deeper parts of the Permo-Triassic basins.
In 1971 the Newmill No.1 well was drilled in the Larne Basin on the basis of surface structure and nearby offshore seismic data. It encountered good reservoir rocks and seals but no significant hydrocarbons. In 1981 and 1983, the Northern Ireland government commissioned Vibroseis seismic reflection surveys in east Co Antrim and west of Lough Neagh which demonstrated that sedimentary rocks beneath the basalt lavas could be imaged moderately successfully. Integration of that seismic data with gravity data and the results from deep boreholes sought to produce exploration models with the aim of stimulating further exploration.
Since then further seismic exploration has been carried out and four wells have been drilled, two in the Larne Basin and two in the Lough Neagh Basin. Slight gas shows were found in the Ballytober Sandstone Formation in Newmill No.1 and Larne No.2, and oil-staining in Annaghmore No.1 indicate the presence of hydrocarbons in these basins. There is one current petroleum licence in south Antrim, operated by InfraStrataplc, and two new seismic surveys were shot across this licence in 2011 and 2012.
Recent advances in seismic acquisition and processing have led to improvements in data quality and InfraStrata has recently drilled a test well in Larne Lough, completed in mid-2015. Conventional reservoir targets in the Triassic, Permian and Carboniferous could be tested with a single well at this location.
The quality of the available 2D seismic data is particularly poor in the Rathlin Basin although deep boreholes, drilled for mineral and geothermal exploration, have provided valuable information about the succession there. Re-processing of the seismic data and modelling of gravity data led in 2008 to Ballinlea No.1 becoming the first exploration well to be drilled in the Rathlin Basin. This borehole was drilled to almost 2700 metres depth and yielded encouraging results, recovering samples of oil to the surface. This represented a significant advance, providing strong evidence for a viable petroleum system in the Rathlin Basin. The current Licensee, Rathlin Energy Ltd., has integrated well, surface and borehole seismic data with the results from recent airborne full tensor gravity surveys to identify a suitable drilling location. At the time of publication the Licensee has submitted an application for planning permission for an exploration well a short distance north of Ballinlea No.1 and this application is subject to an Environmental Impact Assessment. The new well is designed to further evaluate the geological structure and reservoir unit from which oil was recovered in Ballinlea No.1.
Petroleum licensing in Northern Ireland (December 2014)
The Petroleum (Production) Act (Northern Ireland) 1964 vested petroleum in the Department of Enterprise, Trade and Investment (DETI) and enables it to grant licences to commercial companies to search for, bore for and get petroleum. On 30 April 2010, the Department made two new Statutory Rules. The Hydrocarbons Licensing Directive Regulations (Northern Ireland) 2010 implement Council Directive 94/22/EC in Northern Ireland by introducing new arrangements and requirements for granting and using licences relating to the prospection, exploration and production of hydrocarbons. The Petroleum Production (Amendment) Regulations (Northern Ireland) 2010 amend the existing Petroleum Production Regulations (Northern Ireland) 1987 to complement the Hydrocarbons Licensing Directive Regulations by introducing new requirements for applications for petroleum licences and new provisions for licences. The amendments brought licensing arrangements here more closely into line with those in Great Britain. Both sets of Regulations were laid before the Assembly on 5 May 2010 and came into operation on 28 May 2010. They can be accessed on the website of the Office of Public Sector Information (www.opsi.gov.uk).
DETI granted four licences in Northern Ireland in 2011 – two of these licences are still current and are shown on the accompanying map. The Initial Term of these licences is five years after which 50 per cent of the licence area must be relinquished. In addition, the Licensees must commit to drill an exploration well, either at the time of application or before the end of the third year. If a Licensee is unable or decides not to make this commitment then the licence will expire at the end of Year Three.
Officials in the DETI’s Minerals and Petroleum Branch can advise potential Licence applicants on administrative aspects of licensing while GSNI can provide information on the prospectivity of any particular area and the exploration data available for inspection, licensing or purchase.
Petroleum licensing in the territorial waters adjacent to Northern Ireland is administered by the Department of Energy and Climate Change (DECC) in London. Six offshore blocks around Rathlin Island were included in a Frontier Licence awarded to P.R. Singleton Ltd. (now held by Providence Resources plc) by DECC on 22 February 2012 as part of the 26th Seaward Licensing Round. Licence P2123, off the east Antrim coast, was awarded by DECC to a consortium led by InfraStrataplc in December 2013 as part of the 27th Seaward Licensing Round.