Investigation of Geothermal Potential in the Irish Carboniferous Palaeokarst
Nick O'NEILL, Lloyd VAZ, Deirdre LEWIS, Sarah BLAKE, Paul GORDON
[SLR Environmental Consulting (Ireland) Ltd., Ireland]
In accordance with Ireland’s National Mitigation Plan (July 2017) and the GSI Research Roadmap, the GSI commissioned a short-call research project focused on investigating geothermal potential of the Irish Carboniferous karstified limestones at depth. Anecdotal evidence of dropped rods, cavities and non-recovery of core from mineral exploration drilling in Ireland casts doubt on the assumption that Palaeozoic rocks at depth have negligible porosity and permeability. Evidence from the oil and gas industry shows that coalesced collapsed palaeocave carbonate reservoirs exist in the Ordovician Ellenburger Ramp Carbonate play of West Texas. So why not in the Irish Carboniferous? The ‘Coalesced Collapsed Palaeocave’ play, characterised by moderate porosities and permeabilities in the Ellenburger is considered to be a good analogue for geothermal resource potential of the Waulsortian Mudbanks. A review of numerous published articles, well-reports, etc. and personal meetings with Irish Carboniferous Geology experts provided substantial evidence to support the hypothesis of the presence of preserved karst within the Waulsortian at depth. Between the two main Carboniferous Basins viz. Dublin Basin and Shannon Trough, the latter was considered as the better prospect to intercept the Waulsortian coalesced mud mounds at depths of more than 1000m. A focused seismic interpretation was carried out on four recently acquired 2D seismic lines in the north of the Shannon Trough (Kilbricken Mine area) by Hannan Metals Ltd. The analysis showed a number of ‘karst indicators’ (sag features, polygonal faults etc) towards the base of the Waulsortian Formation which were inferred to be related to preserved collapsed structures, like those observed in the Ellenburger Group. The ‘Kilmurry Prospect’ is a proposed drilling target, intersecting a collapsed palaeocave at ~900m depth with a potential for temperatures of up to 30°C. Drilling the prospect will allow the acquisition of a comprehensive suite of wireline logs to prove the exploration model. A recommendation is made to investigate the potential of similar Waulsortian karst systems, in the deeper parts of the Shannon Basin i.e., south of the Kilbricken area, in the Adare region, once the Kilmurry Prospect is proven.
|        Topic: Geology||Paper Number: 12029|