Annaghmore-1 and Ballynamullan-1 Wells, Larne-Lough Neagh Basin, Northern Ireland

Abstract:The stratigraphy encountered in two closely spaced exploration wells drilled on the north-west shore of Lough Neagh, Northern Ireland, is reported. Annaghmore1 was drilled to a depth of 5100ft (1554.5m), and Ballynamullan-1, which was a deviated hole, reached a vertical depth of 4500ft (1371.6m). Both wells drilled through the Antrim Lava Group, the Ulster White Limestone Formation and a Permo-Triassic red-bed sequence comprising the Mercia Mudstone, Sherwood Sandstone, Belfast and Enler groups. The Annaghmore-1 well drilled a thick (542.5m) red-bed section beneath the base of the Belfast Group, which lacked definitive palynomorphs but which is thought to be Permian in age. The upper part of the Triassic sequence and the Lias are absent in the wells, probably as a result of erosion following Late Cimmerian tectonism. Differences of stratigraphical detail between the two wells are attributed to movement on intervening faults at different times. Spore fluorescence studies indicate that the well section is submature to mature for oil generation to 1219m and mature for dry gas beneath 1310m. Apatite fission track analysis suggests that Carboniferous source rocks produced much of their hydrocarbon potential during the Variscan episode.