Abstract The Breagh Field is in UK Blocks 42/12a, 42/13a and 42/8a. It is a gas field with multiple reservoir intervals within sandstones of the Early Carboniferous Yoredale Formation (equivalent to the Middle Limestone Formation within the Yoredale Group onshore). It was the first and is presently the only field developed within these sandstones, offshore UK. Breagh was discovered in 1997 by well 42/13-2 and proved by development well 42/13a-A1. Its crest is at 7110 ft TVDSS (true vertical depth subsea), marked by the unconformity between the base Zechstein and the subcropping Yoredale Formation. It has a free water level at 7690 ft TVDSS, a maximum column height of 510 ft and a field extent of 94 km 2 . Breagh was developed using ten wells from a 12 slot normally unattended platform; five of the wells have been stimulated by hydraulic fractures with proppant injection. The unprocessed gas flows through a 110 km 20-inch diameter pipeline to the Teesside Gas Processing Plant. Production started in 2013, reached a peak rate of 150 MMscfgd in 2014 and, by the end of 2018, had produced 140 bcf. The field is operated by INEOS Oil and Gas UK Ltd (70%) with partner ONE-Dyas B.V. (30%).

Abstract Following the play-opening successes of the Breagh and Pegasus gas fields, we evaluated the potential of the Visean and Namurian (Carboniferous) petroleum plays in the northern Dutch offshore. This evaluation incorporated seismic and well data from the Dutch, British and German North Sea sectors. The abundance and thickness of reservoir-quality Visean–Namurian sandstones was found to increase from Breagh towards the NE. Visean–Namurian coals and shales are considered promising source rocks to charge these reservoirs in the Dutch Central Graben (DCG) and Step Graben (SG). The presence of a mature Paleozoic source rock in the SG and DCG is supported by hydrocarbon shows and vitrinite reflectance data. In the southern E and F blocks, charge may also occur laterally from Upper Carboniferous Westphalian coals. A regional post-well analysis showed that the Visean and Namurian plays are virtually untested in the Dutch northern offshore. Two tests were positive but had high N 2 contents, one was negative, while 10 wells were drilled off-structure and are therefore considered invalid tests of this play. Hence, it is concluded that the Visean and Namurian in the northern Dutch offshore have significant hydrocarbon potential.