Abstract Unconventional hydrocarbon exploration in the UK is in its infancy and Third Energy's activities represent a major step towards unlocking the potential contained within the Carboniferous section beneath North Yorkshire. In the United States, production from unconventional petroleum systems has transformed the country's domestic energy markets. If the UK can replicate this success, it would go some way to offsetting the decline of North Sea production and thereby reduce dependence on foreign imports. At the end of 2015, no other company had undertaken any unconventional exploration in North Yorkshire and great uncertainty remained over the region's prospectivity. To rectify this dearth of information, Third Energy carried out a detailed examination of vintage data from the area and also drilled a new well to acquire a modern, unconventionally focused dataset, including approximately 800 ft of core and 4000 ft of wireline log data. Analysis of the mineralogy, maturity, kerogen type, total organic content, brittleness, porosity and permeability of the Carboniferous Bowland sequence has enabled several intervals to be high graded. Given these results, Third Energy now plan to hydraulically fracture these intervals with the intent of producing the UK's first unconventionally sourced electricity at its Knapton Generating Station.

Abstract Hydrocarbon exploration in North Yorkshire began in 1937, targeting Triassic and Permian reservoirs below the surface expression of the Cleveland Anticline. D’Arcy drilled the successful well Eskdale-2, marking the first gas discovery in the Zechstein carbonates in the UK. Since then approximately 100 wells have been drilled in the basin with exploration success relatively high. Out of the 25 pure exploration wells in the region, 13 have found hydrocarbon accumulations (flowed gas) and eight of the discoveries have been developed to date. The primary reservoir is the Permian-aged Zechstein carbonate sequence and, more specifically, the Z2, Kirkham Abbey Formation (KAF), which is a tight carbonate reservoir overprinted by a high permeability fracture system. Despite considerable investment and effort over the years, the historical development story of these fields has been very much one of repeated technical and investment failure, with approximately 39 Bcf (billion cubic feet) of the mapped gas initial in-place (GIIP) of c . 326 Bcf produced to date, an estimated recovery factor of 12%. Historical production data show that all the Zechstein reservoirs have experienced early water breakthrough, leading to impaired gas rates and low recoveries. The water influx is due to a highly mobile, but finite aquifer, which under field production conditions preferentially flows through the high permeability fracture system, bypassing the gas stored in the tighter matrix. Third Energy is aiming to resolve the issue of water influx by using artificial lift to encourage the gas to flow. A trial is currently being undertaken at the Pickering gas field and, if this programme is successful, this will provide sufficient confidence for a phased redevelopment programme of surrounding fields. Whilst North Yorkshire has experienced only limited exploration and production (E&P) activity in the last decade, solving the issue of premature water influx in the KAF fields, combined with the search for unconventional resources in the Bowland section of the Mid and Lower Carboniferous strata will herald a new and exciting phase of E&P activities for this province.