To date, fractured crystalline basement reservoirs (basement) on the UK Continental Shelf (UKCS) have largely been underexplored, despite the fact that numerous indications of hydrocarbons have been reported from basement in wells dating back to the 1970s. As production from the UKCS continues to decline, and with the exploration potential of more traditional plays becoming increasingly mature, the potential of the overlooked and underrated basement play warrants further exploration. Over the last 10 years, Hurricane Energy (Hurricane) have deliberately set out to explore the potential of this untapped resource, focusing on the Rona Ridge trend, West of Shetland. The Lancaster Field has been penetrated by four wells and benefits from a full 3D seismic survey, and, as such, represents Hurricane's most de-risked basement asset. The level of understanding of the Lancaster reservoir is such that Hurricane is now working towards a phased field development. This paper provides a summary of the geology and reservoir characteristics of the Lancaster Discovery, and a description of the technical progress achieved, to date, in de-risking the Lancaster Field.Gold Open Access: This article is published under the terms of the CC-BY 3.0 license.The Lancaster reservoir is the UK's first fractured basement field and was granted field status in September 2015. The field is delimited by four wells, each of which has been the subject of drill stem testing resulting in oil to surface. Estimates of the resource potential at Lancaster are provided by an independent Competent Persons Report (CPR), commissioned as part of the process for the admission of Hurricane Energy (Hurricane) to the AIM market in 2014. Consequently, this volumetric assessment has been subject to the 2007 SPE/AAPG/WPC/SPEE Petroleum Resource Management System (PRMS). Volumetric ranges are presented as Table 1: however, it should be noted that the volumetric assessment was written prior to the 205/21a-6 horizontal development well drilled in 2014, the productivity of which transformed Hurricane's understanding of the Lancaster reservoir productivity potential. This paper builds on previous publications (Slightam 2012;Trice 2014;Bonter 2015;Belaidi et al. 2016) and provides a summary of the progress Hurricane has made in de-risking Lancaster. The paper is split into five sections covering drilling history, reservoir description, fracture porosity, field simulation and technical de-risking. A concluding section on the future plans for the Lancaster Field is also provided.
Drilling historyThe Lancaster Field is penetrated by four wells, as summarized in Figure 1. The first well was drilled in 1974 and the most recent well in 2014. The objectives of each well and their findings are summarized in this section.Well 205/21-1A was drilled in 1974 and was targeted at a Mesozoic succession directly overlying the Precambrian Basement. The well serendipitously encountered oil within the basement, with shows observed in open fractures (documented in well-site core de...