In the summer of 2018, Wellesley conducted an operated exploration drilling campaign in Quad 35 of the Norwegian North Sea with the aim of discovering sufficient additional resources to commercialise the stranded Grosbeak oil discovery. The drilling campaign was delivered safely and achieved its objective of adding sufficient volumes of oil and gas for development planning to proceed. A cross-disciplinary effort was key to recognising and realising the potential of the area.
Grosbeak and the surrounding area was well known to several members of the Wellesley technical team who were involved in the subsurface analysis and drilling of the original Grosbeak discovery well in 2009. Subsequent appraisal in 2011 left several key geological uncertainties unresolved. In 2015 Wellesley committed to purchasing state of the art broadband seismic data in the area, thus marrying local geological experience with improved imaging of the subsurface. The central perceived challenge with the Grosbeak Discovery was uncertainty in the distribution and continuity of the reservoir sandstones. Analysis of the new data, coupled with a review of core samples taken from earlier wells indicated to the team that the Grosbeak reservoir was potentially more predictable and continuous than was previously thought, justifying an appraisal well to test this concept. Additionally, the nearby Serin and Kallåsen prospects were matured, resulting in three wells being planned, all with the potential for additional volumes to allow a commercial development in the area.
Beyond the technical challenges, further appraisal and commercialisation of the Grosbeak Discovery was previously impeded by the fact that the structure covered three licences, each with different ownership and intentions for the area. Wellesley took the view that the only way to progress the discovery was to assume operatorship of each licence and therefore embarked on the process of establishing a position in the area. Four constructive “win-win” commercial transactions with companies for whom Grosbeak was non-core, coupled with a successful application for open acreage in the 2017 APA licensing round allowed Wellesley to unify Grosbeak under a single operator for the first time. This being achieved, planning of the exploration wells could begin.
With three wells committed in the Grosbeak area, the Wellesley operations team began the process of planning an operated exploration campaign. The objectives were (i) to discover sufficient resources to allow a commercial development on or around Grosbeak, (ii) To establish the scale of the resource for consideration of development concepts, and (iii) to gather all required appraisal information in a single campaign. The Transocean Arctic drilling unit was contracted and thanks to a decision to pre-invest in site surveys, well planning was matured such that the campaign could begin only 4 months after Wellesley assumed operatorship of the acreage. During the 159 day drilling campaign, five boreholes (three top holes and two sidetracks) were drilled, with a total of 12,790 metres drilled. A successful production well test was performed and 486 metres of core was taken. Extensive data acquisition was run in each of the five sections of the wells where hydrocarbons were encountered. This focus on high quality data means that the discoveries made can now be progressed towards development planning. Wellesley’s philosophy of pre-investment and efforts to foster ownership and inclusivity with its licence co-venturers and its partners in the supply chain has delivered outstanding operational efficiencies and with excellent focus on risk management and major accident prevention.
Months from licence award to the start of drilling
Consecutive days of operations
Successful well test performed
Of core cut plus acquisition of extensive log and fluid data over 5 hydrocarbon bearing sections
Million barrels of oil equivalent discovered
Drilled in 3 top-holes and 5 reservoir bores
A minor oil discovery was made at the Kallåsen that in itself was insufficient to aid commercialisation of Grosbeak. The second well in the campaign, on the Serin Prospect proved to be dry. The third well tested Wellesley’s subsurface model on Grosbeak and this borehole penetrated excellent oil-saturated reservoir with very good productive potential. A sidetrack further established the predictability of the Grosbeak reservoir and also discovered good quality oil and gas reservoirs in a shallower sections. Together, the developable resource potential delivered from the campaign is estimated at 100 -192 million barrels of oil equivalent.
With a high-equity operated position, the Wellesley team will now initiate development planning while at the same time generating new prospective ideas elsewhere on the Norwegian Continental Shelf that will form the basis for future exploration drilling campaigns.