Shell has delayed plans to drill on the South Uist (blocks 213/25a and 214/21a) prospect north-west of Shetland. Drilling was to start in May, but the summer is now more likely due to slippage of drilling rig Leiv Eiriksson’s schedule.
Pre-drill estimates point to recoverable reserves of 2.1trillion cu ft of gas (350million barrels oil equivalent), with an upside potential of 4TCF (666million barrels). This is based on Shell’s most recent mapping and interpretation, and field parameters from regional analogues.
If a commercial find is made on licence P799, early development scenario planning points to a floating production solution for gas and/or oil, with an export link to St Fergus in the north-east of Scotland. This would presumably feed through the system that Total has planned for its nearby Laggan/Tormore gas project.
In the case of a gas discovery, a semi-submersible production unit with full processing and compressing facilities is apparently the likely option.
Should oil also be found, a floater with production and water-injection facilities is deemed the most likely option. In both cases, wells would be grouped in subsea templates around the central floater.
A gas floater would likely have plant capable of handling 400million cu ft per day, plus nine producers in two clusters, each 5km from the host.
An oil floater would perhaps be equipped to process up to 150,000 barrels per day and produce from up to 24 production wells arranged in five clusters, backed up by 12 water injectors.
Export would be via BP’s Clair field infrastructure to Sullom Voe.
The super-major reckons that South Uist is one of the few undrilled prospects of its size, potential and quality on the UKCS.
It lies on a large, well defined faulted four-way dip closure clearly resolvable on Shell’s high-density 2D and 3D seismic data.
Data acquired points to a well defined faulted four-way dip closure circa 16km long by 4km wide, with a maximum areal closure of about 84sq km with potential for a 250m vertical gas column.
However, spudding the well is contingent on a successful farm-down of Shell’s 38.5% interest in South Uist in order to reduce the company’s risk and its view on where oil prices are headed.
Licence P799 has an area of around 145sq km and is located about 30km north of the sizeable Laggan (estimated 720billion cu ft recoverable), 35km north-east of the 2007 Tormore discovery (estimated 320bcf recoverable) and 50km north-east of the recent Rosebank I Lochnagar field (estimated 270bcf and 250million barrels oil equivalent recoverable reserves).
According to a South Uist farm-in marketing document obtained by Energy, the previous attempt to drill the South Uist prospect in Q1 2008 using the semi-submersible, Leiv Eiriksson, failed to complete top-hole operations due to a combination of extreme winter weather, issues related to rig intake maintenance over-hang (even though it had stopped off at the Canaries en route for maintenance), borehole instability and “other logistical challenges”.
“These will be effectively mitigated by scheduling the re-drill for Q3 2009 and the use of a revised well design to avoid borehole instability,” says the document.
The South Uist well is expected to cost $89million.
The earlier 214/21-1a well reached about 2,200m total vertical depth and recorded “positive evidence for “thermogenic gas generation”. Two gas samples were taken from the top-hole section of that well and the results seen as “very encouraging”. Shell insists in the document that the co-venturers remain committed to the re-drill and that it considers South Uist to be “one of the few undrilled prospects of its size”, on the UK Atlantic Frontier.
The P799 licence was originally awarded to ConocoPhillips, OMV and Brasoil in 1991 in the 13th (Frontier) UK licensing round. Shell obtained equity in the licence in 1988 and additional equity through the acquisition of Enterprise Oil in 2002.
A modern 3D survey was acquired in 1998, with modern reprocessing undertaken in 2002. The reprocessed data has enabled more accurate definition of the main South Uist closure which was originally identified on the original 3D and older 2D seismic.
ConocoPhillips later relinquished control and Shell became operator from April 1, 2007.
The current co-venturers comprise Shell with 38.5%; ConocoPhillips 25%; INPEX UK 20%; Nippon Oil 10%, and OMV 6.5%.