It is a positive sign that, hearing so often that the Southern North Sea is very near its closing chapter with regards to exploration, the first talk at a one-day conference dedicated to UKCS fields is about an exciting field development in this very area.
At the Memoir 52 launch conference – organised by the Energy Group – that took place yesterday, fields from all over the UKCS were presented at the various stages of their development, with some even decommissioned already. As the conveners Graham Goffey and Jon Gluyas alluded to multiple times during the day, the UKCS may be on the decline in terms on production, the variety of plays still being chased is broader than ever, plus there is increasing/continuing interest to look at other ways to use the subsurface.
Back to the Tolmount field, of which the development and exploration history was nicely set out by Andrew Miles from Premier.
Persistence required to get to the reservoir
The field was first drilled in 2008, through 42/28d-10, but the bit never made it to the reservoir because of mechanical issues. The second attempt was made in 2010 and the well made it deeper into the stratigraphy, but yet again had to be abandoned due to wellbore stability issues. Both listric faults cross-cutting the Jurassic-Triassic overburden as well as unstable Liassic shales were considered a major factor behind the failures.
Finally, in 2011, well 42/28d-12 was successfully drilled into the Rotliegend reservoir. However, it was only the third reservoir penetration (42/28d-13Z) that encountered the gas water contact, confirming a gross gas column of more than 650 ft which increased the field’s GIP significantly (450-800 BCF).
Tolmount East and the million-dollar question
The Tolmount field is a dip-closed faulted anticlinal trap, with the main uncertainty being on the eastern side of the field. Here, uncertainty in depth-conversion prevents drawing conclusions on whether Tolmount is in fact the same pool as Tolmount East (see cross-section above).
The Tolmount East accumulation was appraised last year by well 42/28d-14, but no gas water contact was found, so it is a matter of waiting for early production data to draw conclusions on connectivity. In the meantime, Premier is progressing towards developing Tolmount East and a subsea development scenario has been selected.
Near field exploration potential
During the 32nd licensing round, Premier was awarded a 50 per cent operated interest in Blocks 42/28e and 42/29b in the licence directly to the east of Tolmount and a 50 per cent non-operated stake in Blocks 42/27, 47/2b and 47/3g in the licence immediately to the west of Tolmount. Dana is Premier’s 50 per cent partner in the two licences and the operator of Blocks 42/27, 47/2b and 47/3g (see map above).
Reference to the Tolmount paper:
Miles, A., Allen, M., Fairweather, L., Hilton, J., Sloan, H. & Zapico-Palmero, P. (2020). The Tolmount Field, Block 42/28d, UK North Sea. In: GOFFEY, G. & GLUYAS, J. G. (eds) 2020. United Kingdom Oil and Gas Fields: 50th Anniversary Commemorative Volume. Geological Society, London, Memoirs, 52, 262–272. DOI.