At first glance, the Columbus field looks like a continuation of the Lomond field to the southeast, also because the reservoir in both accumulations is the same – the Paleocene Forties sandstone.
However, when the first well on Columbus was drilled in 2006 – 23/16f-11 by Endeavour – it turned out that the gas-water contact of the 125 ft gas column was deeper than the contact in Lomond. In addition, there was minimal pressure depletion in comparison to Lomond, which also suggested that Columbus is a separate pool.
Late 2007, two appraisal wells were drilled in the northern part of the Columbus discovery, 23/16-12 and 12Z, and again minimal pressure depletion was observed.
Where is the boundary?
Again a year later, the Lomond partnership (now operated by Chrysaor) embarked on a four-sidetrack drilling campaign to narrow down the boundary of the Columbus and Lomond accumulations. The two sidetracks landing in the south (23/21-7 and 23/21-7Y) were proven to be connected to Lomond because of significant pressure depletion. The well in the northwest (23/21-7X) penetrated a 151 ft Forties gas column at nearly virgin pressure, whilst the 23/21-7Z well encountered a gas column with a different contact as Lomond in a poor-quality Forties reservoir.
Even though there certainly must be a barrier between the two accumulations – a barrier that well 23/21-7Z may be located in – it is still a slightly surprising position. Looking at paleogeographic reconstructions (e.g. Eldrett et al., 2015), it seems as if the Columbus and Lomond Forties sandstones are part of the same depositional system coming from the northwest. It would be easier to understand a barrier between two different channel systems, such as is probably the case in the area of Huntington field, the K2 prospect and the Everest field, but being part of the same system, it is a little harder to imagine what causes the subsequent isolation of the two reservoir units.
Near field opportunities
To the south and southwest of Columbus Serica Energy and Summit mapped a number of prospects: Columbus West, South and Southwest. Although the companies relinquished the licence last year based on expected low permeabilities of the Forties reservoirs, mention was made that if more confidence could be gained on the hydrocarbon phase (with gas the preferred candidate), Columbus West could host commercial volumes. Another risk associated with these prospects is the fact that they rely on stratigraphic trapping.
Upon completion of the 21/16f-C1 well, that will be drilled with a 5,600 ft horizontal section, it will be connected to the Arran pipeline from where the hydrocarbons will be piped towards the Shearwater platform where the gas and condensate will be separated. Serica Energy and partners Waldorf (25%) and Tailwind (25%) expect an average gross production of around 7,000 boe/d. Serica expects to be able to produce 14 MMboe from Columbus.
The information on pressure depletion of the Columbus appraisal wells was derived from:
Jena & Olowoleru (2020): The Lomond Field, Block 23/21, UK North Sea. In: Goffey, G. & Gluyas, J.G. (eds). United Kingdom Oil and Gas Fields, 50th Anniversary Commemorative Volume. Geological Society, London, Memoirs, 52, 511-522.