LONDON -- Nautical Petroleum’s latest appraisal well in the Kraken heavy oil field in the UK central North Sea has exceeded expectations. The 9/02b-4 well was drilled to a TD of 4,502 feet (1,372 m) MD. Nautical says the top of the target Heimdal III was encountered at 3,856 ft (1,175 m) with a gross thickness of 160 ft (48.7 m). The well proved a substantially thicker and higher porosity main Heimdal Unit III reservoir than expected.
Early log evaluation suggests the Heimdal III main sand contains 83 ft (25 m) of net oil pay with an average porosity of 38.8% and an average oil saturation of 87.2 %. No oil/water contact was encountered, which indicates that the oil-down-to level has been extended to 3,934 ft true vertical depth subsea (1,199m TVDss), compared with 3,842 feet TVDss (1,171m TVDss) indicated in the earlier 9/02b-2 well.
On completion of wireline logging, a casing string was run and a 50-ft (15-m) interval was perforated. A test string also was run comprising sand screens and an electric submersible pump and the well was production tested. The test program was designed to recover uncontaminated reservoir fluid samples and to confirm the productivity of the reservoir tested in the 9/02-1A discovery well. Nautical says these objectives were fulfilled, although operational problems prevented flow at a stable production rate.
The well was initially pumped at a restricted rate of 300 b/d. A productivity index of 2 b/d per psi confirmed the reservoir’s strong multi-Darcy quality. After this initial flow period, productivity declined markedly. An injectivity test was then completed which revealed an injectivity index of, again, 2 b/d per psi. According to Nautical, this suggests the productivity decline was due to plugging of the sand screens, rather than a reservoir or oil quality issue.
Production was then maintained at a low rate in order to recover oil fluid samples for use in development studies. Analysis indicates in-situ oil viscosity of around 100 cP, similar to the 9/02b-2 well.
Nautical says the lower section of the well will be abandoned and the 9/02b-4z exploration sidetrack will be drilled to the west, targeting prospective resources of 114 MMbbl. This operation should take 14 days to complete.
Steve Jenkins, CEO, said the result “significantly exceeded our pre-drill expectations. The well has encountered significant net pay with excellent oil saturation and porosity, and has substantially increased the oil-down-to over Kraken. We will seek to establish the oil resources implications over the coming weeks.”