Haydn Black’s article is pretty sound all told although there is one part that stands correction.
In the section headed Risk the RPS Energy report was done in 2008 (not 2012) and it estimated the chance of success (petroleum to the surface for testing of its commerciality) of 2% for Bellevue and 0.7% for Thunderbolt.
The 18-24% COS figure was said to have been derived by Global Exploration Services (United Kingdom) and was strongly touted at the time by Bendall, Baldwin and a TXO stooge. Its Report was referenced as an Appendix to the 2012 GSLM Annual Report but not actually made available to shareholders as far as I can recall (only one thumbnail of a Table from it).
Subsequently a report by Senergy estimated a COS of 6% for Bellevue.