Ann: Half-Year 2018 Results and Briefing Pack, page-59

No one values exploration in M&A activity - for the same reason that majors don't report any pre drill estimates.

Quite simply the industry doesn't get pre drill estimates right very often. Looked at statistically - the industry as a whole gets above P50 volumes in about 10-20% of discoveries. The average result per well is around 1/3rd to 1/10th of the original prediction depending on the area looked at. Around 1-2% of discoveries are above any pre-drill estimates, with around 20-30% below any pre-drill estimates. There's lots of examples, training courses etc. that are done on this subject, but no company seems to have successfully cracked this nut globally. It's one of the reasons I put zero emphasis on exploration as my investing strategy (and as I've mentioned before - I'm an exploration geologist)

Example of a study looking at this from Norway - geologically a very well understood part of the world:
https://www.sciencedirect.com/science/article/pii/S0928893700800077
There's probably a good 100 or more papers addressing this topic in the academic literature, Norway makes for great case studies because the regulator records all this information and makes it public - in most countries this information is not known or released.