spudding first well in three years....., page-8

In anticipation of questions ...

Pg is the geological chance of success
Pc is the Commercial chance of success

The truncated reserves distribution cuts out the portion of the distribution that lies below the economic limit (likely to be ~ 10-12 mmbo here). This is why the truncated reserves range is higher than the untruncated reserves range. This is also why you apply the lower chance of success (Pc) to the truncated range.