I've just read the source report. Here is the basis for the assertion;
Today the most straightforward way to assess Scotland’s likely remaining offshore oil wealth is a forward projection of the data of Figure 1. [Figure 1 is UK output since first production.] Using this approach I estimate an ultimate resource of 31 x 109 Bbl, with 11% still remaining to be recovered over the next decade. My total coincides closely with geologically grounded estimates, dating as far back as the mid-1990s, which were based on field-by-field appraisals of the porous volume of reservoir sands.
This completely ignores the fact that the industry forecasts that production will double by the end of next year. As I said in my initial assessment, the report is, at best, misleading. I would now go further and say that it ignores recent developments and instead just extrapolates from historic data.