RE: Will we need another wonga?1 Feb 2019 12:38
Depletion rates are arrived at by deducting what's extracted, per field, from what's extractable. The decline rates, per field, are, for my modelling purposes, started at 7.5% p.a. then updated as actual information from the field operator becomes available. There's volumes of useful information online; http://energyskeptic.com/2015/the-difference-between-depletion-and-decline-rate-in-oil-fields/ being a good entry point to the subject.
Of course changes in stated reserves, improvements in extraction techniques, drilling of additional wells, etc. all help to confuse the picture.