Ann: Appendix 3Y, page-43

When they build up a DCF model, they use certain variables to project the PV10 for the Field, ie,

Field life 10 yrs,
2P2C for Bauna+Patola 51 mmbbls,
10% royalties
POO of USD 55/bbl to calculate Revenue/year
Opex/Capex Cost guidance USD/bbl.
Tax rate & Exchange rate.

Once the PV10 is calculated, they do a sensitivity test, i.e, oil price/ cost/ production/ exchange rate fluctuation.

With the planned remedial work for the ESP's + 2 Patola wells the capex gets split over the timeframe for the planned activity.

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To get an idea, u could go to PetroRio's website & download their DeGolyer certified reserves for Frade & Polvo etc. That should help u understand this better.

This time around KAR r using another mob to sign off the reserves & they haven't released the detailed Report as was the case in the past for their Brazil assets.

http://ri.petroriosa.com.br/servicos-aos-investidores/relatorios-de-certificacao/

https://api.mziq.com/mzfilemanager/v2/d/cecb3d3e-6bd6-4edd-b9b3-3cacde780cac/eda1e601-10f3-4ab7-7fbb-1414e7084e5f?origin=1

Skip to page 40-41 on the above link.
Hope this helps.