Petrophysical Uncertainty

1. Petrophysical Uncertainty Who Cares?

4. Porosity Model Recoverable volume BUT THE EFFECTIVE POROSITY IS NOT THE TRUE POROSITY OF THE MATRIX NTG is estimated using a porosity cut-off

5. Porosity of Clast & Impact on NTG 0 0.2 0.4 0.6 0.8 1 PHI CLAST PHIT ERROR Clast Vol PHI Cut NTG 6% 8% 10% -10% -2% +10% +2% 3.7% 6.7% 9.7% 0% 0% The effective porosity calculated depends on the clast porosity. A Porosity cut-off combined with different estimates of porosity leads to different NTG values The Porosity cutoff depends on the porosity of the clasts Since an increase in the clast volume decreases the effective porosity, the matrix porosity is underestimated and a lower porosity cutoff is required.

6. Probability Distributions Unit 2 P90 = 0.03 P50 = 0.21 P10 = 0.61 But what does this mean ? I am most confident that I have a NTG less than 0.03. But this is an economic producing oil field. The uncertainty range is so large it tells me nothing about reality.

13. Risk – A Bad Example

16. Probability Distributions Average? P50??

18. Monte Carlo Simulations – A Petrophysical Favourite

19. Monte-carlo simulation

21. Creation of Subsurface Models

22. Model Based Approach Subsurface Model 1 Uncertainty Parameter 1 Uncertainty Parameter 2 Uncertainty Parameter 3 Uncertainty Parameter n Monte-Carlo Rules For Dependency Outcome 1 Outcome 2 VOI New Data Risk(s) Acceptable Subsurface Model 2 Subsurface Model n Model Risk(s) no Model valid for Project Decision Gate yes Project Economics Note: different models Can produce different risks. Requires roll-up of models And simulation on a lower resolution

23. Uncertainty & Risk Register

24. Uncertainty & Risk Register Theme Impact of Event Prevention Actions RISK EVENT Residual Risk L/I Mitigation If Event Occurs Decision Gate at Which Risk is Accepted Likelihood/ Impact (L/I)

25. VALUE OF INFORMATION I will drill horizontal wells since the Maximum ENPV is 36.5

26. VALUE OF INFORMATION VOI = 39.5 – 36.5 = $3.0 M

28. END