Increasingly, reduced petrophysical data sets are being used to make critical decisions about the location of deepwater exploration wells. In addition, while drilling deepwater wells, reduced data sets are being used to make well design and completion decisions that may impact the safe operation of the well. However, despite numerous examples in the literature of how data is used to make decisions, very little attention has been given to reliability of the data and its impact on uncertainty, diagnosis, and risk. This presentation will act as a catalyst for starting a discussion on the impact of data reliability on risk assessment. The talk will cover the fundamental principles of uncertainty risk and the impact of data reliability on decision making. Two examples will be used to illustrate the issues. The first will look at risking of exploration wells using AVO response that has low/marginal reliability. The second example will be the risk analysis of a published paper: ‘Detecting Shallow Drilling Hazard in Large Boreholes Using LWD Acoustics’. This paper avoided the issue of data reliability. The potential impact of not considering data reliability will be explored and discussed with the group.

1. From Monte Carlo to Bayes Theory: The Role of Uncertainty in Petrophysics . Simon Stromberg Global Technical Head of Petrophysics Senergy

3. Subsurface Realisation Tables

4. Petrophysical workflows Calculate Volume of Clay Calculate Clay Corrected Porosity Calculate Clay Corrected Saturation Apply cut-offs for net sand, reservoir and pay and averages Volume of Clay Effective and Total Porosity Effective and Total Water Saturation Average Vcl, Por, Phi And HPVOL

5. Petrophysical Base Case Interpretation

6. Petrophysical Base Case Interpretation

9. Sensitivity Analysis of Input Parameters – Single Parameter

10. Sensitivity Analysis of Input Parameters – Single Parameters

13. Partial Derivative Analysis for Waxman-Smits Equation for Saturation

14. Partial Derivative Analysis for A Complete Deterministic Petrophysical Analysis

15. Partial Derivative – Input Data Zonal Averages

16. Partial Derivative – Input Uncertainty

17. Partial Derivative Analysis Results

18. Partial derivative Analysis - Saturation

20. Monte-Carlo Simulation Reference Case Uncertainty Definition Results Sensitivity

21. Models and Equations

22. Results HPVOL (ft)

23. Sensitivity

26. Bayes Theory

28. AVO

29. AVO-Bayes Theory

34. Baseline Interpretation

36. Rock above CP

37. Uncertainty Analysis (Monte Carlo)

39. Results of Monte-Carlo

40. Tornado Plot

43. Bayesian Inversion of Tree

46. Reliability of Diagnosis Chart Regional Data % of well above Below Cp