Estimation Update and Feedback Procedures
147
Step 2: Estimating Pool-Size Distribution
Geological random variables, such as formation thickness, area of
closure, porosity, trap fi ll, water saturation, and others, should be chosen
and their probability distributions constructed from expert opinion and
the results of comparative studies. Rules for constructing these types of
distributions are given in Chapter 5. The distributions can be directly
treated using the Monte Carlo method or they are approximated using
the family of lognormal distributions for pool size calculation (Eq. 5.8).
To verify lognormal approximations, both raw data and approximated
distributions should be shown on the same plot.
Step 3: Estimating Number-of-Pools Distribution
The number-of-pools distribution can be computed by applying
exploration risks and number-of-prospect distributions. For conceptual plays, both play- and prospect-level geological factors should be
presented, whereas for mature plays only prospect-level geological
factors are presented.
Figure 6.1. Discovery sequence plot for 25 Devonian gas plays of the Western
Canada Sedimentary Basin by year of discovery (after Reinson et al., 1993).