Evaluating Conceptual Plays
111
Prospect-Level Geological Factor
The prospect-level geological factor measures the marginal probability
that a geological factor exists for an individual prospect. A prospectlevel geological factor is represented by R (local), and its marginal
probability is denoted by u r . The risk can also be considered as a superpopulation parameter, and can be estimated from data. For the prospect-level geological factor, absence of such factors as closure, reservoir
facies, or porosity will result in a prospect lacking hydrocarbons. This,
however, does not imply that these factors are also absent from other
prospects in the play.
Let R 1 , R 2 , . . . , R k denote the geological factors for an individual
prospect at the prospect level. For example:
R 1 = [presence of closure]
R 2 = [adequate seal], . . . , and so on.
Let us defi ne
G = G 1 ∩ G 2 ∩ . . . G j
R = R 1 ∩ R 2 ∩ . . . R k
A prospect within a play contains hydrocarbons if, and only if, (1) the
play has all play-level geological factor factors and (2) the prospect
meets all prospect-level geological factor requirements. In other words,
a prospect contains hydrocarbons if, and only if, G ∩ R.
Table 5.2. Examples of Play-Level Geological Factors for Various Geological
Models
Play type
Example
Exploration risk
Sandstone
Carbonate
Edge
Eocene to Miocene Cook Inlet,
Alaska; Jean Marie*
0.15
0.15
Top
Belly River, Mission Canyon
0.15
0.44
Base
Mannville, Beaverhill Lake
0.60
0.35
Subunconformity
Jurassic, Mississippian
0.45
0.30
*Added by author. After White (1980).