116
Statistical Methods for Estimating Petroleum Resources
last two columns display the interpretations of each factor as prospect
level or play level. For case I, only the adequate timing factor is considered as a play-level geological factor, whereas in case II, adequate
timing, adequate source, and adequate preservation factors are considered as play-level geological factors. There is no information to suggest
whether these factors are dependent. Therefore, the overall play-level
geological factor is calculated from the multiplication of all play-level
marginal probabilities, whereas the overall prospect-level geological factor is the product of all prospect-level marginal probabilities.
Finally, the exploration risk is the product of overall play and prospect
levels. As seen in Table 5.4, the two overall risks are very different for
these two cases. However, the exploration risk is identical. Because of
the difference in play-level and prospect-level geological factors, subsequent estimations will vary accordingly.
Pool-Size Distribution
In reservoir engineering, a pool size can be calculated by using the following equation:
Pool size = Constant × Pool Area × Net Pay ×
Porosity × Hydrocarbon Saturation ×
(5.8)
Recovery Factor / Gas or Oil Formation Volume Factor
For resource evaluation, Equation 5.8 is adapted to defi ne pool-size
distribution (Roy, 1979). To solve the equation, the various distributions are multiplied together. This type of multiplication can be accomplished using the Monte Carlo method or an operation of lognormal
distributions that approximate the geological random variables.
The Monte Carlo Method
In the 1950s, a procedure known as the Monte Carlo method was used
to solve certain types of mathematical problems. Here, Figure 5.3 displays three examples that illustrate how various numerical procedures
can be applied to different problems. The fi rst example calculates the
area under the line, Y = X (Fig. 5.3A). One can consider that the triangle is located within a square with a unit length. The area beneath the
straight line equals half the unit. On the other hand, the area can also
Statistical Methods for Estimating Petroleum Resources
last two columns display the interpretations of each factor as prospect
level or play level. For case I, only the adequate timing factor is considered as a play-level geological factor, whereas in case II, adequate
timing, adequate source, and adequate preservation factors are considered as play-level geological factors. There is no information to suggest
whether these factors are dependent. Therefore, the overall play-level
geological factor is calculated from the multiplication of all play-level
marginal probabilities, whereas the overall prospect-level geological factor is the product of all prospect-level marginal probabilities.
Finally, the exploration risk is the product of overall play and prospect
levels. As seen in Table 5.4, the two overall risks are very different for
these two cases. However, the exploration risk is identical. Because of
the difference in play-level and prospect-level geological factors, subsequent estimations will vary accordingly.
Pool-Size Distribution
In reservoir engineering, a pool size can be calculated by using the following equation:
Pool size = Constant × Pool Area × Net Pay ×
Porosity × Hydrocarbon Saturation ×
(5.8)
Recovery Factor / Gas or Oil Formation Volume Factor
For resource evaluation, Equation 5.8 is adapted to defi ne pool-size
distribution (Roy, 1979). To solve the equation, the various distributions are multiplied together. This type of multiplication can be accomplished using the Monte Carlo method or an operation of lognormal
distributions that approximate the geological random variables.
The Monte Carlo Method
In the 1950s, a procedure known as the Monte Carlo method was used
to solve certain types of mathematical problems. Here, Figure 5.3 displays three examples that illustrate how various numerical procedures
can be applied to different problems. The fi rst example calculates the
area under the line, Y = X (Fig. 5.3A). One can consider that the triangle is located within a square with a unit length. The area beneath the
straight line equals half the unit. On the other hand, the area can also