20
Statistical Methods for Estimating Petroleum Resources
pools with sizes 221 × 10
6 m
3 and 69 × 10
6 m
3
. The upper half of Figure
2.9 displays the discovery sequence of all commercial pools. Gaps on
the horizontal axis indicate failed exploratory wells. The lower half of
Figure 2.9 displays results from drill stem tests. In this case, the minimum pool size defi ned for this play is 0.001 MMbbls in place. Resource
evaluation can be performed on the discovery data of the upper half, or
on the upper and lower halves together as an integral data set.
The reason for combining noncommercial pools with defi ned pools
in an integrated discovery sequence is to obtain representation from the
small pools. Additional statistical assumptions (such as a constant ratio
between two adjacent size classes) are not required in this approach. On
the other hand, the estimation of reserves from drill stem test results is
time-consuming and requires reservoir engineering expertise.
Figure 2.9. Exploration time series for Beaverhill Lake play. The upper half of
the fi gure represents pools with commercial values; the lower half indicates oil
recovered in drill stem tests.