Page 91 - Principles of Applied Reservoir Simulation 2E

76 Principles of Applied Reservoir Simulation

Table 9-1
SPE/WPC Reserves Definitions

Proved 4 Those quantities of petroleum which, by analysis of geological
reserves and engineering data, can be estimated with reasonable certainty
to be commercially recoverable, from a given date forward, from
known reservoirs and under current economic conditions,
operating methods, and government regulation.
4 In general, reserves are considered proved if the commercial
producibility of the reservoir is supported by actual production
or formation tests.
4 There should be at least a 90% probability (P 90) that the
quantities actually recovered will equal or exceed the estimate.

Unproved Those quantities of petroleum which are based on geologic
reserves and/or engineering data similar to that used in estimates of
proved reserves; but technical, contractual, economic, or regula-
tory uncertainties preclude such reserves being classified as
proved.
Probable 4 Those unproved reserves which analysis of geological and
reserves engineering data suggests are more likely than not to be recover-
able.
4 There should be at least a 50% probability (P 50) that the
quantities actually recovered will equal or exceed the estimate.
Possible 4 Those unproved reserves which analysis of geological and
reserves engineering data suggests are less likely to be recoverable than
probable reserves. I
4 There should be at least a 10% probability (P ]0) that the
quantities actually recovered will equal or exceed the estimate.

The probability distribution associated with the SPE/WPC reserves
definitions can be estimated with relative ease if the modeling team has
performed a sensitivity analysis that generates a set of cases that yield low,
medium, and high reserves estimates. In the absence of data to the contrary, a
reasonable first approximation is that each case is equally likely to occur. Given
this assumption, an average p, and standard derivation o may be calculated from
the sensitivity analysis results to prepare a normal distribution of reserves. For
a normal distribution with mean (J, and standard deviation o, the SPE/WPC