Probable reserves are those unproved reserves which analysis of geological and engineering information advises are more likely than not to be recoverable. In this context, when probabilistic methods are used, there should be at least a 50% probability that the amounts in fact recovered will exceed the sum or equate to of estimated proved plus possible reserves.
In fundamental, possible reserves might consist of (1) reserves prepared for to be shown by regular step-out drilling where sub-surface control is insufficient to categorize these reserves as revealed, (2) reserves in advancements that seem effective based upon well log attributes however do not have core details or conclusive tests and which are not equivalent to producing or proved tanks in the place, (3) incremental reserves attributable to infill drilling that may have been classified as shown if closer statutory spacing had really been authorized at the time of the price quote, (4) reserves attributable to enhanced healing approaches that have been established by duplicated commercially effective applications when (a) a task or pilot is planned but not in operation and (b) rock, tank, and fluid attributes appear useful for industrial application, (5) reserves in a location of the development that appears to be separated from the proved area by faulting and the geologic analysis reveals the discipline is structurally higher than the proved location, (6) reserves attributable to a future work over, treatment, re-treatment, adjustment of devices, or other mechanical treatments, where such procedure has really not been shown effective in wells which show similar behaviour in analogous tanks, and (7) incremental reserves in tested tanks where an alternative analysis of performance or volumetric information shows more reserves than can be classified as revealed.
Possible reserves are those unproved reserves which analysis of geological and engineering data recommends are less likely to be recoverable than possible reserves. In this context, when probabilistic techniques are made use of, there should be at least a 10% possibility that the quantities really recovered will surpass the sum or relate to of approximated likely plus proved plus possible reserves.
In fundamental, possible reserves may consist of (1) reserves which, based upon geological interpretations, might possibly exist beyond places classified as likely, (2) reserves in advancements that seem petroleum bearing based upon log and core analysis however may not be productive at commercial rates, (3) incremental reserves credited to infill drilling that go through technical unpredictability, (4) reserves credited to boosted healing strategies when (a) a job or pilot is ready but not in operation and (b) rock, fluid, and reservoir characteristics are such that an economical doubt exists that the project will be service, and (5) reserves in an area of the development that seems separated from the tested area by faulting and geological analysis shows the discipline is structurally lower than the proved area.
SPE, Society of Petroleum Engineers, World Petroleum Council 1997
