Concentrations of naturally occurring materials in such form that economic extraction is currently or potentially feasible (U. S. Bureau of Mines definition). While Figure R-12 relates to petroleum, similar definitions apply to other materials. SPE/WPC identify reserves as resources that are (1) discovered, (2) recoverable, (3) commercial, and (4) remaining. Contingent resources as the quantities which as of a certain date are estimated to be potentially recoverable from known accumulations but which are not currently considered to be commercially recoverable. They can be further subdivided according to (a) those that could be recovered using proved techniques but where there is currently too much uncertainty to commit to development or where commerciality has yet to be confirmed, (b) those which require unproved techniques to be developed, or (c) those that require further commercial considerations. Prospective resources are the quantities that are estimated to be potentially recoverable from undiscovered accumulations. They can be further divided into prospects that are sufficiently well developed to represent viable drilling targets, leads that require more data to be classified as prospects, and plays that require more data to become prospects or leads. A reservoir is a single subsurface rock formation capable of containing moveable petroleum. A pool is an individual and separate natural accumulation of moveable petroleum that is confined by impermeable rock or by water barriers and is characterized by a single pressure system. A field is an area consisting of pools that are grouped on or related to the same individual geologic structural feature and/or stratigraphic condition. Different pools in a field may be separated vertically by impermeable rock or laterally by structural or stratigraphic barriers. To be considered discovered, an accumulation must have been penetrated by a well that clearly demonstrates the existence of moveable petroleum by recovery of a sample (although sometimes good log or core data may suffice). A decision as to commerciality is up to the country or company concerned with possible development and generally implies that it will be marketable within five years. Proved reserves are those that are commercial under current economic conditions, while probable reserves and possible reserves are based on future economic conditions. The distinction between proved, probable, and possible reflects the range of uncertainty in estimating recoverable volumes, the distinctions often being at cutoffs of 90%, 50%, and 10% probability. Possible reserves have less than a 50% risk that they can be produced economically. The reliability of estimates should improve over time. See Figure R-12 and SPE-WGC (2000).
In November 2011, new industry guidance on resource and reserves estimation was issued. The SPE-PRMS Application Guidelines (PRMS-AG) document was issued in November 2011, jointly sponsored by SPE, AAPG, WPC, SPEE and SEG (http://www.spe.org/industry/reserves.php) and has been widely accepted as the standard in the industry.
Chapter 3 (Seismic Applications) of the PRMS-AG describes the most significant geophysical elements of the PRMS-AG and key issues and implications for the Geoscience community.