This classification is for the Russian Federation. Reserves are calculated separately for oil, dissolved gas, free gas, gas of gas caps, and condensate without deduction for what has already been produced. Predicted resources are assessed for oil-gas province, for offshore areas, for regions, and for areas within regions.
On the basis of recoverable reserves, fields are designated as follows: Unique - more than 300 million tons of oil or 500 billion cu m of gas (2.1 BBO, 17.5 tcf). Tons x 7 = bls; cu m x 35 = cf. Very large - 100-300 million tons oil; 100-500 billion cu m gas. Large - 30-100 million tons oil; 30-100 billion cu m gas. Medium - 10-30 million tons oil; 10-30 billion cu m gas. Small - 1-10 million tons oil; 1-10 billion cu m gas. Very small - less than 1 million tons oil; less than 1 billion cu m gas.
Reserves of oil, gas, and condensate having commercial value are subdivided into catagories A, B, C-1 and C-2. Undiscovered resources are subdivided into prospective D-0, and predicted D-1 and D-2 .
Catagory A reserves are those of pools or parts thereof that are in production. These have been studied in detail with determination of dimernsions of pool, effective thickness, oil-gas saturation, composition and properties of the hydrocarbons, drive, productivity of wells, formation pressure, etc.
Catagory B reserves are those of pools or parts thereof that are not in production but otherwise have had the same properties determined as for the Catagory A reserves.
Catagory C-1 reserves are those of pools or parts thereof that are not yet ready for production, but their productivity has been established on a basis of recovery of commercial flows of oil or gas. Also, geological and geophysical data have been positive for wells that have not yet been tested. Dimensions of pools have been determined by delineation wells. Extensive studies have been completed on properties of reservoirs and the hydrocarbons.
Catagory C-2 reserves are those of non-delineated parts of pools adjacent to sectors with reserves of higher catagory. Dimensions of the pool, reservoir properties, and composition of the hydrocarbons are known in general based on geological and geophysical data.
Catagory D-0 prospective resources are those of areas that are ready for deep drilling. Strata that are productive in other areas have not yet been drilled here. Various properties have been determined by geophysics and by analogy with delineated pools.
Catagory D-1 predicted resources are those of lithologic-stratigraphic complexes assessed within large regional structures that have demonstrated commercial petroleum potential. Assessment is based on analogy with delineated fields within the region.
Catagory D-2 predicted resources are those of large regional structures where no discoveries have as yet been made. Assessment is by analogy with regions where discoveries have been made. (Taken from Geologiya Nefti i Gaza, no. 2, 1998. Digested in Petroleum Geology, vol.33, no. 1, 1998) Copyright 2000 James Clarke. You are encouraged to print out this News Letter and to forward it to others. Earlier News Letters are available at http//:geocities.com/internetgeology/ This News Letter is published without charge in the interest of our science. To subscribe please send your e-mail address to: jamesclarke@erols.com