The purpose of the ANOGRE system is to derive estimates of recoverable and subeconomic undiscovered oil and gas resources in the lower 48 states. Unproduced recoverable hydrocarbons can be classified, by decreasing degree of confidence, into (1) measured (proved) reserves, (2) inferred reserves, and (3) undiscovered recoverable resources.
The bulk of unproduced hydrocarbons can be classified as the sum of measured reserves, inferred (and indicated) reserves, and undiscovered recoverable resources. Inferred reserves are equivalent to about 50 percent of measured reserves. The quantity of known recoverable hydrocarbons is to the volume of drilled rocks (both dry and productive) as the quantity of undiscovered recoverable resources is to the volume of undrilled favorable (potential) rocks times a numerical richness factor f. The quantity of known recoverable hydrocarbons is defined as the sum of cumulative production plus measured and inferred reserves.
Determination of the volume of drilled and potential rocks involves areal and vertical classifications. The volume of potential rocks is defined as the volume of favorable rocks minus the volume of rock (1) occupied by the Stratigraphie unit containing an oil or gas pool, (2) attributable to extensions, revisions, and higher and lower “pays” not yet defined, and (3) proved barren by dry holes.
The U.S. Geological Survey’s Oil and Gas Pool Data Bank, presently the most comprehensive source of digitized United States pool data, is used extensively in making these computations.