RESERVE GROWTH (INFERRED RESERVES)


     Measured reserves of oil or gas are the estimated quantities that
analysis of geological and engineering data demonstrate with reasonable
certainty to be recoverable in future years from known fields under
existing economic and operating conditions. This definition of reserves
more often leads to underestimates than to overestimates of the remaining 
resources in a known field. The difference between proved reserves in 
known fields and remaining recoverable resources in known fields is here called
inferred reserves.

     In the onshore areas and State water areas of the lower 48 States,
the reestimation of reserves in old fields each year has added far more to
measured (proved) reserves than have new discoveries. Therefore, the future
growth of discovered fields will be an important source of additions to reserves. 
The estimate of this growth for conventional fields is provided as inferred 
reserves. Growth of reserves in continuous-type deposits is included within 
the estimates of technically recoverable resources from those types of deposits.

     The Energy Information Administration has created the Oil and Gas
Integrated Field File (OGIFF), which lists the estimated size (cumulative 
production plus proved reserves) for each oil and gas field in the United 
States. Fifteen estimates of size, as estimated in each of the 15 years from 
1977 through 1991, are given for each field. These are the basic data from 
which the pattern of field growth is calculated.

     For the purpose of estimating inferred reserves, the lower 48 
States were divided into five areas, and the fields in these areas were
divided into oil fields and gas fields. The five areas consisted of the
assessment Regions 2, 3 and 4, 5 and 7, 6, and 8 (see fig. 3). 
Growth functions were calculated for each area for the primary commodities,
i.e., oil in oil fields and gas in gas fields. The secondary commodities 
(associated-dissolved gas and NGL) were assumed to grow proportionally to 
the primary commodities. Alaska growth was calculated using national growth 
functions for oil and gas because there were inadequate data to construct 
specific growth functions for that region.