Natural Gas Reserves

Two terms are frequently used to express natural gas reserves: proved
reserves and potential resources. Proved reserves are those quantities of
gas that have been found by the drill. They can be proved by known reservoir characteristics such as production data, pressure relationships, and
other data, so that volumes of gas can be determined with reasonable
accuracy. Potential resources constitute those quantities of natural gas
that are believed to exist in various rocks of the Earth's crust but have not
yet been found by the drill. They are future supplies beyond the proved
reserves.
Different methodologies have been used in arriving at estimates of the
future potential of natural gas. Some estimates were based on growth
curves, extrapolations of past production, exploratory footage drilled, and
discovery rates. Empirical models of gas discoveries and production have
also been developed and converted to mathematical models. Future gas
supplies as a ratio of the amount of oil to be discovered is a method that
has been used also. Another approach is a volumetric appraisal of the
potential undrilled areas. Different limiting assumptions have been made,
such as drilling depths, water depths in offshore areas, economics, and
technological factors.
There has been a huge disparity between "proven" reserves and potential
reserves. Even in the case of the highly mature and exploited United States,
depending upon information sources, the potential remaining gas reserve
estimates vary from 650 Tcf to 5,000 Tcf (Economides et al. 2001). Proved
natural gas reserves in 2000 were about 1,050 Tcf in the United States and
170 Tcf in Canada. On the global scale, it is more difficult to give a good
estimate of natural gas reserves. Unlike oil reserves that are mostly (80
percent) found in Organization of Petroleum Exporting Countries
(OPEC), major natural gas reserves are found in the former Soviet Union,
Middle East, Asia Pacific, Africa, North America, Southern and Central
America, and Europe.