The Importance of Reserve Growth to the Nation's Supply of Natural Gas

Experience shows that initial estimates of the size of newly discovered oil or gas fields are usually too low. As years pass, successive estimates of the ultimate recovery of fields tend to increase. The term "reserve growth" refers to the typical increases in estimated ultimate recovery that occur as oil or gas fields are developed and produced (Arrington, 1960; Attanasi and Root, 1994).

An example for a particular field helps explain the nature of reserve growth. Figure 1 (63k GIF). shows ultimate recovery for a large natural-gas field in Texas as estimated in each year from 1977 through 1991. This gas field was discovered in the mid-1940's. In 1977, its ultimate recovery was estimated to be 2.1 trillion cubic feet of gas (tcfg). One might think that after some 30 years of development and production, the resource potential of a field would be well understood. However, by 1991 the estimated ultimate recovery of this field had increased to 3.1 tcfg. Reserve growth over the 15-year period totaled 1.0 tcfg and shows no signs of stopping.