The term gas reserves may be used in different ways. Most commonly, it is used to mean proved reserves of natural gas. Proved reserves are estimated quantities of natural gas that are recoverable in future years from known reservoirs under existing accessibility, economics, and technology with “reasonable certainty.” Reserves are considered to be proved if economic producibility is supported by actual production or test drilling of the reservoir’s geologic formation. Areas of a reservoir considered to be proved include portions that have been shown by drilling to contain recoverable gas as well as immediately adjacent portions that are believed to be recoverable based on geologic and engineering data.
A second reserve quantity is technically recoverable reserves (TRR). This quantity includes proved reserves plus unproved resources. Unproved resources are additional volumes estimated to be technically recoverable without consideration of economics or operating conditions, based on the application of current technology.
As of December, 2019, the U.S. Energy Information Administration (EIA) estimated proved reserves in the U.S. of 505 Tcf and TRR of 2,865 Tcf as of 2018. Compared to current production rates, these quantities represent 14 and 85 years’ worth of supply respectively. At the end of 2018, the EIA estimated world proved reserves of 7,177 Tcf, equivalent to over 50 years’ worth of supply.