This paper presents the mathematical premises on which are based the estimation of natural gas reserves. The data used in the estimation of natural gas reserves are the records of (1) initial and current reservoir pressures, (2) volume of gas withdrawn, (3) the physical properties of gases, and (4) the physical properties and areal extent of the gas-bearing reservoir. Equations are given which include corrections for the deviation of gases from Boyle's law, and the determination of bottom-hole pressures from well-head pressures in closed wells. Three cases common to the determination of bottom-hole pressures are described. Six cases concerned with the estimation of original and remaining natural gas reserves in a reservoir are set forth.
Not many years past, natural gas wells were valued according to their ability to produce gas—a sum of dollars for each million cubic feet of daily open-flow capacity. Because many in the industry, even as late as 1919, held that the supply of natural gas in the United States had reached its climacteric and would soon be exhausted, little interest was taken in the determination of natural gas reserves within a reservoir, but the determination of reserves became necessary with the enactment of the Federal Tax laws of 1917. The discovery of large gas supplies, mostly west of Mississippi River and far removed from adequate markets, increased the need for precise reserve estimates. To utilize these supplies in distant markets, large capital expenditures were necessary. To insure the safety of these expenditures, as far as