The estimation of proved and probable natural gas reserves must be based firmly not only on detailed knowledge of the engineering factors involved, but, generally even more important, on a thorough knowledge of the geology and potential for additional natural gas discovery. Different areas and even different producing formations within a single area have decidedly different characteristics for natural gas production rates, availability, and recovery. The rate at which a discrete gas reserve can be depleted is very important to pipelines.

As the competition for gas reserves increases, more and more lines are financed on the basis of sound estimates of proved reserves available and judgment with regard to supplies which can be expected reasonably to be developed in the area to be served by the pipeline. A study of the Homeglen-Rimbey field illustrates this important principle. In areas where exploration and development are unusually costly, reserves otherwise would not be developed in a timely fashion.

Important as estimates of proved and probable reserves are, even more important in many cases are studies of the availability of gas reserves--the rate at which they can be produced. A mathematically calculated 20-yr supply of natural gas which actually may require several times that length of time to produce is insufficient in times of peak requirements. There are several methods by which to determine volumes of gas available at any one period from a well, reservoir, pool, field, or even a system. Most of them require use of large numbers of data, and too commonly not all of the necessary data are available. Calculations are long, involved, and arduous. The Davis-Meltzer curve, which is simply a study of the production rate of several depleted or nearly depleted fields where geologic and reservoir conditions are similar, is a simple, reasonable means of determining availability within the accuracy normally required and obviates the laborious calculations of other methods. If likes are compared with likes, the method is superior to any other, but sound judgment in its application is mandatory.

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