Calculating volumetric gas reserves
This program makes a straightforward volume calculation, but be aware that gas reserves are complicated. Gas is rarely the only phase in a reservoir, and its ultimate recovery is a function of many variables, not all geologic. Plumbing, economic, and even regulatory restrictions cloud the issue, along with line pressures and abandonment rates. Gas might exist as a free phase at the top of the reservoir, and also as solution gas, dissolved in associated oil, which won't come out of solution until production drops the reservoir below the bubble point. Gas might contain an undesirable amount of something like H2S or nitrogen, or a desirable amount of something more valuable, like helium. It is often the case that gas will slowly change composition over the life of a producing field.
Volumetrics ignores all of these issues and makes a simple initial guess at the amount of gas which could be in place in a reservoir. As with estimating oil reserves, I find it helpful to check the optimism of a volumetric gas estimate by using the other LogCalc program that projects reserves based upon expected production, decline, and abandonment rates.