GASWAT-PC is a microcomputer material balance program that calculates original gas in place (OGIP) from production history for gas reservoirs with or without water influx. Several well-known analytical techniques, and some extensions and improvements, are applied to a single input data set. The output for each method is given in both tabular and graphical form.

GASWAT-PC also has the capability to predict reservoir pressure and recovery efficiency for a specified production rate if OGIP and aquifer properties are known. An option is included to account for the effect of a large pressure gradient in the water-invaded region.

Case studies illustrate the application of GASWAT-PC to an abnormally pressured reservoir and to two water drive reservoirs. Finally, we compare the pressure performance predicted by a numerical simulator and by GASWAT-PC for a water drive reservoir with a high dip.

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