Abstract: In water drive gas reservoirs, especially large water influx gas reservoirs, the water influx helps to maintain the reservoir pressure, and thus maintain gas productivity at initial productivity, at least until water breakthrough. As a result, the process directly affects the recovery. Therefor, it is of great importance to obtain accurate data of dynamic gas in place and water influx
of the gas reservoir so as to make correct performance forecast.
In this paper, a novel method is proposed. In the method the measured formation pressure and production data are used to build an objective function, and least square best-fitting is performed to obtain automatic matching, and thus the dynamic gas in place and water influx of the gas reservoir can be calculated directly. Comparative analyses of the results from this and other methods indicate that the proposed method is simpler and easier to use as well as accurate and reliable.

Key words: water drive, gas reservoir, reserve calculation, water influx, automatic matching, material balance