A New Method for Determining Original Gas in Place and Cumulative Water Influx in Waterdrive Gas Reservoirs

This paper presents a new method for determining original gas in place and cumulative water influx in waterdrive gas reservoirs. The new method proposed in this paper mainly comprises four procedures: firstly, using the well test analysis results of non-stablized well test which was measured under the initial condition that waterdrive gas reservoir did not produce water, combining with current performance data of waterdrive gas reservoir which produces water at present, to calculate the current effective permeability to gas in the waterdrive gas reservoir by gas phase binomial deliverability equation of gas-water two-phase steady state flow; secondly, using this calculated effective permeability to gas and the gas-water relative permeability curve of reservoir, to calculate the current water saturation; once again, using this calculated water saturation and material balance principle for cumulative water influx, to establish the relationship of the cumulative water influx and original gas in place; finally, using this established relationship of the cumulative water influx and original gas in place, combining with the general form of the material balance equation for waterdrive gas reservoirs, to determine the original gas in place and cumulative water influx. The example study verifies that this new method is reliable.