The gas recovery of water-drive gas reservoirs

This paper proposes a method for determining the gas recovery of water-drive gas reservoirs. First, the water influx coefficient B in the theoretical formula pr = (1-Rg)/(1-RgB) is used to determine the influence of the aquifer behavior. According to the theoretical formula, the relationship between the normalized pressure pr and the degree of the reserve recovery R can be obtained with different values of B, which can be used to determine the activity level of the aquifer behavior. Second, according to pra = (1-Rga)/(1-aEva) (where a = 1-Sgr/Sgi), the relationship between the normalized abandonment pressure pra and the ultimate gas recovery Rra can be obtained, as the Agarwal end-point line. The intersection of the above two lines represents the value of the estimated ultimate gas recovery and the normalized abandonment pressure pra. Finally, an evaluation table and a set of demarcation charts are established, with different values of Sgr/Sgi and Eva as well as the water influx coefficient B, which can be used to determine the gas recovery of water-drive gas reservoirs with different activity levels of the aquifer behavior.