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 Rg 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)Pra=(1-Rga)/(1-aEva) (where a=1-Sgr/Sgia=1-Sgr/Sgi), the relationship between the normalized abandonment pressure Pra and the ultimate gas recovery Rga 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.