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 p(r) = (1-R-g)/(1-R-g(B)) is used to determine the influence of the aquifer behavior. According to the theoretical formula, the relationship between the normalized pressure p(r) and the degree of the reserve recovery R-g can be obtained with different values of B, which can be used to determine the activity level of the aquifer behavior. Second, according to p(ra) = (1-R-ga)/(1-aE(va)) (where a = 1-S-gr/S-gi), the relationship between the normalized abandonment pressure p(ra) and the ultimate gas recovery R-ga 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 p(ra). Finally, an evaluation table and a set of demarcation charts are established, with different values of S-gr/S-gi and E-va 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.