2. a combination-drive reservoir contains 10 mmstb of oil initially in place. the ratio of the original gas-cap volume to the original oil volume, i. e., m, is estimated as 0.25. the initial reservoir pressure is 3000 psia at 150°f. the reservoir produced 1 mmstb of oil, 1100 mmscf of 0.8 specific gravity gas, and 50,000 stb of water by the time the reservoir pressure dropped to 2800 psi. the following pvt is available:

@ 3000 psi: bo = 1.58, rs = 1040, bg = 0.00080, bw = 1.000

@ 2800 psi: bo = 1.48, rs = 850, bg = 1.655, bw = 1.000

the following data are also available: swi = 0.20 cw = 1.5 × 10−6 psi−1 cf = 1 × 10−6 psi−1

calculate:

a. cumulative water influx

b. net water influx

[hint: rearrange the general form of the mbe (eq. 3.7) to calculate we, and then net water influx] (25 points)