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)

answer : (a) volume of the gas = 8.67 ×   l

                (b) second virial coefficient b = -1.21226 l/mole

solution :   given,     t = 300k

                                p = 20atm

                                z = 0.86

                                n = 8.2 mmoles = 8.2 × moles

                                r =   0.082 l atm/k/mol

        find,     (a) volume of gas   and (b) second virial coefficient b at 300k.

formula used :            

                          and            

(a)            

                    = \times 0.082\times 300}{20}[/tex]

                    = 8.67 ×   l

(b)      

                    = (0.00867-1) × 8.659

                    = - 8.5839 l/mole