Question: an oil well has been drilled close to an observation...

An oil well has been drilled close to an observation well. The distance between the drilled well and the observation well is estimated to be 1000 ft. A downhole pressure gauge is installed in the observation well to monitor the reservoir pressure. The drilled well is put on production at a rate of 100 STBD. Use the reservoir data given in the following and calculate the time required to record a pressure drop of 2.5 psi in the observation well. Note that the observation well acts like a point and the flow rate for this well is zero.

Reservoir external radius, re        5000 ft,

Total compressibility, ct        3 x 10^-6 psi-1

Oil viscosity, u    1cP                                                              

Oil formation volume factor, Bo             1.3 bbl/STB,

Reservoir permeability, k        400 mD,

Formation thickness, h        20 ft,

Initial reservoir pressure, Pi        2500 psia,

Formation porosity, (l)        0.15,

Well radius, rw,        0.3 ft.

Skin factor, S,        -2