Straight out of TS1, wellbore storage during a PBU is a must-know. The Guidebook summary (with units) is on 12 WLT 13. A typical problem: wellbore storage time (say for the below well data, choose the closest estimate: A=0.1 hr, B=0.5 hr, C=1 hr, D=2 hr):
Well data:
Wellbore skin and volume (say skin=2 & 30 bbl).
Reservoir thickness & perm (say 10 ft & 60 md).
Fluid viscosity & comprehensibility (say 1 cp and 0.0002 /psi).
12 WLT 13:
Cs = CwbVwb = 0.0002(30 bbl) = 0.006
t (wbs approx) = [170,000(Cs)(e^(0.14*s))]/[kh/u]
t (wbs approx) = [170,000(0.006)(e^(0.14*2))]/[(60*10)/1] = ~2.2 hr
Note that Cs can be calculated using different inputs; the Guidebook shows each of the three equations on one page for immediate use. Note also some of these equations are approximate; problem wording should reflect this and thus hint as to the proper equation to use.
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