this is just one way of understanding this wellbore storage and approach in the interpretation of BU, or DD. It might be considered not accurate for others as other people might have other way of understanding this matter and also might have other approach/method for the interpretation, so read more about the subject it ask others.
Wellbore storage,WBS, occurs when the well is shut on surface, it represents the pressure of the fluid column above the gauge. the data points of this pressure should be excluded in the interpretation because it doesn't represent the real reservoir response. this wbs masks the pressure data of the reservoir.
Now, how do we interpret that in practical form:
- when plotting DP vs. DT on log-log plot either for BU, or DD;
- try to fit a unit slope line(slope=1, or 45degree line) usually on the first 3 or 4 data points.
- at the first data point, tL, which starts to deviate from that straight line, read the time and multiply it by 30 (30*tL), or simply 1 cycle and half after tL.
- the data points after (30*tL) is the start, more or less, of the reservoir respone, it is the data where we can get kh, S,
- the reservoir data will lie on straight line when potting (Pws vs. t for BU) or (Pwf vs. t for DD) on semi-log.