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| Fig. 1. A sample of typical DTR (pressure drop P in blue and log-derivative P' in red) presented in log-log coordinates for PTA type-library analysis |
In particular case when the well has been shut=ij for a long time and then opened for flow the pressure drop will be equal to pressure drawdown:
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\Delta p(t) = p_e - p_{wf}(t) = p_{wf}(t_0) - p_{wf}(t) = \delta p (t) |
as the initial wellbore pressure point represent formation pressure:
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p_{wf}(t_0) = p_e |