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Fig. 4.C.5 – Loglog plot, integral of normalized pressure and derivative
Using the integral preserves the signature of the flow regimes while significantly reducing the
noise. Hence such definitions provide a diagnostic tool where most of the usual well test
methods can be used. In particular, it is clearly possible to get an estimate of the reservoir kh
from the derivative stabilization level. The kh being known, one can then get a first estimate of
the reservoir size from the unit slope late time trend. These calculations are an integral part of
the loglog plot. It is possible to either display the ‘true’ model response, i.e. the response to
the full pressure history, or the response to a single pressure step. The single step response,
used in all the figures above, shows the signature of the model in a clear and usable whereas
the response to the real history is usually very erratic, because the equivalent time is jumping
back and forth in time as illustrated in the figure below.
Fig. 4.C.6 – Loglog plot with ‘true’ model response