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Dynamic Data Analysis – v5.12.01 - © KAPPA 1988-2017
Chapte
r 2 – T heory- p44/743
2.H.3.c
Total compressibility
Illustrated below is the response simulated with default parameters varying the total
compressibility. Values for c
t
are 3.e-6, 1.e-5 and 3.e-5 psi-1. The sensitivities at Early Time
(Storage), Middle time (IARF) and late time (PSS) are strictly the same as for the porosity: A
smaller compressibility produces a higher hump of the early time derivative. Compressibility
does not affect the derivative level when IARF is reached but has a cumulative effect on the
pressure. At late time, compressibility affects the time at which the boundary is detected and
the material balance equation. As for porosity, under-estimating c
t
by 10% will provide an
over-estimation of the reservoir size by 10%, and therefore an over-estimation of the
boundary distance. In fact, on all parts of the response, the influence of porosity and
compressibility will be a function of their product
.c
t
.
Fig. 2.H.15 – Effect of total compressibility, loglog plot
Fig. 2.H.16 – Effect of the total compressibility, semilog and history plot