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Dynamic Data Analysis – v5.12.01 - © KAPPA 1988-2017
Chapte
r 2 – T heory- p41/743
2.H.2.d
Reservoir size
Below is presented the response with all default parameters except the reservoir size, the
radius r
e
. From the reference case we have successively divided / multiplied by 1.5, and the
values of r
e
are 667, 1000, 1500, 2250 and 3375 ft.
The time at which PSS occurs depends on r
e
. As the governing group in the diffusion equation
is t/r², when r
e
is multiplied by 2 the time at which PSS occurs is multiplied by 4. When PSS
occurs the slope of the pressure response, on the history plot, is inversely proportional to the
volume of the reservoir, and therefore inversely proportional to r
e
².
In the shut-in the pressure stabilizes to the average pressure obtained by simple material
balance. Unlike the cases above, the pressures, for a given production, do not stabilize at the
same value. Again the depletion (p
i
–p
av
) is inversely proportional to the reservoir pore volume,
i.e. inversely proportional to r
e
².
Fig. 2.H.9 – Effect of the reservoir size, loglog plot
Fig. 2.H.10 – Effect of the reservoir size, semilog and history plot