Page 219 - KAPPA - Ecrin v4.30 tutorials

Ecrin v4.20 - Doc v4.20.01 - © KAPPA 1988-2011 Saphir Guided Session #8 • SapGS08- 7/11
Note also that the shape and amplitude of the pressure difference is very dependent on the
reservoir pressure, while it does not affect the semi-log derivative curve. By default, the
reservoir pressure is initialized to an arbitrary value (0.95 of the minimum pressure
encountered during the reference fall-off). The plot is used for detecting possible characteristic
flow regimes after the fracture closure. Two flow regimes are possible: pseudo-linear flow
and/or pseudo radial flow: the former is observed when both pressure difference and the
semilog derivative show characteristic half unit slope behavior and are separated by a factor 2
in the ACA plot, and the latter flow regime is recognized when both the pressure difference
curve and the semilog derivative are joined in a single unit slope trend as time increases (data
moving to the left on the x axis). Maximize the ‘ACA plot’, a new toolbar is available. Among
the options there are seven minifrac options:
Change the plot type from square linear flow function (FL^2) to linear (FL) or radial
flow (FR) function. This option is used once the flow regimes have been identified (see
below).
Perform straight line slope regression to the pressure data (available only in
linear/radial flow plots).
Fit a graphical flow regime trend to the data (available only in square linear flow type,
not used for parameters calculations, only visual aid for flow periods determination).
Shift one of the dashed vertical lines which represent start and end of pseudo-linear
and of pseudo-radial flow regimes.
Hide/Show one of the vertical lines.
Manually set the reservoir pressure.
Change the smoothing parameter.
We first start by identifying the flow regimes. Depending on the case, the default reservoir
pressure value can be quite off (as it is the case in this example) which means that the
pressure difference curve should not be considered initially and will be used later on to confirm
the obtained reservoir pressure. In this example we have:
Fig. B02.4 • Initial ACA plot