Ecrin v4.20 - Doc v4.20.01 - © KAPPA 1988-2011
Saphir Guided Session #8 • SapGS08- 6/11
Fig. B02.3 • Square root plot
Go back to the G-Function plot, maximize it and click in the toolbar on the button ‘Show results
in plot’, the results should be:
•
Pump time = 0.1925 hr.
•
Pump volume = 23.26 STB.
•
Closure time = 3.07 hr.
•
Closure pressure =11853.4 psia.
•
Closure G-value = 8.53.
•
G-Function (straight line) slope = 31.57 psia.
Additionally, secondary results are given such as Fracture efficiency (0.81) and Instantaneous
Shut-In Pressure (ISIP) (12123 psia).
We now have defined the closure point with the combined usage of the ‘G-Function’ and
‘Square root’ plots and have obtained all corresponding primary closure parameters. Note that
in this example, the leak-off seems to be of PDL type, additional information such as fissure
opening time and pressure can as well be inferred directly from the G-Function plot (in this
case the observed fissure opening time is read directly as 1.4 hrs, corresponding to 5.3 G
units). The next step is to focus on the after closure analysis.
B02.2 • After Closure Analysis (A.C.A.)
The after closure analysis is made with the last minifrac specialized plot called the ‘ACA plot’.
In this plot the pressure difference (Pi-P) and semi-log derivative FL^2.d(P-Pi)/d(FL^2) are
displayed versus the specialized square linear flow function (FL^2). In this plot,
time is
increasing from right to left.
This function is highly dependent on the closure parameters and hence should be used
after
the closure has been properly assessed with the post shut-in analysis.
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