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Ecrin v4.20 - Doc v4.20.01 - © KAPPA 1988-2011 Saphir Guided Session #8 • SapGS08- 5/11
Note that if no minifrac analysis data exist for the current analysis, the vertical line which
represents the closure point is set to an arbitrary value. This has to be changed by finding the
point where the semi-log derivative departs from a straight line passing by the origin.
In the present case, the pressure data shows an initial hump which is characteristic of a
pressure dependent leak-off (PDL).
Click on , select ‘Draw through origin’ and click on a point of the semi-log derivative
G.dP/dG where the trend is linear (in this case one could select a point corresponding to a
G-value between 6 and 9, or equivalent to a time between 1.7 to 3.5 hr.).
Click next on and drag the vertical dashed line to the point where data separate from the
straight line:
Fig. B02.2 • G-Function plot
The closure point has now been set based on the position of this vertical line. In order to check
closure consistency, we will now use the ‘Square root’ plot.
Minimize the G-Function plot and maximize the ‘Square root’ plot. This plot is similar to the
previous one but displays functions versus the square root of time. In this plot the closure
point should correspond to a local maximum of pressure derivative. Use the vertical zoom
button to zoom on the pressure derivative curve (in red here) around the chosen closure
point and use the button to fine tune the closure to the nearest local maximum point
(initial time data should be ignored here):