DST Analysis - Two Boundary Effects

Hi guys,

I have a quick question regarding DST analysis of boundary effect in Pressure Derivative Plots.

From the late time region of my pressure derivative plot, two boundary effect was apparent which was closed boundary (upward curve) and a constant pressure boundary (downward curve). The constant pressure boundary appears just after the closed boundary so my pressure derivative plot curves upwards then downwards in the late time region.

Here's the thing, both this effect is supported by the geological feature (seal and aquifer support) and the dipping of the reservoir actually accounts for the timing of these two features.

So my question is weather Pressure derivative plot can possibly show two very different boundary effects one after another or is this just another case of ambiguity?

Cheers,
Yusri