Entrapment logic

Under the "Full Material Balance" option the total HC charge ("C") from the Charge model is confronted with the trap capacity ("T"). Usually, for each MC cycle these amount may differ widely. In each case the minimum is retained:

Thus HC-in-Trap = Min(C,T)
The trapping algorithm calculates the subsurface volumes of the charge, using the PVT conditions based on the engineering variables.
An important algorithm is the "confrontation" of the charge and the trap. Here an iterative trial and error procedure is used. In the first trial half the charge is used. If this is too much half this amount is tried. If half the charge is not filling the trap, a further charge of a quarter of the original charge is added. If this is still not filling the trap an eights is added. At that point we have used 0.5 + 0.25 + 0.125 = 0.875 of the available charge. Going back and forth in this way with 15 iterations in which the additional charge volumes become smaller and smaller, the final entrapment volume is found with sufficient accuracy.

The amount of spill is determined for use in further appraisals of other traps that might benefit from this excess charge. In the dynamic entrapment model, the amounts of spill are accumulated in each entrapment step. In all FMB models, the spill is tarnslated to volumes of oil and gas at standard conditions and then filed in the user-defined spill-file.