The temperature and overpressure fields through time are important input to MigriX. Temperature is important for the PVT phase calculations and HC generation, while overpressures will affect the phase and leakage in traps.
The easiest way to modify the temperature and overpressure history is by using the Histories Editor. Alternatively, the parameters can also be set directly in the Input/Histories section of the Project workspace.
Temperature input histories to MigriX are defined using a simple surface temperature and a temperature gradient specified for the time of deposition of each horizon. The same gradient and surface temperature will then be used for all layers at that time. Temperature gradients usually reduces with increasing depth due to compaction. This effect can be mimicked by setting a temperature compaction parameter. The model temperatures will be calculated according to a second-order polynomial:
The gradients and surface temperatures are specified with the Temperature.surface and Temperature.gradient parameters in the Input/Histories section of the Project workspace. Temperature gradients usually reduces with increasing depth due to compaction effect. This depth-dependency of the thermal gradients can be specified by using the Temperature.compaction parameter.
Overpressures back in time can be created by specifying overpressure fractions for time of deposition of each Horizon in the Input/History/Overpressure.fraction variable, which is the fraction (constant or grid) used to multiply the present day overpressure, specified by the OverpressureHistory parameter, to arrive at the overpressures for each timestep.
MigriX uses [MPa] as unit for all input pressure data. If the input grids are supplied in other units, mathematical equations can be used to convert to the [MPa] unit, e.g. use |my_psi_grid.gri| 0.006894759|*| to convert from [psi] to [MPa].
In the event that you only have overpressures for one or a few of the layers being modelled, the mathematical equations can be used for the missing layers, e.g.|my_layer_overpressures.gri|0.8|*|may be used to set the layer overpressures to 80% of the overpressures in the known layer.
