4 Initial pressure
In PANTHER the initial pressure needs to be prescribed in the reservoir, seal, base, and in the fault. To allow modeling of hydrocarbon reservoirs, it is possible to specify different pressure gradients within the reservoir. In addition, overpressures can be accounted for. Note that these are rather simple scenario's, in reality the pressure gradient may be more complex depending on hydrocarbon column height, capillary pressure effects, and water mobility. On this page, first a description is given how pressure are prescribed in the rock formations, in a case where the formations are not offset. In the second section, a description is given on how these pressures are prescribed for an offset geometry, and how the pressures within the fault zone can be specified based on the formation pressures.
Default: 10.5 MPa/km
Gradient used to set the initial hydrostatic pressure. See Figure 1
p(z) = p_grad * z + p_offset
Figure 1 Hydrostatic pressure gradient specified by p_grad and p_offset
Default: 0 MPa.
Pressure offsetting the hydrostatic gradient. See Figure 1
Pressure offset can be positive or negative.
##Hydrostatic overpressure (p_over)
Default: 0 MPa.
Oftentimes, reservoirs and underlying formations are overpressured. Overpressure is defined as the excess pressure with respect to the hydrostatic gradient. A constant overpressure value can be assigned to the reservoir and base formation, which is added to the hydrostatic gradient, giving the water pressure gradient (blue line in Figure 2).
Figure 2 Water pressure profile for hydrostatic gradient and an overpressure p_over
Default: 10.5 MPa/km
In some cases a hydrocarbon is present in the reservoir formation, e.g. oil or gas. To account for the presence of a hydrocarbon, a different pressure gradient can be prescribed within the reservoir interval, p_grad_res. At the base of the reservoir this gradient will connect to the water pressure gradient. As the density of hydrocarbons is lower than that of water, this situation will lead to an additional overpressure at the top of the reservoir, the so-called buoyancy effect. Within the reservoir the water pressure is also computed, here assuming a mobile water phase. Optionally, the water pressure can be assumed in the fault, rather than the gas pressure (REF). <br >
At the moment, it is assumed the reservoir fluid occupies the entire reservoir height. In a future release, it will be possible to specify a reservoir fluid-water contact depth within the reservoir.
Figure 3 Pressure profile (solid line) for hydrostatic gradient and a different reservoir fluid density (green line). Note that the water pressure gradient will also be present in the reservoir (dotted line)