Brine Migration and Pressure Build-Up

The modeling of overpressure is based on combining Navier-Stokes equations with Stokes's law for quantifying the viscous drag from the rocks. These equations are similar to Darcy's law combined with a Kozeny-Carman permeability model. The driving mechanism for pressure build-up is compaction of sediments during burial, topographic relief, aquathermal pressuring, and brine porevolume being replaced by in-situ oil or gas generation.

The overpressures impact on compaction is modeled through the effective stress by including the effect of disequilibrium in the pressure model.

The viscous drag coefficient of each phase is quantified by using the texture and compaction dependent hydraulic radius of the specific phase pore volume. The texture is quantified through the log-normal distribution of minerals and assigned by giving the 50% fractile and the 90% fractile for each end-member mineral or for lithologies specific to a particular stratum and horizontal location. The anisotropy is assigned for each end-member mineral through the aspect ratio of the mineral grain.

The 123D Simulation model incorporates the anisotropy stemming from a specific lithology and from different kind of lithological distributions. The user assigns a certain distribution of the lithologies in each stratum varying horizontally by choosing between a layered distribution, a distribution of lenses, or a distribution which is particular for a delta paleoenvironment.