In our paper “Stress and pore pressure histories in complex tectonic settings predicted with coupled geomechanical-fluid flow models” we used ParaGeo to develop coupled geomechanical-fluid flow models and capture the overpressure generation by disequilibrium compaction and tectonic strain in a mini-basin with two depocenters with an anticline above a diapir in the center. One of the objectives was to quantify the likely error in predicting overpressure using equivalent depth methods in basins with active tectonics.
We first target a present day geometry defined according to a published interpreted seismic section of the Titan mini-basin from Kane et al (2012) as a base case that we later will perturb introducing 20% of additional shortening to develop what if scenarios. We chose to focus on modelling the classic sediments and not including prediction of the salt behavior. To that end we used a rigid surface (part line) in ParaGeo to prescribe the displacements in the salt-sediment interface during basin history. This enabled to have high degree of control in the evolutionary slat-sediment boundary as well as facilitating the introduction of additional shortening relative to the base case. In addition we also defined cases that included two high perm sand layers to account for the effect of lateral pressure transfer.
The results shown that:
The two depocenters are in horizontal compression whereas the central anticline above the diaper is in horizontal extension as indicated by the predicted effective stress ratios (in both, base case and case with 20% additional shortening).
The additional 20% of shortening lead to an increase of overpressure of up to 10 MPa in the depocentres.
In the central anticline there is tectonic vertical compaction that increased in the case with additional shortening.
The equivalent depth method underpredicted overpressure by 17% of the total overpessure in the depocenter.
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