ParaGeo Hydro-Mechanical (HM) models to investigate overpressure development and evolution of sediment properties in the East Coast Basin, New Zealand
- Josh
- Oct 6
- 2 min read
A new paper from the GeoPOP4 project has recently been published (Open Access) in JGR: Solid Earth. In the paper ParaGeo is used to develop coupled Hydro-Mechanical (HM) models to investigate overpressure development and the evolution of sediment properties in the compressional tectonically active East Coast Basin (New Zealand). The key aspects of the modelling approach are summarised in the following bullet points:
A column model geometry is adopted to develop HM models for five key wells. The simplified geometry facilitates calibration of the models, testing different hypotheses and obtaining valuable insights that otherwise would be difficult to achieve.
A regional analysis of East Coast Basin data and bibliography research on tectonic compaction provided constraints on the boundary conditions for modelling sedimentation, erosion, tectonic compression and lateral drainage according to the geological history in the five wells.
The effects of sedimentation, tectonic deformation and uplift with erosion on the evolution of overpressure, stress paths and mechanical properties are analysed. The findings are then used to guide the calibration of the models with well data.
The key findings from the paper are:
The recent (i.e. ~ < 3 Ma b.p.) tectonic compression episodes are most likely the main cause of the high, relatively shallow overpressures encountered in the East Coast Basin wells at present day, while disequilibrium compaction is likely to play a secondary role.
Erosion results in the removal of the overburden sediments (removal of the mechanical load associated with the weight of the eroded sediments), overpressure dissipation in the sedimentary column and sediment consolidation. Consequently, the exhumated sediments are often over-consolidated, and hence, further relevant mechanically induced overpressure development does not occur until the yielding limit is exceeded.
Only the most recent erosive events have an observable effect on present day porosity and overpressure, whereas the past erosive events have been overridden with subsequent sedimentation and tectonic deformation. However, those have an impact on the sediment deformation and thermal histories.
The modelled stress paths have predicted yielding on the compressional side of the yield surface. However, it should be noted that this is influenced by the modelling assumptions, i.e.:
The adopted modelled geometries assumed uniform strain and hence do not allow for strain localisation or boundary condition discontinuities
No over-consolidation from diagenesis has been considered
The paper hence demonstrates that HM modelling is a powerful tool that enables the improvement of our understanding of the evolution of overpressure, sediment properties and physics of the geological system due to the different processes occurring during the history of a basin.
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