Restoration Modelling
Geological restoration consists of simulating basin's structural evolution backwards in time, from present day to a paleo time of interest. This technique has been widely used to validate structural interpretations on seismic sections, as well as a source of understanding of basin evolution and the likely fluid migration pathways. The workflow for classical restoration techniques consists of back-stripping the top surface to a restoration datum (often assumed flat) while relying on geometric and kinematic assumptions such as area (2D) or volume (3D) preservation as a proxy for mass conservation or assuming vertical shear displacements, tri-shear kinematics, etc. Once the top layer is completely back-stripped it is removed and the process is repeated for the next layer. During this process decompaction laws are used to recover the initial layer thicknesses as the sediment burial depth reduces.
ParaGeo can perform finite-element geomechanical-based restorations on both 2D and 3D structures. The geometry is discretised into a finite element mesh. Each formation layer is assigned material properties (often assumed elastic) to model sediment rheology while faults are modelled via frictionless contact surfaces. This enables recovery of the brittle deformation history that created the present day configuration. ParaGeo has a wide range of tools that may be deployed to facilitate the restoration of specific classes of structure which encompass; specific treatments for the top horizon surface during back-stripping, conditions to ensure closure of faults, a range of constitutive models, etc. For example, nonlinear constitutive models may be used in regions of ductile deformation (e.g. constant volume Von Mises plasticity) and bedding plane slip can be represented by orthotropic elasticity, orthotropic plasticity (Hill model) or by introducing planes of weakness at selected locations in the model.
Geometries at the end of several restoration stages
Top surface bed-length preservation and bedding plane slip model applied to restoration of a fold
The decompaction models in ParaGeo have been designed with flexibility in mind. User-defined decompaction curves can be calibrated to be consistent with the available field-data (e.g. a porosity trend that shows porosity preservation with depth on overpressured sediments). In addition, ParaGeo contains methods to introduce non-vertical decompaction in restorations, for example to model the recovery of the ductile strain that occurs prior to fault initiation in a shortening environment. This leads to improved recovery of the restored paleo-bed lengths that are often underestimated with classical restoration techniques.
Our flagship in terms of geological modelling is a robust framework developed in ParaGeo that integrates restoration and forward modelling for both 2D and 3D structures. Using restoration results we can semi-automatically generate input data for our forward models comprising:
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Initial geometry
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Boundary displacements
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Depositional surfaces
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Fault propagation pathways
Framework integrating restoration and forward simulation
Two decompaction curves for two different scenarios
In ParaGeo you can restore 3D models either sequentially or in a parallel simulation with domain decomposition. The geometry to be restored may be imported from 3rd party mesh generators (e.g. Eclipse, Gmsh, Hypermesh, GoCad, etc) and converted to ParaGeo format using available conversion functionality. There is a dedicated restoration to forward simulation workflow for 3D models at regional scale (100s of km) using hexahedral meshes.
3D Restoration of a model at a regional scale (100s of km) with a hexahedral mesh. V.E. = 3. This model is taken from ParaGeo user's manual tutorial.