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Geological Forward Modelling

Geological forward modelling is the simulation and prediction of the structural evolution of a basin honouring the physics of the involved processes (e.g. sedimentation, burial, compaction, overpressure generation, diagenesis, erosion, etc). The technique provides a description of the evolution of the full stress and strain tensors during basin history and captures evolutionary flow pathways. The predicted structural development is a result of the constitutive response of the sediments to the applied boundary conditions and constraints. As such this technique has been widely used to gain a better understanding of the geology at sub-surface and to investigate the controlling factors on the deformational style (e.g. influence of overpressure on structural style, influence of geometry and properties of a frictional detachment on predicted folds and faults, etc.).

Forward geological modelling of GoM style Minibasins

ParaGeo geological forward models may be mechanical only, hydro-mechanical or thermo-hydro-mechanical.  In the latter two cases the fields are coupled and if a field is not represented it may be defined as a prescribed field. Numerous boundary conditions may be applied including:

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  • Sedimentation and erosion

  • Tectonic displacement

  • Stress loads

  • Fluid flux and prescribed pore pressure

  • Thermal flux and prescribed temperature

 

ParaGeo material library has a wide range of constitutive models to simulate numerous sediment rheologies including:

 

  • Isotropic or anisotropic elasticity

  • Poroelasticity

  • Nonlinear elasticity, elastic creep and elastic hysteresis

  • Critical state plasticity to capture ductile-brittle behaviour

  • Shear plasticity (Drucker-Prager)

  • Viscoplasticity for modelling of salt

  • Diagenetic reactions

  • Rotating Crack and embedded fracture

Predicted horizontal and vertical strain distributions across a fold developed on top of a salt layer

​The evolution of properties as stiffness, strength and permeability with compaction are captured during the simulation. Additionally, the sediment hydraulic behaviour may be characterised via the input of any porosity-permeability function, including anisotropic and transverse isotropic laws.

 

Geological forward models often require representation of faults and/or fractures and the influence they have on the evolution of the mechanical, fluid flow and thermal fields. In ParaGeo faults and fractures may be modelled following either:

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  • A discrete approach via contact surfaces

  • A continuum approach defining a zone of elements with lower strength

  • A continuum approach via embedded fracture models

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When using either of the previous approaches faults may be propagated to newly deposited units. This is achieved by defining the propagation pathway of the fault. Then contact surfaces are extended following such direction or in case of the continuum approach, elements are weakened along the fault propagation path. This may happen right after deposition or at any time defined by the user.

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In addition, the integrated restoration-forward modelling workflow in ParaGeo facilitates constraint of the forward models using the results from geomechanical restorations in order to reduce the uncertainity in boundary kinematics and fault propagation pathways and improve the accuracy in predicting a given structure of interest.

Forward geological modelling of a synthetic thrust with discrete fault propagation. Formations (top) and horizontal strain (bottom). In the strain plot blue colours indicate compressional strain whereas red colours indicate extensional strain.

Sedimentation with pinchout on a 3D hexahedral mesh forward geological model. Vertical scale exaggerated by a factor of 5.

ParaGeo has a proven working technology for performing integrated restoration and forward modelling of both 2D and 3D structures with specialized functionality designed to deliver solutions for the most complex and demanding cases.

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For example, 3D forward modelling at regional scale (100s of km) where the formations and layers have a very high aspect ratio (the thickness dimension is very small compared to the layer extension in-plane). For such scenarios, hexahedral elements are used to discretize the model domain in order to reduce the required number of elements and save computational power.  Specialized functionalities incorporated into ParaGeo are then used to:

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  • Import hexahedral grids from third party software (e.g. Eclipse) and convert it to a ParaGeo model

  • Build 3D hexahedral mesh from Zmaps

  • Extract the list of node numbers defining the boundaries to apply boundary conditions (note that we support non-flat ragged boundaries)

  • Perform sedimentation on a structured mesh including pinchouts

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A dedicated workflow for integrating restoration and forward modelling of such 3D regional scale models discretized in hexahedral meshes can be found in the Parageo user manual.

Evolutionary results from a tutorial example in ParaGeo user manual to demonstrate restoration / forward simulation workflow for 3D regional scale (100s of km) models

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