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Material Models

A backbone of finite element geomechanical analysis are the constitutive models that simulate material rheology. These exert a first-order control in the predicted evolutionary structural style. For example, critical state constitutive models may predict either ductile deformation with compaction, or brittle deformation with dilation, depending on the relationship between the current material strength and the stress path. ParaGeo has a wide range of constitutive models available that accurately captures the evolution of different classes of materials. The material definition is a modular design so that simple models may be defined for initial validation and then later enriched incrementally (e.g. plasticity or diagenetic properties may be added to a previously defined poroelastic material to capture yielding once yield strength is reached). Available material models include:

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  • Isotropic, transverse isotropic and anisotropic elasticity

  • Poroelasticity

  • Critical state plasticity: SR4, SR3 and Modified Cam-Clay with non-associative flow rules

  • Shear plasticity with hardening: Von-Mises, Drucker-Prager, Hill plastic anisotropy

  • Viscoplasticity: Hershel-Bulkley, Creep law based on Munson-Dawson model

Shear localizations (faults) predicted by the critical state constitutive law in a sandbox-scale rift model

Critical state theory highlighted in an SR4 yield surface (left). The SR4 plasticity model allows flexibility in defining the yield surface shape and location of the critical state relative to the peak strength (right).

Thermally-controlled diagenetic reactions may be added to critical state model characterisations for geological time-scale applications. The diagenesis models allow for:

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  • Non-mechanical porosity loss and the resulting permeability reduction

  • Diagenetic compressional strength increase leading to over-consolidation (yield surface increase)

  • Diagenetic tensional strength increase due to cementation

  • Diagenetically induced stiffness increase

  • Diagenetically induced compressibility reduction

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In addition, a given material may be assigned more than one diagenesis reaction which may be active at different temperature ranges (e.g. shallow carbonate cementation, smectite to illite transformation, etc)

Example of results extracted from a depositional column model with diagenesis. The areas shaded in blue indicate the diagenetically modified sediment properties

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