ParaGeo is designed to solve single-field, two-field and multi-field coupled problems including:

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• Single field: Mechanical, thermal, porous flow

• Two field: Hydro-mechanical, thermo-mechanical, thermal-flow applications

• Multi-field: Coupled Thermo-Hydro-Mechanical problems

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In coupled problems the governing equations for each of the fields are solved, namely:

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• The mass-momentum balance for the mechanical field

• Darcy flow equation for the fluid flow field

• Advective-diffusion equation for the thermal field

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The coupling procedures capture both the strongly and weakly coupled interactions between the individual fields. For example, compactive volumetric strain (porosity decrease) from the mechanical field leads to an increase in fluid pore pressure. Changes in pore pressure influence the stress path of the mechanical field and consequently the material evolution. The temperature transfer depends on the bulk thermal conductivity which is calculated from the relative contribution of the grain and pore fluid thermal conductivities and hence is updated with compaction. At the same time compaction may be influenced by temperature via a diagenesis law or due to temperature dependent compressibility law in the material or temperature-dependent creep in salt adjacent to the structure.

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In general, coupled simulations are transient, and both staggered and iterative coupling approaches are available. Large geometrical changes, including sedimentation and erosion, are enabled by the adaptive remeshing and mapping procedures. Specialised procedures have also been implemented for coupled analysis of faults and fractures. These facilitate fluid flow across and along discrete contact surfaces and thermal flow across contact surfaces. The influence of fracture/fault pore pressure on the potential for slip along the contact surface is also taken into account.