Faults and fractures in ParaGeo may be modelled either in a continuum or discrete manner. The optimal strategy and functionality adopted will depend on the target application, the type of modelling and the relative scales of the model geometry and the features (fault/fractures). Here we can classify the modelling approach for the different features as follows:

 

•Faults

 

▪Discrete faults via contact. This would be the main method to model faults in both production time scale models (e.g. MEMs) where resolving fault mechanics may be of primary interest and evolutionary models over geological time scales where the fault offset may be large relative to the layer thicknesses. However, in 3D evolutionary models where the faults are expected to propagate in the formations deposited during the simulated history, the required geometric intersections may be difficult to resolve and often would require non-trivial user intervention to ensure appropriate fault propagation pathways. Hence in such modelling scenarios a more pragmatic approach using continuum fault modelling is preferred.

 

▪Continuum faults. Continuum faults can either be prescribed or predicted. Strain localisation bands predicted by critical state models when the stress paths intersect the yield surface on the shear side (often refereed as wet side) are an example of continuum fault representation. This approach usually requires usage of a critical state model to capture the mechanical properties of the formations so that the faults may then be represented as a path of elements with a decreased strength relative to the formations. In ParaGeo such fault path may be prescribed using part geometry (geometry entities not belonging to the model domain which may overly it) to identify the elements intersecting by its pathway. Also continuum fault modelling allows to account for the effect of faults on the flow field without considering the mechanical effects. In such scenarios Fracture_data is used to deploy the embedded fracture framework for the flow field. It is noted that embedded fracture functionality for the mechanical field is generally not appropriate for modelling the mechanical behaviour of continuum faults.

 

•Fractures

 

▪Discrete fractures via contact. Often adopted in reservoir models where the fracture scale is large relative to the element length and the fracture density / number of fractures in the model is handleable. If the number of fractures is very large an approach combining discrete fractures and embedded fractures may be adopted there the main (larger scale) fractures may be represented in a discrete manner whereas the secondary fractures may be modelled by the embedded fracture approach. Discrete fractures may be present in the initial geometry or may be imported and intersected into a continuum geometry to obtain a geometry with the discrete fractures (e.g. in ParaGeo we can import fractures defined from Fracman data).

 

▪Embedded fractures (continuum). This approach is usually adopted when the scale of the fracture is small relative to the element. Embedded fractures are modelled by inserting planes of weakness with a given orientation in the mesh element centres. Different mechanical models are available in ParaGeo (e.g. Bandis model). The effect of the fractures in the flow field may also be accounted for by defining a fracture permeability. Several fracture sets with different properties (orientation, spacing. mechanical properties, flow properties, etc) may be assigned to the target formations. In ParaGeo we can also use spatial grids to define regions of the model that contain fractures while considering intact formations everywhere else.

 

 

The different data structures documented here are:

 

1.Fault_set used to identify the geometry sets defining the pre-existing discrete faults and / or the part geometry sets defining the fault propagation pathways as well as default properties for propagated faults. Required for restoration to forward modelling conversion to identify the faults during the processing of restoration results.

 

2.Fault_insertion used to propagate faults at paths defined via part geometry. Here we distinguish between two modes of fault propagation namely fault insertion (discrete faults where the geometry is split) and fault seeding (continuum faults).

 

3.Fault_relief_set specialised 2D functionality to add a curvature to the intersection of a discrete fault with the top surface to facilitate climb up of the fault in compressional scenarios.

 

4.Fault_smooth_set specialised 2D functionality to smooth fault curvature during a simulation and hence prevent ragged fault shapes or too abrupt changes in fault angle that may result from large strain

 

5.Fracture_data defining fracture properties that can be assigned to any material data.

 

6.Fracture_set defining data for import of fracture sets from Fracman in order to create a fractured geometry (with discrete fractures) from an initial unfractured geometry.

 

 

 

Examples for Discrete Faults via contact

 

Tutorial examples demonstrating modelling of discrete faults are:

 

Rest_002: Restoration and forward modelling of a normal fault

 

Geol_001: Geological modelling workflow

 

MEM_001: MEM workflow

 

Cont_002: Flow and thermal contact

 

 

 

Examples for Continuum Faults

 

Tutorial examples demonstrating modelling of continuum faults are:

 

Ex_010: Continuum fault flow model

 

 

 

Examples for Discrete Fracture modelling and discrete fracture import

 

Tutorial examples demonstrating import of discrete fractures are:

 

Fract_001: Import of discrete fractures

 

 

Tutorial examples demonstrating modelling of discrete fractures are:

 

Fract_002: Discrete fracture modelling

 

 

 

Examples for Embedded fracture

 

Tutorial examples demonstrating modelling of embedded fractures are:

 

Mat_003: Continuum Fracture Modelling

 

Fract_003: Modelling of Embedded fractures