Mech_005 Formation of Salt Diapirs (Bench Scale)

This example provides an introduction to the workflow for the formation of salt diapirs on different bench scale models in 2D.  The models aim to capture buoyancy driven ascent of salt and breakthrough of overburden and syn-sedimentary growth under extensional and compressional tectonic settings.

 

Features of the 2D examples include:

1.Salt material modelled with Herschel-Bulkley viscoplastic material model and Sand material modelled with SR4 plasticity model.

2.Extensional and compressional tectonic movement setting.

3.Layer sedimentation using variable sedimentation rates / fixed sedimentation horizons.

4.Stratigraphy pinchout.

5.Adaptive mesh refinement with plastic/viscoplastic coarsening data and plastic/viscoplastic strain rates.

6.Single/Multiple seed point/s for diapir/s formation.

 

The documentation assumes that the following examples have been undertaken beforehand:

1.Mesh_001 - 2-D Unstructured Mesh Generation.

2.Mech_001 - Mechanical Analysis Introduction.

3.Mech_002 - Uniaxial Burial of a 2000m Sediment.

4.Mech_004 - Biaxial Test on Sand with Adaptive Remeshing.

 

Notes on Pinchout in ParaGeo:

•Pinchout of stratigraphy layers is only available in 2D.

•Self-pinchout is not permitted.

•Pinchout code is only available to be run sequentially.

 

Material Properties

 

The materials (arbitrary) used in the models are:

•Salt - modelled with Herschel-Bulkley viscoplastic properties.

•Sand - modelled with the SR4 plasticity material model. Two sand materials (Sand_1 and Sand_2) are modelled with the same properties but with different hardening data. Sand_2 is 'stronger' than Sand_1 with four times higher pre-consolidation pressure values in the hardening table.  Note that Sand_2 material is used in Case03 only.

•Elastic - Base layer material below salt is modelled as elastic (Case03 only).

 

Units are in Pa, mm and hrs.

 

Data File

 

* Material_data                    

! ----------------------------------------

 Material_name                  "Salt"

! --------------------------------------------------------

 Initial_mass_scaling_constant     1E-6

 Grain_density                    970.0   ! Kg/m3

! --------------------------------------------------------

 Elastic_model_type                   1   ! Isotropic

 Elastic_properties  IDM=2

  /"Young's Modulus (E)"/       100000   ! Pa

  /"Poisson's Ratio (v)"/         0.49

! --------------------------------------------------------

 Viscoplastic_material_type           1  

 Viscoplastic_properties  IDM=3

  /Yield Strength/                 0.2

  /Initial K (viscosity)/         2.78   ! 10000Pa.s scaled to 2.78 Pa.hrs

  /Exponent n/                     1.0

 

 

* Material_data                    

! ----------------------------------------

 Material_name                  "Sand_1"

! --------------------------------------------------------

 Initial_mass_scaling_constant     1E-6

 Grain_density                   2710.0   ! Kg/m3

! --------------------------------------------------------

 Porosity                          0.35

! --------------------------------------------------------

 Elastic_model_type                   1   ! Isotropic

 Elastic_properties  IDM=2

  /Young's Modulus (E)/          75000   ! Pa

  /Poisson's Ratio (V)/           0.20

! --------------------------------------------------------

 Regularisation_type                  1

 Regularisation_properties  IDM=4

  /Characteristic length/          3.5

  /Parameter A/                    0.0

  /Exponent n/                     0.6

  /Maximum change factor/          100

! --------------------------------------------------------

 Plastic_material_type                2 ! SR4 Model

 Plastic_properties     IDM=9

  /Tensile intercept/            20.0

  /Pre-consolidation pressure/ -3000.0

  /Friction parameter/           65.00

  /Dilation parameter/          68.70

  /Beta0 (deviatoric plane)/      0.60

  /Beta1 (deviatoric plane)/      0.60

  /Alpha (deviatoric plane)/      0.25

  /Exponent n/                    0.95

  /Exponent m/                   0.77

 Hardening_type                       1

 Hardening_properties  IDM=18 JDM=3

  /Vol.Plastic Strain/  -0.006 -0.003   0.0 0.003 0.006 0.009 0.012 0.015 0.018 0.021 0.024 0.027 0.030 0.033 0.036 0.039 0.042 0.045

  /Pre-consol. press./   -8243  -5011 -3000 -1769 -1026  -586  -329  -182   -99   -53   -28 -14.5  -7.5  -4.0  -2.2  -1.3  -0.9  -0.7

  /Tensile intercept /    20.0   20.0  20.0  11.8   6.8   3.9   2.2   1.2   0.8   0.5   0.3  0.15  0.08  0.04  0.02  0.01  0.01  0.01

 

 

* Material_data                    

! ----------------------------------------

 Material_name                  "Sand_2"

! --------------------------------------------------------

 ( ... )

! --------------------------------------------------------

 Plastic_material_type                2 ! SR4 Model

 Plastic_properties     IDM=9

  /Tensile intercept/            20.0

  /Pre-consolidation pressure/ -12000.0

 ( ... )

 Hardening_properties  IDM=18 JDM=3

  /Vol.Plastic Strain/  -0.006 -0.003   0.0 0.003 0.006 0.009 0.012 0.015 0.018 0.021 0.024 0.027 0.030 0.033 0.036 0.039 0.042 0.045

  /Pre-consol. press./ -32972  -20044  -12000  -7076  -4104  -2344  -1316  -728  -396  -212  -112  -58  -30  -16  -8.8  -5.2  -3.6  -2.8

  /Tensile intercept /    20.0   20.0  20.0  11.8   6.8   3.9   2.2   1.2   0.8   0.5   0.3  0.15  0.08  0.04  0.02  0.01  0.01  0.01

 

 

* Material_data                    

! ----------------------------------------

 Material_name                  "Elastic"

! --------------------------------------------------------

 Initial_mass_scaling_constant     1E-6

 Grain_density                   2710.0   ! Kg/m3

! --------------------------------------------------------

 Porosity                          0.35

! --------------------------------------------------------

 Elastic_model_type                   1   ! Isotropic

 Elastic_properties  IDM=2

  /Young's Modulus (E)/          75000   ! Pa

  /Poisson's Ratio (V)/           0.20

 

1.Salt layer is modelled with Herschel-Bulkley viscoplastic properties with material name Salt.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2.Sand layers (pre-existing and sedimentation layers) are modelled with the SR4 plasticity material model with material name Sand_1.  This material is used for all three simulation cases.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3.For Case03, an additional sand material Sand_2 is defined for alternate sand layers.  This has the same material properties as Sand_1 but with four times higher pre-consolidation pressure values in the hardening table.

 

 

 

 

 

 

 

 

 

 

 

 

4.The base layer below salt (Case03) is modelled with elastic material properties with material name Elastic.

 

 

 

Simulation Cases

 

Three cases are considered with a full description of the data provided for the Case 1 Base Case with Extension only.  Subsequent cases will only contain description of key data different from the base case.

 

Case 1 Base Case with Extension only

 

Case 2 Extension and Compression with Variable Sedimentation Rate

 

Case 3 Formation of Turtle Back Structures