Step 1 Restoration

 

The base case consists of simple restoration with three stages; one stage for translation of the current top surface to the restoration surface and two stages with deactivation of the top formation and restoration of the next top surface to the restoration surface. This example is field scale and considers decompaction.

 

Basic Set Up: Data file description

The initial data file for the project is: Rest_002\Data\Rest_002_Step1.dat.   The basic data includes:

1Geometry_set data that define the west boundary and the fault hanging wall and footwall.

2 Fault_set data to identify the fault.

3Contact data for the fault (Contact_set, Contact_property and Contact_global).

4Stratigraphy_definition for the three formations present in the model and corresponding Stratigraphy_horizon data.

5Group data for the three formations which are assigned the "Elastic" properties using Group_control_data and Group_data data structures.

6Geostatic_data to initialize the model to a porosity trend via Spatial_variation_definition and Spatial_variation_values data structures.

7A Material_data and Fluid_properties data structures defining the material properties for the formations.

8Support data (Support_data) defining fixity in X direction at the west boundary.

9Mesh control (Mesh_control) and Unstructured mesh generation data (Unstructured_mesh_data) defining a constant mesh size of 0.25m.

10Part geometry data (Part_geometry_set, Part_line and Part_nodal_data) to define the restoration surface.

11Restoration_data defining the restoration operation, restoration top surface boundary conditions and assigning a part geometry as a restoration surface.

12Control data (Control_data) for two stages defining:

(a)  Incremental solution algorithm (Type 1),

(b) Target number of time steps of 8000,

(c) Maximum number of time steps of 10000,

(d) Duration of t=1 Ma,

(e) Plot file output every 0.2 Ma,

(f) Plot file output at the end of the stage,

(g) Screen message output every 500 mech steps,

(h) Output of a restart file at the end of the stage.

13Geometry data (nodal_data, Geometry_line and Geometry_surface) for definition of the 2D geometry.

 

The Geometry_set data for each of the boundaries is defined by:

1The name of the geometry set.

2A description for the geometry set.

3The geometry entities that constitute the geometry set.

 

Data File

 

 

* Geometry_set                    NUM=1

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

 Name                     "fault1_ftw"

 Lines                         IDM=3

   2  5  8

 

* Geometry_set                     NUM=2

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

 Name                     "fault1_hgw"

 Lines                         IDM=3

   14 17 20

 

* Geometry_set                     NUM=3

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

 Name                     "West"

 Lines                         IDM=3

   4 7 10        

 

* Geometry_set                   NUM=4

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

 Name                     "East"

 Lines                         IDM=3

   12 15 18

 

* Geometry_set                    NUM=5

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

 Name                     "Basal_horizon"

 Lines                         IDM=2

          1 11  

 

1Five geometry sets are defined:

a.Two for the fault hanging wall and fault footwall

b.Three for model sides and basal boundaries

 

The Fault_set data is used to identify geometry entities which form part of individual faults. This can be used to track fault geometries during restoration and insert faults later during the restoration-derived forward simulation.

 

Data File

 

 

* Fault_set                     NUM=1

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

 Name                 "Fault1"

 Hangingwall_set  "fault1_hgw"

 Footwall_set     "fault1_ftw"

 Contact_sets   IDM=1

   "All"

 

 

1A fault set is defined for the normal fault.

2Name "Fault1" is defined for the fault set.

3Geometry sets defining fault hanging wall and fault footwall are assigned.

4Contact_set named "All" is assigned to the fault set

 

Contact data to define a frictionless contact surface for the fault.

 

Contact_set

Data File

 

 

* Contact_set                  NUM=1

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

 Name                        "All"

 Algorithm                   "Penalty"

 Property_name               "Block_friction"

 Global_update_frequency     1000

 Field_factor                0.2

 Buffer_factor               5.0

 Geometry_sets     IDM=2

   "fault1_ftw"

  "fault1_hgw"

 

 

1A single contact set is defined

2Penalty algorithm is selected (currently only option available)

3"Block_friction" property is assigned to the contact set

4Global contact search frequency is set to every 1000 mech steps

5Field factor is set to 0.2 so the maximum normal gap is defined as Gn = 0.2· lfacet where Gn is the normal gap and lfacet is the contact facet length.

6The buffer factor for defining the buffer box size is set to 5.0 (the candidate target facets that can potentially establish a contact relationship with a given contactor node are those within the buffer box during a global search update). In this case the buffer box for a given node is an sphere centred at the node with radius R=5.0· lfacet  where lfacet is the average length of the facets that terminate on the node.

7Included geometry sets in this contact sets are "fault1_ftw" and "fault1_hgw"

 

 

Contact_property

Data File

 

 

* Contact_property               NUM=1

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

 Name                      "Block_friction"

 Compression_model      1                  

 Compression_properties IDM=1

  /"Normal Penalty"/                  2000

 Adhesion_model         1                  

 Adhesion_properties IDM=1

  /"Normal Penalty"/                  2000

 Tangential_model       2                

 Tangential_properties IDM=2

  /"Tangential Penalty"/               100

  /"Friction coefficient"/             0.0

 

 

1A contact property named Block_friction is defined.

2Linear elastic compression model is assigned (compression model 1) with a normal penalty stiffness of 2000 MPa.

3Linear adhesion model is assigned (adhesion model 1) with a normal penalty stiffness of 2000 MPa.

4Coulomb friction model is assigned for tangential contact (tangential model 2) with a tangential penalty stiffness of 100 MPa and a friction coefficient of 0.0.

 

 

Contact_global

Data File

 

 

* Contact_global                  NUM=1

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

 Included_contact_sets    IDM=1

   "All"

 

 

1Contact_global data structure is defined to specify that defined contact set  named "All" is active.

 

 

The stratigraphy is defined by:

1Defining the existing stratigraphy layer depositional order and the group associated with each layer (via Stratigraphy_definition).

2Defining the topology of the top surface horizon for each stratigraphy layer (via Stratigraphy_horizon).

The stratigraphy is defined in a similar way to Mech_002 where there is a fuller description provided.

Note that in geomechanical restoration simulations initialization the definition of the stratigraphy is compulsory.

 

Stratigraphy_definition

Data File

 

 

* Stratigraphy_definition

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

 Unit_Names    IDM=3

   "formation1"

   "formation2"

   "formation3"

 

 

1Three formations present in the initial model.

2The group names coincide with their respective horizon names and unit names, so only the unit order is required.

 

 

Stratigraphy_horizon

Data File

 

 

* Stratigraphy_horizon NUM=1

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

 Name          "formation1"

 Lines         IDM=2

   3 13

 

* Stratigraphy_horizon NUM=2

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

 Name          "formation2"

 Lines         IDM=2

   6 16

 

* Stratigraphy_horizon NUM=3

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

 Name          "formation3"

 Lines         IDM=2

   9 19

 

 

 

1The stratigraphy horizons for the three formations must be defined.

 

 

 

The Group_data data structure is compulsory and defines the properties for each geometry group.  For this example these comprise:

1The name of the group.

2The element type.

3The material assigned to the group.

4The surfaces that define the geometry for the group.

5The type of porous flow.

 

Data File

 

 

* Group_data  NUM=1

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

 Group_name                 "formation1"

 Element_type                      TPM3V

 Material_name                 "Elastic"

 Surfaces  IDM=2

   1 4

 Porous_flow_type                      5

 

 

* Group_data  NUM=2

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

 Group_name                 "formation2"

 Element_type                      TPM3V

 Material_name                 "Elastic"

 Surfaces  IDM=2

   2 5

 Porous_flow_type                      5

 

 

* Group_data  NUM=3

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

 Group_name                 "formation3"

 Element_type                      TPM3V

 Material_name                 "Elastic"

 Surfaces  IDM=2

   3  6

 Porous_flow_type                      5

 

 

1Three groups are defined using the TPM3V (3 noded plane strain triangular elements using the average Volume formulation).  

2The material assigned to these element groups is "Elastic".

3The geometry entities (surfaces) defining each group are assigned.

4The simulation will be performed using the porous flow type number 5 (hydrostatic drained assumptions with vertical effective stress calculated using the buoyant density).

 

The Group_control_data  data structure is compulsory and defines:

1The groups number of geometry groups in the problem, where each geometry group relates to a region with specific properties; e.g. regions with different material assignments, individual stratigraphy layers, etc.

2Whether the group is active or inactive in the fields; i.e. geomechanical, porous flow, thermal, that are being solved.

 

Data File

 

 

* Group_control_data

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

 Group_numbers                 IDM=3

   1 2 3

 Active_geomechanical_groups   IDM=3

   1 1 1

 

Three groups are present in the simulation with the geomechanical active.

 

Geostatic data is used to initialize the model with an specified porosity distribution via Spatial_variation_values. That porosity distribution will be used also to calculate decompaction.

 

Data File

 

 

* Geostatic_data            NUM=1

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

 Groups   IDM=3

   "formation1"

   "formation2"

   "formation3"

 Porosity_spatial                         1  

 Pore_pressure_distribution   "Hydrostatic"

 

 

* Spatial_variation_definition NUM=1

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

 Description     "Porosity vs. Depth"

 Type                      "Absolute"

 Distribution       "Depth_dependent"

 Variation_assignment             1

 

 

* Spatial_variation_values    NUM=1

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

 Description  "Normal Compaction Trend"

 Time                        0.0

 Values_vs_depth     IDM=35 JDM=2

/Depth/   0        179.3    ...    6097.4

/Porosity/ 0.48834  0.44717  ...           0.039523

 

 

 

1Geostatic initialization is applied to the 3 formations present in the model.

2Porosity is initialized with the data defined in the Spatial_variation_definition number 1.

3The Spatial_variation_definition is assigned the porosity trend in depth defined in the Spatial_variation_values number 1.

 

The material properties for the material "Elastic" as well as its associated fluid properties are defined in the datafile.

 

Data File

 

 

* Material_data NUM=1

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

 Material_name                 "Elastic"

 Isotropic_elastic_properties     IDM=2

  /Young's Modulus/              50000

  /Poisson's Ratio/               0.20

 Grain_density                     2760

 Grain_stiffness                  30000

 Porosity                          0.50    

 Singlephase_fluid                    1

 Decompaction_Type                    1

 Decompaction_spatial                 1

 Decompaction_properties          IDM=1

  /Maximum porosity inc/         0.001  

 

 

* Fluid_properties NUM=1

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

 Fluid_type                     "Water"

 Density                          1000

 

1A single material is used for the simulation.

2The material is named "Elastic".

3Elastic properties (Young's modulus and Poisson's ratio) are defined for the material.

4Grain properties (density and stiffness) are defined.

5An arbitrary initial porosity of 0.5 is defined.

6Fluid properties number 1 are assigned to material "Elastic".

7Decompaction_type is set to 1 in order to decompact to a prescribed porosity trend.

8Spatial_variation_values number 1 is assigned as the porosity trend to calculate decompaction (Decompaction_spatial = 1).

9The maximum porosity increment between consecutive time steps is set to 0.001.

10Definition of a fluid with its fluid density is compulsory for groups with porous_flow_type = 5.

 

 

The support data is used to define the fixity in X direction at pin location.

 

Data File

 

 

* Support_data

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

 Displacement_codes IDM=3 JDM=3

  /Set 1/     1 0 0

  /Set 2/     0 1 0

  /Set 3/     1 1 0

 Displacement_code_geom_set IDM=1

   "West"

 Displacement_code_geom_ass IDM=1

   1

 

 

 

1Three displacement code sets are defined.

2Displacement code set number 1 (fixity in X direction) is assigned to the West boundary.

 

 

An "unstructured mesh" with 125m size plane strain triangular elements is defined for this example.

 

Data File

 

 

* Mesh_control_data

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

 Generation_algorithm  2

 Mesh_generation_flag  0

 

 

* Unstructured_mesh_data

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

 Default_element_size       125

 Element_size_bounds  IDM=2

  /Max. Element Size/       125

  /Min. Element Size/       125

 

1The algorithm used for this simulation is set to 2  (i.e. unstructured mesh).

2The mesh generation flag is set to 0 so analysis will be performed after mesh generation (default).

3The element size is set to 125 m.

 

 

Restoration data and restoration surface data are defined.

 

Data File

 

 

* Part_geometry_set         NUM=1

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

 Name    "Restoration_surface"

 Part_lines      IDM=1

   1

 

* Part_line                 NUM=1

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

 Facets      IDM=2  JDM=1

   1 2

 

* Part_nodal_data           NUM=1

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

 Nodes      IDM=2

   1 2

 Coordinates   IDM=2 JDM=2

 -100.0        1700

 6100.0        1700

 

* Restoration_data

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

 Restoration_surface       "Restoration_surface"

 Operation_type                      "Translate"

 Decompaction_Type                  "Continuous"

 Move_to_surface_type               "Bed_length"

 Pin_coordinates   IDM=1

   0.0

 

1Part_geometry_set, Part_line and Part_nodal_data structures are used to define a flat restoration surface with 1700 m of elevation

2A Restoration_data structure is defined (compulsory for geomechanical restoration simulations).

3The part geometry named "Restoration_surface" is assigned as a restoration surface.

4The restoration operation for the first control stage is set to "Translate" (the model top surface is unfolded and translated to coincide with the restoration surface).

5Move_to_surface_type is set to "Bed_length" to assume bed length preservation on the top surface.

6The pin coordinates are at X=0 (same as pinned West boundary)

7For subsequent control stages an identical Restoration_data structure will be defined except the operation type which will be set to "Restore".

 

 

The current analysis considers two control stages with identical data defined by the Control_data structure in which control data for the geomechanical fields is provided.  For more information see Solution Control Data.

 

Data File

 

 

* Control_data

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

 Control_title        "Translate formation1"

 Solution_algorithm                       1

 Target_number_time_steps              8000

 Maximum_number_time_steps            10000

 Termination_time                       1.0

 Output_frequency_plotfile               -1

 Output_frequency_restart                -1

 Screen_message_frequency               500

 Output_time_plotfile                   0.2

 

 

 

 

1Duration for each control stage is 1.0 Ma.

2The solution algorithm is set to number 1, i.e. Transient dynamic algorithm.

3The target number of time steps is set to 8000 for each control stage duration of 1.0 Ma, i.e. time step size of approximately 1.25·10-4.

4The maximum number of time steps is set to 10000.

5The first control stage is set to terminate at time = 1 Ma.

6Information will be displayed on the screen (command prompt) every 500 mech steps.

7A plot file is requested every 0.2 Ma (Output_time_plotfile=0.2) and at the end of the stage (Output_frequency_plotfile=-1).

8Output of a restart file is requested at the end of the control stage.

 

A summary of the data for defining the 2D geometry for this example is presented bellow. These data comprise nodal_data, Geometry_surface and Geometry_line data structures.

 

Nodal_data

Data File

 

 

* nodal_data  

 node_number IDM=16

  1  2  3  4  5  6  7  8  9  10

  11 12 13 14 15 16

 coordinates IDM=3 JDM=16

   0           0      0 !1

   3366.05     0      0 !2

   .

   .

   .

   2500        1500   0 !16

 

1All the nodes that will be used to define geometry lines are defined here.

 

 

 

Surfaces

Data File

 

 

* geometry_surface NUM=1

 surface_type     1

 lines        IDM=4

 1 2 3 4

 

* geometry_surface NUM=2

 surface_type     1

 lines        IDM=4

 3 6 5 7

 

 .

 .

 .

 

* geometry_surface NUM=6

 surface_type     1

 lines        IDM=4

 16 18 19 20

 

1Six surfaces are defined (two per each formation).

2Each surface is defined by four lines.

3Surfaces are type 1 (linear parametric).

 

 

 

Lines

Data File

 

 

* geometry_line NUM=1

 line_type  1

 points        IDM=2

  1 2

 

* geometry_line NUM=2

 line_type  1

 points        IDM=2

  2 3

 

 .

 .

 .

 

* geometry_line NUM=20

 line_type  1

 points        IDM=2

  16 14  

 

1Twenty lines are defined.

2Lines are type 1 (line connecting two nodes).

 

 

 

Results

The result files for the project are in directory: Rest_002\Step1\Results  

 

 

Rest_002_Step1

Results after each restoration stage for step 1.

 

 

The list of generated .geo files after restoration is:

 

Rest_002_Step1_Formation3.geo

Rest_002_Step1_Formation2.geo

Rest_002_Step1_Formation1.geo