02 - Restoration

 

The geomechanical restoration of the defined 2D geological structure is performed with a total of 15 stages; one stage for geostatic initialization to an average shale porosity trend and fourteen stages for translation /deactivation and restoration to one of the four restoration surfaces. The four different restoration surfaces are defined to be consistent with the first four stratigraphy horizon tops to restore the layers that are onlapping (see picture below) and thereafter the fourth restoration surface is maintained until the end of the simulation.

 

Geol_001_02_01

 

Image of example showing two of the four restoration surfaces pinned on the west boundary

 

 

 

The restoration data files for the project are in: Geol_001\02_Restoration\Data. The data comprises:

 

1.Geol_001_rest.dat: Main restoration data file.

2.Geol_001_RestSurf01.dat: Part geometry data for restoration surface 01.

3.Geol_001_RestSurf02.dat: Part geometry data for restoration surface 02.

4.Geol_001_RestSurf03.dat: Part geometry data for restoration surface 03.

5.Geol_001_RestSurf04.dat: Part geometry data for restoration surface 04.

6.Geol_001.geo: ParaGeo geometry file in "HDF" format.

 

 

The two main simulation stages are:

•Stage 1: Geostatic initialization

•Stages 2 - 15: Fourteen restorations stages to restore the 14 formation layers from Tertiary_10 to Turonian_02.

 

 

The flowchart below summarises the data input and results output files involved in the restoration process.

 

Geol_001_02_10

Summary flowchart of data input files and results output files in restoration process

 

 

 

Basic Set Up: Data file description (Geol_001_rest.dat)

The basic data includes:

 

1.Geometry_data to read the .geo file containing the 2D geometry.

2.Group data for the sixteen formations which are assigned either "Elastic" or "Elastic_Stiff" properties using Group_control_data and Group_data data structures.

3.Geometry_set data that define the stratigraphy horizons, model boundaries, faults and detachments hanging walls and footwalls.

4.Stratigraphy_definition and Stratigraphy_horizon identifying the sixteen formations top horizons and basal horizon.

5.Two Material_data and one Fluid_properties data structures defining elastic material properties with vertical decompaction for the formations. The two base layers are defined stiffer elastic properties to maintain the detachment as flat as possible.

6.Geostatic_data to initialize the model to an average shale porosity NCT (Normal Compaction Trend) (Ewy et al. 2020) via Spatial_variation_definition and Spatial_variation_values data structures.

7. Fault_set data to identify the faults.

8.Contact data for the faults (Contact_global, Contact_set, Contact_surface and Contact_property).

9.Support data (Support_data) defining fixity in X direction at the West boundary.

10.Mesh control (Mesh_control_data) and unstructured mesh generation data (Unstructured_mesh_data) defining element mesh sizes between 50m and 80m.

11.Damping data (Damping_global_data) to define velocity damping of 0.02.

12.Output data (Output_data) to define the data for output to plot files.

13.Include data to read in the four part geometry data (Part_geometry_set, Part_line and Part_nodal_data) defining the four restoration surfaces.

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

15.Control data (Control_data) for geostatic initialization stage defining:

(a)  Incremental solution algorithm (Type 1),

(b)  Factor of critical time step = 0.9,

(c)  Target number of time steps = 2000,

(d)  Maximum number of time steps of 1E7,

(e)  Duration of t = 1 Ma,

(f)  Screen message output every 500 mech steps,

(g)  Plot file output every 0.2 Ma,

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

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

16.Control data (Control_data) for the fourteen restoration stages (Tertiary_10 to Turonian_02) with the same control data as the geostatic initialization stage apart from:

(a)  Target number of time steps = 20000.

 

•Geometry_data, Group_data, Group_control_data and Geometry_set data can be copied from the Step 3 data file Geol_001_geom_Step3.dat and the following changes made:

•Group_data for the oldest two layers ("Basement" and "Turonian_01") defined with the stiffer elastic material "Elastic_Stiff".

•Four additional Geometry_set data structures are included for definition of "Fault_01_hgw_bas", "Fault_02_hgw_bas", "Detach_01_ftw" and "Detach_02_ftw". Note that these geometry sets will be used in the Contact_set and Contact_surface definitions.

 

 

Geometry data

Data File

 

* Geometry_data

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

 File_name         "Geol_001"

 File_format            "hdf"

 

1.The geometry is read from the Geol_001.geo file with "HDF" format from the Step 1 workflow. Note that the geometry file name can be defined with or without an extension, however, the file itself must have the extension ".geo".

 

 

 

Group data

•The Group_data data structure is compulsory and defines the properties for each geometry group

•The material assigned to the group. Note that the two oldest layers ("Basement" and "Turonian_01") which are below the detachment are defined with the stiffer elastic material "Elastic_Stiff". This facilitates recovery of the fault displacement and folding deformation while preventing excessive bending of the detachment.  

 

Data File

 

* Group_data                       NUM=1

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

 Group_name               "Basement"

 Element_type             "Tpm3"

 Material_name            "Elastic_Stiff"

 Porous_flow_type                    5

 Surfaces                         IDM=1

   6

 

* Group_data                       NUM=2

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

 Group_name               "Turonian_01"

 Element_type             "Tpm3"

 Material_name            "Elastic_Stiff"

 Porous_flow_type                    5

 Surfaces                         IDM=1

   21

 

* Group_data                       NUM=3

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

 Group_name               "Turonian_02"

 Element_type             "Tpm3"

 Material_name            "Elastic"

 Porous_flow_type                    5

 Surfaces                         IDM=3

   5   17   18

 

   (...)

 

* Group_data                      NUM=16

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

 Group_name               "Tertiary_10"

 Element_type             "Tpm3"

 Material_name            "Elastic"

 Porous_flow_type                    5

 Surfaces                         IDM=1

  11

 

1.A Group_data data structure is defined for each of the sixteen formations:

a.Element_type is set to TPM3 (3 node 2D plane strain triangular element).

b. The material assigned to all element groups is "Elastic" with the exception of the oldest two layers (Basement and Turonian_01) assigned "Elastic_Stiff".

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

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

 

 

 

Geol_001_02_06

ParaGeo group data for individual formation layers (image scaled vertically by 2 to aid identification)

 

 

Group control data

•The Group_control_data  data structure is compulsory and defines:

1.The group numbers 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.

2.Whether 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=16

   1    2    3    4    5    6    7    8    9   10

  11   12   13   14   15   16

 Active_geomechanical_groups      IDM=16

   1    1    1    1    1    1    1    1    1    1

   1    1    1    1    1    1

 

1.Group_control_data is used to define the geomechanical field as active for the sixteen formation groups.

 

 

 

 

 

Geometry set data

•Four additional Geometry_set data structures are included for definition of "Fault_01_hgw_bas", "Fault_02_hgw_bas", "Detach_01_ftw" and "Detach_02_ftw". These geometry sets will be used in the Contact_set and Contact_surface definitions.

 

Data File

 

* Geometry_set                     NUM=1

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

 Name                     "Base"

 Lines                            IDM=1

  68

 

   (...)

 

* Geometry_set                     NUM=29

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

 Name                     "Fault_02_hgw"

 Lines                            IDM=9

  53   56   57   58   60   61   62   63   64

 

 

* Geometry_set                     NUM=30

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

 Name                     "Fault_02_ftw"

 Lines                            IDM=9

 101  102  103  104  105  106  107  108  109

 

 

* Geometry_set                     NUM=31

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

 Name                     "Fault_01_hgw_bas"

 Lines                            IDM=14

   1   16   42   43   44   45   46   47   48   49

  50   51   52   40

 

 

* Geometry_set                     NUM=32

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

 Name                     "Fault_02_hgw_bas"

 Lines                            IDM=10

  53   56   57   58   60   61   62   63   64   41

 

 

* Geometry_set                     NUM=33

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

 Name                     "Detach_01_ftw"

 Lines                            IDM=1

  87

 

 

* Geometry_set                     NUM=34

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

 Name                     "Detach_02_ftw"

 Lines                            IDM=1

  86

 

1.Thirty-four Geometry_set data structures are defined:

a.Sixteen for the stratigraphy horizons.

b.Three for the model boundaries (base, west and east).

c.Two faults.

d.Three detachments - two separate ones and one encompassing both detachments.

e.Six for the three contact surfaces  (Fault_01, Fault_02, Detach_full) hanging wall and footwall parts.

f.Additional 4 for definition of "Fault_01_hgw_bas", "Fault_02_hgw_bas", "Detach_01_ftw" and "Detach_02_ftw" which will be used in the Contact_set and Contact_surface definitions (see picture below).

 

 

 

 

Geol_001_02_09

 

Geometry sets for faults and detachments hanging walls and footwalls

 

•Stratigraphy_definition and Stratigraphy_horizon data can be copied from the Step 3 data file Geol_001_geom_Step3.dat.

•The stratigraphy is defined by:

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

2.Defining the topology of the top surface horizon for each stratigraphy layer including basal horizon (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.

 

Data File

 

* Stratigraphy_definition

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

Units                            IDM=16

   "Basement"

   "Turonian_01"

   "Turonian_02"

   "Turonian_03"

   "Turonian_04"

   "UCT"

   "Tertiary_01"

   "Tertiary_02"

   "Tertiary_03"

   "Tertiary_04"

   "Tertiary_05"

   "Tertiary_06"

   "Tertiary_07"

   "Tertiary_08"

   "Tertiary_09"

   "Tertiary_10"

 Basal_horizon            "Base"

 

 

 

* Stratigraphy_horizon             NUM=1

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

 Name                     "Basement"

 Lines                            IDM=1

   6

 

   (...)

 

 

* Stratigraphy_horizon             NUM=17

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

 Name                     "Base"

 Lines                            IDM=1

  68

 

1.Stratigraphy_definition defines the stratigraphy for a geomechanical analysis:

a.Units lists the names identifying the top horizons for the sixteen formation layers present in the initial model in depositional order from oldest to youngest.

b.Basal_horizon defines the Stratigraphy_horizon name of the basal horizon for the model "Base".

 

2.Seventeen Stratigraphy_horizon data structures are defined:

a.Sixteen for the top surface of each stratigraphy layer.

b.One for the basal horizon.

 

 

 

Geol_001_02_05

Stratigraphy horizons, model boundaries, faults and detachments (image scaled vertically by 2 to aid identification)

 

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

•Stiffer elastic properties are defined for the base and Turonian_01 layers so that the detachment can be maintained as flat as possible.

 

Data File

 

* Material_data                    NUM=1  

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

 Material_name                  "Elastic"

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

 Units IDM=4

  /Stress/            "MPa"

  /Length/              "m"

  /Time/               "Ma"

  /Temperature/   "Celsius"

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

 Grain_density                      2700  

 Grain_stiffness                   30000

 Porosity                           0.60          

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

 Elastic_properties     IDM=2

  /Young's Modulus/               5000

  /Poisson's Ratio/              0.20

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

 Singlephase_fluid                    1  

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

 Decompaction_Type                    1

 Decompaction_spatial                 1

 Decompaction_properties          IDM=1

  /Maximum porosity inc/         0.001  

 

 

 

* Material_data                    NUM=2  

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

 Material_name                  "Elastic_Stiff"

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

   (...)

 Elastic_properties     IDM=2

  /Young's Modulus/              20000

  /Poisson's Ratio/              0.20

   (...)

 Decompaction_properties          IDM=1

  /Maximum porosity inc/         0.001  

 

 

 

* Fluid_properties                 NUM=1

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

 Fluid_type                      "Water"

 Density                           1000

 

1.Two elastic materials are used for the simulation named "Elastic" and "Elastic_Stiff".

2.Elastic properties (Young's modulus = 5000 MPa and Poisson's ratio = 0.2) are defined for the "Elastic" material and stiffer properties (Young's modulus = 20000 MPa) defined for "Elastic_Stiff".

3.Grain properties (density and stiffness) are defined.

4.An arbitrary initial porosity of 0.6 is defined.

5.Fluid_properties number 1 is assigned to both materials.

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

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

8.In Decompaction_properties, the maximum porosity increment between consecutive time steps is set to 0.001.

9.Definition of a fluid with its fluid density is compulsory for groups with Porous_flow_type = 5 defined in Group_data.

 

 

 

 

 

•Geostatic data is used to initialize the model with a specified porosity distribution via Spatial_variation_definition and Spatial_variation_values data structures.

•Note that this porosity distribution will also be used to calculate decompaction.

 

Data File

 

* Geostatic_data            NUM=1

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

 Groups   IDM=16

  "Basement"

 "Turonian_01"

 "Turonian_02"

 "Turonian_03"

 "Turonian_04"

 "UCT"

 "Tertiary_01"

 "Tertiary_02"

 "Tertiary_03"

 "Tertiary_04"

 "Tertiary_05"

 "Tertiary_06"

 "Tertiary_07"

 "Tertiary_08"

 "Tertiary_09"

 "Tertiary_10"

 Porosity_spatial            1  

 

 

 

* Spatial_variation_definition NUM=1

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

 Description     "Porosity vs. Depth"

 Type                      "Absolute"

 Distribution       "Depth_dependent"

 Variation_assignment             1

 

 

 

* Spatial_variation_values    NUM=1

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

 Description  "Shale Average NCT"

 Time                        0.0

 Values_vs_depth     IDM=24 JDM=2

/Depth/   0       200     ...    4600

/Porosity/ 0.5890  0.4849  ...         0.0124

 

1.Geostatic initialization is applied to the 16 formations present in the model.

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

3.The Spatial_variation_definition is assigned the porosity trend according to depth defined in the Spatial_variation_values number 1 (see picture below).

 

 

Geol_001_02_02

Normal compaction trend (decompaction trend) defined according to natural shale porosity data from samples collected in hydrostatic sediments from different parts of the world (Ewy et al. 2020)

 

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            "Fault_01"

 Hangingwall_set "Fault_01_hgw"

 Footwall_set    "Fault_01_ftw"

 Contact_sets  IDM=1

   "All"  

 

 

 

* Fault_set                     NUM=2

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

 Name            "Fault_02"

 Hangingwall_set "Fault_02_hgw"

 Footwall_set    "Fault_02_ftw"

 Contact_sets  IDM=1

   "All"        

1.Two fault sets are defined.

2.Names are defined for the fault set.

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

4.Contact_sets named "All" is assigned to both fault sets.

 

 

Geol_001_02_07

Fault_set definitions for "Fault_01" and "Fault_02"

 

 

Data related to fault surfaces are defined through Contact_set, Contact_global, Contact_surface and Contact_property data structure to define frictionless contact surfaces for the faults and detachments.

 

Contact set data

Data File

 

* Contact_set                  NUM=1

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

 Name                        "All"

 Geometry_sets   IDM=6

  "Fault_01_hgw_bas"

 "Fault_01_ftw"

 "Fault_02_hgw_bas"

 "Fault_02_ftw"

 "Detach_01_ftw"

 "Detach_02_ftw"

 Algorithm                   "Penalty"

 Property_name               "Faults"

 Global_update_frequency     1000

 Field_factor                0.3

 Buffer_factor               5.0

 All_geometry_flag           0        

 

 

1.A single contact set named "All" is defined.

2.Six geometry sets are included in the contact set definition.

3.Penalty algorithm is selected (this is currently the only option available).

4."Faults" property is assigned to the contact set.

5.Global contact search frequency is set to every 1000 mech steps.

6.Field factor is set to 0.3 so the maximum normal gap is defined as Gn = 0.3· lfacet where Gn is the normal gap and lfacet is the contact facet length.

7.The 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.

8.Global geometry flag is set to OFF as included geometry sets are defined.

 

 

Geol_001_02_08a

Contact_set definition "All"

 

 

 

Contact global data

Data File

 

* Contact_global                  NUM=1

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

 Included_contact_sets    IDM=1

   "All"

 

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

 

 

 

 

 

Contact surfaces data

Data File

 

* Contact_surface                  NUM=1

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

 Name              "Fault_01_hgw_bas"

 Surface_interaction  IDM=3

  "Detach_01_ftw"

 "Detach_02_ftw"

 "Fault_01_ftw"

 

 

* Contact_surface                  NUM=2

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

 Name              "Fault_02_hgw_bas"

 Surface_interaction  IDM=2

  "Detach_02_ftw"

 "Fault_02_ftw"

 

 

* Contact_surface                  NUM=3

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

 Name              "Detach_01_ftw"

 Surface_interaction  IDM=1

   "Fault_01_hgw_bas"

 

 

* Contact_surface                  NUM=4

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

 Name              "Detach_02_ftw"

 Surface_interaction  IDM=2

   "Fault_01_hgw_bas"

   "Fault_02_hgw_bas"        

 

1.Four Contact_surface data structures define the contact surfaces that can interact with the defined surface.

 

 

 

Geol_001_02_08b

 

Definitions of contact surfaces that can interact with the defined surface

 

 

Contact property data

Data File

 

* Contact_property               NUM=1

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

 Name                      "Faults"

 Compression_model      1                  

 Compression_properties IDM=1

  /"Normal Penalty"/                  5000

 Adhesion_model         1                  

 Adhesion_properties IDM=1

  /"Normal Penalty"/                  5000

 Tangential_model       2                

 Tangential_properties IDM=2

  /"Tangential Penalty"/              5000

  /"Friction coefficient"/             0.0

 

1.A contact property named "Faults" is defined.

2.Linear elastic compression model is assigned (compression model 1) with a normal penalty stiffness of 5000 MPa.

3.Linear adhesion model is assigned (adhesion model 1) with a normal penalty stiffness of 5000 MPa.

4.Coulomb friction model is assigned for tangential contact (tangential model 2) with a tangential penalty stiffness of 5000 MPa and a friction coefficient of 0.0 (i.e. frictionless).

 

 

 

 

The support data is used to define the fixity in X direction at the West boundary.

 

Data File

 

* Support_data

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

 Displacement_codes IDM=2 JDM=3

  /Set 1/     1 0

  /Set 2/     0 1

  /Set 3/     1 1

 Displacement_code_geom_set IDM=1

   "West"

 Displacement_code_geom_ass IDM=1

   1

 

1.Three displacement code sets are defined.

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

 

 

 

 

An "unstructured mesh" with plane strain triangular elements with size between 50m and 80m is defined for this example.

 

Data File

 

* Mesh_control_data

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

 Generation_algorithm  2

 Mesh_generation_flag  0

 

 

* Unstructured_mesh_data

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

 Default_element_size       80

 Element_size_bounds  IDM=2

  /Max. Element Size/       80

  /Min. Element Size/       50

 

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

2.The mesh generation flag is set to 0 to perform the analysis after mesh generation (default).

3.The mesh element size is defined to be between 50m and 80m.

 

 

 

 

 

Data File

 

* Damping_global_data

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

 Percentage_damping    0.02

 

1.Velocity damping of 0.02 is utilised.

 

 

 

Data File

 

* Output_data

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

 Nodal_output_flags  IDM=7

  /Displacements/   1

 /Velocity/        1

 /Pore pressure/   0

 /Temperature/     0

 /Mech_fixity/     1

 /Mech_ext_force/  1

 /Mech_int_force/  1

 

1.Nodal data for displacements, velocities, geomechanical fixities, external and internal forces are output.

 

 

 

 

Stage 1: Geostatic initialization

 

Control data

The solution control data to initialize the model to an average shale porosity trend via spatial data is described below.

 

Data File

 

* Control_data

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

 Control_title             "Geostatic"

 Solution_algorithm                  1

 Factor_critical_time_step         0.9

 Target_number_time_steps         2000

 Maximum_number_time_steps    10000000

 Duration                          1.0

 Screen_message_frequency          500

 Output_time_plotfile              0.2

 Output_frequency_plotfile          -1

 Output_frequency_restart           -1        

 

 

1.The current control stage is given a title "Tertiary_10".  This will be re-named appropriately for each of the subsequent control stages.

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

3.The factor critical time step is set to 0.9.

4.The target number of time steps is set to 2000.

5.The maximum number of time steps is set to 10000000.

6.The duration for control stage is set to 1.0 Ma.

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

8.A plot file is requested every 0.2 Ma and at the end of the stage.

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

 

 

 

Stages 2 - 15: Restoration of 14 formation layers from Tertiary_10 to Turonian_02

 

Data for the fourteen restoration stages 2 to 15 comprise:

•Include data structure to read in the four restoration surface part geometry data files.

•Definition of restoration data (Restoration_data) to translate / restore to the defined restoration surfaces.

•Solution control data to define the solution algorithm, output and termination data for the current stage in the geomechanical field.

 

The table below summarises the model data that is defined for each of the fourteen restoration stages - "Y" signifies that it is defined and a greyed-out cell with "->" signifies non-defined model data, however, the last defined model data is carried over to the current stage.

 

 

Restoration Stages

Model Data

Stage 2

(Tertiary_10)

Stage 3

(Tertiary_09)

Stage 4

(Tertiary_08)

Stage 5

(Tertiary_07)

Stages 6 - 15

(Tertiary_06 - _01, UCT, Turonian_04 - _02)

Include

Geol_001_RestSurf01.dat

Geol_001_RestSurf02.dat

Geol_001_RestSurf03.dat

Geol_001_RestSurf04.dat

->

Restoration data

Y (Translate)

Y (Restore)

->

->

->

Solution control data

Y

Y

Y

Y

Y

Stage termination time

2

3

4

5

6 - 15

 

 

•Restoration data and restoration surface data are defined.

•The part geometry data defining the four restoration surfaces are contained in four separate files Geol_001_RestSurf0#.dat and read in using the Include data structure.

 

Data File

 

* Include

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

 Filename  "Geol_001_RestSurf01.dat"

 

 

 

* Restoration_data

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

 Restoration_surface         "Restoration_surface"

 Operation_type                        "Translate"

 Decompaction_Type                     "Top_layer"

 Num_substeps                                    5

 Move_to_surface_type                 "Bed_length"

 Pin_coordinates   IDM=1

   14372.9

 

1.Include data structure is used to read the part geometry data defining the restoration surface which is defined in a separate file.

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

3.The part geometry named "Restoration_surface" is assigned as a restoration surface and read in via Include.

4.The restoration operation for the second control stage is set to "Translate" (the model top surface is unfolded and translated to coincide with the restoration surface which happens to be the same as the top stratigraphy horizon in this example).

5.Decompaction_type is set as "Top_layer". This vertical decompaction model aims to maximize consistency between restoration and forward modelling (see a detailed explanation below)

6.Num_substeps, defining the number of data outputs over the duration of each stage, is set to 5. In this manner we aim to obtain a smoother interpolation of the boundary kinematics for forward modelling (i.e. when Num_substeps is not defined or set to 1, only final state at the end of each restoration stage is used to calculate the boundary kinematics for forward modelling so a linear interpolation is used).

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

8.The pin coordinates are at X=14372.9 (corresponding to the West boundary).

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

 

The Decompaction_type "Top_layer" is a vertical decompaction model that aims to maximise the consistency between restoration and forward modelling in terms of accommodation space created before a layer is deposited (and hence deposition thickness) and geometrical and compaction state of all the layers prior to deposition of a layer. The model is illustrated in the figure below. From state 1 to 2 a translate operation with decompaction is performed. Note that the top layer already follows the Normal Compaction Trend (NCT) at state 1. During such restoration stage (from 1 to 2) the layers below the top layer are decompacted to the NCT with the depth being calculated from the base of the top formation. In the next restoration stage top layer is removed (from 2 to 3) and the translate and decompaction operation for the remaining layers is performed (from 3 to 4). Note that this model ensures consistency when considering the forward model sense because in the forward model the accommodation space for deposited layers between the sedimentation horizon (restoration surface) and the top surface is generated due to the motion of the boundaries (e.g. basal boundary in this column example) and compaction (i.e. from 6 to 5 the accommodation space for the first layer to be deposited is generated. Then from 5 to 4 the first sedimented layer is deposited. Before the initial layer compacts due to the weight of the deposited layer its porosity trend follows the NCT which is consistent with the corresponding restoration state).

 

Geol_001_02_11

Schematic restoration sequence with the decompaction model "Top_layer"

 

 

Restoration surface part geometry data

•Data defining the four restoration surfaces assigned in Restoration_data.

 

Data File (Geol_001_RestSurf0#.dat)

 

* Part_geometry_set         NUM=1

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

 Name    "Restoration_surface"

 Part_lines      IDM=1

   1

 

 

* Part_line                 NUM=1

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

 Facets      IDM=2  JDM=NNN

 1    2

   (...)

 

 

 

* Part_nodal_data           NUM=1

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

 Nodes      IDM=NNN+1

 1    2    3    4    5    6    7    8    9    10

   (...)

                                                         

 

 Coordinates   IDM=2 JDM=NNN+1

  (...)

 

1.Part_geometry_set, Part_line and Part_nodal_data structures are used to define each of the four onlapping restoration surfaces which are consistent with the first four stratigraphy horizon tops.

2.All four restoration part geometry sets are given the same name "Restoration_surface".

3.Note that "NNN" represents number of facets and nodes which could be different for each of the restoration surfaces.

 

Identical solution control data for the geomechanical field is defined for each of the fourteen restoration Control_data structure. The first restoration control stage is described below.

 

Data File

 

* Control_data

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

 Control_title           "Tertiary_10"

 Solution_algorithm                  1

 Factor_critical_time_step         0.9

 Target_number_time_steps        20000

 Maximum_number_time_steps    10000000

 Duration                          1.0

 Screen_message_frequency          500

 Output_time_plotfile              0.2

 Output_frequency_plotfile          -1

 Output_frequency_restart           -1        

 

 

1.The current control stage is given a title "Tertiary_10".  This will be re-named appropriately for each of the subsequent control stages.

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

3.The factor critical time step is set to 0.9.

4.The target number of time steps is set to 20000.

5.The maximum number of time steps is set to 10000000.

6.The duration for control stage is set to 1.0 Ma.

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

8.A plot file is requested every 0.2 Ma and at the end of the stage.

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

 

 

 

Results

The result files for the project are in directory: Geol_001\02_Restoration\Results.

 

In the porosity plot below, it can be seen that the decompaction model "top_layer" considers decompaction of the top stratigraphy layer separately from the rest of the model, i.e. the top layer is decompacted according to the NCT and the rest of the model is decompacted according to the NCT but as if the top layer is not present.  This is done in order to maximize compatibility between restoration and forward simulation, otherwise thicknesses are not consistent.

 

 

 

Geol_001_02_03

 

Porosity results at initial and end of stage 08 restoration (T=9 Ma)

 

 

 

The geometry configuration at the end of several restoration stages are shown below.

 

 

 

Geol_001_02_04

 

Geometry configuration at various restoration stages

 

Generated .geo files

The list of generated .geo files after restoration is:

 

Geol_001_rest_Tertiary_01.geo

Geol_001_rest_Tertiary_02.geo

Geol_001_rest_Tertiary_03.geo

Geol_001_rest_Tertiary_04.geo

Geol_001_rest_Tertiary_05.geo

Geol_001_rest_Tertiary_06.geo

Geol_001_rest_Tertiary_07.geo

Geol_001_rest_Tertiary_08.geo

Geol_001_rest_Tertiary_09.geo

Geol_001_rest_Tertiary_10.geo

Geol_001_rest_Turonian_02.geo

Geol_001_rest_Turonian_03.geo

Geol_001_rest_Turonian_04.geo

Geol_001_rest_UCT.geo