Step04 Restoration

Contents

In the present workflow step the restoration will be performed. It should be noted that in most restorations the data required is very similar except the data relative to specific assumptions. Hence an overview of the restoration datafile is provided here while only the most relevant data will be described in detail.

The data files for restoration simulation are in: Geol_003\Case01\Step04_Restoration\Data. Those files are:

1.Geol_003_Case01_Step04_rest.dat main datafile for the restoration simulation.

2.Geol_003_Case01_Step03_geom_tet.geo geometry with the TET mesh for the model obtained from the previous workflow step.

3.Geol_003_Case01_Step03_geom_tet.geometry datafile with the group and geometry set data. This will be read within the main restoration data file via the data structure Include. This file was obtained from the previous workflow step.

4.Geol_003_Case01_Step01_Facies.spat file containing the facies spatial grid to be assigned to the model mesh. This file was obtained during Zmap import data.

5.Geol_003_Case01_Step04_rest.mat material datafile containing the materials used in the simulation.

6.Geol_003_Case01_Step04_geostatic.dat containing the geostatic data and compaction curves defining the initial porosities and the decompaction curves for each Facies to be used during restoration. This will be discussed in detail below.

7.Geol_003_Case01_Step04_restsurf.dat datafile containing the restoration surface.

Geol_003_Case01_Step04_rest.dat file overview

During the present restorations the following assumptions will be made:

•We will use adaptivity data to demonstrate its usage. This will be described in detail below.

•The top surface boundary condition will include usage of membrane elements

•Facies will be used

The data defined to perform the present restoration encompasses:

1.Geometry_data to read the Geol_003_Case01_Step03_geom_tet.geo file

2.Geometry_set data defined within the Geol_003_Case01_Step03_geom_tet.geometry file (read via Include data structure)

3.Group_data and Group_control_data defined within the Geol_003_Case01_Step03_geom_tet.geometry file (read via Include data structure)

4.Material_data defined within the Geol_003_Case01_Step04_rest.mat file (read via Include data structure)

5.Stratigraphy_definition and Stratigraphy_horizon data defining the full stratigraphy (required for restoration simulations). Note that definition of Basal_horizon keyword within Stratigraphy_definition is required for restoration to forward conversion.

6.Support_data with normal displacement constraints applied on the East and South boundaries.

7.Data required to apply facies distribution to the model, i.e:

a.Facies_definition assigning material properties to each facies number

b.Facies Spatial_grid defined within the Geol_003_Case01_Step01_Facies.spat file (read via Include data structure) which contains the distribution of facies numbers

c.Spatial_state_set to assign the facies numbers from the grid to the model mesh

8.Geostatic_data with compaction curves for each facies defined within the Geol_003_Case01_Step04_geostatic.dat file (read via Include data structure)

9.Damping_global_data defining damping to be used for the simulation

10. Restoration_data defining the restoration options / assumptions for the different stages, i.e.:

a.Operation_type "None" with Decompaction_type "None" for the initialisation stage (first stage)

b.Operation_type "Translate" with Decompaction_type "Top_layer" and usage of membrane elements for the second stage. Output of the restored formation facies distribution into spatial grid is requested.

c.Operation_type "Restore" with Decompaction_type "Top_layer" and usage of membrane elements for the third and subsequent stages. Output of the restored formation facies distribution into spatial grid is requested.

11. Definition of the restoration surface via part geometry data within the Geol_003_Case01_Step04_restsurf.dat file (read via Include data structure)

12. Data required to use remeshing during restoration, i.e.:

a.Initial mesh generation data (Mesh_control_data and Unstructured_mesh_data) which is compulsory at first stage to allow using adaptivity

b.Adaptivity data (Adaptivity_control_data and Adaptivity_set_data) defined at the forth stage (as an example that it is not required from the beginning)

13. Control_data for each stage

Below the data relative to usage of adaptivity and facies distribution is explained in more detail.

Data relative to usage of facies

Facies definition

The assignment of facies to each element and the assignment of material properties to each Facies is performed in the main restoration data file (Geol_002b_Case02_rest.dat) and is described below.

Data File

* Include

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

Filename Geol_003_Case01_Step01_Facies.spat

* Spatial_state_set NUM=1

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

Spatial_grid "Geol_003_Case01_properties"

Groups IDM=10

"formation01"

"formation02"

(...)

"formation10"

State_variables IDM=1

"Facies"

* Facies_definition

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

Facies_names IDM=4

"Mech_100_00_00_00"

"Mech_80_00_20_00"

"Mech_20_00_80_00"

"Mech_00_00_100_00"

Facies_ids IDM=4

1 2 3 4

•Include data structure is used to read the file containing the Facies grid.

•Spatial_state_set data structure is used to assign the Facies ID numbers in the spatial grid to the model mesh. Note that the grid is defined as a Spatial_grid_group with HEX elements and full topology being defined as the values will be mapped to the TET model mesh.

•Facies_definition is used to assign/link material properties (including decompaction curves) to each facies ID number. In Facies_names the list of material names (Material_data) corresponding to each number listed in Facies_ids is provided.

Geostatic data for models with facies

The different facies are initialised using different porosity vs. depth curves. This is described below.

Data File

* Geostatic_data NUM=1

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

Name "Initialisation01"

Facies IDM=4

"Mech_100_00_00_00"

"Mech_80_00_20_00"

"Mech_20_00_80_00"

"Mech_00_00_100_00"

Facies_porosity_spatial IDM=4

11 12 13 14

Pore_pressure_distribution "Hydrostatic"

* Spatial_variation_definition NUM=11

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

Description "Mech_100_00_00_00"

Type "Absolute"

Distribution "Depth_dependent"

Variation_assignment 11

* Spatial_variation_values NUM=11

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

Description "Mech_100_00_00_00"

Time 0.0

Values_vs_depth IDM=30 JDM=2

/Depth/ 0 100 ... 10000

/Porosity/ 0.4100 0.3978 ... 0.0280

* Spatial_variation_definition NUM=12

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

Description "Mech_80_00_20_00"

(...)

•A single Geostatic_data structure is defined for all the facies with a different porosity vs. depth curve being assigned for each facies using Facies and Facies_porosity_spatial keywords.

Output of facies grids for later usage during forward modelling

At the end of each restoration stage a Spatial_grid with the Facies ID numbers distribution for the formation / group being back stripped needs to be output in order to allow the corresponding facies assignment during sedimentation in the forward simulation. The required data is described below.

Data File

* Restoration_data

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

Restoration_surface "Restoration_surface"

Operation_type "Translate"

Decompaction_Type "Top_layer"

Move_to_surface_type "Vertical"

Spatial_grid_facies "Fac"

Bed_length_constraint_type "Bed_force1"

Bed_length_constraint_data IDM=3

/Stiffness/ 1E12

/Maximum Tension/ 1E3

/Gf/ 100

State_reinit_flag 1

•Spatial_grid_facies keyword is used to request and define the name of the Spatial_grid that will be output at the end of each restoration stage for the back-stripped formation.

•The output file for each formation N will be named according to the following criteria: Geol_003_Case01_Step04_rest_Fac_formationN.spat with the grid name and formation name appended to the restoration simulation data file name.

Data relative to usage of adaptivity

Initial mesh generation

Definition of initial mesh generation data within the first stage is compulsory if adaptivity is going to be used at any stage of the simulation as data required to perform remeshes is generated during such step. Note that if a simulation is run without initial mesh generation and at some point it fails due to element inversion upon excessive mesh distortion / deformation, the simulation will not be able to be restarted with adaptivity data and will be required to perform the run from the start including initial mesh generation instead.

Data File

* Mesh_control_data

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

Generation_algorithm 2

Mesh_generation_flag 0

* Unstructured_mesh_data

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

Default_element_size 200

Element_size_bounds IDM=2

/Max. Element Size/ 200

/Min. Element Size/ 200

• Mesh_control_data and Unstructured_mesh_data are defined in the initial stage as required.

Adaptivity data

In this example adaptivity is not actually needed to avoid any mesh distortion issue and finalize the simulation but is used for demonstrative purposes. In the present example we will assume that adaptivity is required from stage 4 (back-stripping of formation08) and consequently the data is defined in such stage.

Data File

* Adaptivity_control_data

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

Error_evaluation_frequency 4000

Remesh_type "Global"

Default_element_sizes IDM=2

/Max./ 200.0

/Min./ 200.0

Maximum_remesh_frequency 5

Mapping_output_flag 4

Rem_output_flag 1

Remesh_sets IDM=1

* Adaptivity_set_data NUM=1

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

Groups IDM=8

1 2 3 4 5 6 7 8

Distortion_area_data IDM=1

15.0

Region_type "All"

Element_sizes IDM=2

/Max./ 200.0

/Min./ 200.0

•Adaptivity_control_data is defined for a Global remesh with a target element size of 200 m and:

oError_evaluation_frequency set to 4000 to perform a mesh distortion check every 4000 mech steps (note that every stage is solved with approximately 20000 mech steps so this corresponds to 5 adaptivity checks per stage)

oMaximum_remesh_frequency set to 5 to enforce a remesh every 5 adaptivity checks regardless on whether or not the remeshing criteria is satisfied in the check.

oMapping_output_flag set to 4 requests that the plot files before and after every remesh are output to Geol_003_Case01_Step04_rest_BeforeMap.plt and Geol_003_Case01_Step04_rest_AfterMap.plt files respectively.

oRem_output_flag set to 1 requests the output of a .rem file which may be used for debugging purposes in the case of a remesh failure (not generally required).

•Adaptivity_set_data with a target element size of 200 m for all the groups is defined.

Results

The results for the present workflow steps are provided in Geol_003\Case01\Step04_Restoration\Results. Note that only a selection of the results are provided.

The key result files for the forward modelling comprise:

•Geol_003_Case01_Step04_rest_formationNN.geo a .geo file containing the restoration results at the end of each restoration stage. Those will be processed in the subsequent workflow step to generate forward simulation data.

•Geol_003_Case01_Step04_rest_Fac_formationNN.spat a spatial grid containing the facies ID number distribution for each deposited layer

Loading the file Geol_003_Case01_Step04_rest.xmf in ParaView the full series of plot files (.plt) at all output times can be visualised.

Initial Facies and porosity distribution after geostatic stage in the model. V.E.=3