Case 4 Initialization with initial overpressure (via spatial grids)

Contents

In this exercise an initial overpressure will be prescribed during initialization. This will be performed using special functionalities of Spatial Grids so it is recommended to complete first the tutorial SpatVar_001. The data files for this exercise are located in Geost_001\Exercices\Case 4\Data. Look for ! TODO text in the datafile and follow the instructions.

The basic definition of the model is described in Case 1. Here the data required to define an evolving prescribed pore pressure during initialization is described.

Geostatic_data

Data File

* Geostatic_data NUM=1

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

Groups IDM=1

"formation0"

Porosity_spatial 1

K_value_x 0.7

K_value_y 0.7

Time_curve 100

1Difference in Geostatic_data relative to Case 1 is that keyword Pore_pressure_distribution is not used as pore pressure will be defined via spatial grids.

Spatial grids

Data File

* Spatial_grid NUM=1

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

Name "Pore_Pressure"

Type "Nodal"

Nodal_variables IDM=1

"Pore_nod"

Time_variation_assignment IDM=5

2 3 4 5 6

Node_numbers IDM=2052

2052

* Spatial_variation_values NUM=2

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

Grid_name "Pore_pressure"

Time 0.00000

Grid_number 1

Values IDM=1 JDM=2052

* Spatial_variation_values NUM=3

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

Grid_name "Pore_pressure"

Time 0.4000

Grid_number 1

Values IDM=1 JDM=2052

9.108

4.572540331

* Spatial_variation_values NUM=4

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

Grid_name "Pore_pressure"

Time 0.60000

Grid_number 1

Values IDM=1 JDM=2052

18.216

9.145080661

* Spatial_variation_values NUM=5

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

Grid_name "Pore_pressure"

Time 0.8000

Grid_number 1

Values IDM=1 JDM=2052

27.324

13.71762099

* Spatial_variation_values NUM=6

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

Grid_name "Pore_pressure"

Time 0.95000

Grid_number 1

Values IDM=1 JDM=2052

36.432

18.29016132

1In file geost_001_case4.spat a Spatial_grid with several Spatial_variation_values are defined.

2A Spatial_grid named "Pore_pressure" is defined.

3Spatial grid Type is set to Nodal. This type requires an existing mesh which will be used to assign values at each mesh node. In this case the mesh already exist in the geost_001_case4_geom.geo file (note that mesh generation data is not present in the geost_001_case4.dat file in order to avoid creation of a new mesh).

4The nodal variables that will be defined are "Pore_nod" (pore pressure defined at nodal basis).

5Time_variation_assignment keyword is used to assign several Spatial_variation_values data structures (by number) that will be effective at specified times. This allows to define evolving prescribed values. Here spatial variation values 2, 3, 4, 5 and 6 will be used to prescribe an evolving pore pressure that will be increasing from t=0 to t=0.95 (note that Spatial_variation_values NUM=1 contains values to initialize Porosity vs depth in geostatic).

6Node_numbers of the mesh must be defined. The mesh contains 2052 nodes. Mesh topology is not required as it is already stored into the .geo file.

7Five Spatial_variation_values data structures containing values of pore pressure at each node at specified times are defined. They can be assigned to grid 1 via both, Grid_number or Grid_name (only one of those is required).

8The time from which values will be used to prescribe pore pressure it is specified in each Spatial_variation_values data structure. Note that the change of prescribed values from two consecutive Spatial_variation_values (e.g. 0 Ma to 0.4 Ma) will be instantaneous (values are not interpolated at intermediate times).

9Values of pore pressure at each of the 2052 nodes are provided.

10Note that pore pressure values are defined to consider an onset of overpressure at 1000 m depth.

Geost_001_Case4_PorePressure

Prescribed pore pressure at time 1.0

Include

Data File

* Include

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

Filename geost_001_case4.spat

1the file containing the spatial grid and values to prescribe pore pressure (geost_001_case4.spat) is included into the simulation via the data structure Include.

Spatial_boundary

Data File

* Spatial_boundary NUM=1

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

Name "Pore_pressure"

File_name "geost_001_case4"

Boundary_type "Spatial_grid"

Spatial_grids IDM =1

"Pore_Pressure"

Prescribed_components IDM=1 JDM=1

1The Spatial_boundary data structure is used to prescribe values of pore pressure as a function of time via spatial grids. For more information see Spatial_boundary reference manual page.

2An arbitrary name "Pore_pressure" is defined for the spatial boundary.

3The file name containing the spatial grid and the spatial variation values as a function of time is specified without extension.

4The spatial grid "Pore_pressure" is assigned to prescribe values of pore pressure

5Prescribed_components keyword is used to specify which variables will be prescribed. Number 4 corresponds to Pore Pressure. For more information see Spatial_boundary reference manual page.

Results

The result files for the project are in directory: Geost_001\Exercises\Case4\Results

Geost_001_Case4_Results

Evolution of prescribed pore pressure