Val_005d Kerogen thickness
Contents
Problem Description
The user is assumed to have undertaken the example Val_005c beforehand.
The influence of the specification of kerogen layer thickness is demonstrated here. The present example is a variation of the oil and gas expulsion example for kerogen B. The data files are identical to Val_005c for kerogen B with the exception of the data required to include kerogen layer thickness. Note that this includes definition of stratigraphy data (described in detail later). When thickness is defined, the change in porosity and pore pressure are both scaled by "thickness/formation thickness". Therefore, for this single element example with dimensions of 10m x 10m (i.e. formation thickness = 10m), if thickness of e.g. 5m is defined, then the change in both porosity and pore pressure is reduced by a factor of 0.5. Conversely, as in Val_005c, when thickness is not defined, then the computed element volume with thickness = formation thickness would be used.
Two examples are simulated here: 1Thickness set to 10m to validate against the result with no thickness definition - results should be exactly the same for changes in porosity and pore pressure. 2Thickness set to 5m to compare against thickness=10m results - results should be reduced by a factor of 0.5. |
Data File Description
The data files for the oil and gas expulsion process for kerogen B with kerogen thickness definition are in ParaGeo Examples\Validation\Val_005\Val_005d\Data. Only the key data structures required for the kerogen thickness specification are described here, these include: •Kerogen_kinetics - include definition of kerogen thickness. •Geometry_set - include geometry definition for base and top of example model. •Stratigraphy data is required for the ParaGeo code to identify the base and top of the model to get the thickness: oStratigraphy_definition - defines the unit name and basal horizon. oStratigraphy_horizon - defines the top horizon data. oStratigraphy_surface_load - define data to de-active the default stratigraphy surface loading.
Kerogen_kinetics
Geometry_set data
Stratigraphy data
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Results for porosity change and pore pressure generation with different kerogen thickness definition
The results files for the oil and gas expulsion for kerogen organofacies type B with kerogen thickness definitions are in ParaGeo Examples\Validation\Val_005\Val_005d\Results. In this directory, the spreadsheet mat_kerogenB_expulsion_thick.xlsx contains: •history results output from the simulations. •comparison plots of porosity change and pore pressure generation for Val_005c (no thickness definition) vs thickness=10m vs thickness=5m (Figure 1).
The figure below shows the ParaGeo results for (a) porosity change and (b) pore pressure generation with different kerogen thickness definition for kerogen B. Observed are: •identical results for the case with no thickness definition (Val_005c) and the case with thickness=10m. This is as expected because the kerogen thickness definition of 10m is the same as the formation thickness definition (i.e. 10m) which is used by default if no kerogen thickness is defined as in Val_005c. •results with thickness=5m are scaled down by a factor of 0.5 as expected due to kerogen thickness being halved.
Note that the amount of pore pressure generated here is artificially high due to the pseudo-artificial conditions of the single element model. A more suitable example to observe overpressure due to hydrocarbon generation would be a uniaxial column with sediment compaction and increasing temperature with burial Kin_001.
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