Topic overview. 1 (Interpretation & depth conversion). 2 Geohistory. 3 Isostasy. 4 Tectonics. 5 Temperature. 6 Source rock matuartion. (7 Hydro carbon migration). Geohistory Movie. What is Basin Modeling.
1 (Interpretation & depth conversion)
6 Source rock matuartion
(7 Hydro carbon migration)
Click on figure
More:What can basin modeling tell us
The first step in a basin analysis study is to build the input geological section. This step involves transferring the seismic profile into the modelling tool.
The next step will be to simulate a geohistory for the geological section. It is necessary to make a complete geohistory before moving on to any of the other tasks.
During the subsidence analysis you will draw the work you completed in the geohistory reconstruction to constrain the model.The purpose of this task is to calculate the palaeo heatflow over the section.
The temperature modelling depends on the calculated heat flow history.
The final step in this module is the source rock maturation modelling. This depends on the temperature history of the basin, and on the time.
Possible HC migration modelling follows, when the maturity is calculated.
Please note the dependencies in the modelling tasks, and that the uncertainty increases during the modelling tasks.
Present-day stratigraphic thicknesses in a basin are a product of cumulative compaction through time. Geohistory reconstruction relies primarily on the decompaction of the stratigraphic units to their correct thickness at the various times in the evolution - in addition to fault restoration and corrections due to palaeo water depth variations.
The decompaction of stratigraphic units requires the variation of porosity with depth to be known. Estimates of porosity from boreholes suggest that normally pressured sediments exhibit an exponential relationship between porosity and depth. It is given on the form
f = foe-cy
where f is the porosity at any depth y, fo is the surface porosity and c is a coefficient that is dependent on lithology and describe the rate at which the exponential decrease in porosity takes place with depth.
The decompaction technique seeks to remove progressive effects of rock volume change with time and depth. One by one layer is removed, and the layers underneath are decompacted. Any compaction history is likely to be complex, being affected by lithology, overpressure, diagenesis and other factors. Consequently, what are needed are some general porosity-depth relationship which hold good over large depth ranges.
Click image to
When reconstructing the basin evolution, one by one layer is removed,
and the layers underneath are decompacted acording to the porosity-depth relationship.
The faults blocks are also translated up the fault system until the top timeline
is continuous across the fault surface.
The movie starts from 250 M years ago and progress to present time
Click image to start movies
Animation of the basin evolution of a section over Sørvestlandshøgda over geological time. Different colours indicate sediments of different age. Note the time scale in the lower part of the figure.
The movie starts from 52 M years ago and progress to present time
Animation of the basin evolution of a section over Sørvestlandshøgda over Tertiary time (detailed view of the previous movie). Different colours indicate sediments of different age. Note the time scale in the lower part of the figure.
- matrix density
- pore water density
- Elastic parameters
- Viscous parameters
rm= 3.3 g/cm3
Illustration of the Airy model. This assumes that the compensation takes place locally and instantaneously over geological time scales. The earth is reacting to loads as if it was ‘floating’ on a fluid mantle.
The Airy model can overestimate isostatic subsidence leading to underestimated heat flow.
The earth’s response to loading show that the lithosphere acts as an elastic shell. If a load is applied to the elastic lithosphere, part of the applied load will be supported by the lithosphere, and part by buoyant forces of the mantle underneath, acting through the lithosphere.
Effect of Elastic Lithospheric Thickness on Isostatic Subsidence:
Viscous response over time
Instant elastic response
Will approximate the Airy model with time
about the mechanical
division of the earth
The straight red line, are the
position the basin strata had
250 Ma. ( Surface level )
The varying level lines
shows how the strata
downward in the crust.
The animation shows how the istostatic movements are affected by sedimentation, erosion, fault movements and variation in the palaeo water depth over time.
Look on a flow diagram visualising this prosess
Present day geometry
Compare isost. + tect. subs.
with geohistory basement
Paleo Heat Flow
Here is shown how the heat flow history changes over geological time, due to the amount of lithospheric stretching over the basin.
The heatflow is to a certain degree also affected by sedimentation and erosion.
The temperature history of the basin is calculated after the heatflow modeling is finished. The temperature depends on
1) the basin geometries calculated in the geohistory analysis
2) the heat flow history from the tectonic modelling
3) the palaeo surface temperature
4) the thermal conductivity and heat capacity structure of the sediments.
Temperatur development movie
Animation showing how the temperature regime in the basin changes over time due to sedimentation, erosion and heat flow history.
There is now a wealth of geochemical evidence that petroleum is sourced from
biologically-derived organic matter buried in sedimentary rocks. Organic-rich rocks
capable of expelling petroleum compounds are known as source rocks.
The parameters governing the formation of petroleum are
3) organic matter type
Thus the reliability of the prediction of oil and gas formation depends on
1) the reliability of the temperature history
2) the reliability of the organic kinetic parameters used in the maturation modelling
hydrocarbon maturation movie
Animation showing the deposition of source rock and the transformation
from organic matter to hydrocarbons in the source rock.