Transcript E-Modul - University of Stavanger

Title page
Topic overview
What is Basin Modelling
Topic overview
1 Interpretation &
depht convertion
2 Geohistory
3 Isostasy
1 (Interpretation &
depth conversion)
4 Tectonics
5 Temperature
2 Geohistory
6 Hydrocarbon
Maturation
3 Isostasy
7 Hydrocarbon
Migration
4 Tectonics
5 Temperature
6 Source rock
matuartion
(7 Hydro carbon
migration)
Geohistory Movie
Developers
References
Title page
Topic overview
What is Basin Modelling
1 Interpretation &
depht convertion
2 Geohistory
3 Isostasy
4 Tectonics
5 Temperature
6 Hydrocarbon
Maturation
7 Hydrocarbon
Migration
What is Basin Modeling
The aim of basin modeling is to quantify the mechanisms that is forming sedimentary
basins, and the generation of hydrocarbons.
Basin modeling is the quantitative integrated study of sedimentary basins. It is of
multidisciplinary nature, and includes disciplines like geophysics, sedimentology,
structural geology and geochemistry.
A knowledge of the behaviour of the lithosphere is essential if we are to understand the
initiation and development of sedimentary basins.
This module is focused on extensional basins. The formative mechanisms of
sedimentary basins fall into three classes:
Click on figure
for enlarging
a) loading on the lithosphere causes deflection, and therefore subsidence
b) thinning of the lithosphere by mechanical stretching is accompanied
by fault-controlled subsidence
c) purely thermal mechanisms, such as heat conduction.
More: What can basin modeling tell us
Developers
References
Title page
Topic overview
What is Basin Modelling
1 Interpretation &
depht convertion
What can basin modelling tell us?
Basin modeling is well suited for
2 Geohistory
1) geohistory analysis
3 Isostasy
4 Tectonics
5 Temperature
6 Hydrocarbon
Maturation
7 Hydrocarbon
Migration
2) modelling of isostatic response to sedimentation, erosion and fault movements
3) estimating tectonic subsidence (amount and timing of of stretching)
4) model the palaeo heatflow into the basin
5) predicting area, timing, duration and rate of source rock maturation, together with
timing of fault movements and prospective trap formation
6) evaluation of the effect of faulting on maturation timing and distribution
7) reconstructed fault geometries give insight into possible role of faults as conduits or
barriers between mature sources and potential reservoir through time
Back
8) burial and temperature history can give insight into possible diagenetic effects on
porosity (e.g. quartz cementation).
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References
Title page
Topic overview
What is Basin Modelling
1 Interpretation &
depht convertion
2 Geohistory
Work path of basin modeling
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.
3 Isostasy
4 Tectonics
5 Temperature
6 Hydrocarbon
Maturation
7 Hydrocarbon
Migration
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.
Back
Please note the dependencies in the modelling
tasks, and that the uncertainty increases
during the modelling tasks.
Developers
References
Title page
Topic overview
What is Basin Modelling
1 Interpretation &
depht convertion
2 Geohistory
3 Isostasy
4 Tectonics
5 Temperature
6 Hydrocarbon
Maturation
7 Hydrocarbon
Migration
Section 1: Interpretation & depth conversion
To do basin modelling information on stratigraphy, lithofacies distribution,
and major structural features of the basin is required.
As input an interpreted seismic section is the best starting point for building
a geological model. This includes geometries and ages of the various
horizons.
In addition you need information about the
1) time to depth conversion factors. If the section is in seismic two way
travel time, it has to be converted to depth. In this case, you need
conversion factors.
2) palaeo water depths.
3) eroded or non-depositional surfaces. This includes information on the
magnitude of erosion and the time-span of the non-deposition.
4) lithological boundaries and lithology types. Many important input
parameters are tied directly to lithofacies, e.g. porosity-depth
trends.
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References
Title page
Topic overview
What is Basin Modelling
1 Interpretation &
depht convertion
2 Geohistory
3 Isostasy
Section 2: Geohistory
Geohistorical analysis is the reconstruction in time and space of the
sedimentary basin development. This can incorporate a high resolution
sequence stratigraphic framework, and structural reconstruction of normal
and reverse faults.
4 Tectonics
5 Temperature
6 Hydrocarbon
Maturation
7 Hydrocarbon
Migration
The geohistory reconstruction provides the basis for all additional geological
modelling on the section. It is thus important to do the modelling as correct
and realistic as possible. The aim of the geohistorical analysis is to get the
basin geometry through time correct.
It is of special importance to restore the faults in a proper manner. If this
cannot be done, the basin geometries will be significantly wrong.
Geohistory
movies (2)
Developers
References
Title page
Topic overview
What is Basin Modelling
1 Interpretation &
depht convertion
2 Geohistory
3 Isostasy
4 Tectonics
5 Temperature
6 Hydrocarbon
Maturation
7 Hydrocarbon
Migration
Geohistory Input Data
The data we need to make reliable modeling:
From the seismic section:
lithologies
definition of faults
We must know about:
erosion and non-deposition
porosity depth functions
palaeo water depths
Back
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References
Title page
Topic overview
What is Basin Modelling
1 Interpretation &
depht convertion
2 Geohistory
3 Isostasy
4 Tectonics
Decompaction
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.
5 Temperature
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
6 Hydrocarbon
Maturation
7 Hydrocarbon
Migration
f = foe-cy
Back
Click image to
watch animation
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.
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References
Title page
Topic overview
What is Basin Modelling
1 Interpretation &
depht convertion
2 Geohistory
3 Isostasy
4 Tectonics
Fault Restoration
Fault restoration capabilities are important for several reasons. Without fault
restoration the basin geometry through time will, in many cases, be
incorrect. This will affect the estimated temperature regime of the basin, and
thus the predicted maturation history. Not less important is the insight into
the geometry of possible hydrocarbon migrition pathways and traps through
time.
5 Temperature
6 Hydrocarbon
Maturation
7 Hydrocarbon
Migration
There are several different methods for fault restoration. We are using
vertical simple shear. It is found that this method give very good results,
appropriate for basin modelling purposes.
The method is called vertical shear method of the following reason: If you
think of a fault block as consisting of a deck of cards, the cards remain
vertical throughout the fault restoration process. During the reconstruction,
the cards are translated up the fault system until the top timeline is
continuous across the fault surface. Once the bars have been moved
horizontally, their vertical position are determined by drawing upwards from
their new positions along the fault plane.
Back
The resulting displacement has significant lateral as well as vertical
translation.
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References
Title page
Topic overview
What is Basin Modelling
1 Interpretation &
depht convertion
2 Geohistory
3 Isostasy
4 Tectonics
Decompaction/fault restoration
Back
5 Temperature
6 Hydrocarbon
Maturation
7 Hydrocarbon
Migration
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.
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References
Geohistory
Back
The movie starts from 250 M years ago and progress to present time
Click image to start movies
Next movie
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.
Title page
Topic overview
Geohistory
What is Basin Modelling
1 Interpretation &
depht convertion
Previous
3 Isostasy
movie
4 Tectonics
2 Geohistory
The movie starts from 52 M years ago and progress to present time
5 Temperature
6 Hydrocarbon
Maturation
7 Hydrocarbon
Migration
Back
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.
Developers
References
Title page
Topic overview
What is Basin Modelling
1 Interpretation &
depht convertion
2 Geohistory
3 Isostasy
4 Tectonics
5 Temperature
6 Hydrocarbon
Maturation
7 Hydrocarbon
Migration
Section 3: Isostasy
The sediments accumulating in a basin represent a load on the lithosphere. Isostasy is
the principle of Archimedes applied on the earth’s upper layers. It is one of the main
processes operating in basin formation.
The theoretical isostatic deflections are calculated due to the loading/unloading of
sediments and water through time. Isostatic movements are often calculated using an
Airy approximation. This assumes that the compensation takes place locally and
instantaneously over geological time scales.
More realistic models incorporate the effects of the elastic stiffness and the viscous
flow that can occur in two dimensions.
Elastic and viscous models each requires various earth parameters.
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Title page
Topic overview
What is Basin Modelling
Isostatic parameters
1 Interpretation &
depht convertion
2 Geohistory
Sediments
- matrix density
- pore water density
- porosity
3 Isostasy
4 Tectonics
5 Temperature
6 Hydrocarbon
Maturation
7 Hydrocarbon
Migration
Moho
Lithospheric thickness
- Elastic parameters
- Viscous parameters
Mantle lithosphere
- Astenospheric
density
Back
Astenosphere
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Title page
Topic overview
What is Basin Modelling
Airy Model
1 Interpretation &
depht convertion
2 Geohistory
rs =
2.8 g/cm3
3 Isostasy
4 Tectonics
5 Temperature
h
subs.
6 Hydrocarbon
Maturation
7 Hydrocarbon
Migration
rm = 3.3 g/cm3
Back
•
Local & instant response
•
subsidence = (rs / rm ) x h
•
In this case
• subsidence = 0.85 x h
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.
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References
Title page
Topic overview
What is Basin Modelling
1 Interpretation &
depht convertion
2 Geohistory
3 Isostasy
Elastic model
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.
4 Tectonics
Sediments
5 Temperature
Crust
6 Hydrocarbon
Maturation
Instant response
7 Hydrocarbon
Migration
Effect of Elastic Lithospheric Thickness on Isostatic Subsidence:
1000
Sediment load
500
0
Airy
0
1
km
5 km
25 km
50 km
100 km
-500
Back
-1000
-80
-60
-40
-20
0
Distance (km)
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References
20
40
60
80
Title page
Topic overview
What is Basin Modelling
1 Interpretation &
depht convertion
2 Geohistory
3 Isostasy
Viscous Effect on Isostatic Subsidence
It is also known that the lithosphere has a viscosity which varies strongly with depth.
However, the viscosity is large enough to act as an elastic plate over short time periods.
Over long time spans the applied loads will start to subside into the lithosphere. Isostatic
equilibrium will be achieved over hundred s of millions of years.
4 Tectonics
5 Temperature
Sediments
6 Hydrocarbon
Maturation
7 Hydrocarbon
Migration
Sediments
Crust
Crust
Instant elastic response
Viscous response over time
Back
Subsidence[m]
Tickhness[m]
Will approximate the Airy model with time
Developers
References
Title page
Topic overview
What is Basin Modelling
1 Interpretation &
depht convertion
2 Geohistory
3 Isostasy
4 Tectonics
5 Temperature
6 Hydrocarbon
Maturation
7 Hydrocarbon
Migration
Compositional division of the earth
There are three main compositional units of the earth; the crust, mantle and core.
Crust: The crust is an outer shell of relatively low density rocks. The oceanic crust is thin,
ranging from approximately 4 to 20 km in thickness, and with an average density of 2900 kg m -3.
The continental crust is thicker, ranging from 10 to 70 km, and with an ‘average’ thickness of around
35km.
Information on the density of crustal rocks has been obtained largely by observations on seismograms,
coupled with laboratory experiments. The existence of a low velocity crust was discovered by the
geophysisist
Mohorovicic shortly after the turn of the century. The boundary between the crust and mantle is called
Moho.
The Moho can vary in depth considerably over relatively short distances.
Mantle: The mantle is divided into 2 layers, the upper and the lower mantle. The upper mantle
extends to about 650-700 km. The lower mantle extends to the outer coreat 2900 km.
Read more:
about the mechanical
division of the earth
Back
Developers
References
Title page
Topic overview
What is Basin Modelling
1 Interpretation &
depht convertion
2 Geohistory
3 Isostasy
4 Tectonics
5 Temperature
6 Hydrocarbon
Maturation
7 Hydrocarbon
Migration
Mechanical division of the earth
The mechanical divisions of the interior of the Earth do not necessarily match the compositional
zones. One of the mechanical zoneations of interest in basin studies is the diffrentiation between the
lithosphere and asthenosphere. This is because the vertical motions in sedimentary basins are
responses to deformations of this zone.
Lithosphere: is the rigid outer shell of the Earth, comprising the crust and upper part of the mantle.
It is of particular interest to note the difference between the thermal and elastic thicknesses of the
lithosphere.
It is generally believed that the base of the lithosphere is represented by an isotherm of 1100-1300 oC,
at which mantle rocks approach their solid's temperature. This defines the thermal lithosphere.
The rigidity of the lithosphere allows it to behave as a coherent plate, but only if the upper half of the
lithosphere is sufficiently rigid to retain elastic stresses over geological time scales. This is the elastic
lithosphere. The thickness of the elastic lithosphere varies around the globe. In our area the thickness
is estimated to 1 to 40 km.
Back
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References
Isostasy
The straight red line, are the
position the basin strata had
250 Ma. ( Surface level )
The varying level lines
shows how the strata
subside non-linear
downward in the crust.
Back
The animation shows how the istostatic movements are affected by
sedimentation, erosion, fault movements and variation in the palaeo
water depth over time.
Title page
Topic overview
What is Basin Modelling
1 Interpretation &
depht convertion
2 Geohistory
3 Isostasy
4 Tectonics
5 Temperature
6 Hydrocarbon
Maturation
7 Hydrocarbon
Migration
Section 4: Tectonics
The “observed” subsidence estimated by geohistory analysis is mainly due to two
processes: isostatic movements and tectonic movements due to lithospheric thinning.
The tectonic subsidence is commonly deduced by the McKenzie model. McKenzie
showed that sedimentary basins could form when the lithosphere is stretched, resulting
in reduced crustal thickness and upwelling of hot mantle material. After the stretching
event the surface will subside due to thermal contraction of the lithosphere (see next
page).
The sum of the isostatic calculations and the tectonic modelling will be compared with
the “observed” subsidence (calculated by the geohistory analysis). The amount of
stretching is then the tuning parameter. When the fit is acceptable, the amount of
stretching over the basin is quantified. And simultaneously, the palaeo heat flow history
is found. This is again input to the temperature modeling.
Look on a flow diagram visualising this prosess
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References
Title page
Topic overview
What is Basin Modelling
Total subsidence
1 Interpretation &
depht convertion
2 Geohistory
3 Isostasy
Total (Geohistory) Subsidence =
Isostatic + Tectonic Subsidence
Time
4 Tectonics
5 Temperature
6 Hydrocarbon
Maturation
Isostatic
subsidence
7 Hydrocarbon
Migration
Tectonic
subsidence
Subsidence
Back
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Title page
Topic overview
What is Basin Modelling
1 Interpretation &
depht convertion
2 Geohistory
3 Isostasy
Schematic Illustration of Stretching
Before stretching
bc
Crust
After stretching
C/bc
C
4 Tectonics
5 Temperature
6 Hydrocarbon
Maturation
7 Hydrocarbon
Migration
Mantle lithosphere
(or sub-crust)
SC/bsc
SC
• Thermal
expansion
bsc
Thermal equilibrium
Upwelled
Astenosphere
• Thermal subsidence
Back
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• Subsidence
due to
thinning
References
Title page
Topic overview
What is Basin Modelling
Flow diagram
1 Interpretation &
depht convertion
Geohistory
Reconstruction
2 Geohistory
3 Isostasy
4 Tectonics
5 Temperature
6 Hydrocarbon
Maturation
7 Hydrocarbon
Migration
Present day geometry
Load history
Isostatic
Subs.
Tectonic
Subs.
Compare isost. + tect. subs.
with geohistory basement
subsidence
No
Back
Developers
Subs.
OK?
References
Yes
Paleo Heat Flow
Thermal Model
Title page
Topic overview
What is Basin Modelling
Heatflow
1 Interpretation &
depht convertion
2 Geohistory
3 Isostasy
4 Tectonics
Back
5 Temperature
6 Hydrocarbon
Maturation
7 Hydrocarbon
Migration
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.
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References
Title page
Topic overview
What is Basin Modelling
Section 5: Temperature
1 Interpretation &
depht convertion
2 Geohistory
3 Isostasy
4 Tectonics
5 Temperature
6 Hydrocarbon
Maturation
7 Hydrocarbon
Migration
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
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References
Title page
Topic overview
What is Basin Modelling
1 Interpretation &
depht convertion
2 Geohistory
Thermal reconstruction
3 Isostasy
4 Tectonics
Back
5 Temperature
6 Hydrocarbon
Maturation
7 Hydrocarbon
Migration
Animation showing how the temperature regime in the basin changes
over time due to sedimentation, erosion and heat flow history.
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References
Title page
Topic overview
What is Basin Modelling
Section 6: Source rock maturation
1 Interpretation &
depht convertion
2 Geohistory
3 Isostasy
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.
4 Tectonics
5 Temperature
6 Hydrocarbon
Maturation
7 Hydrocarbon
Migration
The parameters governing the formation of petroleum are
1) temperature
2) time
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
Developers
References
Title page
Topic overview
What is Basin Modelling
1 Interpretation &
depht convertion
2 Geohistory
Source rock maturation
3 Isostasy
4 Tectonics
5 Temperature
6 Hydrocarbon
Maturation
Back
7 Hydrocarbon
Migration
Animation showing the deposition of source rock and the transformation
from organic matter to hydrocarbons in the source rock.
Developers
References
Title page
Topic overview
What is Basin Modelling
1 Interpretation &
depht convertion
2 Geohistory
3 Isostasy
Hydrocarbon migration
Hydro-carbon migration is not treated in this module, but is often the final modelling
task in basin modelling. Hydrocarbon migration (also termed secondary migration)
concentrates petroleum into specific sites (traps) where it may be commercially
extracted.
4 Tectonics
5 Temperature
6 Hydrocarbon
Maturation
7 Hydrocarbon
Migration
The mechanics of hydrocarbon migration from source to reservoir are well studied. The
main driving forces behind the migration is buoyancy (caused by the density contrast
between the petroleum and pore water), and pore pressure gradients which attempts to
move all pore fluids (both water and petroleum)to areas of lower pressure.
Developers
References
Title page
Topic overview
What is Basin Modelling
1 Interpretation &
depht convertion
2 Geohistory
3 Isostasy
4 Tectonics
5 Temperature
6 Hydrocarbon
Maturation
7 Hydrocarbon
Migration
Developers
Module made by
Student
Hege Anita Handeland
Petroleum Technology Dept.
Stavanger University College
NORWAY
Student
Odd Egil Overskeid
Petroleum Technology Dept.
Stavanger University College
NORWAY
Topic Author and Coordinator
Dr. Willy Fjeldskaar
Chief Scientist
Petroleum Technology - Research and Development
Rogaland Research
[email protected]
NORWAY
Developers
References
Title page
Topic overview
What is Basin Modelling
1 Interpretation &
depht convertion
2 Geohistory
3 Isostasy
4 Tectonics
References
The source for animations and movies are taken from BMT - Basin Modeling Toolbox, a
trademark of RF-Rogaland Research, Stavanger, Norway. BMT is also marketed by
Geologica as.
Text provided by Willy Fjeldskaar.
5 Temperature
6 Hydrocarbon
Maturation
7 Hydrocarbon
Migration
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References
Title page
Topic overview
What is Basin Modelling
BMT
1 Interpretation &
depht convertion
2 Geohistory
3 Isostasy
4 Tectonics
5 Temperature
6 Hydrocarbon
Maturation
7 Hydrocarbon
Migration
Back
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References