Lecture 2 Basin Fills
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Geological Modeling:Modeling Long-term Basin Fills
Dr. Irina Overeem
Community Surface Dynamics Modeling System
University of Colorado at Boulder
September 2008
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Course outline 1
Lectures by Irina Overeem:
Introduction and overview Deterministic and geometric models Sedimentary process models I Sedimentary process models II Uncertainty in modeling
Lecture by Overeem & Teyukhina: Synthetic migrated data
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Motivation
Prediction of source rocks, reservoir, seals and trapsrequires an understanding of large-scale structural andstratigraphic evolution of the depositional sequences
within a basin (i.e. in the exploration phase).
Stratigraphic evolution determines the large-scalegeometry of the depositional sequence, as well as thesmaller-scale sedimentary facies and thus the potentialreservoir properties.
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The interplay of sediment supply,sea level and subsidence
A/S ratio (Jervey, 1988)
A = accommodation = the space made available for potentialsediment accumulation by tectonics and sea level change.
S = supply = amount of sediment being delivered to a basin.
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Sea level and Climate
Milankovitch cycles drive glaciations and consequently
sea level fluctuations
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Sediment Supply
Which process would one need to capture to get first-order estimate ofsediment supply?
The sedimentary material is derived from rivers (77%), wind-blown dust (2%),
coastal erosion (1%), ice (9%), vulcanic ejecta (<1%) and biogenics (8%),aerosols and groundwater (Open University, 1989).
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Conceptual longterm basin fill
Courtesy Christopher Kendall, University of South Carolina, US A
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Numerical Modeling of long-term basin fills A simple case: sediment supply into
a stable basin
Sediment supply (constant, 4 grainsize classes)
Process: River channel switching
Process: Delta Plume deposition
Model Example: SedFlux-3D
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Hypopycnal Plume
Steady 2D advection-diffusion equation:
where: x, y are coordinate directions
u, v are velocities
K is turbulent sediment diffusivity
I is sediment inventory
is the first-order removal rate constant
uI vI I I I K K
x y y y x xP
¨ ¸x x x x x x¨ ¸ ! © ¹ © ¹
x x x x x xª ºª º
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Plume examples
River Mouth Angle = 45 ºRiver Mouth Angle = 15 º
Data courtesy, Kettner and Hutton, CSDMS
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Stochastic avulsion mechanism
At specific time steps, t + t , the river mouth angle, A, changes by an
amount drawn from a Gaussian distribution. The rate of switching is
controlled by changing the scaling factor, of the Gaussian deviate, X .
t t t A A U( ! ( X U Q( !
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Avulsions of main delta lobe
High avulsion frequency results in
uniform progradation
Low avulsion frequency results in
distinct lobe formation and locally
enhanced progradation
The scaling factor = 0.3 The scaling factor = 0.03
Depth
in m
100m
200m
300m
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The simple case: sediment supply intoa stable basin
10 by 10 km basin, 40m water depth, single river, time-continuous supply
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Visualize horizon slices,strike and dip sections
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SedFlux-3D experiment of a Rift Basin
Example: Lake Malawi, Eastern Rift of the Great Rift Valley
Formed ~35 million year s ago due to the rifting and separ ation of the African and
Ar abian plates. The lithosphere has stretched significantly and is as a result only
20 km thick as opposed to the normal 100 km.
Lake dimensions: 560 km long, 75 km wide
Bordered by the Livingston Mountains (1500m above lake level), short, steepdr ainage basins.
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Conceptual Model
Courtesy Lacustrine Rift Basin Research Program, University of Miami, US A
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SedFlux-3D experiment of a Rift Basin(scenario funded by EXXON-Mobil TX, US A)
user-specified rapid subsidence
5 alluvial fans and their deltas fill the basin
eustatic sea level change
duration of experiment = 180,000 yrs
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User-defined subsidence
Stack of Matlab grids subsidence rate S = f(x,y,t) [L /T]
S(t0) = subsidence rate at start of simulation
S(ti) = subsidence rate at specified time I
Linear interpolation of subsidence rates in intermediate time steps
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Rift Basin
rivers carry Qs and Qb
rivers carry only Qs
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Airgun seismic profile in N-Lake Malawi
6 dgr. dipping clinoforms
Gilbert type delta deposition
continuous, high-amplitude reflectors,
Hemi-pelagic sedimentation
Courtesy Lacustrine Rift Basin Research Program, University of Miami, US A
TWT
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longitudinal section at 40 km
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Longitudinal section at 50 km
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A couple of other basinfill models
M AJOR ONES: SEDSIM, DIONYSUS
QDSSM (Meijer, 2002)
Integrated tectono-sedimentary model (Clevis, 2003)
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SEDSIM: sediment transport based on fluiddynamics (Navier-Stokes equation)
First version developed at Stanford University, US A (Tetzlaff & Harbaugh)
Further developed at University of Adelaide and CSIRO, Australia (Dyt &Griffiths)
SEDSIM example: 16 Ma of basin evolution simulated for explorationpurposes (Courtesy of CSIRO, Perth, Australia)
Input variables:
Initial topography
Sea-level history
Sediment supply Ocean currents and wind field
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25 September 2010 25
Coarse sand
Medium sand
Fine sand
Clay
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DIONISOS
Developed at IFP (Granjeon & Joseph, 1999) Based on diffusion equation (dynamic-slope model)
Used in exploration
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25 September 2010 27
QDSSM (Meijer, 2002)
Diffusion-advection
Delta model
Short-range tra sport algorit
Long-rangetra sport algorit
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25 September 2010 29
Integrated tectono-sedimentarymodel (Clevis, 2003)
Diffusion-advection eqn
Foreland-basin setting
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