SYNTHETIC SEISMIC MODELING WITHIN THE BURIED
MARATHON COMPLEX, TERRELL AND PECOS
COUNTIES, TEXAS
Richard J. Erdlac, Jr.*
University of Texas of the Permian Basin
Center for Energy & Economic Diversification
Douglas B. Swift*
Petroleum Consultant
*Formerly:
West Texas Earth Resources Institute
Marathon Complex In
Brewster, Pecos, &
Terrell Counties
Landsat black and white
image of surface Marathon
folds in Brewster County.
Map displaying Marathon trend
from surface outcrop (outlined in
red) as it extends into subsurface.
Subsurface Marathon Complex In Pecos & Terrell Counties
Isopach from base
of Cretaceous to
top of Wolfcamp
displays trend of
overthrusting.
Isopach thin is to
the south whereas
isopach thick is to
the north of dense
clustering of 100’
contour intervals.
Delaware –
Val Verde
Basins
2D Seismic
Data
(Vintage 1970-72)
203B – Brown-Basset
Field
201 & 109C – Marathon
overthrust region
Geophysical Micro-Applications (GMA)
Wavelet Types Available
► Ricker
► Ormsby – greater
control of frequencies for better matching
seismic data processing; wavelet of 1, 5, 42, and 48 Hz;
100 traces generated, 4 ms sample rate, 300 ms AGC,
5% noise applied to final result.
► Klauder
► Butterworth
Geophysical Micro-Applications (GMA)
Ray Tracing Methodologies
► Normal Incidence – rays
traced upward at 90o to body, with
diffraction at body intersections and and layers using Snell’s Law
(Exploding Reflector; Zero Offset).
► Diffraction Method – 2D
in GMA; simulates full diffraction patterns.
► Vertical Incidence – rays
travel straight down from surface, no
diffraction at intersecting points; simulate perfectly migrated
synthetic seismic profile.
► Image Ray – employs
same downward path as in Vertical Incidence;
allows for diffraction according to Snell’s Law.
Brown-Bassett Field Seismic Modeling
Brown-Basset Field In Terrell County
As Shown On A Production Map
(Map courtesy of Midland Map Company)
Brown-Bassett
Brown-Basset Field In Terrell County
As Displayed At 200 Ft CI At Top Of
Devonian With Line 203B
(Data courtesy of Geological Data Services)
(Contouring using GeoGraphix)
Brown-Bassett Field Seismic Modeling
Seismic Line 203B As It Crosses W End Of Brown-Bassett
(Interpreted as primarily a faulted hanging wall)
Basement uplift showing 2 possible interpretations:
A) Predominantly folded strata over an uplifted basement
block.
B) Predominantly faulted strata beds with up-dip trap
potential of the footwall strata against the hanging wall
block.
Brown-Bassett Field Seismic Modeling
Dry Fork Ridge Anticline, Wyoming
Map view and cross sections. (Hennings & Spang, 1987)
Brown-Bassett Field Seismic Modeling
BB Model 3 In Depth – 1,500 feet structural
relief on top of blue limestone.
BB Model 3 – Interpreted Synthetic Seismogram
Ormsby Wavelet, Vertical Incidence
BB Model 3 In 2-Way Time
BB Model 3 – Synthetic Seismogram
Ormsby Wavelet, Vertical Incidence
Brown-Bassett Field Seismic Modeling
BB Model 4 In Depth – 2,500 feet structural
relief on top of blue limestone.
BB Model 4 – Interpreted Synthetic Seismogram
Ormsby Wavelet, Vertical Incidence
BB Model 4 In 2-Way Time
BB Model 4 – Synthetic Seismogram
Ormsby Wavelet, Vertical Incidence
Brown-Bassett Field Seismic Modeling
Model 3
Both models
display footwall
reversal of the
type observed on
seismic profile
VVBGS 203B.
Note
footwall
reversal.
Is it real?
Model 4
Thus, there is a
strong correlation
that the footwall
structure found on
the seismic profile
is not real.
Variable Syntectonic Sedimentation In Overthrust Seismic Modeling
Production displaying
fields located along the
subsurface Marathon
orogeny.
Isopach from base of
Cretaceous to top of
Wolfcamp displays trend of
overthrusting. Isopach thin
is to the south whereas
isopach thick is to the north
of dense clustering of 100’
contour intervals.
VVBGS 201
DBGS 109C
Variable Syntectonic Sedimentation In Overthrust Seismic Modeling
DBGS 109C
This line appears to show relatively straight
line fault boundaries, with near horizontal
reflectors within each thrust block.
This line displays fault surface boundaries that
are also deformed within each thrust unit.
Internal reflections demonstrate internal folding
near toe of each thrust unit, as well as dip that
parallels the thrust boundary.
VVBGS 201
Variable Syntectonic Sedimentation In Overthrust Seismic Modeling
Sandbox experiments involving
various amounts of syntectonic
sedimentation demonstrate an
affect upon the geometry of the fault
blocks as well as the internal
geometry of the
deforming strata.
From Storti and McClay, 1995.
Variable Syntectonic Sedimentation In Overthrust Seismic Modeling
No Syntectonic Sedimentation – 57% shortening
Low Syntectonic Sedimentation – 43% shortening
Intermediate Syntectonic Sedimentation – 32%
shortening
High Syntectonic Sedimentation – 17% shortening
Variable Syntectonic Sedimentation In Overthrust Seismic Modeling
Ormsby Wavelet, Diffraction Method
High Syntectonic Sedimentation – 17% shortening
Ormsby Wavelet, Vertical Incidence Method
No Syntectonic Sedimentation – 57% shortening
Variable Syntectonic Sedimentation In Overthrust Seismic Modeling
DBGS 109C
The high syntectonic sedimentation model
(17% shortening) tended to better match
the geometry of the various reflectors
found on profile DBGS 109C.
The deepest high amplitude reflectors on
the model show a pull-up whereas the
deep high amplitude reflectors on line
109C are depressed (push-down). This
suggests relative stacking of lower
velocity rock when compared to model.
Variable Syntectonic Sedimentation In Overthrust Seismic Modeling
VVBGS 201
The no syntectonic sedimentation model (57%
shortening) tended to better match the geometry of
the various reflectors found on profile VVBGS 201.
Image of model reversed to better compare with line.
One difference between data and model is that
the thrust sheets on line 201 may be truncated
along an erosional surface, which is not
present on model. Otherwise, geometry of
model is similar to line 201.
CONCLUSIONS
► Reflection seismic data is the result of measurements of energy
reflections off impedance contrasts within subsurface strata.
This data approximates the actual subsurface geology.
► Structural complexities and highly dipping strata cannot be well
imaged, if at all.
► The reflections observed on the seismic data can be modeled by
the use of reasonable geologic geometries that can mimic those
observed on real world data.
► This represents a powerful, yet underutilized, tool for testing
geologic analogs in structurally complex areas.
► This type of investigation can assist in determining the level of
reality, and thus the level of risk, for geologic interpretations.