1. Improving Reservoir Characterization
of Karst-Modified Reservoirs
with 3-D Geometric Seismic Attributes
Susan E. Nissen1, E. Charlotte Sullivan2,
Kurt J. Marfurt3, and Timothy R. Carr4
1
Consultant, McLouth, KS
Pacific Northwest National Labs, Richland, WA
2
College of Earth and Energy, University of Oklahoma, Norman, OK
3
4
Department of Geology and Geography, West Virginia University,
Morgantown, WV
2. Outline
• Characteristics of karst-modified reservoirs
• Multi-trace geometric seismic attributes
• Seismic-based examples of
• Collapse structures
• Polygonal features
• Oriented lineaments
• Interpretation workflow for karst-modified
reservoirs
• Conclusions
3. Karst Modified Reservoirs
• Carbonate reservoirs
• Rocks modified by dissolution during
subaerial exposure
• May also have hydrothermal and tectonic
overprints
4. Examples of karst features that can affect
reservoir performance
Collapse features Residual Solution-enlarged
• Compartmentalize paleo-highs fractures
reservoir • May be hydro- • Fluid conduits (if
• Affect deposition carbon traps open) or barriers
of overlying strata (if filled)
Loess-filled fractures, Missouri
Cockpit karst, Jamaica
Cave collapse facies in image log www.cockpitcountry.com
Ft. Worth Basin, Texas
5. Interpretation of Karst Features
• Well data alone is insufficient for identifying the
spatial extent and distribution of local karst features.
• Karst features with substantial vertical relief can be
readily identified using 3-D seismic.
• Critical features relating to reservoir character are
often subtle and not readily detected using standard
3-D seismic interpretation methods.
• Multi-trace geometric seismic attributes can help!
6. Multi-Trace Geometric Seismic Attributes
• Calculated using multiple input seismic traces
and a small vertical analysis window
• The analysis "box" moves throughout the entire
data volume => attributes can be output as a 3-
D volume
• Provide quantitative information about lateral
variations in the seismic data
7. Multi-Trace Geometric Seismic Attributes
• Coherence - A measure of the trace-to-trace similarity of
the seismic waveform
Reference Trace
• Dip/azimuth - Numerical
estimation of the Instantaneous dip =
Dip with highest
instantaneous dip and coherence
azimuth of reflectors
Dips
tested
• Curvature – A measure of the Positive
Curvature
bending of a surface (~2nd Cu Zer
rv o
atu
Zero
Curvature
derivative of the surface)
re
Negative
Anticline Curvature
Di
p
X Pl pin R Flat
an g
e
Syncline
Z Curvature (k)=1/R After Roberts, 2001
8. Mid Continent examples
Central Kansas Uplift
Ord. Arbuckle
- Collapse structures
Mississippian - Polygonal features
- Oriented lineaments
Ft. Worth Basin
Ord. Ellenburger
9. Collapse Features – Fort Worth Basin
vertical seismic section
Pennsylvanian Caddo • Collapse features
are visible as
depressions on the
~2600 ft 3-D seismic profile
Collapse features
• Collapse features
extend from the
Ellenburger through
Pennsylvanian
strata
Ordovician Ellenburger
10. Attribute time slices near the Ellenburger
Amplitude Coherence
fault
N
Dip/Azimuth Most Negative Curvature
W E
Collapse
S
features
3 mi
11. Collapse features line up at the intersections
of negative curvature lineaments
Coherence Most Negative Curvature
Time = 1.2 s
1 mi
12. Polygonal Features
Ordovician Arbuckle Ordovician Ellenburger
Kansas Fort Worth Basin
1 mi 1 mi
1 mi
1.6 km 1.6 km
1.6 km
Diameters ~700-900 ft Diameters ~1400-1600 ft Diameters ~1200 -3500 ft
Vertical relief generally 2 ms (~15 ft) or less
13. Cockpit
Cockpits
karst Arbuckle Polygonal Karst
-- Cockpit Karst
(After Cansler and Carr, 2001)
doline
cone
1 m i
1 .6 k m
Morphological map Arbuckle structure overlain
Arbuckle time structure with paleotopographic
of karst area in New
overlain by most positive divides in Barton Co., KS
Guinea (Williams,
curvature (Cansler, 2000)
1972)
14. Ellenburger polygonal karst
- tectonic collapse structures
Collapse feature Faults
at topographic high
Collapse Features Coincide with
Deep Basement Faults
N
Ellenburger
Basement
15. Oriented lineaments -- Kansas Mississippian
Lineament trend vs.
oil/water production
14 100
90
12
5 year water production (x104 Bbl)
5 year oil production (x104 Bbl)
80
10
70
60
8
50
6
40
30
4
20
2
10
0 0
0 100 200 300 400 500 600 700 800 0 100 200 300 400 500 600 700 800
distance to NE lineament (ft) distance to NE lineament (ft)
14 100
90
12
5 year water production (x10 Bbl)
5 year oil production (x104 Bbl)
80
4
10
70
60
8
50
6
40
4 30
20
2
10
0 0
0 100 200 300 400 500 600 700 800 0 100 200 300 400 500 600 700 800
0.5 mile distance to NW lineament (ft) distance to NW lineament (ft)
16. Workflow for Identification of Karst Overprints
Using Multi-Trace Attributes
Interpret features relating to
Extract attributes structure, geomorphology,
Volumetric
along horizon and reservoir architecture
attributes
or time slice on attribute slices
Identify dominant karst
Predict general production
Horizon geomorphology (e.g., polygonal
performance based on
picks karst vs. groundwater-sapped
type of karst overprint
plateaus)
Core and Separate subaerial karst Identify areas of
log data from tectonic overprint enhanced or occluded
porosity/permeability
Measure distance from
oriented lineaments.
Outline potential reservoir
Production Identify preferred orientations compartment boundaries
data of fluid conduits vs. barriers (fluid barriers)
17. Conclusions
• Coherence, dip/azimuth, and curvature
extractions are valuable for establishing seismic
geomorphology
• Different attributes reveal different details about
karst features
• A workflow utilizing multi-trace attributes, along
with geologic and production information, can
improve characterization of karst-modified
carbonate reservoirs
18. Acknowledgements
Devon Energy
Grand Mesa Operating Company
John O. Farmer, Inc.
Murfin Drilling Company
IHS - geoPLUS Corporation
Seismic Micro-Technology, Inc.
U. S. Department of Energy
Petroleum Research Fund
State of Texas ATP
Kansas Geological Survey, University of Kansas
University of Houston
Hinweis der Redaktion
We will look at examples of the application of volumetric seismic attributes to three areas An Ordovician Ellenburger aquifer in the Fort Worth Basin, north Texas . An Ordovician Arbuckle reservoir in Kansas And a Mississippian reservoir in Kansas
Vertical cross section from a 3-D survey in the Fort Worth Basin of north Texas. Here, collapse features extend from the Ordovician Ellenburger carbonates through Mississippian and Pennsylvanian shales, siltstones, and limestones- a vertical distance of about 2600 ft.
Different attributes show different information about the collapse features Coherence better at showing features than conventional amplitude slice Dip/azimuth shows that they are depressions, sense of motion on faults Volumetric curvature shows more detailed, somewhat polygonal features not evident on the other attributes
Comparison of polygonal features in Kansas Arbuckle and Fort Worth Basin Ellenburger.
A horizon structure map of the Arbuckle surface from a 3D seismic survey in Kansas shows approximately 100 ft (30 m) of local relief, with northwest to southeast-trending ridges. Individual cones and dolines can be seen, some with diameters <1000 ft (300 m). Most Positive curvature extracted along the Arbuckle horizon shows a network of polygonal features with average diameters of approximately 750 ft (230 m). Most of these features have no apparent relief on the seismic structure map. This seismic geomorphic landscape is reminiscent of polygonal or cockpit karst, as described by Williams (1972). Polygonal karst forms in uplifted low-relief strata that have been fissured by a system of joints. Stream sinks are initiated at locations of maximum fracturing. Scattered small depressions expand and capture smaller neighbors until the entire surface is occupied by adjoining polygonal depressions. Polygonal karst has been identified by Cansler and Carr (2001) on the Arbuckle erosional surface elsewhere in Kansas using well data. In their study area, dolines are up to 250 ft (75 m) deep and are localized in areas as wide as 1 mile (1.6 km). Typically, they are 10-60 ft deep (3-20 m) with diameters of 1000-2000 ft (300-600 m). Cansler and Carr (2001) concluded that it is likely that the surface is pitted with a large number of smaller dolines that are too small in area to delineate with well spacing or < 10 ft (3 m) in depth. We appear to be imaging just such features with our seismic curvature map.
Polygonal geomorphology, similar to the cockpit karst identified in the Kansas Arbuckle, is also seen on the surface of the Ordovician Ellenburger horizon in the Fort Worth Basin. Most negative curvature time slices near the Ellenburger show polygonal geometry and corresponding coherence slices show circular collapse features that line up at the intersection of curvature lineaments. However, when we examine the 3D visualization of coherence extracted along the top of the Ellenburger, we see that the collapse features occur near the tops of topographic highs, as well as at valley heads and that the rims of the “cockpits” are rather wide. Although the presence of subaerial karst is well established in the Ellenburger by the presence of cavern collapse facies in conventional cores, this karst forms a pervasive background and is not limited to areas of the large collapse features. Many of the collapse features coincide with deep basement faults, or occur along Pennsylvanian age fractures and small faults. In addition, dolomite and native copper cements in fracture fill indicate flow of burial fluids. These lines of evidence indicate that the polygonal geomorphology and extensive collapse features in the Fort Worth basin data set are more likely controlled by tectonic processes than subaerial weathering. Implications from these studies are that tectonic and subaerial karst processes may be linked, with subaerial karst forming at intersections of tectonic joints. Reactivation of zones of weakness allows migration of fluids (meteoric and hydrothermal) along the same vertical pathways through time.
In a Mississippian reservoir in central Kansas that is subjacent to a pre-Pennsylvanian unconformity and karst surface, lineaments in the long wavelength Most Negative curvature volume, extracted along a horizon corresponding to the base of the aquifer supporting the reservoir, are correlated with fluid production in the reservoir. These lineaments are dominated by two orthogonal directions (northeast and northwest), which line up with regional structural trends. Wells situated near northeasterly oriented lineaments have lower oil production and a thicker basal conglomerate above the unconformity surface than do wells more distant from the northeasterly trending lineaments. The presence of rotated blocks of dolomite and green shale in cores is suggestive of low permeability debris fill. The northeasterly trending lineaments may relate to a high concentration of shale-filled fractures that either degrade the quality of the limestone reservoir or serve as compartment boundaries. Proximity to northwesterly trending lineaments correlates with higher water production, but has no relationship with oil production, suggesting that northwesterly trending lineaments correspond to open fractures that connect directly to the underlying aquifer.