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.
Nissen karst brilliant
Improving Reservoir Characterization of Karst-Modified Reservoirswith 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 2College of Earth and Energy, University of Oklahoma, Norman, OK34 Department of Geology and Geography, West Virginia University, Morgantown, WV
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
Karst Modified Reservoirs• Carbonate reservoirs• Rocks modified by dissolution during subaerial exposure• May also have hydrothermal and tectonic overprints
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, JamaicaCave collapse facies in image log www.cockpitcountry.com Ft. Worth Basin, Texas
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!
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
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
Mid Continent examples Central Kansas Uplift Ord. Arbuckle - Collapse structuresMississippian - Polygonal features - Oriented lineaments Ft. Worth Basin Ord. Ellenburger
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
Attribute time slices near the Ellenburger Amplitude Coherence fault N Dip/Azimuth Most Negative CurvatureW E Collapse S features 3 mi
Collapse features line up at the intersections of negative curvature lineaments Coherence Most Negative CurvatureTime = 1.2 s 1 mi
Polygonal Features Ordovician Arbuckle Ordovician Ellenburger Kansas Fort Worth Basin 1 mi 1 mi 1 mi 1.6 km 1.6 km 1.6 kmDiameters ~700-900 ft Diameters ~1400-1600 ft Diameters ~1200 -3500 ft Vertical relief generally 2 ms (~15 ft) or less
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)
Ellenburger polygonal karst - tectonic collapse structuresCollapse feature Faultsat topographic high Collapse Features Coincide with Deep Basement Faults N Ellenburger Basement
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)
Workflow for Identification of Karst Overprints Using Multi-Trace Attributes Interpret features relating to Extract attributes structure, geomorphology,Volumetric along horizon and reservoir architectureattributes 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 oflog data from tectonic overprint enhanced or occluded porosity/permeability Measure distance from oriented lineaments. Outline potential reservoirProduction Identify preferred orientations compartment boundaries data of fluid conduits vs. barriers (fluid barriers)
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
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