E. Charlotte Sullivan

Application of new seismic attributes to collapse chimneys in the Fort Worth Basin

Three-dimensional seismic volumes from the central Fort Worth Basin display roughly circular collapse chimneys that extend vertically about 800 m from the Ordovician Ellenburger Formation to the Atokan (middle Pennsylvanian) Caddo Limestone. Collapse chimneys in carbonates may be caused by subaerial karst, hydrothermal, or tectonic extensional processes. We use 3D multitrace geometric attributes including coherence, volumetric curvature, and energy-weighted, coherent amplitude gradients to investigate details of the origin of these structures. The Ordovician Ellenburger surface resembles a subaerial karst landscape of cockpits, dolines, and frying-pan valleys, while resistivity-based wireline image logs record 50 m of karst breccia facies. However, images from coherence and long-wavelength most-positive and most-negative-curvature volumes show many of the 800-m collapse features are associated with basement faults or with subtle Pennsylvanian and younger tectonic features, rather than with intra-Ellenburg...

Volume-based curvature computations illuminate fracture orientations — Early to mid-Paleozoic, Central Basin Platform, west Texas

Volumetric curvature analysis is a simple but computationally intensive procedure that provides insight into fracture orientation and regional stresses. Until recently, curvature analysis has been limited to computation along horizon surfaces that may be affected by unintentional bias and picking errors introduced during the interpretation process. Volumetric curvature is best estimated in a two-step process. In the first step, we use a moving-analysis subvolume to estimate volumetric reflector dip and azimuth for the best-fit tangent plane for each sample in the full volume. In the second step, we calculate curvature from adjacent measures of dip and azimuth. We use larger curvature analysis windows to estimate longer wavelength curvatures. Such a technique allows us to output full 3D volumes of curvature values for one or more scales of analysis. We apply these techniques to a data set from the Central Basin Platform of west Texas and find lineaments not observable with other seismic attributes. These lineaments indicate that, in the lower Paleozoic interval, a left-lateral shear couple oriented due east-west controls the local stress regime. Such a model predicts that extension faulting and fractures will be oriented northeast-southwest. The example demonstrates the potential of this new technology to determine stress regimes and predict azimuths of open fractures.

Rock-property and seismic-attribute analysis of a chert reservoir in the Devonian Thirty-one Formation, west Texas, U.S.A.

In west Texas, fractured-chert reservoirs of Devonian age haveproducedmorethan700millionbarrelsofoil.Aboutthe same amount of mobile petroleum remains in place. These reservoirsarecharacterizedbymicroporosity;theyareheterogeneous and compartmented, which results in recovery of less than 30% of the oil in place. In this case study the objective was to use cores, petrophysical logs, rock physics, and seismic attributes to characterize porosity and field-scale fractures.Therelationsamongporosity,velocity,andimpedancewereexploredandalsoreactionsamongproduction,impedance, and lineaments observed in 3D attribute volumes. Laboratory core data show that Gassmann’s fluid-substitution equation works well for microporous tripolitic chert. Also, laboratry measurements show excellent linear correlation between P-wave impedance and porosity. Volumetric calculations of reflector curvature and seismic inversion of acoustic impedance were combined to infer distribution of lithofaciesandfracturesandtopredictporosity.StatisticalrelationswereestablishedbetweenP-wavevelocityandporosity measured from cores, between P-wave impedance and producing zones, and between initial production rates and seismic “fracture lineaments.”The strong quantitative correlation between thick-bedded chert lithofacies and seismic impedance was used to map the reservoir. A qualitative inverse relation between the first 12 months of production and curvaturelineamentswasdocumented.

Channel Detection Using Seismic Attributes On the Central Basin Platform, West Texas

The Devonian Thirtyone Formation is a prolific producer on the Central Basin Platform in west Texas having produced over 750 MMBBL from chert reservoirs and containing as much as 650 MMBBL remaining reserves. One of the play concepts for this reservoir is laminated beds deposited as turbidites in a deep sea environment. The locations of the lobes and channels and their feeder channels cannot uniquely be determined from well control and 2-D seismic.

Volume‐based shape index attribute illuminates subtle (sub‐seismic?) karst

For a 3-D seismic volume, we determine a Shape Index to describe the geometric shape of a calculated surface at every point within the volume. With this Shape Index, we can tell whether the local surface is in the form of a dome, bowl, ridge, valley, or saddle. We apply this technique to a data set from the Central Basin Platform of West Texas and can illuminate subtle karst features that influence production but are unobservable on other seismic displays.

Karst related vertical collapse structure and related lineament detection by seismic attributes on Fort Worth basin seismic data volume

Here in this study we present a case study of karst related vertical collapse structure detection using a P wave 3D land seismic data collected in the Fort Worth Basin, Wise county, North central Texas. A major aspect of this study is to illustrate the improvement rendered to the interpretation process by using various new generation attributes and how they considerably improve fracture like lineament and related structure detection.

Bottoms Up Karst: New 3-D Seismic Attributes Shed Light On the Ellenburger (Ordovician) Carbonates In the Fort Worth Basin (north Texas, USA)

3-D seismic volumes from the central Fort Worth Basin display fractures and collapse features that extend vertically some 800 m from the Ordovician Ellenburger Formation to the middle Pennsylvanian Caddo Limestone. These features have been attributed to collapse of subaerial karst features in the Ellenburger. We have used dip derivative and coherence seismic attributes to investigate the origin of these features. Although time slices through the Ellenburger contain features that can be interpreted as cockpit karst, dolines and frying pan valleys, the alignment of many sinkhole features in the Ordovician Ellenburger coincide with later age Pennsylvanian lineaments. In addition, the length of the vertical collapse features is excessive for simple Ellenburger cavern collapse, and horizon slices on the Pennsylvanian Caddo limestone lack exposure features of significant magnitude to produce 800+m of top-down karst. By incorporating the timing constraints provided by better imaging of subtle lineaments in the seismic volume, we hypothesize late stage fault collapse and possible burial fluid origin for the vertical collapse chimneys. The presence of burial fluid dissolution and overburden collapse has basinwide implications for distribution of fractures, calcite cement, and reservoir compartmentalization.