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

Abstract

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 Pennsylvanian͒ 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 energyweighted, 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-Ellenburger collapse. We hypothesize that although the Ellenburger surface does contain a subaerial karst overprint, the first-order control on the formation of the vertically extensive collapse chimneys is bottoms-up tectonic-induced extensional collapse. Although these collapse chimneys have been affected by burial fluid diagenesis, the main consequence of burial fluid flow may be limited to the documented cementation of macrofractures. The apparent dominance of tectonic extension processes over subaerial karst and hydrothermal processes has basinwide implications for distribution of fractures, late-stage cements, and reservoir development and compartmentalization.

Analysis of the Cleburne, Texas, Earthquake Sequence from June 2009 to June 2010

“…This linear trend is consistent with the kinematic estimates of fault length for individual events like those documented in Table 2 and may represent the fault on which the earthquakes occurred. The north to north-northeast trend is also comparable with the trend of many known faults in Texas, Oklahoma, and Louisiana (Ewing, 1990) as well as the orientation of current stress field that supports normal faulting motion along faults that trend northeast-southwest (Sullivan et al, 2006;Tingay et al, 2006). Although the orientation of the fault estimated by the locations departs slightly from the mapped faults in the region as documented in Figure 1, the departure is small and may reflect local variations in strike within the region.…”

“…1). This estimate is based on the type and trend of faults most prevalent in the area (Sullivan et al, 2006;Tingay et al, 2006) and is close to the observed north to north-northeast trend of earthquake locations in this study. The focal mechanism solutions discussed earlier are consistent with this geologic expectation.…”

The Dallas-Fort Worth Earthquake Sequence: October 2008 through May 2009

“…2) that intersects the Dallas-Tarrant county line approximately at the location of the DFW focus. The map indicates the vertical offset on this fault is about 80 m. According to Sullivan et al (2006) and Tingay et al (2006), the present-day maximum principal stress direction in the Fort Worth basin is vertical, and the maximum horizontal stress is N 40°-47°E. Thus, stress is favorably oriented to reactivate normal-faulting motion along this mapped fault, and the trend of the epicenters in Figure 8 is consistent with seismic motion along such a reactivation.…”

Two-year survey comparing earthquake activity and injection-well locations in the Barnett Shale, Texas

“…2). Studies of regional stress (17,18) find that the present-day regional stress system favors normal-faulting motion along NE-SW trending faults.…”