Print this pageThe Effects of Horizontal Fault Curvature and Displacement on Thrust Closure Geometry
HENNINGS, PETER H., and BRUCE H. PRINE
We have conducted 3D geometric analyses, using GeoSec 3D, on a suite of exposed, oilfield-scale structures in Wyoming and Alberta, to determine the effects that horizontal variations in fault curvature and displacement have on the size, style, and internal character of hanging-wall thrust closures. The 3D models were constructed using geologic maps, topographic maps, aerial and oblique photography, cross sections, and seismic data.
Our results indicate that the primary controls on the strike-parallel geometry (closure) in hanging-wall anticlines are: (1) the degree of map-view curvature of the thrust surface near its termination, (2) the magnitude and horizontal gradient in thrust displacement (the horizontal angle between the deformed loose-line and its restored counterpart), and (3) the degree to which the competent lithotectonic unit passes over the curved segment of the thrust surface. In structures with fault curvatures that are less than 20 degrees, and displacement gradients that are less than 10 degrees, we observe the following attributes: hanging-wall anticlines plunge toward their terminations at less than 10 degrees, the deformation of the hanging-wall can be considered to be plane-strain, the geometry is often dominated by detachment folds that are parallel to the strike of the main thrust, and reservoir compartmentalization is low. Structures with larger fault curvatures (10 to 35 degrees) are often associated with large displacement gradients (10 to 30 degrees). In these cases hanging-wall anticlines plunge toward their terminations at angles up to 45 degrees, they often have zones of rapid loss in stratigraphic sepWe have conducted 3D geometric analyses, using GeoSec 3D, on a suite of exposed, oilfield-scale structures in Wyoming and Alberta, to determine the effects that horizontal variations in fault curvature and displacement have on the size, style, and internal character of hanging-wall thrust closures. The 3D models were constructed using geologic maps, topographic maps, aerial and oblique photography, cross sections, and seismic data.
Our results indicate that the primary controls on the strike-parallel geometry (closure) in hanging-wall anticlines are: (1) the degree of map-view curvature of the thrust surface near its termination, (2) the magnitude and horizontal gradient in thrust displacement (the horizontal angle between the deformed loose-line and its restored counterpart), and (3) the degree to which the competent lithotectonic unit passes over the curved segment of the thrust surface. In structures with fault curvatures that are less than 20 degrees, and displacement gradients that are less than 10 degrees, we observe the following attributes: hanging-wall anticlines plunge toward their terminations at less than 10 degrees, the deformation of the hanging-wall can be considered to be plane-strain, the geometry is often dominated by detachment folds that are parallel to the strike of the main thrust, and reservoir compartmentalization is low. Structures with larger fault curvatures (10 to 35 degrees) are often associated with large displacement gradients (10 to 30 degrees). In these cases hanging-wall anticlines plunge toward their terminations at angles up to 45 degrees, they often have zones of rapid loss in stratigraphic sepWe have conducted 3D geometric analyses, using GeoSec 3D, on a suite of exposed, oilfield-scale structures in Wyoming and Alberta, to determine the effects that horizontal variations in fault curvature and displacement have on the size, style, and internal character of hanging-wall thrust closures. The 3D models were constructed using geologic maps, topographic maps, aerial and oblique photography, cross sections, and seismic data.
Our results indicate that the primary controls on the strike-parallel geometry (closure) in hanging-wall anticlines are: (1) the degree of map-view curvature of the thrust surface near its termination, (2) the magnitude and horizontal gradient in thrust displacement (the horizontal angle between the deformed loose-line and its restored counterpart), and (3) the degree to which the competent lithotectonic unit passes over the curved segment of the thrust surface. In structures with fault curvatures that are less than 20 degrees, and displacement gradients that are less than 10 degrees, we observe the following attributes: hanging-wall anticlines plunge toward their terminations at less than 10 degrees, the deformation of the hanging-wall can be considered to be plane-strain, the geometry is often dominated by detachment folds that are parallel to the strike of the main thrust, and reservoir compartmentalization is low. Structures with larger fault curvatures (10 to 35 degrees) are often associated with large displacement gradients (10 to 30 degrees). In these cases hanging-wall anticlines plunge toward their terminations at angles up to 45 degrees, they often have zones of rapid loss in stratigraphic separation along strike, and the deformation geometry is complex and highly three-dimensional producing reservoir compartmentalization.