Acadian detachment and wrench faults in central Pennsylvania: Implications for the Marcellus Shale reservoir integrity and gas productivity in the hinge of the Pennsylvania salient

2020 ◽  
Vol 8 (1) ◽  
pp. T151-T165
Author(s):  
Dengliang Gao ◽  
Emily Roberts ◽  
Connor Geiger ◽  
Peter Sullivan

High-quality 3D seismic data in Clearfield County, central Pennsylvania, reveal subsurface structural details of regional flat-top, box-shaped folds, convergent reverse faults, and cross-regional lineaments in the hinge of the Pennsylvanian salient. Cross-stratal variations in structural relief, bed curvature, and seismic facies indicate that the deformational intensity increases from below the Salina (Upper Silurian) to the Onondaga (Middle Devonian) and then decreases from the Onondaga to the Elk (Upper Devonian). The pre-Onondaga isochron thickness sees an increasing trend but the post-Onondaga isochron thickness sees a decreasing trend on the anticlinal axes. The seismically imaged subsurface structures are consistent with outcrop and topographic observations, wireline and formation microimager (FMI) logs, and gravity and magnetic intensity measurements. The Marcellus Shale (Middle Devonian) gas exploration and production data indicate that the operational activity and gas productivity drop significantly in Clearfield County and other counties in the hinge of the Pennsylvanian salient. We interpret that the regional folds and faults and cross-regional lineaments are detachment and wrench faults that were most likely caused by gravitational sliding above the Salina (salt) during the Acadian (Middle Devonian-Early Mississippian). We infer that the co-occurrence of the regional and the cross-regional faults, particularly the cross-regional wrench faults, might have had a significant impact on the Marcellus Shale reservoir integrity and gas productivity in the hinge of the Pennsylvania salient. These observations and interpretations demonstrate the dynamic interplay among tectonic deformation, syntectonic deposition, and shale gas retention, thus entailing significant geologic, economic, and environmental implications in the Appalachian Basin.

2018 ◽  
Vol 6 (4) ◽  
pp. SN85-SN99 ◽  
Author(s):  
Dengliang Gao ◽  
Thomas Donahoe ◽  
Taizhong Duan ◽  
Peter Sullivan

Three-dimensional seismic data in southwestern Pennsylvania in the Appalachian Plateau demonstrate that the structural style in the Devonian section is dominated by east-vergent folds and reverse faults, which contrasts with that in the Valley and Ridge Province where west-vergent folds and thrusts dominate. Vertical (cross-stratal) variations in fold curvature and fault throw indicate that the intensity of shortening increases from the Salina (Upper Silurian) to the Onondaga (Middle Devonian) and then decreases from the Onondaga to the Elk (Upper Devonian). Lateral (along-stratal) variations in fold curvature and fault throw indicate that the folds and faults tend to propagate in the cross-strike and along-strike directions. Isochron thickness below the Onondaga increases on the anticlinal, up-thrown side of the faults, whereas isochron thickness above the Onondaga increases to the synclinal, down-thrown side of the faults. In concert with seismic structure and isochron thickness, seismic facies see vertical and lateral variations that are spatially and temporally related to folds and faults. Four years of gas production data from the Middle Devonian Marcellus Shale show that the gas productivity drops near the regional reverse faults, whereas regional drilling patterns from a broader perspective of the Plateau reveal operational gaps near major cross-regional wrench faults. These observations are indicative of the dynamic interplay among hinterland-vergent detachment deformation, syntectonic sedimentation, and shale gas preservation during the Acadian (Middle Devonian–Early Mississippian).


Sign in / Sign up

Export Citation Format

Share Document