Fractures in Strata Overlying a Laramide Thrust: Teapot Dome, Wyoming

By

Scott P. Cooper and John C. Lorenz

Sandia National Laboratories, Albuquerque, NM

Laurel B. Goodwin

New Mexico Institute of Mining and Technology, Socorro, NM

Mark Milliken

Rocky Mountain Oilfield Testing Center, Casper, WY

Teapot Dome is an asymmetric, basement-cored, Laramide-age anticline. A systematic study of natural fractures indicates that lithology and structural position control outcrop and subsurface fracture patterns.

Three primary through-going fracture sets were documented within this context. Relatively few in number, the oldest fracture set is oblique to the hinge of the anticlinal fold. The majority of these fractures strike NW to WNW and abutting relationships indicate they predate folding. A second set of fractures consists of bed-normal extension fractures striking subparallel to the fold hinge. A third set consists of bed-normal extension fractures striking normal to the fold hinge. In many areas this fracture set is spatially related and subparallel to NE-striking, normal and normal oblique-slip faults that maintain a roughly perpendicular orientation to the fold hinge. Fractures, deformation bands and faults, with conjugate geometries oriented such that they have a vertical bisector to the acute angle and strike subparallel or normal to the axis of the anticline and have a normal sense of displacement, are also observed.

Fracture abutting relationships and the spatial relationship of fractures, deformation bands, and faults relative to the fold indicate the deformation process was a dynamic interactive system, wherein progressive folding was driven by displacement on the basement-involved thrust fault. Normal faulting perpendicular and parallel to the fold hinge accommodated extension associated with the three dimensional bending of beds across the fold. Fractures also formed in response to the fold form (driven by the basement thrust) and to displacements along faults.

AAPG Search and Discovery Article #90004©2002 AAPG Rocky Mountain Section, Laramie, Wyoming