Structural Geometry and Evolution of the Painter and East Painter Reservoir Structures,

Wyoming Overthrust Belt

By

Joseph Dischinger and Shankar Mitra

University of Oklahoma, Norman, OK

Serial balanced cross-sections and interpreted logs and dipmeter data from over fifty wells have been integrated to develop a three-dimensional structural model of the Painter and East Painter Reservoir structures in the Wyoming overthrust belt. The structures are interpreted as a pair of faulted detachment folds formed along the hanging-wall ramp within Triassic-Jurassic units in the Absaroka thrust sheet. The Painter structure verges to the east, and is characterized by a gentle back limb and a steeply-dipping to overturned forelimb, whereas the East Painter structure displays steep dips on both limbs. The front limbs of both structures contain forelimb thrust faults with small displacements. A tight syncline separates the structures and contains a number of out-of-syncline thrusts within the Jurassic Twin Creek limestones. Cross sections through the structures are restored using line-length balancing for the Nugget sandstones and area balancing of the Thaynes limestones, Ankareh shales, and Twin Creek limestones. The structures are interpreted to have initiated as a pair of asymmetric detachment folds cored by ductile limestones and shales of the Triassic Thaynes and Ankareh formations. Increasing shortening resulted in tightening of the structures, the development out-of-syncline thrusts, and the propagation of thrust faults on the steep forelimbs. The tight geometry of the East Painter structure resulted from frictional resistance to fault slip along the hanging-wall ramp within the Triassic- Jurassic units. The balanced three-dimensional structural model ensures consistency of the structural geometry of all interpreted horizons, and has been used to construct improved structural maps of reservoir units.

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