ABSTRACT: Structural Geology of the Circle Ridge Oil Field, Fremont County, Wyoming

ANDERSON, THOMAS C., Conoco, Inc., Casper, WY

The Circle Ridge oil field is located about 60 mi northwest of Riverton, Wyoming, in the Wind River basin. The field was discovered in 1923, and has produced over 28 MMBO from five reservoirs in the Phosphoria, Tensleep, Ranchester, Darwin, and Madison formations. The average surface elevation is 7200 ft above sea level, and the depth of oil production ranged from 300 to 1500 ft. There are 200 wells in the field, which has been on waterflood since 1979. The field currently produces about 1500 BOPD.

Circle Ridge is a well-expressed, doubly plunging, surface anticline with exposed section from the Lower Cretaceous Mowry to the

Permian Phosphoria formations, which provides a rare opportunity to integrate surface and subsurface geology in an attempt to obtain a three-dimensional view of a Rocky Mountain foreland structure.

Because the only preexisting surface geologic map of the area was published in 1944 at a scale of 1:48000, I remapped the surface geology at the more detailed scale of 1:6000. Much more extensive faulting was recognized, as well as several areas of small-scale accommodation folding. In addition, the presence of an erosional remnant(?) of the Jurassic Nugget Formation was discovered.

Twenty-two stratigraphic cross sections link the extensive well control, and four balanced structural cross sections were constructed and restored to the predeformation state. The overturned southwest flank of the structure is still not well understood due to the lack of well control in this area and the nearly unusable seismic data.

AAPG Search and Discovery Article #91017©1992 AAPG Rocky Mountain Section Meeting, Casper, Wyoming, September 13-16, 1992 (2009)