ABSTRACT: The Ames Astrobleme
The origin of an unusual structural feature near the town of Ames, in the southeastern part of Major County, Oklahoma, has been subject to much speculation. Maps of subsurface horizons show an intriguing circular closure around a low of some 20 mi2 in area approximately centered at the town of Ames. Early drilling revealed an unusually thick, low Hunton section, so an initial characterization was "The Hunton Graben." Subsequent deeper drilling discovered Arbuckle dolomite production on a circular rim around this low. Drilling, mapping, and core studies now indicate the structure is an impact crater, or astrobleme.
Initial Arbuckle dolomite wells were located on the rim of the impact crater. While significant oil and gas discoveries have been found, the prolific oil production from wells located on the crater floor established this structure as possibly the largest known productive astrobleme.
The first crater-floor well, the D. & J. Gregory 1-20 (T21N, R9W), may be the largest oil well established from a single pay in Oklahoma. The pay zone is granite breccia formed as a characteristic central rebound feature in larger astroblemes. Conservatively estimated primary recoveries are over 4 million bbl of oil for this well. Later crater-floor wells have established production from granite wash overlying brecciated dolomite and from solution-enhanced porosity and fracture systems all sealed by Oil Creek shale.
AAPG Search and Discovery Article #90991©1993 AAPG Mid-Continent Section Meeting, Amarillo, Texas, October 10-12, 1993.