Fluid Inclusion Evidence for the Migration of Anomalously Hot Fluids in the Silurian/Devonian Hunton Group below the Pre-Mississippian Unconformity Surface, Anadarko Basin, Oklahoma

Albrecht J. Schwalm and Robert C. Burruss

Fluid inclusion assemblages in vug- and fracture-filling diagenetic minerals in the carbonates of the Hunton Group record anomalously high homogenization temperatures and salinities. Temperature profiles of single wells display maxima directly below or close to the unconformity with the overlying Woodford Shale, and decrease gradually or abruptly downward. In a few wells, suitable diagenetic minerals directly above the unconformity in the Woodford Shale contain fluid inclusions with homogenization temperatures comparable to those below the anomaly. Highest temperatures coincide with a high-permeability zone developed towards the top of the Hunton carbonates. The thickness and permeability of this zone depends on the development of a paleokarst after Hunton deposition and re controlled by the paleogeographical position within the basin. Depending on the location within the basin, fluids evolve generally from meteoric or moderately saline (up to ~10 weight% NaCl equivalent) with temperatures of 80° to 120° C to highly saline (up to ~26 weight% NaCl equivalent) with temperatures up to 260 degrees C, followed by a decrease in temperature with either increasing or decreasing salinities. Associated petroleum inclusions suggest that the hottest temperatures coincide with peak petroleum migration. Temperature anomalies are highest in the north near the Hunton subcrop on the basin shelf where the total Hunton thickness is generally <100 feet, and the strongly karsted carbonates are sandwiched in between the Woodford and Sylvan Shales resulting in a h ghly focused flow.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California