Silurian reservoirs in upward-shoaling cycles of the Hunton group, Mt. Everette and southwest Reeding fields, Kingfisher County, Oklahoma.

Abstract

The Chimneyhill subgroup is an upward-shoaling sequence, at the top of which are hydrocarbon-bearing, crinoid-rich, skeletal buildup reservoirs of the Clarita formation. These buildups contain biomoldic and other solution porosity created during subaerial exposure and dolomitization prior to Henryhouse sedimentation. Away from the buildups, time-equivalent, non-porous arthropod wackestones provide up-dip barriers to hydrocarbon migration. Transgressive argillaceous lime-mudstones and wackestones of the Henryhouse formation provide the overlying seal for the Clarita skeletal buildup reservoir. During Henryhouse deposition, progradation of shallow-shelf carbonate sediments produced a second upward-shoaling sequence that ended with the deposition of an oolite shoal complex. Inter-ooid solution porosity in the shoal grainstones, created during subaerial exposure prior to Woodford shale sedimentation (late Devonian-early Mississippian) provides a second reservoir. A third reservoir locally occurs at the top of the Henryhouse and is related to dolomitization and leaching (especially of skeletal-rich facies) at the unconformity.-J.M.H.