The Late Ordovician-Devonian-age Hunton Group is a major oil and gas reservoir in the Anadarko Basin. The Hunton carbonates were deposited on a gentle ramp in an epeiric sea. Supratidal, intertidal and subtidal facies can be recognized in core and outcrop and are distributed subparallel to bathymetric contours.

Sequence-stratigraphy concepts are directly applicable to the exploration for oil and gas in the two types of Hunton reservoirs. The first type (Type 1) forms during shallowing (progradational phase) associated with the highstand systems tract of the Henryhouse-Haragan/Bois d'Arc sequence. The second (Type 2) is associated with the intra-Hunton sequence boundary at the top of the Chimneyhill Subgroup and the pre-Woodford sequence boundary.

Type 1 reservoirs are common in the Henryhouse Formation where grain-rich intertidal facies were burrowed and dolomitized. Burrowing generated a pore fluid network in the sediments. Dolomitizing fluids permeated the carbonate and preserved porosity and permeability. Subsequent dissolution removed nondolomitized fossils, creating moldic porosity. Type 2 reservoirs were impacted by meteoric diagenesis associated with sequence boundaries. In this case, the spatial relationship of the reservoir to the unconformity and flow regime were critical. Diffuse flow dissolution generated moldic porosity in grain-rich intertidal facies. Typical karst features usually developed in areas where focused flow occurred along fractures in relatively impermeable rocks.

By integrating a precise understanding of the sequence stratigraphy with facies analysis and distribution, it is possible to predict the anticipated reservoir types in a prospective area and improve reserve estimates.

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