ABSTRACT

Current development of the Hunton Group (Ordovician, Silurian) in the West Carney Hunton field (WCHF) began in 1996 when Altex Resources placed the Decker #1 (NE sec. 1-15N-2E) on a large beam pump and soon realized that a large amount of oil and gas could be produced by moving lots of water. The field, which now covers parts of Townships 15 & 16 N., Ranges 1E. to 3E., has been aggressively developed by Altex, New Dominion, Marjo, and several other companies. As of January 2002, the field had about 250 producing wells.

The Hunton ranges in thickness from 26 ft in the east to 140 ft in the west; however the thickness varies significantly across short distances, apparently due to erosion during sea level lowstands during Hunton and pre-Woodford times. No Keel Fm has been identified. Thus far, only the Cochrane and Clarita Formations have been found in cores. Three unconformity-bounded sequences appear to be present: Lower Cochrane, Upper Cochrane, and Clarita. The field is primarily developed in a open-shelf, fossiliferous limestone macrofacies of the lower Cochrane Fm., in strata dominated by thick accumulations of large pentamerid brachiopods (Silurian Benthic Assemblage zone 3), with rapid lateral facies changes to echinoderm grainstones, and some coral-stromatoporoid dominated facies (B.A. 2). Upper Cochrane, also in open-shelf facies (B.A. 2 & 3), has been identified by its conodont fauna in two wells, the Bailey 2-6 and the Carney Townsite 2-5. These two wells, and the Griffen #1-14, also contain faunas of the Clarita Formation, contained in a shoal-water dolomite facies. Stratigraphic position, measured in terms of footage above the Sylvan Fm., suggests that both the Upper Cochrane and the Clarita lie in incised valleys carved into the Lower Cochrane, or in low-lying topography surrounding a residual highland. About 180 wells produce from the limestone macrofacies and about 50 produce from dolomite facies both peripheral to, and inside, the field.

Karst processes affected the entire Hunton in WCHF. Solution enlarged fractures are common, and probably provide the main reservoir flow pathways, although many are completely filled by sediment ranging from clay to fine sand. Karst features are present from the top to the base of the Hunton in almost every well. Terra rosa is common, especially near the base of the Hunton. Collapse and mosaic breccias are common, but are largely tightly cemented and do not provide significant porosity and permeability. Steep dips, interpreted as sinkhole collapse, are present in one well. Porosity is largely secondary, consisting mainly of vugs, solution-enhanced fractures, and interparticle porosity created by dissolution of grains, matrix, and cement. Porosity "zones" are not traceable laterally, and well porosity is poorly correlated with productivity of an individual well.