Subsurface Study of Oolitic Reservoirs in Mississippian Ste. Genevieve Limestone, Western Kentucky

Kevin S. McIntire

In western Kentucky, near the Indiana, Kentucky, and Illinois borders, a series of 15 to 40-ft thick shallowing-upward oolitic carbonate cycles are found in the Ste. Genevieve Limestone (Middle Mississippian). These oolitic zones, which represent tidal-bar belts and at least one marine sand belt, are referred to by drillers as the Aux Vases limestone, and the O'Hara limestone.

O'Hara oolitic tidal bars are up to 27 ft thick, 0.5 to 2 mi wide, and up to 10 mi long. The Hebbardsville oil field in Henderson County, Kentucky, is in an O'Hara tidal bar. Aux Vases oolitic tidal bars are smaller, ranging from 0.25 to 0.5 mi wide and up to 6 mi long. Tidal bars within both intervals are oriented north-northwest to south-southeast.

A single marine sand belt was identified, within the O'Hara, at North Zion oil field in Henderson County, Kentucky. The belt is oriented perpendicular to the tidal bars and is up to 21 ft thick, 1.5 mi wide, and 2 mi long.

Eight lithofacies are recognized in the Aux Vases and O'Hara intervals: (1) skeletal dolomitic wackestone-grainstone, (2) oolitic-skeletal grainstone, (3) echinoderm-bryozoan dolomitic wackestone-grainstone, (4) bryozoan-echinoderm wackestone-grainstone, (5) skeletal dolomitic wackestone, (6) olive-green shale (present only in the Aux Vases), and (8) bedded anhydrite. These lithofacies are assigned to either of five depositional environments: (1) prodelta, (2) open marine, (3) oolitic shoal/interbar area, (4) lagoon, (5) tidal flat/supratidal flat.

Porosity in the O'Hara and Aux Vases is early secondary or primary. Most hydrocarbon production is related to stratigraphic traps but structural noses and closures influence traps.

AAPG Search and Discovery Article #91023©1989 AAPG Eastern Section, Sept. 10-13, 1989, Bloomington, Indiana.