Abstract: Implications for a Dolomite "Fairway" in the Trenton Limestone in Southwestern Indiana

KEITH, BRIAN D.
Indiana Geological Survey and Department of Geological Sciences, Indiana University
and JOHN C. HOHMAN
Department of Geological Sciences, Indiana University, Bloomington, IN

To date, areas of oil production from the Trenton Limestone (Ordovician) in the Illinois Basin are restricted to fractured limestones over anticlinal structures in east central Illinois and porous grainstone lenses over structural highs in southern Illinois. Isolated occurrences of noncommercial oil in south central Indiana are found in probable fractured limestone along the eastern margin of the Illinois Basin. The only commercial production in Indiana from the Trenton is from medium crystalline brownish dolomite in the northern part of the state from the largely abandoned Trenton Field and smaller individual fields.

In southwestern Indiana, a distinctive dolomite zone of microcrystalline light gray dolomite occurs within the Trenton Limestone. This dolomite has density log-derived porosity values ranging from less than 5 % to more than 20 %. Net thickness of the zone ranges from a few ft to more than 40 ft. Slight oil shows have been reported from many of the wells penetrating this zone, and a heavy oil residue can be seen in samples from one well in Martin County. The lateral boundaries of the north-northeast trending zone are not well defined due to limited control, but the zone appears to vary from 12 to 50 mi wide, and is approximately 80 to 100 mi long.

The oil shows suggest that the zone was a migration pathway for hydrocarbons, although no commercial production has been found to date. Potential clearly exists for a new petroleum play in southwestern Indiana, if a suitable trap can be found.

AAPG Search and Discovery Article #90930©1998 AAPG Eastern Section, Columbus, Ohio