Depositional Systems and Reservoir Quality of Clinton Sandstone, Guernsey County, Ohio

Brian Keltch

The Lower Silurian Clinton sandstone is the best producer of gas and oil in eastern Ohio. Successful exploration for its subtle stratigraphic traps requires detailed knowledge of its depositional systems, which were defined by sandstone thickness maps, gamma-ray log cross sections covering a 25-mi area, log signatures, and four slice thickness maps. Two cores and some thin sections helped substantiate environmental interpretations based on logs.

These deltaic deposits produce from multistory and laterally discontinuous distributary mouth bars, distributary channels, and delta-plain point bars that are predictably interrelated, each having a unique isopach pattern, log signature, and production characteristics.

Distributary mouth-bar reservoirs occur in more than 70% of the wells. They have coarsening-upward log signatures and elongate isopach patterns, and are 0-22 ft thick. They also exhibit poor production, with median payout times exceeding 5 years.

Distributary channel-fill reservoirs are superimposed on underlying mouth-bar deposits. They have blocky log signatures and form linear, narrow shoestrings. These reservoirs are found in 18% of the wells, and more than 70% of the wells reach payout in less than 2 years.

Meander point-bar reservoirs are the best economically but are encountered in only 8% of the wells. These fining-upward, ovoid to kidney-shaped reservoirs are prolific gas producers and range up to 25 ft thick.

Isopach maps define and project the extent of distributary channels, but point bars, because they are thin, are not apparent and must be identified by cross sections, log signatures, and stratigraphic position.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.