ABSTRACT

The Lower Silurian Clinton Sandstone is the most commonly drilled formation of eastern Ohio, and succesful exploration for its subtle stratigraphic traps requires detailed knowledge of its depositional systems. Two high-constructive cratonic delta systems (the Claysville and Salt Fork Deltas) are present in Guernsey County Ohio, and appear typical of the small deltaic complexes found along the eastern margin of the Clinton-Medina production trend.

Criteria used to define depositional environments and patterns include: sandstone isopach maps, gamma-ray log cross- sections, log signatures, and slice isopach maps.

Production from these deltaic deposits occurs in multistory and laterally discontinuous sandstone bodies deposited as distributary mouth bars, distributary channel fills, and delta plain point bars. The three types of sandstone bodies are interrelated in a predictable manner each having a unique isopach pattern, log signature, and production characteristics. Distributary mouth bar sandstones, the most common reservoirs, are characterizied by coarsening upward log signatures and elongate to lobate isopach patterns. Distributary channel fill deposits are the most prolific reservoirs, are superimposed on underlying mouth bar deposits, have blocky log signatures and form linear, narrow "shoestrings". Meander point bar deposits fine upward and have ovoid to kidney shaped isopach patterns.

Careful subsurface mapping combining log signature, thickness, and depositional models is essential to a successful exploration program.