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Six types of petroleum-producing configurations are recognizable in the oil and gas fields of the Lima-Indiana trend whose reservoirs are the Trenton Limestone of Ordovician age. The data that support recognition of these six structural, structural-stratigraphic, and possibly stratigraphic-permeability trapping configurations are mixed, but involve consideration of the pattern of 34 fields or pools on the main anticlinal trend of the Findlay arch as well as 12 smaller fields or pools to the northwest in the Michigan basin and 20 fields to the southeast at the updip edge of the Appalachian basin.
The reservoir is mainly dolomite and the producing portion of the reservoir generally occurs near the top of the Trenton Limestone. The more porous dolomite has been analyzed chemically for Ca/Mg ratios, Na, Sr, Fe, and other elements in cores to supplement petrographic studies off the main oil field trend in Wyandot County.
The six play configurations are the following. (1) An anticlinal trap along the crest of the Findlay arch. Here, as elsewhere, the seal and presumably the source are the overlying Utica Shale. (2) A faulted anticlinal trap on the western side of the Findlay arch. The fault, the Bowling Green fault, generally limits production to the upthrown eastern side. (3) An updip facies change from the Trenton Limestone into the overlying Utica
Shale to the south. This change, together with draping of the Utica over the underlying competent Trenton, traps petroleum along the southwestern extension of the Lima-Indiana trend. (4) Fracture systems related to regional fracturing of the early Paleozoic rocks. Apparently these systems have provided fracture-enhanced reservoirs. Similar configurations are well known in the Scipio-Albion trend in southern Michigan. Secondary dolomitization and sulfide mineralization are common in association with these fractured features. (5) Possible porosity-permeability traps, probably on structure, where dolomite is replaced laterally by dense limestone. (6) Small anticlinal terraces off the main arch system, related to minor production. These terraces appear as down-to-the-basin noses on struct ral maps.
Considered together, the Lima-Indiana fields are a "giant" field extending 120 mi (193 km) in Ohio and another 50 mi (80 km) in Indiana. Before 1900, thousands of wells were drilled, as shallow as 1,100 ft (334 m), producing over 220 million bbl of oil at initial rock pressures between 100 and 450 psi (690 and 3,100 kPa). Exploration continues at a modest pace.
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