The Albion-Scipio trend is a remarkable series of synclinal oil and gas traps formed in rocks of Middle Ordovician age. Except for Silurian reefs, most of Michigan's oil and gas traps are related to anticlines--many to fracture systems on their flanks. The Albion-Scipio trend is a conspicuous exception because oil and gas occur only in synclines between low-relief anticlines. Nearly 59 million barrels of oil, 3.5 million barrels of L.P.G., and 50 billion cubic feet of gas have been produced since its discovery in 1956. Cumulative oil production alone exceeds 70 times the total produced from all other Middle Ordovician reservoirs discovered in Michigan prior to 1956.

The Albion-Scipio trend is not a single, simple syncline. It consists of several coalescing, linear, and narrow oil fields, each less than a mile wide. Development drilling has resulted in the merging of several fields into a narrow productive area nearly 24 miles long. Several small fields, not yet joined to the central reservoir area, extend the full length of the trend, nearly 35 miles. More than 550 producing wells and 400 dry holes have now been drilled on 20-acre and 10-acre drilling units. Closely spaced wells provide excellent control for geologic investigations. Oil reservoirs are found in fractured and dolomitized limestone in the Trenton Limestone and Black River Group. Individual synclines are offset but are joined together by narrow, fractured, and dolomitized productive reas which curve around the ends of the anticline, thus forming a nearly continuous oil reservoir. The Trenton Limestone is overlain by thick shale units. Except for a few very thin shale units, the Trenton and Black River consist only of carbonate rock.

Most wells are completed as flowing wells with potentials of several hundred barrels of oil per day, but are prorated to 110 barrels per day. Porosity and permeability differ considerably from well to well, and in different parts of the trend. Most porosity is intercrystalline, but large vugs and open fissures also are present. Original bottom-hole pressure averaged about 2,050 psi. at the northern end of the trend and about 1,600 psi. at the southern end. Most of this difference is related to the difference in depth.

Many Trenton tests drilled on the southern edge of the Michigan basin, west of the Washtenaw anticlinorium, have not revealed definite Trenton anticlinal structures such as those found in the anticlinorium. Total differences in relief west of the anticlinorium are of about the same magnitude as in the trend. Studies suggest that the Trenton surface in this region is one of many low-relief flexures having about the same magnitude of relief as those found along the trend. In this region, one other field with characteristics similar to those of the trend has been found. It is the Hanover field, about 6 miles northeast of the trend. Discovered in 1959, Hanover has produced nearly a million barrels of oil from nine wells. Other reservoirs probably exist in this region, but they will be har to find.

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