Abstract

Wells drilled into the Trempealeau formation in south central Ohio require adherence to special plans and attention to detail at the price of plans and attention to detail at the price of economic success. This formation is marked by nonconformance, paraffin production, delicate oil-water contact, and a susceptibility to drilling-induced damage. This paper provides guidelines for completion practices that have been based on 30 years of practices that have been based on 30 years of drilling in the Trempealeau formation and presents typical job designs.

GEOLOGY

The Trempealeau is a dolomitized limestone of the Cambrian Age. Sometimes referred to as the Copper Ridge, the Trempealeau is found throughout most of Ohio. It is located on the western edge of the Appalachian Basin and the eastern flank of the Findley Arch. The Trempealeau is the basal unit of the Knox Group (Fig. 1). It is believed that the Trempealeau was originally deposited as a limestone in a shallow, low energy, marine environment. Dolomitization apparently occurred prior to deposition of the Ordivician Strata, and as a result, the formation is generally a fine to coarsely crystalline, partly sandy dolomite that is light colored with a granular texture. The Trempealeau is marked by the Knox Unconformity (Fig. 2). This uncomformity acted as a path for hydrocarbons that migrated from the path for hydrocarbons that migrated from the Appalachian Basin. The eroded remnant left by the uncomformity serves as a permeable and porous trap and has up to 110 ft of local relief. Hydrocarbon traps are found in the tops of buried hills (Fig. 2). The productive porosity in the Trempealeau is secondary and is caused by dolmitization and dissolution. Average thickness of the Trempealeau is 300 ft, and vugular porosities are as high as 30% in its upper zones. The Trempealeau is subdivided into six zones (A through F). Only the upper two zones, E and F, have the potential for hydrocarbon production. If pre-Ordivician erosion has removed the upper two pre-Ordivician erosion has removed the upper two zones, no commercial production would be expected-even from a structurally high area. Natural fractures are not well documented; however, core observations and stimulation results indicate that a significant network of natural fractures may exist. The possible existence of these natural fractures has been indicated by early water breakthrough in producing wells.

FIELD HISTORY

The first documented Trempeleau producing well was drilled in 1909 in Seneca County, Ohio. Small, isolated producing pools of Cambrian oil were documented between 1909 and 1961 in west- central Ohio with initial productions of 25 to 100 BOPD with accompanying salt water production. The discovery well that started the modern Trempealeau boom was United Producing Company's Orrie Myers #1, which was drilled in the Canaan Township of Morrow County, Ohio. It was drilled to a depth of 3174 ft, and completed in the Trempealeau zone through perforations at 2908 to 3031 ft. The well, initially flowed 200 BOPD of 39 deg. API gravity oil.

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