The Michigan basin's Antrim Shale is one of the most actively drilled gas plays in the United States. Last year, Otsego County, the focus of current drilling activity, was among the leaders in gas well completions.

The Antrim is a geologically complex target. Gas producing horizons, located in the black shale facies, are primarily the result of a combination of high kerogen contents and permeability enhancing fracture systems. Preliminary depositional environment and facies work is being incorporated into a depositional model which will assist in the identification of possible areas with greater organic matter preservation. Structural mapping has located subsurface geological variations likely to influence the development of fracture systems. Combined, these geologic factors suggest where gas generation and storage, and permeability are sufficiently enhanced to create economic completion targets.

All Antrim wells require stimulation treatments. Stimulation design and success, in part, is affected by the Antrim stratigraphy. Mineralogie and lithologie differences between the black shales and the gray shales that bound them appear to influence the response of the Antrim to hydraulic fracturing. Correlation of core analyses to geophysical logs will enable better location of target horizons and better control in the design of well completions.

The Antrim appears to be geologically complex in the study area and this complexity has significant influence on gas productivity. This paper presents initial results from a geologic evaluation in a four township area of southeastern Otsego County, the center of present activity. The purpose of this study is to use geologic factors to better define the location and production of gas from the Antrim Shale. Incorporation of these results in designing exploration and exploitation strategies could enhance gas production.

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