Open File Report 96-23

Fracture Patterns and Their Origin in the Upper Devonian Antrim Shale Gas Reservoir of the Michigan Basin: A Review

Robert T. Ryder¹

Open-File Report 96-23

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards and stratigraphic nomenclature. Any use of trade names is for descriptive purposes only and does not imply endorsement by the USGS.

¹U.S. Geological Survey, Reston, Virginia 22092

CONTENTS

Introduction
Fracture characteristics
	Outcrop measurements
	Subsurface measurements
Regional and local structural domains accompanying Antrim Shale gas accumulation
	Proterozoic basement terranes and tectonic trends
	Structural trends in Devonian strata
	Effects of Alleghanian compression
	Modern in situ stresses of the northern Midcontinent
	Post-Paleozoic uplift of the Michigan basin
Unusual stratigraphic features underlying the Antrim Shale gas accumulation
Mineralogy of fractured intervals
Patterns of gas production and chemistry of associated reservoir water
Summary and discussion of fracturing mechanisms
References cited

ILLUSTRATIONS
Figure 1. Map of Michigan showing the Antrim Shale gas accumulation and the approximate outcrop pattern of the Antrim Shale and equivalent strata
Figure 2. Correlation chart showing Upper Devonian and adjoining strata in the Michigan basin (Gutschick and Sandberg, 1991).
Figure 3. Map of part of Otsego County, Michigan showing location of Antrim Shale gas wells used for fracture studies by Cain (1991), Decker and others (1992), Caramanica (1993), and Dellapenna and Harrison (1993)
Figure 4. Borehole map of the Latuszak B1-32 well, Otsego County, Michigan (Cain, 1991) showing fracture intensity in the Antrim Shale
Figure 5. Borehole map of the Rachow B3-31 well, Otsego County, Michigan (Caramanica,1993) showing fracture intensity in the Antrim Shale
Figure 6. Michigan basin and adjoining area showing Proterozoic basement provinces and major structures (Budai and Wilson (1991)
Figure 7. Michigan basin and structure contour map drawn on the top of the Traverse Group (Fisher and others, 1988)
Figure 8. Structure contour map on top of the Traverse Group across a 28-township area of the Antrim Shale gas-producing trend in Otsego County and adjoining Antrim and Montmorency Counties, Michigan (Decker and others, 1992)
Figure 9. Structure contour map on top of the Lachine Member of the Antrim Shale in a four-township area in southern Otsego County, Michigan (Manger and others, 1990)
Figure 10. Average gas production rates from the Antrim Shale in a four-township area in southern Otsego County, Michigan (Decker and others, 1992)

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