1. Role of Fractures in Michigan Oil and Gas Reservoirs
Dr. William B. Harrison, III
Department of Geosciences
Western Michigan University

2. Advanced Characterization of Fractured Reservoirs in Carbonate Rocks: The Michigan Basin
U.S.DOE-funded, 3-year research project to 2001
University/industry consortium for data gathering and research
Document role of fractures in Michigan carbonate reservoirs

3. Project Goals and Objectives
Characterization of Fractures in Michigan Reservoirs
Quantifying Fracture Patterns at a Variety of Scales
Developing a Basin Model for Fracture Development
Determine role of Fractures in Hydrocarbon Emplacement or Production

7. Types of Fractured Reservoirs
Type 1 - Fractures provide all reservoir storage, matrix tight. Fractures provide porosity and permeability. Ex. Antrim Shale
Type 2 - Fractures connect porous and permeable matrix zones. Most reservoir storage and porosity in matrix. Permeability enhanced by fractures. Ex. Niagaran Reef
Type 3 - Fractures initiate porosity/permeability in tight rock. Later solution enhancement creates reservoir quality. Ex. Albion-Scipio Field Trenton

8. Origin of Fractures
External stress on some portion of rock mass exceeds the breaking strength of the rock.
Three dimensional stress field is designated Sigma-1, Sigma-2, and Sigma-3. Usually one vertical and two horizontal directions, all at right angles to each other.
Most fractures are sub-vertical to vertical

9. Regional Analysis of Stress Fields and Fracture Development
Intraplate stresses develop throughout the crust, mostly originating at plate boundaries
Contemporary stress fields reflect modern Plate movements
Paleostress fields are recorded in the rocks and reflect ancient plate movements
Contemporary and paleo-stress fields may have different orientations

10. Sources of Data for Analyses of Fractures
Outcrop measurements
Oriented cores
Borehole imaging logs
Borehole breakout and induced fracture orientations
Structural trend mapping
Remote sensing and stream drainage mapping

11. Fracture Orientations from Outcrop Measurements
From Versical, 1991
M.S. Thesis, W.M.U

13. Antrim Shale Fracture Orientations
From Dellapenna Thesis, 1991

14. Correlation of Fracture Frequency to Logs - Antrim Shale
From Dellapenna Thesis, 1991

15. Modeling Michigan Structures and Fractures using Riedel Shears
Assumes effective stress is horizontal
Shear is the primary mechanism for development of structures
Fractures will develop at predictable angles to shear direction
Reactivation of structures from basement and throughout the sedimentary column

16. Riedel Shear Model for Left Simple Shear
From Versical, 1991
M.S. Thesis, W.M.U

17. Reidel Shear Development from Basement Fault

18. Anticlinal Structures created by Paired Reidel Shear Faults
From Versical, 1991
M.S. Thesis, W.M.U

19. Clayton Field Structural Interpretation from Seismic

20. Structural Contour Map on Top of Basement

21. Structural Model of Albion-Scipio Field
Riedel Shear model with left-lateral shear
Localized small-scale folds within field fit shear model
Reactivated basement fault or “zone of weakness” is probable Principle Displacement Zone

22. Structural Axis Trends in a Portion of Albion-Scipio Field
From Versical, 1991
M.S. Thesis, W.M.U

23. Fold Orientations and Left-Lateral Wrench Fault Model
From Versical, 1991
M.S. Thesis, W.M.U

24. Albion-Scipio Field, Riedel Shear Model

25. Summary and Conclusions
New 3-Year DOE Project on fractures in Michigan reservoirs in underway.
Research consortium between Michigan Tech. and Western Michigan Universities.
Initial phase is to classify types of fractured reservoirs and determine origin of fractures.

26. Summary and Conclusions
Fractures are present in most reservoirs, but play vastly different roles depending on lithology and fabric of the matrix.
Fractures enhance permeability and porosity and may be very significant in diagenetic changes.
Stresses that control fractures mostly arise outside the Michigan basin at plate margins.