Role of Fractures in Michigan Oil and Gas Reservoirs

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Role of Fractures in Michigan Oil and Gas
Reservoirs

• Dr. William B. Harrison, III
• Department of Geosciences
• Western Michigan University

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Advanced Characterization of Fractured Reservoirs
in Carbonate Rocks The Michigan Basin

• U.S.DOE-funded, 3-year research project - 1998 to
  2001
• University/industry consortium for data gathering
  and research
• Document role of fractures in Michigan carbonate
  reservoirs

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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

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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

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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

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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

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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

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Fracture Orientations from Outcrop Measurements
From Versical, 1991 M.S. Thesis, W.M.U
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Antrim Shale Fracture Orientations
From Dellapenna Thesis, 1991
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Correlation of Fracture Frequency to Logs -
Antrim Shale
From Dellapenna Thesis, 1991
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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

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Riedel Shear Model for Left Simple Shear
From Versical, 1991 M.S. Thesis, W.M.U
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Reidel Shear Development from Basement Fault
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Anticlinal Structures created by Paired Reidel
Shear Faults
From Versical, 1991 M.S. Thesis, W.M.U
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Clayton Field Structural Interpretation from
Seismic
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Structural Contour Map on Top of Basement
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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

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Structural Axis Trends in a Portion of
Albion-Scipio Field
From Versical, 1991 M.S. Thesis, W.M.U
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Fold Orientations and Left-Lateral Wrench Fault
Model
From Versical, 1991 M.S. Thesis, W.M.U
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Albion-Scipio Field, Riedel Shear Model
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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.

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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.