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

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

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

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

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

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

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

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

Antrim Shale Fracture Orientations From Dellapenna Thesis, 1991

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

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

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

Reidel Shear Development from Basement Fault

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

Clayton Field Structural Interpretation from Seismic

Structural Contour Map on Top of Basement

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

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

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

Albion-Scipio Field, Riedel Shear Model

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.

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.