Rock Fracture Mechanics

ABSTRACT: This course will treat natural fractures in rock (veins, dikes, joints and faults) from a predictive, mechanical perspective. We will cover the basics of engineering fracture mechanics and how it can be applied to geologic and reservoir fracture problems. Fracture opening and slip distributions, spacing, propagation paths, stress drops, and near-tip processes will be analyzed, using geologic examples as constraints for theoretical models. Problems will be considered at the crustal, reservoir and outcrop scale. In addition, we will discuss models for in situ stress magnitudes and the role of pore pressure in rock fracture. Students will be introduced to 2d and 3d elastic fracture codes for predicting stress, strain and displacements induced by fractures. Although the course will emphasize the mechanical aspects of fracture, the impact of fractures on subsurface permeability will be an integral part of our discussion.

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Instructor:

Jon Olson
Dept. of Petroleum and Geosystems Engineering
Office: CPE 5.168B
phone: 471-7375
e-mail: jolson@pe.utexas.edu
Office hours: MWF 1-2.

Meeting:

MWF 11am, 3 credits, Rm. CPE 2.206.

Grading:

Mid-term Exam, 30%
Problem sets, 30%
Final Project, 30%
Class participation, 10%

University Policies

The University of Texas at Austin provides upon request appropriate adjustments for qualified students with disabilities. For more information, contact the Office of the Dean of Students at 471-6259, 471-4241 TDD or the College of Engineering Director of Students with Disabilities at 471-4382.

Scholastic dishonesty will not be tolerated and incidents of dishonesty will be reported.

Course Outline:

Introduction, discussion of syllabus
Fracture morphology

• joints
• shear fractures
• coring-induced fractures

Introduction to Fracture Mechanics

• Griffith energy balance
• Crack tip displacement modes
• Stress intensity analysis
• Crack extension laws
• Process zone
• Displacement field around a crack
• Stress field around a crack

Basic Jointing Theory

• Fracture initiation
• Fracture propagation (critical and subcritical)
• Fracture propagation paths and mechanical interaction
• Fracture arrest
• Fracture aperture prediction

Natural hydraulic fracturing

• In situ stress state
• Poroelastic parameters
• The fracturing cycle

Fracture networks

• Fracture spacing and bed thickness
• Clustered spacing
• Orthogonal fractures
• En echelon fractures
• Sheared joints vs. shear joints
• Faulting and fracturing
• Folding and fracturing
• Multiple episodes of jointing
• 2d elastic modeling

Deformation field around faults

• Stress and strain fields
• Surface deformation
• Surface deformation monitoring methods

Reservoir engineering

• Fracture permeability and porosity
• Reservoir compartmentalization
• Fracture identification logs
• Fracture statistics
• Geometric analysis of wellbore/fracture intersections
• Percolation theory

Special half-day labs (to be scheduled):

1. Visit to the Bureau of Economic Geology to examine fractured core
2. Field trip to fractured outcrops in Austin area

Textbook:

Fracture Mechanics of Rock, 1987, Barry Kean Atkinson, ed., Academic Press, 534 p.

Additional References:

Fracture of Brittle Solids, 1975, B. R. Lawn and T. R. Wilshaw, Cambridge University Press, 204 p.

Selected Articles:

Surface morphology on cross-fold joints of the Appalachian Plateau, New York and Pennsylvania, Bahat and Engelder, Tectonophysics 104, p. 299-313, 1984.

IGC Fieldtrip Y385: Physical and hydrologic-flow properties of fractures, Barton and Hsieh, 28th Int. Geol. Cong., Fieldtrip Guidebook T385, 1989.

Fluid flow along potentially active faults in crystalline rock, Barton, Zoback and Moos, Geology 23(8), p. 683-686, 1995.

Field relations between dikes and joints: emplacement processes and paleostress analysis, Delaney, Pollard, Ziony, and McKee, JGR 91(B5), p. 4920-4938, 1986.

Orthogonal fracture systems at the limits of thrusting: an example from southwestern Wales, Dunne and North, JSG 12(2), p. 207-215, 1990.

Using joint interactions to estimate paleostress ratios, Dyer, JSG 10(7), p. 685-699, 1988.

Natural hydraulic fracturing , Engelder and Lacazette, Proc. of Int. Symp. on Rock Joints, Loen, Norway, June 4-6, 1990, p. 35-43.

The origin and spacing of cross joints: examples from the Monterey Formation, Santa Barbara Coastline, California, Gross, JSG 15(6), p. 737-751, 1993.

Classification of structures on joint surfaces, Hodgson, Amer J. Sci. 259, p. 493-502, 1961.

Regional study of jointing in Comb Ridge Navajo Mountain area, Arizona and Utah, Hodgson, AAPG 45(1), p. 79-116, 1961.

The fracture process zone in granite: Evidence and effect, Labuz, Shah, Dowding, Int. J. Rock Mech. Min. Sci. & Geomech Abstr 24(4), p. 235-246, 1987.

Differences in fracture characteristics and related production: Mesaverde Formation, Northwestern Colorado, Lorenz and Finley, SPE Form. Eval, p. 11-16, 1989.

Regional fractures II: Fracturing of Mesaverde reservoirs in the Piceance Basin, Colorado, Lorenz and Finley, AAPG 75(11), p. 1738-1757, 1991.

Regional fractures I: A mechanism for the formation of regional fractures at depth in flat-lying reservoirs, Lorenz, Teufel and Warpinski, AAPG 75(11), p. 1714-1737, 1991.

Small-scale fracture density in Asmari Formation of Southwest Iran and its relation to bed thickness and structural setting, McQuillan, AAPG 57(12), p. 2367-2385, 1973.

Fracture density in the deep subsurface: techniques with application to Point Arguello Oil Field, Narr, AAPG 75(8), p. 1300-1323, 1991.

Joint spacing in sedimentary rocks, Narr and Suppe, JSG 13, p. 1037-1048, 1991.

Joint pattern development: effects of subcritical crack growth and mechanical crack interaction, Olson, JGR 98(B7), p. 12251-12265, 1993.

The initiation and growth of en echelon veins, Olson and Pollard, JSG 13(5), p. 595-608, 1991.

Inferring paleostresses from natural fracture patterns: a new method, Olson and Pollard, Geology 17, p. 345-348, 1989.

Progress in understanding jointing over the past century, Pollard and Aydin, GSA Bull 100(8), p. 1181-1204, 1988.

Formation and interpretation of dilatant echelon cracks, Pollard, Segall and Delaney, GSA Bull. 93, p. 1291-1303, 1982.

Joint development in perturbed stress fields near faults, Rawnsley, Rives, Petit, Nencher and Lumsden, JSG 14(8/9), p. 939-951, 1992.

Analogue simulation of natural orthogonal joint set formation in brittle varnish, Rives, Rawnsley and Petit, JSG 16(3), p. 419-429, 1994.

Joint spacing: analogue and numerical simulations, Rives, Razack, Petit and Rawnsley, JSG 14(8/9), p. 925-937, 1992.

Role of fluid pressure in jointing, Secor, Amer J. Sci 263, p. 633-646, 1965.

Rate-dependent extensional deformation resulting from crack growth in rock, Segall, JGR 89(B6), p. 4185-4195, 1984.

Formation and growth of extensional fracture sets, Segall, GSA Bull 95, p. 454-462, 1984.

Joint formation in granitic rock of the Sierra Nevada, Segall and Pollard, GSA Bull. 94, p. 563-575, 1983.

Nucleation and growth of strike slip faults in granite, Segall and Pollard , JGR 88(B1), p. 555-568, 1983.