1. Web-based Class Project on Rock Mechanics REPORT PREPARED AS PART OF COURSE CEE 544: ROCK MECHANICS WINTER 2015 SEMESTER INSTRUCTOR: PROFESSOR DIMITRIOS ZEKKOS DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING UNIVERSITY OF MICHIGAN Historical, theoretical and practical perspectives on hydraulic fracturing Prepared by: Austin Boles With the Support of:

2. Overview 1. History 2. Uses of hydraulic fracturing (HF)  In-situ stress measurement  Reservoir stimulation  Conventional vs. HVHF 3. The theory  The Mohr circle basics  Fracture orientation, regional stress field, pressure considerations, fluid penetrability and viscosity, etc. 4. What really happens in practice…  Premature screen-outs, high treating pressures, perforation practices, arbitrarily oriented wellbores, etc.

3. History First experimental well in 1949 (Kansas) Replaced explosives as dominant fracturing method 19492015 http://www.kgs.ku.edu/Publications/PIC/pic32.html

4. In-situ Stress Measurement Assumptions:  Homogeneous, elastic, isotropic rock Need to know:  Tensile strength of rock mass  Fluid pressure Result: initial stresses at the point of fracture. https://clu-in.org/products/newsltrs/tnandt/view.cfm?issue=0204.cfm

5. Reservoir Stimulation Purpose is to increase flow of formation fluids (hydrocarbons) to the wellbore. Conventional vs. High Volume Hydraulic Fracturing http://www.undeerc.org/bakken/images/content/image1.png

6. Theory Fracture initiation, propagation and orientation are dependent on:  Wellbore fluid pressure  Mechanical properties of the formation  Prevailing in-situ stress regime  Orientation of the wellbore  Fluid penetrability and viscosity Most of the literature relies on Mohr-Coulomb failure criterion

7. Effect of Fluid Pressure Differential stress, orientation of principal stress, cohesive strength important! High differential stress in the tensile regime produces regular, parallel fractures. Hydrostatic conditions produce many randomly oriented fractures. Cosgrove, 1995

8. From a pressure point of view… Hubbert and Willis, 1957 *Breakout pressure is less with a penetrating fluid.

9. What happens in practice? Premature screen-outs: breakout pressure required exceeds design pressures of wellbore or wellhead equipment. “Near wellbore tortuosity” High treating pressures: Diagnostic tool to evaluate fracture growth patterns. Simultaneous propagation of multiple fractures. Role of perforation practices: orientation of perforations will determine fracture initiation sites and orientations. Arbitrarily oriented wellbores: Fracture turning, twisting, and linking can all occur.

10. More Information More detailed technical information on this project can be found at: http://www.geoengineer.org/education/web-based-class-projects/rock- mechanics