Translating the Micro-scale to the Macro-scale: Fracture Geometry
The recent growth in shale gas extraction, geothermal energy development and storage of anthropogenic gases and fluids has led to increased human interaction with the Earth’s subsurface. A management challenge for these subsurface sites is to optimize extraction/storage approaches to yield maximum potential while minimizing risks. Fractures are one of the dominant factors that influence the success or failure of these management tasks because all subsurface activities perturb fluid pressures and stresses in rock, causing mechanical discontinuities to open, close, initiate, coalesce and/or propagate, while natural and engineered fluids can result in geochemical alterations that lead to crack growth. The goal to sustain production/isolation throughout the life-cycle of a subsurface site makes it necessary to detect and image fracture systems to monitor alterations as well as to link geophysical measurements to mechanical and hydraulic integrity of the subsurface rock.
In this presentation, the role of micro-scale properties and behavior on the fracture geometry and the detection of crack initiation & propagation is examined through three topics: (1) existence of converted modes linked to fracture void geometry; (2) identification of a geophysical precursor for a system transitioning from meta-stability to unstable behavior with specific focus on crack nucleation, propagation and coalescence; and (3) understanding the role of depositional layers and mineral fabric on tensile crack formation and geometry. The results from these studies advance current understanding of which microscopic properties of evolving fracture systems are most useful for predicting macroscopic behavior and the best imaging modalities to use to identify the seismic signatures of time evolving fracture properties.
Dr. Laura J. Pyrak-Nolte is a Distinguished Professor of Physics & Astronomy, in the College of Science, at Purdue University. She holds courtesy appointments in the Lyle School of Civil Engineering and in the Department of Earth, Atmospheric and Planetary Sciences, also in the College of Science. Dr. Pyrak-Nolte holds a B.S. in Engineering Science from the State University of New York at Buffalo, an M.S. in Geophysics from Virginia Polytechnic Institute and State University, and a Ph.D. in Materials Science and Mineral Engineering from the University of California at Berkeley where she studied with Dr. Neville G. W. Cook. Her interests include applied geophysics, experimental and theoretical seismic wave propagation, laboratory rock mechanics, micro-fluidics, particle swarms, and fluid flow through Earth materials. In 1995, Dr. Pyrak-Nolte received the Schlumberger Lecture Award from the International Society of Rock Mechanics. In 2013, she was made a Fellow of the American Rock Mechanics Association (ARMA). She a past-President of the American Rock Mechanics Association, President of the International Society for Porous Media, and Vice-President for North America for the International Society of Rock Mechanics and Rock Engineering.