Applications of Variational Fracture: Enhanced Geothermal Systems

点击翻译按钮获取中文摘要

BourdinDMS-0908267 This award is funded under the American Recovery andReinvestment Act of 2009 (Public Law 111-5). Enhanced geothermal systems represent a virtually untapped,clean, renewable, economically viable, and widely availablesource of energy. They rely on harvesting heat by circulatingwater through artificially stimulated fracture systems in deephot dry rocks. This project provides a predictive understandingof the mechanisms commonly used to generate these systems:pressure- and temperature-driven fracture. The modeling andanalysis are based on a variational fracture formulation, whichhas been developed over the last ten years or so and has strongmathematical and mechanical foundations. The investigatorextends this formulation to dynamic fractures and improves itsimplementation on parallel supercomputers. He extends its scopeby studying and implementing two approaches to the penalizationof material interpenetration along crack lips. He developsvariational models for the pressure- and temperature-drivenfracture problems, approximates them using the idea ofGamma-convergence, implements the regularized models on parallelsupercomputers, and conducts large scale realistic validationexperiments that are compared with existing engineeringliterature. This project is a first step in a nascentmulti-disciplinary initiative fostered through the Center forComputation and Technology at LSU, involving mathematicians,computational scientists, and engineers. It supports theparticipation of two undergraduates and one graduate student peryear. As the Nation strives to reduce its carbon footprint,protect its economy from fluctuating oil prices, and increase itsenergy independence, Enhanced Geothermal Systems (EGS) representa virtually untapped, clean, renewable, economically viable andwidely available source of energy. They rely on harvesting heatby circulating water through artificially stimulated, highlyconnected fracture systems in deep hot dry rocks. A recentMIT-led interdisciplinary assessment panel commissioned by theDepartment of Energy estimates that even without major technicalbreakthroughs EGS could cover 20% of the estimated US electricityneeds by 2050, in an economically viable way and with onlymarginal carbon emission and land use. A major technical issueidentified in this report is the creation of sufficientlyconnected fracture systems. The investigator develops apredictive understanding of two mechanisms commonly used togenerate these systems: pressure- and temperature-drivenfracture, based on a mechanically faithful and mathematicallysound variational formulation of fracture developed over the lastdecade. This model is extended to account for the specifics ofEGS, then implemented on parallel supercomputers. Large scalenumerical simulations are performed using the cyberinfrastructureprovided by the TeraGrid, to allow EGS designers to devisestimulation patterns maximizing the efficiency and sustainabilityof new systems. This project is a first step in a nascentmulti-disciplinary initiative fostered through the Center forComputation and Technology at LSU, involving mathematicians,computational scientists, and engineers. It supports each yearthe participation of two undergraduates and one graduate student.