UNS: Fluid-driven Fracture of Elastic Materials, Flowback Dynamics and the Effect of Proppants

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1509347 (Stone)The goal of the proposed research is to explore fluid dynamics phenomena that are related to hydraulic fracturing - an area of national importance for domestic energy production. The work proposed is based on fundamental theoretical analysis and elegant experiments conducted in simplified and very well-controlled systems of gelatin to model an elastic geological formation. When the pressure is relieved after hydraulic cracking of an elastic material, the fluid can flow back. This is a process that occurs in hydraulic fracturing and has implications for the production of hydrocarbons as well as for the environment, since hydraulic fracking fluids need to be monitored in the subsurface. In contrast to fluid-driven cracking of elastic materials, for which there is a substantial theoretical literature but only limited experiments, there is a much smaller literature on flowback when the pressure controlling injection is released. This proposal is about laboratory experiments and mathematical modeling to (i) understand and characterize the coupled fluid flow and elastic stresses of fluid-driven cracking followed by flowback as the elastic stresses relax, and (ii) will do so including a particle-laden fluid (the proppant). The experiments will make use of gelatin materials that are elastic but brittle and have been described previously in the solid-earth geophysics literature for the study of fluid-driven cracks. Hence, there will be a link between fluid injection and flowback to the elastic response of the bulk material, with results interpreted using appropriately scaled quantities and dimensional analysis. These experimental and modeling efforts will be among the first to describe the dynamics of flowback and the role of the proppant. Graduate students will be involved in research and a series of outreach lectures, the Harvard and Princeton holiday lectures on engineering and science for children and families, will be offered based on the research findings of the project.