Micromechanics of Hydro-Thermo-Mechanical Processes in Rock Accounting for Thermal Convection
Publication: Journal of Engineering Mechanics
Volume 145, Issue 8
Abstract
This paper presents the results of a comprehensive micromechanical study to improve the understanding of the coupled hydro-thermo-mechanical (HTM) processes during injection of pressurized cold fluid in permeable hot rock. At the microscopic level, it is expected that fluid flow–induced convective temperature changes in the voids will dominate the conductive heat flow from grain to grain. However, the coupled interactions between fluid flow, thermal convection, and conduction, and the resulting changes in local permeability due to thermo-poroelastic stresses at the grain scale remain poorly understood. Moreover, almost all previous studies at a large scale have focused only on thermal conduction. This study used the discrete-element method (DEM) modified to account for convective heat transport to model the particulate interactions between rock grains and between rock deformation, fluid pressure, and temperature. The results indicate that wellbore pressure, provided it is less than the fracturing threshold, has a less significant role in rock cooling around the wellbore, which is governed predominately by rock permeability, as previously thought. Different applied flow rates into the wellbore resulted in low and high wellbore pressures at short times in the absence of rock fracturing. As expected, convective heat transport dominated over conduction, resulting in a cooled ring around the wellbore without a significant thermal gradient zone due to conductive heat flow. As the fluid infiltrates and cools the rock, preferential fluid flow paths occur as fingering instabilities that are oriented toward the minimum principal horizontal stress even in the absence of initial local anisotropic porosity variations.
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Acknowledgments
Financial support provided by the US Department of Energy under DOE Grant No. DE-FE0002760 is gratefully acknowledged. The opinions expressed in this paper are those of the authors and not the DOE.
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Published In
Journal of Engineering Mechanics
Volume 145 • Issue 8 • August 2019
Copyright
©2019 American Society of Civil Engineers.
History
Received: May 22, 2018
Accepted: Dec 5, 2018
Published online: May 28, 2019
Published in print: Aug 1, 2019
Discussion open until: Oct 28, 2019
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