H13A-1465
Estimation of Fluid Viscosity Effects on the Onset of Thermal Convection within a Three-Dimensional Fault
Monday, 14 December 2015
Poster Hall (Moscone South)
Fabien Magri1,2, Norihiro Watanabe1, Wenqing Wang1 and Victor Malkovsky3,4, (1)Helmholtz Centre for Environmental Research UFZ Leipzig, Leipzig, Germany, (2)Freie Universitat Berlin, Berlin, Germany, (3)Russian Academy of Sciences, 3Institute of the Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry (IGEM), Moscow, Russia, (4)Mendeleyev University of Chemical Technology, Moscow, Russia
Abstract:
Linear stability analysis (i) and numerical simulations of density-driven flow (ii) are presented in order to estimate the effects of temperature-induced fluid viscosity variation on the onset of free thermal convection within a three-dimensional fault embedded into impermeable rocks. (i) The strongly-coupled equations of density-driven flow are linearized. The solution was obtained through expansion into a Fourier series. Simple polynomial expressions fitting the neutral stability curves are given for a range of fault aspect ratios and fluid viscosity properties, providing a new tool for the estimation of critical Rayleigh numbers in faulted systems. The results are validated against the limiting case of constant viscosity. (ii) 3D numerical simulations of free convection within a fault are run using the finite element technique in order to verify the theoretical results. It turned out that at average geothermal temperature conditions, thermal convection can develop within faults which permeability is three times lower than the case of a fluid with constant viscosity, in agreement with the developed linear theory.The polynomial expressions of this study can be applied to any numerical model for testing the feasibility of fault-convection in 3D geothermal basin.
