Thermal convection of temperature‐dependent viscous fluids within three‐dimensional faulted geothermal systems: Estimation from linear and numerical analyses
Thermal convection of temperature‐dependent viscous fluids within three‐dimensional faulted geothermal systems: Estimation from linear and numerical analyses
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DOI：
10.1002/2015wr018001
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发表时间：
2016-04
影响因子：
5.4
通讯作者：
V. Malkovsky;F. Magri
中科院分区：
文献类型：
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作者：
V. Malkovsky;F. Magri
本文提出了密度驱动流动的线性稳定性分析和数值模拟，以估计温度相关的流体粘度变化对嵌入不透水岩石中的三维断层内自由热对流发生的影响。对密度驱动流的强耦合方程进行了线性化处理。通过展开傅里叶级数得到了解。给出了断层长径比、流体粘度和导热系数非均质性范围内中性稳定性曲线的简单多项式拟合表达式，为断层系统临界瑞利数的估计提供了一种新的工具。对温度不变粘度（即常数）的极限情况进行了验证。为了验证理论结果，利用有限元技术对断层内的自由对流进行了三维数值模拟。结果表明，在平均地热温度条件下，断层内的热对流比流体粘度等情况下的渗透率低4倍，这与已发展的线性理论一致。本研究的多项式表达式可应用于任何三维地热盆地断层对流可行性测试的数值模型。
Linear stability analysis and numerical simulations of density‐driven flow are presented in order to estimate the effects of temperature‐dependent fluid viscosity variation on the onset of free thermal convection within a three‐dimensional fault embedded into impermeable rocks. The strongly coupled equations of density‐driven flow are linearized. The solution was obtained through expansion into Fourier series. Simple polynomial expressions fitting the neutral stability curves are given for a range of fault aspect ratios, fluid viscosity properties, and thermal conductivity heterogeneity, providing a new tool for the estimation of critical Rayleigh numbers in faulted systems. The results are validated against the limiting case of temperature‐invariant viscosity (i.e., constant). 3‐D 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 up to 4 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 3‐D geothermal basin.