Numerical Calculation Method of Fault Flow-Thermal Coupling Based on Cubic Law
Received date: 2020-07-09
Revised date: 2020-08-03
Online published: 2021-01-29
For the ore-forming process of hydrothermal deposits,the seepage of fluids in the rock matrix and fissures (faults) produces material and energy transmission,and forms orebodies at specific locations with changes in temperature and pressure.Because the width of the fault is much smaller than the dimension of its extension direction,it causes problems such as difficulty in modeling numerical models and low calculation efficiency.According to the geometric characteristics of the fault,it can be generalized into a space surface to reduce the difficulty of modeling.The generalized fault uses the cubic law in rock mass fracture seepage theory to calculate the fault seepage problem.The seepage of hydrothermal fluid is not limited to faults,but also occurs in bedrock,and this process is calculated using Darcy’s law. The fracture flow in the fault and the Darcy flow in the bedrock interact with each other.In order to ensure the continuity of the pressure,velocity,mass,and energy of the seepage field in the numerical model calculation domain,the flow-heat coupling calculation is required.The purpose of this study is to verify the feasibility and rationality of the generalization method of the fault space surface,and to solve the problem of flow-heat coupling between the fissure flow in the fault and the Darcy flow in the bedrock.The viscosity of fluid has the property of changing with temperature.This article will discuss whether the change of viscosity has an effect on the calculation result of the numerical model initially.Based on the theoretical formula of cubic law,the formula is derived according to the characteristics of small fault thickness,and the flow-heat coupling control equation of fracture flow and Darcy flow is obtained. In order to verify the rationality of the control equations,numerical model experiments are used for verification and analysis.After analysis,it is considered that the method of calculating the seepage of the fault using cubic law is feasible when the internal structure of the fault is not taken into consideration,which can reduce the difficulty of modeling the numerical model.Because the fault uses a spatial surface,the reduction of the dimension compared to the overall model also brings increased computing efficiency. After analyzing the results of the numerical experiments,it is considered that the coupling control equation is reasonable and effective for the calculation of the flow-heat coupling between the bedrock and the fault,which is in accordance with the laws of seepage and heat conduction.Based on the original experimental numerical model,a model in which the viscosity coefficient of the fluid does not change with temperature is established,and the change curves of mass and heat conduction flux are compared.It is found whether the change of the fluid viscosity is considered to have a significant effect on the calculation result of the numerical model.
Gang CHEN , Ling MA , Hongsheng GONG . Numerical Calculation Method of Fault Flow-Thermal Coupling Based on Cubic Law[J]. Gold Science and Technology, 2020 , 28(6) : 846 -858 . DOI: 10.11872/j.issn.1005-2518.2020.06.122
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