The dynamic system of hot fluid seepage, chemical component diffusion and reaction in porous media can be expressed as:
geochemistry
In the above formula, v is the actual velocity of pore fluid, q is permeability, v=q/φe, φe is effective porosity, that is, connected porosity; κ = κ/μ, κ is the permeability coefficient and μ is the viscosity coefficient of the fluid; G is the acceleration of gravity; ρ is the total density of the fluid; Z is the coordinate in the vertical direction; P is the pressure in the fluid; T is time; T represents the temperature of the fluid; CE=( 1-φ)cmρm+φcfρ, which is equivalent heat capacity; Cm and CF are the specific heat of porous media and fluid respectively; ρm and ρ are the densities of porous media and fluid respectively; φ is the total porosity of the medium; Similarly, κE=( 1-φ)κm+φκf is equivalent thermal conductivity, and κm and κf are thermal conductivity of porous media and fluid respectively. A represents the intensity of heat source (or sink, that is, destination, gathering area and gathering area), such as radioactive decay heat, chemical reaction heat, etc. Without heat source or heat sink, a = 0；; Ci, Di and Ri respectively represent the concentration and diffusion coefficient of component I in the fluid, and the generation (source) or loss (sink) of component I in unit time and unit volume due to the reaction between the fluid and surrounding rock medium. When the reaction is mainly a solution-precipitation reaction, the expression of Ri is shown in formula (4. 127); ρ0 is the reference density of the fluid when the fluid temperature is T0 and the component concentration is zero (pure water), α is the thermal expansion coefficient, and βi is the solute expansion coefficient of component I. ..
Equation (4. 129a) shows that the divergence of fluid velocity in the system is zero everywhere, which is a mathematical expression of the incompressible fluid mass conservation theorem. Equation (4. 129b) is the differential form of the permeability law, that is, the permeability q is directly proportional to the head gradient, but in the opposite direction, from high head to low head; The water head consists of the pressure P in the fluid and the gravity potential gpz of the fluid. Equation (4. 129c) shows that the rate of change of thermal energy with time in fluid micelles can be attributed to thermal convection term δ (ρ qcft), thermal conduction term δ (κ E δ T) and heat source term. The negative sign in front of the heat convection term indicates that the velocity gradient direction (from low speed to high speed) is the "outflow" direction, which leads to the reduction of heat. Formula (4. 129d) is an expression of conservation of components in fluid. The change rate of component concentration can also be attributed to convection term δ (qci), diffusion term δ (φ di δ ci) and reaction term. Equation (4. 129e) is a fluid constitutive equation, which shows that the fluid density decreases with the increase of temperature and increases with the increase of dissolved component concentration.
When the dynamic parameters such as porosity, permeability and diffusion coefficient of the system to be studied are determined, and the initial conditions and boundary conditions are determined, computer programming and solution can be carried out by using mathematical methods such as finite element and finite difference, which is called computer simulation.
Dynamics of geological fluid migration-reaction process is a very important aspect of geochemical dynamics. Although the dynamic processes of various geochemical processes vary widely, they are almost all related to the movement (or transport) of fluids and the chemical reaction between fluids and media (soil, rocks, etc.). Many geological processes must involve fluids, while others are greatly accelerated by the participation of fluids. The function of fluid often involves not only the transportation of fluid, but also the reaction between fluid and surrounding media, and the two are coupled with each other. Mantle convection, crust-mantle exchange, magma chamber dynamics, hydrothermal mineralization dynamics, or supergene and environmental geochemistry dynamics all belong to the geological fluid migration-reaction process dynamics. Therefore, the dynamics of geological fluid migration-reaction process has important theoretical significance.
Simply put, the dynamics of geological fluid migration-reaction process is to study the flow and reaction of geological fluid in soil or surrounding rock medium under different temperature and pressure conditions. The migration-reaction process dynamics of geological fluid is different from the groundwater dynamics studied by hydrology: firstly, geological fluid is not limited to water, it can be solution, gas or even magma with high viscosity; Secondly, groundwater dynamics rarely considers the driving effect of hot fluid, the diffusion movement of various components in fluid and the chemical reaction between fluid and surrounding media. The migration-reaction kinetics of geological fluid is also different from water-rock reaction kinetics and geological fluid mechanics. Water-rock reaction kinetics relatively ignores the transport of energy and substances by geological fluids, but focuses on the determination of chemical reaction mechanism and reaction rate between fluids and surrounding media. Geological fluid mechanics relatively ignores the chemical reaction between geological fluid and surrounding media, but focuses on the movement of fluid in geological body. In many geological processes, such as magmatic dynamics and hydrothermal mineralization, the driving effect of heat (magmatic heat) on fluid, the movement of fluid, the diffusion movement of various components in fluid and the chemical reaction between fluid and surrounding media (surrounding rocks) are coupled and inseparable, and the research on this kind of geological process dynamics belongs to the dynamic category of geological fluid transport-reaction process. Therefore, the transport-reaction dynamics of geological fluid is the synthesis of geochemical dynamics and geological fluid mechanics, and it is the frontier field of geoscience development in the future.
In recent years, Yu Chongwen put forward the research object, theory and methodology of "generalized geochemical dynamics", pointing out that geochemical system is a complex dynamic system, and the ultimate goal of geochemistry is to explore the complexity of geochemical system and clarify the mechanism and development law of complexity. Generalized geochemical action can be understood as the movement of earth materials, and the study of generalized geochemical dynamics covers chemical movement, mechanical movement and magnetic movement. Yu Chongwen put forward three basic theoretical problems of generalized geochemical dynamics: ① nonlinear dynamics of generalized geological processes; (2) Complexity of coupling system of generalized geological process and spatio-temporal structure; ③ Self-organized criticality and chaotic edge of generalized geological system. The generalized geological system and generalized geological process here refer to all geological, geochemical and geophysical systems and processes. It can be seen that the generalized geochemical dynamics contains all the dynamic research contents of the earth's material movement.