7. Modeling Transport of Chemical Species

This chapter is devoted to the transport of chemical species dissolved in the fluid phases that occupy the void space, with or without chemical reactions. Solute fluxes are due to diffusion, dispersion, and advection. Various sources and sinks, as well as chemical reactions and interphase transfers are discussed and integrated in the species (first microscopic and then macroscopic) mass balance equation. Like any other model of transport, the core of the solute transport model is the mass balance of the considered chemical species. The discussion leads to a well-posed model of the solute transport problem. (mass balance equations for the chemical species, initial and boundary conditions, constitutive relations, etc. To facilitate the discussion, a review of selected topics of chemistry that describe source/sink and interphase exchange phenomena that occur within the considered fluid(s) is presented in this chapter. One such topic is chemical reactions that occur within the fluids that occupy the void space. Adsorption, solid dissolution and precipitation are also modelled. The presentation considers also sinks and sources in the form of extraction and injection of solute carrying fluids through wells. Obviously, the presentation of the chemical aspects should be considered merely as a brief introduction to some of the essentials and to the employed terminology. Following the methodology presented in this book, once phenomena are understood at the microscopic level, where they really occur, they are incorporated in the macroscopic ones The discussion in this chapter includes the effects of temperature, but the subject of flow and transport under non-isothermal conditions is discussed in Chap. 8. The objective is to derive models that describe solute transport not only at laboratory scale domains, but also at large natural domains, primarily in heterogeneous geological formations. The material presented in this chapter should be of use for those dealing with phenomena of transport in geological formations. However, the material will also be useful to chemical engineers who design chemical reactors in the Chemical Engineering industry. Appendix A discusses chemical reactors, and the various phenomena of transport that occur in them.