Abstract

Recently, there is an increased interest in reactive flow in porous media, in groundwater, agricultural and fuel recovery applications. Reactive flow modeling involves vastly different reaction rates, i.e., differing by many orders of magnitude. Solving the ensuing model equations can be computationally intensive. Categorizing reactions according to their speeds makes it possible to greatly simplify the relevant model equations. Indeed some reactions proceed so slow that they can be disregarded. Other reactions occur so fast that they are well described by thermodynamic equilibrium in the time and spatial region of interest. At intermediate rates kinetics needs to be taken into account. In this paper, we categorize selected reactions as slow, fast or intermediate. We model 2D radially symmetric reactive flow with a reaction-convection-diffusion equation. We show that we can subdivide the PeDaII phasespace in three regions. Region I (slow reaction); reaction can be ignored, region II (intermediate reaction); initially kinetics need to be taken into account, region III (fast reaction); all reaction takes places in a very narrow region around the injection point. We investigate these aspects for a few specific examples. We compute the location in phase space of a few selected minerals depending on salinity and temperature. We note that the conditions, e.g., salinity and temperature may be essential for assigning the reaction to the correct region in phase space. The methodology described can be applied to any mineral precipitation/decomposition problem and consequently greatly simplifies reactive flow modeling in porous media.

Highlights

  • The efficiency of improved or enhanced oil recovery (IOR/EOR) processes is often influenced by the composition of the flowing aqueous phase and is affected by the mass exchange between fluid and solid phases [1]

  • Other reactions occur so fast that they are well described by thermodynamic equilibrium in the time and spatial region of interest

  • Very fast and very slow reactions can be decoupled from the reactions that occur at intermediate rates; at intermediate rates kinetics needs to be taken into account

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Summary

Introduction

The efficiency of improved or enhanced oil recovery (IOR/EOR) processes is often influenced by the composition of the flowing aqueous phase and is affected by the mass exchange between fluid and solid phases [1]. When a fluid is injected into an oil reservoir, the chemical species in the solution will interact with the species in the reservoir fluids contained in the pores and/or the substances on the rock grains As these species are subject to transport in the reservoir, in the numerical modelling of the process it is essential to know the final composition of the solution at the end of each timestep [6,7,8]. The kinetics of the reactions in this case determines the composition of the fluid (and the efficiency of the injected chemical) This poses challenges when the results of the lab-scale experiments are translated to large-scale field applications, because different time and length scales are involved.

Physical and mathematical model
Reaction rates
Transport equations
Discussion of the scales
Summary of the mathematical model
Final note on the length scale
Analytical steady-state solutions of the model equations
Regime a
Regime b
Regime c DaII Pe2
Phase space
Quantitative behaviour of minerals in three regions of the phase space
Conclusion
Concentration profile in regime a
P e dcss dr
Findings
Phasespace in regime c
Full Text
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