Pore scale simulation study of transverse dispersion of solute in porous media with different cementation degrees

doi:10.13745/j.esf.sf.2023.9.32

Abstract

Abstract:

Deeply understanding and accurately characterizing the transverse dispersion behavior of solutes at the pore scale is crucial for unveiling the internal mechanisms of solute transport phenomena and enhancing the precision of solute transport simulations. In this study, utilizing a pore-scale simulation method, we have investigated the transverse dispersion behavior of solutes in porous media with varying degrees of cementation. The findings of this research are as follows: The transverse dispersion of solutes increases with the cementation degree, although the degree of enhancement is lower compared to longitudinal dispersion. The transverse dispersion does not exhibit a significant scale effect within the range of simulated cementation degrees. The study revealed that the difference between the transverse diffusion coefficient (D_T) and the longitudinal diffusion coefficient (D_L) in all media is not constant but gradually increases, eventually reaching a steady state with solute transport. Both the asymptotic value of D_L/D_T and the time required to reach this value are influenced by the cementation degree. There is a notable discrepancy between assuming D_T to be one order of magnitude smaller than D_L and the actual solute dispersion behavior. By comparing the probability density of the lateral and longitudinal components of flow velocity and the probability density of the advective rate of solutes in different media, this paper elucidates the internal mechanisms underlying the variations in solute transverse dispersion characteristics and highlights the differences between transverse and longitudinal dispersion behaviors.

Key words: transverse dispersion, porous media, cementation degree, pore scale, numerical simulation

CLC Number:

P641.2
X523

HOU Yusong, HU Xiaonong, WU Jichun. Pore scale simulation study of transverse dispersion of solute in porous media with different cementation degrees[J]. Earth Science Frontiers, 2024, 31(3): 59-67.

Figures/Tables 8

Fig.1 Schematic diagram of porous medium structure and bonding process (a), and spatial distribution of solute particles at different times (b)

Table 1 Properties of porous media

多孔介质	孔隙率n	平均粒径r_avg/mm	胶结体积比例P_c/%
PM43	0.43	2.00	0.0
PM35	0.35	2.12	2.26
PM30	0.30	2.20	4.67
PM25	0.25	2.28	8.13

Fig.2 Second spatial central moment along the transverse direction M2,T(a) and the second spatial central moment along the longitudinal direction M2,L(b)

Table 2 Solute dispersion characteristics

多孔介质	m_T	m_L	D_T,asym/(m²·s^-1)	(D_L/D_T)_asym	t_asym/s
PM43	1.029	1.037	1.50×10^-8	14.40	1 080
PM35	0.988	1.016	1.76×10^-8	25.71	1 080
PM30	1.007	1.073	2.23×10^-8	31.04	1 896
PM25	1.003	1.295	2.48×10^-8	77.59	7 500

Fig.3 Solute transverse dispersion coefficient DT (a) and longitudinal dispersion coefficient DL (b) in different media

Fig.4 The ratio of longitudinal dispersion coefficient of solute to transverse dispersion coefficient in different media DL /DT

Fig.5 Probability density distributions (PDF) of transverse |vx|/|vx|avg and longitudinal |vz|/|vz|avg flow velocity components in different media

Fig.6 Probability density distributions (PDF) of solute transverse and longitudinal advective rates in different media

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