Stochastic Simulation of Colloid Transport under Unfavorable Attachment Conditions by Full Enumeration
Abstract
Colloid transport in water-saturated porous media is significantly influenced by colloidal interactions with grain surfaces, particularly under unfavorable attachment conditions. Near-surface fluid domain colloids experience low fluid drag and DLVO forces that slow their downgradient translation relative to colloids in bulk fluid. Near-surface fluid domain colloids may reenter the bulk fluid via diffusion and expulsion at rear flow stagnation zones, they may immobilize (attach) via primary minimum interactions, or they may move along a grain-to-grain contact to the near-surface fluid domain of an adjacent grain. We formulated a simple stochastic model that accounts for colloid transfer between the bulk and near-surface fluid domains and immobilization. Colloid movement is described by a Markov chain, i.e., a sequence of trials in a dual network of unit cells, which contain a pore and a grain. Using combinatorial analysis that utilizes the binomial coefficient, we were able to derive analytical solutions for both colloid breakthrough curves and transient colloid retention profiles. To parameterize the network model, we performed mechanistic pore-scale simulations in a single unit cell that determined the likelihoods and timescales associated with the above colloid mass transfer processes. The model predicts emerging colloid transport behaviors including extended tailing, the transition from log-linear to nonmonotonic retention profiles, and matches experimentally observed data.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.H44F..05H
- Keywords:
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- 1829 Groundwater hydrology;
- HYDROLOGYDE: 1847 Modeling;
- HYDROLOGYDE: 1859 Rocks: physical properties;
- HYDROLOGYDE: 1875 Vadose zone;
- HYDROLOGY