This paper presents a pore-scale model proposed for numerical simulation of fines migration in porous media. The model simulates the behavior of spherical particles with different radii in flow by coupling lattice Boltzmann method (LBM) as a computational fluid dynamics (CFD) solver for the simulation of the fluid flow with a rigid body physics engine responsible for the simulation of the particulate transports. To achieve this, the basic LBM algorithm was extended to treat the curved particle boundaries, and a fluid-particle force interaction was implemented in order to account for the exerted force acting on the particles by the fluid and subsequent particulate movements. The accuracy and reliability of the proposed numerical model were successfully validated by simulating Poiseuille flow and Stokes flow and comparing the simulation results with those of the analytical solution. Thereafter, it was employed to simulate the migration of fine particles through synthetic 2D porous media. The simulation results were also presented to investigate the influence of fines migration on the porosity and permeability of the medium, and more interestingly on the hydraulic tortuosity as a criterion for changes in preferential flow path. As will be shown, the developed numerical method is able to successfully capture major retention mechanisms responsible for fines migration associated formation damage including external cake formation by the large particles, internal cake formation by the small particles, pore plugging, and surface deposition. This work provides a framework for further investigations regarding pore-scale phenomena associated with fines migration in the porous media.

In a gas condensate reservoir, a drastic pressure drop in the vicinity of the wellbore makes it subject to gas condensate drop‐out. This phenomenon can adversely affect the productivity of the well and reduce gas recovery. The objective of this paper is to conduct a two‐phase fluid flow simulation on two‐dimensional porous media to understand the effect of the gas condensate drop‐out on the gas relative permeability values. In order to do so, lattice Boltzmann (LB) modelling was applied as a computational fluid dynamics (CFD) approach to perform the simulations in homogeneous and heterogeneous porous structures. The developed model was constrained by periodic boundary conditions at inlet and outlet and bounce‐back boundary condition at fluid‐solid interfaces. It was shown that the model can appropriately monitor formation and movement of the condensate droplets as a result of the pressure drop as well as blockages due to the entrance of the droplets into the throats. A consistent decrease in gas relative permeability values with condensate saturation was observed. It was also indicated that the condensate droplets become mobile at higher critical saturations in the heterogeneous system due to the dominance of capillary forces over viscous forces in the less permeable areas. Such dominance results in more severe blockages in the heterogeneous systems, as the simulation results confirmed.

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Abstract. Connecting tropical rainforests to larger rivers, tropical headwaters export large quantities of carbon and nutrients as dissolved organic matter (DOM), and are thus a key component of the global carbon cycle. This DOM transport is not passive, however; sunlight and microbial activity alter DOM concentrations and compositions, affecting riverine greenhouse gas emissions and downstream ecosystems. The effects of sunlight and microbial turnover/activity on DOM concentrations and compositions in tropical headwaters are currently poorly understood, but novel Size Exclusion Chromatography (SEC) techniques coupled to suitable detectors can for the first time quantify their influences. Here, we present in-situ incubation experiments from from headwaters of the Essequibo River, in the Iwokrama Rainforest, Guyana, where sunlight oxidised up to 9% of dissolved organic carbon (DOC) over 12 hours, at higher rates than in larger tropical rivers. DOM transformations occurred in both photo-sensitive and supposedly photo-resistant pools. Microbial activity had varying, less clear influences on DOC concentrations over the same time span; compositionally, this appeared to extend beyond known bio-labile components. Biopolymers were particularly reactive to both processes. We show sunlight has the greater potential to mineralise headwater DOM and thus potentially influence degassing. Our approach provides a future template to constrain DOM transformations along river networks, identify biogeochemical activity hotspots, and improve greenhouse gas emissions estimations under changing environmental conditions.