Multiobjective optimization of the particle aspect ratio for gravel pack in a methane-hydrate reservoir using pore scale simulation

- The shear strength and permeability of gravel pack were simulated using DEM and CFD, respectively.
- Particles with higher aspect ratios exhibited higher shear strength and permeability.
- Multiobjective optimization enabled us to produce a strategy for optimizing the aspect ratio.

In gas production from methane-hydrate (MH) reservoirs, consolidation induces invasion of the reservoir, and the gravel pack may be replaced by the invading sand. Therefore, the gravel pack of an MH reservoir must have a high shear strength and a higher permeability than the reservoir. In this study, we investigated the shear strength and permeability of different particles, with the gravel aspect ratio as the design variable. Particles with aspect ratios of 1, 1.5, 2, and 2.5 were packed under isotropic compression using discrete-element method (DEM) simulations. Particles with an aspect ratio of 1.5 exhibited the lowest void ratio. Shear strength was measured using triaxial compression DEM simulations, with the 2.5 aspect ratio particles exhibiting the highest value. Permeability was evaluated using pore scale computational fluid dynamics (CFD) simulation of the particle pack generated by the DEM. Particles with an aspect ratio of 2.5 exhibited the highest permeability. The performance of the four types of particles was compared using multiobjective optimization, with shear strength and permeability as the objective functions. Particles with an aspect ratio of 2.5 exhibited the highest performance against both objective functions.

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