Speaker: Ahmad Mostafa

Date: Thursday 10th of November 2022, 1:15 pm.

Coal is fractured by nature; it is a dual porosity/permeability system made up of a porous matrix surrounded by fractures known as (figure (1), scale II). The orientation of this quasi-orthogonal cleat network including tensile fractures or face cleats, and compressive and strike-slip fractures or butt cleats depends on the principal stress’s direction (Laubach et al., 2017) and provides pathways for fluid flow with apertures up to 100 microns. In contrast, methane gas is stored within the low porosity coal matrix with pore sizes generally varying from a few to several dozens of nanometers (Li et al., 2017) (Wang et al., 2018). The model implemented in the open-source software Yade DEM (Smilauer et al., 2015) is based on the hydro-mechanical model proposed by (Catalano et al., 2014). The coal matrix is treated as an assembly of bonded particles interacting one with another through elastic-brittle contact laws as initially proposed by (Scholtes and Donze, 2013). The pore space is discretized into tetrahedra, generated from a regular triangulation of the particle’s centers. Knudsen and surface diffusions as well as sorption processes are modeled considering the coal matrix as a microporous material. The method is hydro-mechanically coupled in the sense that changes in pore pressure produce hydrostatic forces that deform the solid skeleton, while deformation of the pore space induces pore pressure changes that promote interpore flow. In addition, sorption induced deformations are taken into account by considering an additional pressure term related to the concentration of gas within the medium (the so-called solvation pressure) (Vandamme et al., 2010). The cleat system is considered as a discrete fracture network where a single-phase advection flow takes place. The ultimate goal of my PhD thesis is to combine the models describing the different transport processes at stake in both the coal matrix and the cleat network to provide a multi-scale model able to simulate the hydro-mechanical behavior of coal in the context of coal bed methane recovery.