Modelling of chemo-poromechanical coupling applied to the CO₂ storage in coal

The geological storage of CO₂ in aquifers reservoirs such as limestone and sandstone, coal is a possible way to reduce greenhouse gas emission into the atmosphere. However, the injection of CO₂ may modify petrophysical (porosity and permeability), mineralogical (transformations) and mechanical (deformations, strength) properties of reservoir rocks (limestone, sandstone, coal). In the case of coal, the injection of CO₂ can also induce matrix swelling due to adsorption processes. The focus of this thesis is to translate in terms of phenomenological models, the behaviors and chemo-poromechanical coupling of reservoir rocks of coal type. In this work, we focused particularly on the study of CO₂ injection into coal. For this, two models of homogenized coal porosity have been developed by taking into account the adsorption phenomenon, known to be the main mechanism of production or sequestration of CO₂ in many coal reservoirs. The first model allows the study of the poroelastic behavior of coal in the case of a single injection of CO₂, and the second model allows the study of the poroelastic behavior of coal in the case of an injection of CO₂ with methane CH₄ recovery. The adsorption process is classically modelled using Langmuir's isotherm (for one gas in the first model and for two gases in the second model). The implementation of these models in Code-Aster (a fully coupled Thermo-Hydro- Mechanical analysis code for structures calculations, developed by Electricity of France - EDF) allowed us to make numerical simulations of CO₂ storage in coal. For a single injection of CO₂ into coal (first model), the coal matrix behaved in two different ways: it swells (resulting in the decrease of coal porosity) when the adsorption phenomenon is taken into account and shrinks (resulting in the increase of coal porosity) otherwise. Being in good agreement with the results in specialized literature in this field, it shows the ability of the model to predict the poroelastic behaviour of coal to CO₂ injection. Also with the first model, we studied particularly through numerical simulations the influence of coal's hydromechanical properties (Biot's coefficient, bulk modulus), Langmuir's adsorption parameters and the initial liquid pressure in rock mass during CO₂ injection in coal. In the case of methane recovery (second model), a coupling of Code-Aster and a reactive transport code, HYTEC (Hydrological Transport coupled with Equilibrium Chemistry, developed by Mines Paris Tech) was needed to handle the above calculation of partial pressures of the two gases (CO₂ and CH₄) at each time step. Digital development work on the two computers codes (Code-Aster and HYTEC) was then necessary. This thesis proposed a method of coupling between the two codes whose techniques are widely described in the manuscript. (author)