Modélisation multi-échelle et optimisation du stockage de CO2 dans un réservoir de gaz de charbon

Keywords

CO2 storage, Coalbed methane, Mutiscale modelling, Poromechanics, Transport in porous media

Subject details

In the recent decades, the greenhouse effect is primarily caused by enormous additional quantity of carbon dioxide injected to the atmosphere by fossil fuel burning activities. To attain the objective of limiting the global warming below 2 degrees Celsius in 2050, development of CO2 capture and storage technologies needs to be well studied. One of the most popular technique is the geological CO2 storage. This aims at injecting CO2 into underground geologic formations allowing durable CO2 sequestration with large stored quantities. CO2 is firstly captured, pressurized and then injected into specific porous rock formations capable of storing CO2 for long terms. This project deals with the CO2 storage potential in unminable coalbed methane reservoirs. The coalbed methane reservoir referring to an unconventional reservoir presents a specific geologic formation composed of a natural fracture networks (cleats) of low permeability and coal seam matrix characterized by abundant adsorption sites for gas. The latter offers a huge potential of gas storage within the nanopores with a pore size typically of several nanometers. CO2 storage in the coal seam consists in using preferential adsorption of CO2 compared to other gases. When injecting CO2 into coal reservoirs, CO2 is adsorbed at the adsorption sites within the coal matrix and the methane is released and recovered as free gas. CO2 remains stored within the coal seam. However, high gas pressure injection may close the natural fractures and stop the injection procedure. Understanding these complex phenomena by modelling is very important to enhance the injection procedure and to optimize different parameters as injection gas pressures, injection time, gas composition, etc., considering the multiphysical mechanisms (adsorption isotherm, transport mechanism, poromechanics). Several scientific barriers need to be overcome: - Coal characterization: characterization of coal samples from coal seam gas reservoirs using a porosimetry technique is required to quantify pore size distribution, porosity and permeability. This important information will be used to model the CO2 storage process. - Gas mixture adsorption isotherms: developing a model to predict the adsorbed quantities of a mixture and the adsorption-induced force (namely solvation force) for a given pore size distribution of the coal matrix. Understanding the effect of the adsorption-induced force on the poromechanical behavior of the matrix for a given pore size distribution. - Modelling the coupling between transport and poromechanical response of the medium to predict the time-dependent deformation (change in permeability). - Numerical tools allowing to carry out realistic simulations on the reservoir scale and to optimize the parameters in order to maximize the CO2 stored quantity. Understanding the complex behavior of the porous medium and the gases adsorbed on the surface of coal nanopores requires the combination of knowledge from different disciplines: geosciences, solid and fluid mechanics, thermodynamics, transport in porous media, mathematics and numerical modelling. The proposed doctoral project brings together these skills in order to develop a fundamental research to build an original mathematical model. This model will use the skills of the research team, on the one hand, in multiscale modeling techniques and, on the other hand, in petroleum engineering. The thesis project will be developed within close co-working with the team in LNCC (Laboratório Nacional de Computação Científica, Brazil), which will contribute to develop the poromechanical multiscale model and to study the CO2 adsorption phenomena in nanoporous materials.