Thesis defense of Mahdi Mansouri

Room: E018

Mahdi Mansouri will defend his thesis "A study of the physical and chemical mechanisms induced by CO2 storage in deep saline aquifer geological reservoirs" in the amphitheater E018.

CO2 sequestration in geological reservoirs is a reliable mitigation method to reduce atmospheric CO2, albeit challenging, involving multiphase reactive flow processes. CO2 is captured fromthe power plants’ atmosphere, purified, transported, and injected in deep geological reservoirs covered with an impermeable caprock that prevents leakage to the atmosphere. The success of secure and permanent storage of CO2 in subsurface formations depends mainly on our understanding of physical and chemical mechanisms induced by CO2 sequestration. The distribution of CO2 and the displacement patterns are fluid, rock, and flow properties functions. Fluid displacement is composed of a series of pore invasions that build up the overall front behavior. However, the link between pore invasion mechanisms and global front behavior is not clear. Moreover, the injected CO2 reacts with the brine and disturbs the prevailing thermodynamic equilibrium. CO2 dissolution triggers a chain of reactions resulting in alteration of petrophysical and physicochemical porous media by induced dissolution and precipitation kinetics. So far, the definition of pore-scale parameters describing the inducedmechanisms is lacking for understanding mineral trapping. The two main objectives of this Ph.D. are (i ) to address triggered pore invasion mechanisms at each flow regime to quantify the role of pore-scale phenomena on the front behavior and interfacial dynamics, (i i ) to investigate the kinetics of calcite dissolution, the evolution of the reactive surface area and to monitor porous media alteration, to quantify the effect of SO2 impurities on the CO2 storage.

We use micromodels, i.e., a transparent replica of porous media network made in synthetic materials. The experimental setup consists of a microscope coupled with a high-resolution camera to visualize flow and reaction processes at the pore-scale. We developed a general theoretical model based on Navier-Stokes volume averaging that considers inertia, viscous, and capillary forces and allows us to evaluate the predicted invasion processes.

We conducted a series of drainage experiments (a non-wetting fluid displacing a wetting fluid) for various flow rates, fluid pairs, and wettability conditions. We identified the classical flow regimes of immiscible displacement and captured fundamental pore invasion mechanisms and their interface dynamics. The viscous flow regime is characterized by pores that are invaded simultaneously with a continuous interface displacement due to viscous forces dominancy and inertia effects. We observed that threshold capillary pressure defines the invasion condition at the capillary flow regime. At this condition, Haines jumps (i.e., sudden interface movement at a pore throat) are the primary pore invasion mechanism. The interface expands laterally, and only corner wetting fluid and films are retained in drained pores. The crossover flow regime is characterized by pore by pore invasion and a front showing a mixed capillary and viscous flow regime behavior. The results of our model agree with the experiment results. Besides, we explored a large range of conditions numerically to predict flow regime transitions.

We investigated the dynamics of waiting times (when the interface is pinned at a pore throat before Haines jump) and corner flows for the capillary flow regime. Ourresults suggest a continuous flow in the body of the wetting fluid during pinning. It is observed the dynamics of the corner flow have an important effect on reaching the invasion threshold pressure and on the definition of waiting times. By theoretical developments, we are able to predict the waiting time and corner flow velocity.

Finally, a novel silicon-glass micromodels preparation method and design are proposed to study reactive transport. Micron-scale calcite minerals are grown in a mi-cromodel resembling carbonate rocks. Raman spectroscopy results help monitor and characterize the evolution of the aqueous phase composition, reactive surface area, and kinetics of reactions. Experimental results and main geochemical mechanisms are compared with simulations performed with PHREEQC (a geochemical modeling software). This study highlighted the relationship between pore-scale mechanisms and the front dynamics. In addition, the presented experimental setup paves the way for an accurate study of kinetic parameters and minerals nucleation. The results obtained during this Ph.D. will serve to optimize the process of CO2 sequestration in geological reservoirs.