In this work, a novel globally implicit framework for reactive multiphase flow and transport has been implemented using the simulator DARTS and the geochemical package Reaktoro. This framework applies the Operator-Based Linearization (OBL) approach together with a Gibbs Energy Minimization (GEM) scheme to model complex nonlinear reactive transport and flow. Using component- to element-based transport allows for numerically stable equations. This formulation is used to model the dry-out effect and subsequent precipitation of minerals in the near-wellbore region of subsurface aquifers when injecting CO$_2$. A kinetic rate in combination with Reaktoro equilibrium calculations is implemented to achieve more accurate precipitation results. The kinetic products are not considered inside of Reaktoro and also not as an element. The consistency at the phase transition boundary has been corrected by using a projection of a plane within the hypercube of zero charge balance. Highly sensitive reactions such as pH, require a high resolution to produce physical results. The parameterization grid can be implemented such that some species have a high resolution within a small variation of concentration. Reaktoro is highly accurate for the complex multiphase thermodynamic and chemical equilibrium calculation, but at phase transition boundaries, the equilibration of the state can be nonphysical. The results have been benchmarked against the existing geochemical simulator from Shell, showing that more physics needs to be implemented, but gives an overall accurate result.

Hydrogen storage in porous media is a potential solution to the energy distribution problems we might face in the future. Intermittent energy sources such as solar and wind energy need to be accompanied with temporary energy storage to accomodate the times when production and demand do not match. Hydrogen is an energy carrier with a large mass energy density as it can be made completely green through electrolysis and it will not release greenhouse gasses when used to produce energy through combustion process. However it has to be stored in large enough volumes to reach the required energy demand. The storage can be done in the subsurface in either aquifers, depleted hydrocarbon reservoirs or salt caverns which are giant porous or cave volumes available to store compressed gases. At this moment, there is a lack of knowledge for safe and efficient hydrogen storage at reservoir (continuum cm and above) scale and pore scale (micrometer-scale). In a reservoir model the relative permeability and capillary pressure are key parameters to characterise flow behaviour and capacity. These are upscaled parameters we can find through pore-network modelling, among other approaches. For a pore-network model, the contact angle and accompanying wettability characteristics (i.e., interfacial tension) are important to obtain reliable upscaled functions and parameters.
Through the use of a captive bubble method, in this thesis work, we have been able, for the first time, to characterize the contact angle of a hydrogen/brine/rock system at different pressures, temperatures, salinity's and rock compositions. It was found that the contact angle of a hydrogen/brine/rock system is in the range of between 21.1 and 43 degrees. Moreover, for the studied range of varying parameters, the contact angle stayed remained relatively constant. The results of this study are published in the Journal of Advances In Water Resources (https://doi.org/10.1016/j.advwatres.2021.103964).