In depleted or low-pressure subsurface reservoirs, the formation of CO₂ hydrate at low temperatures, induced by vaporization and isenthalpic expansion during dense CO₂ injection, can significantly impair well injectivity. The formation of CO₂ hydrates is governed by multiple factors, including CO₂ availability and its solubility, the properties of the surrounding fluids, and the characteristics of the rock. A key parameter influencing water activity and CO₂ solubility is the salinity of in-situ brine, which affects both the thermodynamics and kinetics of hydrate formation. The impact of salinity varies with the type and concentration of dissolved salts. This study investigates the impacts of two prevalent formation water salts, NaCl and CaCl₂ on CO₂ hydrate induction time, hydrate saturation, rock permeability reduction, and their implications for CO₂ injectivity. Coreflood experiments were performed under dynamic flow conditions, supplemented by computed tomography (CT) scanning to provide in-situ saturation profiles. The primary aim is to establish a correlation between the aforementioned parameters and mean ionic activity, thereby facilitating a generalized application of the results irrespective of the specific salt type. Empirical results indicate a marginally extended induction period at elevated initial salinity levels. Furthermore, an increase in mean ionic activity correlates with a decrease in hydrate saturation, which consequently leads to less significant reductions in permeability and injectivity.

In this work, we present a kinetic simulation model for gas hydrates in porous media using the Operator-Based Linearization (OBL) technique. The OBL approach introduces algebraic operators that represent the physical terms in the mass and energy balance equations. Operators are calculated only in supporting points comprising the discretized parameter space, and operator values and partial derivatives for linear system assembly are readily obtained through (multi-)linear interpolation. Taking advantage of this setup, the implementation of advanced thermodynamic models for hydrate formation and dissociation under kinetic assumptions is simplified. We test the assumptions for thermodynamic modelling by analysing the Gibbs energy surfaces of the fluid and hydrate phases and demonstrate that, in the limit, the thermodynamic equilibrium for both kinetic and equilibrium reaction models is equivalent. We compare the simulation results with the published experimental results for CH₄-hydrates and extend the assessment to a CO₂-hydrate formation experiment in a semi-batch, constant-pressure configuration. The model reproduces the main pressure–temperature transients and hydrate evolution for both CH₄- and CO₂-systems. We demonstrate applicability at core scale for hydrate formation and, at field scale, for gas production from CH₄-hydrates by thermal stimulation and depressurization. The interaction of thermal-compositional phenomena (phase changes, adiabatic expansion, kinetic rates, and reaction enthalpy) gives rise to highly nonlinear physics that an appropriate OBL discretization resolves. Overall, the patterns of hydrate formation and dissociation are highly sensitive to the kinetic-rate inputs; hence, the appropriate choice of the reaction model remains a key consideration from both physical and numerical perspectives.

Gas hydrates are crystalline compounds of water and small guest molecules, relevant both as a hazard in hydrocarbon production and CO2 sequestration, and as a potential energy resource in natural reservoirs. This work presents a kinetic simulation model for hydrate formation and dissociation in porous media, implemented using the Operator-Based Linearization (OBL) technique. We verify thermodynamic assumptions through Gibbs energy analysis, showing consistency between kinetic and equilibrium reaction models. The framework is validated against literature on methane hydrates and can be extended to CO2 systems. Applications are demonstrated at core and field scales, including gas production by depressurization and thermal stimulation. Results highlight the strong influence of kinetic parameters on hydrate behavior, underscoring the importance of selecting appropriate reaction models for accurate physical and numerical predictions.

Injection of high-pressure CO₂ into depleted gas reservoirs can lead to low temperatures promoting formation of hydrate in the near wellbore area resulting in reduced injection rates. The design of effective mitigation methods requires an understanding of the impact of crucial parameters on the formation and dissociation of CO₂ hydrate within the porous medium under flowing conditions. This study investigates the influence of water saturation (ranging from 20% to 40%) on the saturation and kinetics of CO₂ hydrate during continuous CO₂ injection. The experiments were conducted under a medical X-ray computed tomography (CT) to monitor the dynamics of hydrate growth inside the core and to calculate the hydrate saturation profile. The experimental data reveal increase in CO₂ hydrate saturation with increasing water saturation levels. The extent of permeability reduction is strongly dependent on the initial water saturation: beyond a certain water saturation the core is fully blocked. For water saturations representative of the depleted gas fields, although the amount of generated hydrate is not sufficient to fully block the CO₂ flow path, a significant reduction in permeability (approximately 80%) is measured. It is also observed that the volume of water+hydrate phases increases during hydrate formation, indicating a lower-than-water density for CO₂ hydrate. Having a history of hydrate at the same water saturation leads to an increase in CO₂ consumption compared to the primary formation of hydrate, confirming the existence of the water memory effect in porous media.