Accurately measuring wettability is of the utmost importance because it influences several reservoir parameters while also impacting reservoir potential, recovery, development, and management plan. As such, this study proposes a new formulated mathematical model based on the correlation between the Amott-USBM wettability measurement and field NMR T₂LM log. The exponential relationship based on the existence of immiscible fluids in the pore space had a correlation coefficient of 0.95. Earlier studies on laboratory core wettability measurements using T₂ distribution as a function of increasing water saturation were modified to include T₂LM field data. Based on the trends observed, water-wet and oil-wet conditions were qualitatively identified. Using the mean T₂LM for the intervals of interest and the formulated mathematical formula, the various wetting conditions in existence were quantitatively measured. Results of this agreed with the various core wettability measurements used to develop the mathematical equation. The results expressed the validity of the mathematical equation to characterise wettability at the field scale. With the cost of running NMR logs not favourable, and hence not always run, a deep ensemble super learner was employed to establish a relationship between NMR T₂LM and wireline logs. This model is based on the architecture of a deep learning model and the theoretical background of ensemble models due to their reported superiority. The super learner was developed using nine ensemble models as base learners. The performance of nine ensemble models was compared to the deep ensemble super learner. Based on the RMSE, R², MAE, MAPD and MPD the deep ensemble super learner greatly outperformed the base learners. This indicates that the deep ensemble super learner can be used to predict NMR T₂LM in the field. By applying the methodology and mathematical formula proposed in this study, the wettability of reservoirs can be accurately characterised as illustrated in the field deployment.

As industry moves from fossil fuels to green energy, substituting hydrocarbons with hydrogen as an energy carrier seems promising. Hydrogen can be stored in salt caverns, depleted hydrocarbon fields, and saline aquifers. Among other criteria, these storage solutions must ensure storage safety and prevent leakage. The ability of a caprock to prevent fluid from flowing out of the reservoir is, thus, of utmost importance. In this review, the main factors influencing fluid flow are examined. These are the wettability of the caprock formation, the interfacial tension (IFT) between the rock and the gas or liquid phases, and the ability of gases to diffuse through it. To achieve effective sealing, the caprock formation should possess low porosity, a disconnected or highly complicated pore system, low permeability, and remain strongly water-wet regardless of pressure and temperature conditions. In addition, it must exhibit low rock–liquid IFT, while presenting high rock–gas and liquid–gas IFT. Finally, the effective diffusion coefficient should be the lowest possible. Among all of the currently reviewed formations and minerals, the evaporites, low-organic-content shales, mudstones, muscovite, clays, and anhydrite have been identified as highly effective caprocks, offering excellent sealing capabilities and preventing hydrogen leakages.

The transition to a hydrogen-based energy system requires safe and efficient large-scale storage solutions. Underground hydrogen storage (UHS) has emerged as a promising candidate, but the effectiveness and long-term security of UHS depend on a fundamental understanding of hydrogen transport mechanisms in subsurface environments. Among these, hydrogen diffusion into formation water plays a key role in governing mass loss, geochemical reactions, and microbial activity. This study presents a combined experimental and mathematical approach to quantify hydrogen diffusion in distilled water and brine at temperatures of 30 °C, 45 °C, and 60 °C, and pressures near 6.5 MPa. A new formulation is proposed that accounts for non-constant gas compressibility and enables systematic identification of the initial non-diffusive regime in pressure-time data. The methodology was validated by measuring the diffusion coefficient of CO₂ in distilled water, giving values consistent with those reported in the literature. Experimental results showed that hydrogen diffusion coefficients increase with temperature, from 3.6 $$\:\pm\:$$ 0.4 × 10⁻⁹ m²/s at 30 °C to 6.1 $$\:\pm\:$$ 0.3 × 10⁻⁹ m²/s at 60 °C. An additional series of tests on brine demonstrated that increasing salinity from 0 to 10,000 ppm of NaCl salt reduces the hydrogen diffusion coefficient to 5. $$\:8\pm\:$$ 0.2 × 10⁻⁹ m²/s at 60 °C. This methodology offers a robust framework for characterizing gas diffusion in aqueous systems, providing critical input not only for modeling hydrogen behavior in geological storage formations but also for optimizing hydrogen production via water electrolysis and its utilization in fuel cells.

Clathrate hydrate-based technologies are considered promising and sustainable alternatives for the effective management of the climate change risks related to emissions of carbon dioxide produced by human activities. This work presents a combined experimental and computational investigation of the effects of the operational procedures and characteristics of the experimental configuration, on the phase diagrams of CO₂-H₂O systems and CO₂ hydrates’ formation, growth and dissociation conditions. The operational modes involved (i) the incremental (step-wise) temperature cycling and (ii) the continuous temperature cycling processes, in the framework of an isochoric pressure search method. Also, two different high-pressure PVT configurations were used, of which one encompassed a stirred tank reactor and the other incorporated an autoclave of constant volume with magnetic agitation. The experimental results implied a dependence of the subcooling degree, (P, T) conditions for hydrate formation and dissociation, and thermal stability of the hydrate phase on the applied temperature cycling mode and the technical features of the utilized PVT configuration. The experimental findings were complemented by a thermodynamic simulation model and other calculation approaches, with the aim to resolve the phase diagrams including the CO₂ dissolution over the entire range of the applied (P, T) conditions.

Clathrate hydrate-based technologies have been considered as promising and sustainable alternatives for the effective management of the climate change risks related to emissions of carbon dioxide, produced by human activities. This work presents a combined experimental and computational investigation of the effects of the operational procedures and characteristics of the experimental configuration, on the phase diagrams of CO2-H2O systems and CO2 hydrates formation, growth and dissociation conditions. The operational modes involved (i) the incremental (step-wise) temperature cycling and (ii) the continuous temperature cycling processes, in the framework of an isochoric pressure search method. Also, two different high pressure PVT configurations were used, of which one encompassed a stirred tank reactor and the other incorporated an autoclave of constant volume with magnetic agitation. The experimental results implied a dependence of the subcooling, (P, T) conditions for hydrate formation and dissociation and thermal stability of the hydrate phase on the applied temperature cycling mode, and the technical features of the utilized PVT configuration. The experimental findings were complemented by a thermodynamic simulation model and other calculation approaches, with the aim to resolve the phase diagrams including the CO2 dissolution over the entire range of the applied (P, T) conditions.