Mohamed Mahmoud

Residual trapping of CO₂ ganglia in porous media is critical for geo-storage success and de-risking, yet widely used models do not incorporate an explicit continuous wettability variable despite evidence of its primary control on trapping efficiency. A physics-informed machine learning framework is developed to address this gap.,A curated database of 146 CO₂/brine/rock measurements, spans 2.3-12,100 mD in consolidated rock, porosity of 7.9-38%, and water-, intermediate- and non-water-wet states harmonized through a wettability-index Wi. Twelve physics-informed variables including the Leverett length and a modified reservoir quality index (MRQI) feed statistical models, seven machine learning algorithms, and a mixed-effects treatment of inter-study heterogeneity.,An additive correlation with three predictors and four fitted coefficients, incorporating the square root of initial gas saturation (√Sgi), wettability-index (Wi), and MRQI, achieves R² = 0.607 and RMSE = 6.40%. Residual analysis revealed systematic over-prediction of intermediate-wet samples, motivating the Wettability-Modulated MRQI (WM-MRQI) correlation in which wettability acts as a non-linear modulator of saturation-history and rock-quality terms, achieving R2 = 0.631 (RMSE 6.20%) with four coefficients, improving 31% on the re-fitted Land benchmark (R2 = 0.483), and retaining R2 = 0.57 under leave-one-source-out validation through 33 contributing studies. A non-parametric upper-bound analysis and mixed-effects decomposition confirms an irreducible predictive ceiling from inter-laboratory heterogeneity, measurement noise, and absent controls including pore-structure descriptors. Prediction intervals achieve 94.5% coverage in-sample and 91.8% with held out data. Feature attribution analysis identifies saturation-wettability interactions as a dominant signal (48%), validating the non-linear modulation mechanism and supporting practical de-risking of storage operations

Deep saline aquifers offer the largest global capacity potential for geologic carbon storage, yet storage performance is frequently constrained by coupled limitations on \COtwo{} dissolution (solubility trapping) and injectivity under high-salinity conditions. Elevated ionic strength suppresses \COtwo{} solubility via ``salting-out'' effects. Meanwhile, near-wellbore dry-out during injection of dry or undersaturated \COtwo{} can concentrate brine and precipitate salts, reducing permeability and injectivity. Mineralogy and \COtwo{}-brine-rock wettability further control multiphase flow topology, interfacial area for dissolution, capillary trapping, and compatibility of additives with reservoir surfaces. This review critically evaluates chemical pre-flush and additive-enabled conditioning strategies intended to (i) increase local aqueous \COtwo{} dissolution capacity, (ii) mitigate or prevent dry-out-driven salt precipitation and near-wellbore formation damage, and (iii) enhance \COtwo{}-brine contact through mobility control. We synthesize and compare evidence for four strategy families: (1) freshwater and engineered low-salinity (LoSal) pre-flush slugs and intermittent re-wetting; (2) chelating agents (e.g., EDTA/GLDA/DTPA) that complex multivalent cations and alter dissolution/precipitation pathways; (3) surfactant-derived \COtwo{} foams, including \COtwo{}-soluble surfactants designed for foam generation at the displacement front with achievable injectivity; and (4) nanoparticle-assisted and hybrid foam systems that extend foam stability under harsh salinity and temperature.

In-situ hydrogen production from natural gas reservoirs (IHP-NG) is an emerging pathway for low-carbon hydrogen by converting methane-rich subsurface resources while retaining carbon-bearing byproducts underground. This review critically evaluates the reaction mechanisms, experimental and modelling evidence, techno-economic position, life-cycle implications, and deployment challenges of IHP-NG. Unlike heavy-oil in-situ combustion gasification, IHP-NG is governed mainly by methane conversion reactions, including steam methane reforming, partial oxidation, autothermal reforming, methane cracking, dry reforming, and water--gas shift, alongside competing pathways such as methanation, reverse water--gas shift, and coking. Existing studies show that high temperature, adequate steam supply, controlled oxidant dosage, effective catalysis, and selective H2 recovery are essential for meaningful hydrogen generation. However, uncertainties remain around reservoir heterogeneity, heat management, catalyst stability, well integrity, H2 separation, and carbon retention. Techno-economic and life-cycle assessment indicates that IHP-NG is a process-integration concept, not an inherently cheaper or cleaner hydrogen route. Its competitiveness and carbon advantage depend on high H2 yield, reliable separation, infrastructure reuse, verifiable CO2 retention, low methane and H2 losses, and manageable monitoring and liability costs. Field-scale validation is therefore essential before IHP-NG can be deemed a credible low-carbon hydrogen pathway.

The growing urgency of climate change mitigation and the commitment of many countries to reduce greenhouse gas emissions have increased interest in hydrogen as a low-carbon energy carrier. However, the transition to a hydrogen-based economy faces challenges related to large-scale and long-term storage. Underground hydrogen storage has been proposed as a viable and scalable solution, but it also raises concerns regarding storage security and gas purity. This study investigates hydrogen adsorption, short-term reactivity, and long-term cyclic hydrogen–pyrite interactions using synthetic silica- and carbonate-based cores containing 10 wt.% pyrite.Pyrite-bearing cores had 28–100% more apparent hydrogen adsorption than pyrite-free cores depending on lithology and temperature measured in a hydrogen adsorption experiment. To test reactivity of pyrite under conditions similar to those found in a reservoir, short-term batch experiments were performed at approximately 750 psi, gas analyses reveal the measurable amounts of H­2S. Long-term cyclic experiments were carried out for three weeks at 60 °C to assess the evolution of reactions over extended storage time, replenishing the hydrogen gas periodically and measuring the gas composition. During the first week, the production of H2S rose, peaked around 7 days and then dropped significantly in following weeks and consistently stayed low throughout the 3rd week. These findings highlight the risk of hydrogen loss through mineral reduction and contamination of the stored gas, both of which decrease storage efficiency and increase safety hazards. To achieve high-purity UHS, site selection must explicitly account for reservoir mineralogy, particularly the presence and abundance of pyrite.

Underground hydrogen storage (UHS) is a promising option for large-scale energy storage to support the hydrogen (H2) economy; however, its effective implementation requires understanding hydrogen–brine multiphase flow behavior in geological rocks under pore-scale heterogeneity. This study presents an integrated experimental investigation of H2-brine drainage in sandstone and carbonate rocks using capillary pressure, nuclear magnetic resonance (NMR), and electrical resistivity measurements. Pore-scale drainage mechanisms are inferred from NMR T2 relaxation distributions rather than direct pore-scale imaging. Capillary pressure experiments showed decreasing water saturation with increasing pressure, indicating hydrogen invasion, with irreducible water saturation reflecting macropore dominance. Carbonate samples exhibited lower irreducible water saturation (31.9–34.5%) than sandstone samples (36.3–41%). Electrical resistivity increased nonlinearly with decreasing saturation. NMR revealed preferential macropore drainage followed by limited micropore drainage. These observations provide experimental insight into equilibrium H2-brine drainage behavior and highlight the importance of pore-scale heterogeneity for future multiphase-flow characterization and reservoir modeling relevant to underground hydrogen storage.