Gases, Volume 6, Issue 1 (March 2026) – 16 articles

Gas condensate banking can significantly reduce near-well gas productivity by as much as ~60% in tight gas reservoirs. Existing treatment techniques are resource demanding and could alter the reservoir structure permanently. This study investigates the effectiveness of enhanced electrokinetic oil recovery (EK-EOR) as a low-impact alternative for treating condensate banks. Using compositional reservoir simulation (CMG GEM), the influence of key reservoir and operational parameters—porosity, permeability, producer well location (i, j), injection rate, and injection pressure—on cumulative gas production (CGP) was examined. A Box–Behnken design of experiments was employed to generate 62 simulation runs, and a proxy model was developed to approximate full-field responses. Statistical validation showed strong model fidelity (R² = 0.99, AAPE = 2.2%). The proxy was then optimized using a genetic algorithm (GA) to identify conditions that maximize gas recovery. Results indicate that lower injection rates and lower injection pressures maximize CGP through enhanced electro-osmotic flow and reduced water blocking, achieving a peak cumulative gas of 4.06 × 10⁸ ft³. A secondary optimum at high injection pressure could be attributed to re-pressurization and partial re-vaporization of condensate near the wellbore. Reservoir quality also exerted a strong control: higher permeability and moderate porosity favoured gas yield, while optimal producer placement near the reservoir boundary increased drainage efficiency. This study demonstrates a systematic optimization framework combining design of experiments, proxy modelling, and evolutionary algorithms to evaluate EK-EOR performance. Full article

This study numerically investigates the conversion of a Heavy-Duty (HD) Spark-Ignition (SI) Compressed Natural Gas (CNG) engine to operate with hydrogen-rich syngas produced from waste plastic pyrolysis. The engine was modeled with a one-dimensional simulation tool. Fuel-specific properties were included through a tabulated Laminar Flame Speed (LFS) approach, and knock occurrence was predicted with a Tabulated Kinetic of Ignition (TKI) model. Full-load simulations revealed that direct substitution of CNG with syngas leads to abnormal combustion. With adjusted values of Spark Advance (SA) to avoid knock, syngas operation resulted in average reductions of approximately 15% in brake torque and 6% in total efficiency compared to the CNG baseline. Parametric analyses showed that Late Intake Valve Closing (LIVC) provides no benefits, whereas increasing the Compression Ratio (CR) partially recovers performance and efficiency, with knock being a limiting factor. Lastly, a complete engine map of the converted configuration was generated, reporting Brake-Specific Fuel Consumption (BSFC) and emissions. Overall, the study demonstrates that HD SI engines can be operated on hydrogen-rich syngas at the cost of moderate performance penalties. Moreover, it provides a robust modeling framework to support system-level and well-to-wheel assessments of syngas-based powertrains. Full article

Synthetic natural gas (SNG) production from biomass residues represents a promising strategy to reduce greenhouse gas emissions and enhance energy security in regions with abundant agricultural waste. This study evaluates the thermodynamic performance of SNG synthesis from rice husk (RH) and empty fruit bunches (EFB) bio-oils, major residues in the department of Bolívar, Colombia. The process was simulated in Aspen Plus^®, integrating syngas data and methanation under equilibrium conditions at 320 °C and 30 bar, complemented by hydrogen injection via alkaline electrolysis to maintain an H₂/CO ratio above 3. Energy and exergy analyses were performed to quantify efficiencies and irreversibilities. Results indicate carbon conversion rates of 48.3% for EFB and 47.4% for RH, producing SNG with 96% CH₄ suitable for grid injection. Energy efficiencies reached 71.9% and 71.0%, while exergy efficiencies were 87.2% and 82.9%, respectively, aligning with or surpassing literature benchmarks. The main irreversibilities occurred in methanation and CO₂ removal, highlighting thermal integration and gas recycling as key improvement strategies. These findings demonstrate the potential of leveraging local biomass for clean energy production and support the development of Power-to-Gas systems in Colombia. Full article

This research investigates wettability-induced, preferential, pressure-driven bubble nucleation of gases from a multi-gas dissolved liquid system in hydrophilic and hydrophobic glass vials. The hydrophobic glass surfaces were prepared using (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane (HT). Degassed deionized water in a vial, placed inside a pressure cell, was saturated with a precisely controlled mixture of CO₂ and CH₄ gases at either 6000 mbar or 3000 mbar for 24 h. To initiate the pressure-driven bubble nucleation process, a 500 mbar step-down pressure was applied to the pressure cell every 15 min until bubble nucleation was observed. CH₄ and CO₂ volume fractions were measured using micro-gas chromatography (Micro-GC), while a digital microscope was employed to observe the bubble nucleation process. No bubble nucleation was observed in the case of the hydrophilic vial even when the system pressure was brought to atmospheric pressure. In the case of the hydrophobic vial, the average onset bubble nucleation pressures were 4800 mbar and 2000 mbar for 6000 mbar and 3000 mbar saturation pressures, respectively. The average feed gas concentrations during saturation were 84.44 ± 0.14% and 15.44 ± 0.2% of CH₄ and CO₂, respectively, while at the onset pressure for bubble nucleation, the concentrations shifted to 85.24 ± 0.48% and 13.12 ± 0.52% of CH₄ and CO₂, respectively, when the saturation pressure was 6000 mbar. The average feed gas concentrations during saturation were 85.12 ± 0.28% and 14.67 ± 0.1% of CH₄ and CO₂, respectively, and the average concentrations of CH₄ and CO₂ gases at onset pressure for bubble nucleation were 86.06 ± 1.21% and 12.03 ± 1.03%, respectively, when the saturation pressure was 3000 mbar. The increase in CH₄ concentration is attributed to its preferential separation during the bubble nucleation process. Full article

This study examines how different sustainability assessment approaches influence climate-policy choices when evaluating greenhouse gas (GHG) emissions across industrial value chains. Using Spain as an empirical setting, we apply Environmentally Extended Input–Output Tables combined with Production Layer Decomposition to quantify Scope 1–2–3 emissions and assess economic and employment impacts. The results show that indirect emissions dominate most value chains, revealing structural dependencies that are not captured by sector-level inventories. Incorporating social and economic dimensions highlights the need for transition pathways that minimise employment disruption while maximising environmental gains. Although public procurement can enhance the uptake of emerging low-carbon and circular-economy technologies, it has limited quantitative influence on total value-chain emissions. The findings demonstrate that value-chain-based sustainability assessments provide a more comprehensive basis for designing coherent, equitable, and effective decarbonisation strategies. Full article

An experiment was conducted to produce synthesis gas (main components CO and H₂) via plasma–steam gasification of brown coal with an ash content of 9% and a volatile matter yield of 48%. Satisfactory agreement between the calculation results and experiments for various types of solid fuel allowed the TERRA thermodynamic calculation program to be verified. A thermodynamic analysis of plasma–steam gasification of shale, brown, and hard coals was performed over a wide range of their characteristics (ash content 3–88%, volatile yield 5–50%) at temperatures from 600 to 3000 K. The composition of the gas and condensed phases of the gasification products, the degree of carbon gasification, and the specific energy consumption for the process were calculated. Although solid fuels differ significantly in ash content and volatile matter yield, synthesis gas is the primary gaseous product of their gasification, with a higher hydrogen concentration than carbon monoxide, thereby improving the environmental performance of solid fuels. In all types of fuels, the maximum synthesis gas concentration occurs between 1200 and 1600 K, with low ballast impurities (H₂O, CO₂, N₂) and zero harmful emissions (NO_X, SO_X). Synthesis gas combustion heat ranges from 10,475 to 11,570 kJ/m³. A 100% gasification rate occurs at temperatures between 1250 and 1300 K. Energy consumption varies between 0.7 and 2.7 kWh/kg. In solid fuel plasma–steam gasification, the volatile yield reduces specific energy consumption, but the ash content has a negligible effect. Plasma–steam gasification of solid fuels containing 9 and 88% ash and 48% and 50% volatile yield shows a 12% reduction in specific energy consumption. Plasma–steam gasification of solid fuels with volatile yields of 48 and 5% and ash contents of 9% and 3%, respectively, results in a 60% reduction in specific energy consumption. Full article

In South Asia, smog has become a critical environmental concern that endangers public health, ecosystems, and the regional climate. To determine the primary causes of smog formation in Lahore during peak polluted months (October and November), the current study develops a dual analytical framework that combines cutting-edge machine learning with sector- and pollutant-specific emission analysis. To assess their relationship with Air Quality Index (AQI) and create a high-accuracy predictive model, meteorological factors and emission data from key sectors are used to build Random Forest and extreme gradient boosting (XGBoost) models. The current study evaluates the joint effects of weather and emission loads on AQI variability by integrating atmospheric dynamics with comprehensive emission profiles. The XGBoost model forecasts important pollutants from the transportation, industrial, and agricultural sectors, including carbon dioxide (CO₂), oxides of nitrogen (NO_x), Volatile Organic Compounds (VOCs), and particulate matter, in the second analytical tier. Particulate matter (PM), NO_x, and transport-related pollutants are consistently identified by the models as the primary predictors of AQI, with high prediction performance. Furthermore, a 3-fold split is used for cross-validation, making sure that each fold maintained the data’s chronological order to avoid leakage. The model has modest root mean square error (RMSE) levels (4.32 and 8.14) and high coefficient of determination (R²) values (0.93–0.99). Approximately 90% of Lahore’s annual emissions resulted from the transportation sector. These results offer aid to policymakers to anticipate air quality, identify important emission sources, and execute targeted initiatives to minimize smog and promote a healthier urban environment. The current study also helps in analyzing the causes of atmospheric and sectoral pollution. While the study captures smog dynamics during peak pollution months, its temporal scope is limited, and finer spatial measurements could further improve the generalizability of the results. Full article

This review examines the emerging concepts of hydrogen production and storage directly within hydrocarbon reservoirs (in situ), evaluating their technical feasibility, infrastructure requirements, challenges, and potential role in net-zero strategies. The in situ hydrogen production involves injecting substances, like water or gases, into the reservoir where they react with the natural materials underground. Heat and catalysts can also help speed up chemical reactions. Techniques such as methane reforming, steam gasification, and aquathermolysis show promise for producing hydrogen efficiently while keeping carbon emissions low. There are several benefits when producing and storing hydrogen underground, including lower costs, less need for surface equipment, and reduced gas emissions. However, there are still certain challenges to this process, such as finding the optimal reaction conditions and keeping the reservoir stable over time. This review outlines key technological breakthroughs, real-world applications, and future research directions for in situ hydrogen generation and storage initiatives to help meet net-zero emission goals by 2050. Full article

This study presents a techno-economic assessment of a modular, solar-assisted methane pyrolysis pilot plant designed for sustainable hydrogen production in Nigeria using concentrated solar power (CSP). Driven by the need to convert flare gas into value and reduce emissions, the work evaluates a hypothetical 100 kg/day hydrogen system by integrating a methane pyrolysis reactor with a solar heliostat–receiver field. Process modelling was carried out in DWSIM, while solar concentration behavior was represented using Tonatiuh. The mass–energy balance results show a hydrogen output of 3.95 kg/h accompanied by 12.30 kg/h of carbon black, with the reactor demanding roughly 44 kW of high-temperature heat at 900 °C. The total capital cost of the ≈50 kW pilot plant is approximately USD 1.5 million, with heliostat and receiver technologies forming the bulk of the investment. Annual operating costs are estimated at USD 69,580, alongside feedstock expenses of USD 43,566. Using annualized cost and discounted cash flow approaches, the resulting levelized cost of hydrogen (LCOH) is USD 5.87/kg, which is competitive with off-grid electrolysis in the region, though still above blue and gray hydrogen benchmarks. The results indicate that hydrogen cost is primarily driven by solar field capital expenditure and carbon by-product valorization. Financial indicators reveal a positive NPV, a 13% IRR, and a 13-year discounted payback period, highlighting the promise of solar-assisted methane pyrolysis as a transitional hydrogen pathway for Nigeria. Full article

This study examines the determinants of U.S. CO₂ emissions and provides evidence to inform more effective carbon-reduction policies. Using Autoregressive Distributed Lag (ARDL) and Nonlinear ARDL (NARDL) models, the analysis covers January 1997 to February 2022 across four end-use sectors: Residential, Commercial, Industrial, and Transportation. The models capture both long-run equilibria and short-run adjustments between emissions and key drivers, including industrial production, interest rates, climate policy uncertainty (CPU), and energy prices. Results indicate a long-run asymmetric relationship in which economic growth and interest rates differentially affect total emissions, while CPU exerts a significant negative influence only in the transportation sector. Methodologically, the combined ARDL–NARDL approach offers robust evidence of nonlinear and asymmetric effects of macroeconomic and policy variables on emissions. These findings underscore the need to integrate economic and financial conditions into climate policy design and suggest that sector-specific measures—particularly targeting transportation—may substantially improve the effectiveness of carbon-mitigation strategies. Full article

Anaerobic digestion (AD) of ensiled orange peel waste (OPW) offers a promising pathway for the valorisation of citrus-processing residues and the generation of renewable energy. This study evaluated the impact of two carbon-based materials, biochar and granular activated carbon (GAC), on methane yield and process stability using Biochemical Methane Potential (BMP) tests. The experimental setup consisted of two consecutive cycles, the second of which was designed to examine microbial acclimation by reusing both the digestate (as the inoculum) and the previously added carbon materials. Ensiled OPW exhibited a methane yield of 578 ± 59 mL_CH4/g_VS during the initial cycle, confirming its high biodegradability. The addition of biochar and GAC resulted in comparable yields (approximately 520–560 mL_CH4/g_VS) and did not enhance the ultimate methane potential; however, both additives proved fully compatible with the process. In the subsequent cycle, a marked increase in methane production was observed, with OPW reaching approximately 730 mL_CH4/g_VS, primarily attributed to improved microbial adaptation. Kinetic analysis revealed moderate enhancements in degradation rates, which were more pronounced when higher biochar dosages were used. Overall, ensiled OPW emerges as a highly suitable substrate for AD. At the same time, biochar and GAC did not adversely affect the AD process under the tested conditions; however, their potential benefits have yet to be fully demonstrated and warrant further investigation, particularly under continuous reactor operating conditions. Full article

Gas injection is a well-established method for enhancing oil recovery by improving oil mobility, primarily through viscosity reduction. While its application in heavy oil reservoirs is extensively studied, the specific impact of carbon dioxide (CO₂) injection pressure on fluid viscosity reduction and the ultimate recovery factor from light oil reservoirs has not been fully investigated. To address this gap, this experimental study systematically explores the effects of CO₂ injection pressure and reservoir permeability on light oil recovery. This study conducted miscible, near-miscible, and immiscible gas injection experiments on two core samples with distinct permeabilities (13.4 md and 28 md), each saturated with light oil. CO₂ was injected at five different pressures, including conditions ranging from immiscible to initial reservoir pressure. The primary metrics for evaluation were the recovery factor (measured at gas breakthrough, end of injection, and abandonment pressure) and the viscosity reduction of the produced oil. The results conclusively demonstrate that CO₂ injection significantly enhances light oil production. A direct proportional relationship was established between both the injection pressure and the recovery factor and between permeability and overall oil production at the gas breakthrough. However, a key finding was the inverse relationship observed between permeability and viscosity reduction: the lower-permeability sample (13.4 md) consistently exhibited a greater percentage of viscosity reduction across all injection pressures than the higher-permeability sample (28 md). This unexpected trend is aligned with the inverse relationship between the permeability and the recovery factor after the gas breakthrough. This outcome suggests that enhanced CO₂ solubility, driven by higher confinement pressures within the nanopores of the lower-permeability rock, promotes a localized, near-miscible state. This effect was even evident during immiscible injection, where the low-permeability sample showed a noticeable viscosity reduction and superior long-term production. These findings highlight the critical role of pore-scale confinement in governing CO₂ miscibility and its associated viscosity reduction, which should be incorporated into enhanced oil recovery design for unconventional reservoirs. Full article

This study provides a comprehensive analysis of the impact of different marine fuels such as heavy fuel oil (HFO), methane, methanol, ammonia, or hydrogen, on energy efficiency and pollutant emissions in maritime transport, using a combined application of the Energy Efficiency Design Index (EEDI), Energy Efficiency Operational Indicator (EEOI), and Carbon Intensity Indicator (CII). The results show that methane offers the most balanced alternative, reducing CO₂ by more than 30% and improving energy efficiency, while methanol provides an intermediate performance, eliminating sulfur and partially reducing emissions. Ammonia and hydrogen eliminate CO₂ but generate NO_x (nitrogen oxides) emissions that require mitigation, demonstrating that their environmental impact is not negligible. Unlike previous studies that focus on a single fuel or only on CO₂, this work considers multiple pollutants, including SO_x (sulfur oxides), H₂O, and N₂, and evaluates the economic cost of emissions under the European Union Emissions Trading System (EU ETS). Using a representative model ship, the study highlights regulatory gaps and limitations within current standards, emphasizing the need for a global system for monitoring and enforcing emissions rules to ensure a truly sustainable and decarbonized maritime sector. This integrated approach, combining energy efficiency, emissions, and economic evaluation, provides novel insights for the scientific community, regulators, and maritime operators, distinguishing itself from previous multicriteria studies by simultaneously addressing operational performance, environmental impact, and regulatory gaps such as unaccounted NO_x emissions. Full article

Solar energy enhances the energy and environmental performance of coal gasification by lowering carbon emissions and increasing the yield and quality of synthesis gas. This patent review surveys recent global advances in solar thermochemical reactors for coal gasification, focusing on key innovations disclosed in patent applications and grants, with particular attention to technologies that improve process efficiency and sustainability. The novelty of the review is that unlike most patent reviews that focus primarily on statistical indicators such as application counts, geography, and classification, this work integrates qualitative analysis of specific technical solutions alongside statistical evaluation. This combined approach enables a deeper assessment of technological maturity and practical applicability. Fifteen patents from different countries were reviewed. The largest number (8, 53%) belongs to the United States. China has the second place with 4 (27%). The remaining countries (the EU, Korea, and Russia) hold 1 patent (7% each). The present work emphasises the technological and engineering solutions associated with the integration of solar energy into gasification processes. The author’s design is free of the disadvantages of its counterparts and is a simplified design with a high degree of adaptability to various types of fuel, including brown coal, biomass, and other carbon-containing materials. Full article

Methoxy radicals (CH₃O•), formed as intermediates during methane oxidation, may play an underexplored but locally significant role in the atmospheric oxidation of dimethyl sulfide (DMS), a key sulfur-containing compound emitted primarily by marine phytoplankton. This study presents a comprehensive computational investigation of the reaction mechanisms and kinetics of DMS oxidation initiated by CH₃O•, using density functional theory B3LYP-D3(BJ)/6-311++G(3df,3pd), CCSD(T)/6-311++G(3df,3pd), and UCBS-QB3 methods. Our calculations show that DMS reacts with CH₃O• via hydrogen atom abstraction to form the methyl-thiomethylene radical (CH₃SCH₂•), with a rate constant of 3.05 × 10⁻¹⁶ cm³/molecule/s and a Gibbs free energy barrier of 14.2 kcal/mol, which is higher than the corresponding barrier for reaction with hydroxyl radicals (9.1 kcal/mol). Although less favorable kinetically, the presence of CH₃O• in localized, methane-rich environments may still allow it to contribute meaningfully to DMS oxidation under specific atmospheric conditions. While the short atmospheric lifetime of CH₃O• limits its global impact on large-scale atmospheric sulfur cycling, in marine layers where methane and DMS emissions overlap, CH₃O• may play a meaningful role in forming sulfur dioxide and downstream sulfate aerosols. These secondary organic aerosols lead to cloud condensation nuclei (CCN) formation, subsequent changes in cloud properties, and can thereby influence local radiative forcing. The study’s findings underscore the importance of incorporating CH₃O• driven oxidation pathways into atmospheric models to enhance our understanding of regional sulfur cycling and its impacts on local air quality, cloud properties and radiative forcing. These findings provide mechanistic insights that improve data interpretation for atmospheric models and extend predictions of localized variations in sulfur oxidation, aerosol formation, and radiative forcing in methane-rich environments. Full article

Carbon Capture, Utilization and Storage (CCUS) is a critical area of research due to its potential to significantly reduce CO₂ emissions from industrial processes and fossil fuel-based power generation. Aqueous amine solutions are commonly used as chemical solvents for CO₂ capture. However, their application is disfavoured by the high energy requirements and related operational costs, toxicity, and corrosion issues. To address these limitations, research is in general focused on developing novel solvents that can overcome the drawbacks of traditional amines. This development needs the study of phase equilibria in systems for which detailed physicochemical data are often scarce in the literature. In particular, understanding the solubility of gases (CO₂) in possible solvent mixtures is essential for evaluating their suitability for chemical or physical absorption processes. In this work, a dedicated setup was installed to generate the experimental data for these novel systems. This unit was designed to measure the solubility and diffusivity of gases in low-volatility liquids that could be alternative CO₂ solvents. A detailed experimental procedure was established, and the unit was initially validated by measuring CO₂ solubility in a 30 wt% monoethanolamine (MEA) solution, one of the most widely used industrial solvents. The experiments were conducted under conditions representing both the absorption and the regeneration sections of a CO₂ removal plant. The resulting equilibrium data were analyzed by employing several thermodynamic models, and the model providing the best representation was selected. Full article