Abstract Solidified natural gas (SNG) is a potential alternative to liquefied and compressed natural gas for natural gas storage, but its environmental performance has not been quantified. This study presents the first life cycle assessment of SNG production via clathrate hydrate formation, comparing unpromoted methane hydrate (sI), methane–tetrahydrofuran (THF) hydrate (sII), and methane–1,3-dioxolane hydrate (sII). A gate-to-gate assessment was performed using ReCiPe 2016 (H) with a functional unit of 1 MJ of natural gas stored as methane hydrate. Since unconverted methane is recycled, all configurations consume the same net quantity of methane, and the higher conversion of the promoted systems (42.0% versus 10.0%) instead reduces electricity demand from 0.116 to approximately 0.030 kW h MJ–1. The unpromoted process had the lowest impact in all 18 midpoint categories, including the lowest global warming potential (0.070 kg CO2-eq MJ–1) and end point single score (1.83 mPt). The global warming potentials of the 1,3-dioxolane- and THF-promoted processes were 3.0 and 4.7 times higher, with promoter production contributing 83% and 89%, respectively. Paired Monte Carlo analysis confirmed these rankings, with 1,3-dioxolane outperforming THF in 87–100% of iterations depending on the category. The ranking was unchanged under a 20-year characterization horizon and would be reversed only if more than 2.5% of the unconverted methane recycle stream were lost, or if the production burden of 1,3-dioxolane were 81% lower than that of its 1,4-dioxane proxy. Thermodynamic promotion therefore increases rather than redistributes environmental burdens, and the stoichiometric promoter makeup, not hydrate formation, is the principal environmental barrier to promoted SNG.
Abstract Ion-specific interactions at fluid-mineral interfaces play a critical role in controlling wettability and multiphase flow in porous materials. In this study, a series of two-phase flow experiments were conducted on miniature oil-wet carbonate cores to investigate how aqueous chemistry regulates dynamic wettability evolution and pore-scale displacement behavior. Companion cores were conditioned using a common aging protocol to establish comparable mean oil-wet states and subsequently subjected to waterflooding under controlled chemical environments. Fluid configurations and in situ geometric contact angles were characterized at successive imaging stages using high-resolution X-ray microcomputed tomography. As wettability evolved in response to controlled aqueous chemistry toward less oil-wet states, the pathways of pore-scale invasion were correspondingly reorganized. Morphology-based analysis of the oil displaced between consecutive imaging stages quantified the relative volume contributions of piston-like invasion and wetting-layer drainage to incremental oil recovery. Piston-like invasion dominated initial displacement, whereas wetting-layer drainage accounted for most later-stage recovery during low-salinity flooding. These stage-dependent contributions connect brine-associated wettability changes with the pore-scale processes responsible for oil mobilization.
Abstract Low-salinity waterflooding is widely recognized as a promising enhanced oil recovery method, yet its reported performance remains highly variable because the observed response reflects not only brine composition, but also the displacement state of the porous medium at the time the injected brine is introduced. While most previous studies have focused on optimizing brine chemistry, the mechanistic role of injection timing and displacement history has received far less attention. In this study, we investigate how the timing of brine switching governs low-salinity response in chalk by introducing an early tertiary flooding design, in which the injected brine is switched immediately after secondary brine breakthrough. This approach enables controlled probing of an intermediate saturation state representative of the reservoir region just behind the advancing flood front. The resulting recovery behavior was interpreted together with ion chromatography measurements to track brine displacement and chemical-front propagation. The results show that the apparent efficiency of low-salinity flooding is strongly governed by displacement history. Conventional tertiary injection produced negligible incremental recovery, whereas early tertiary injection of diluted seawater yielded 11.3% additional oil recovery (11.8% when formation water was used as the tertiary brine), comparable to values commonly reported for secondary low-salinity flooding. Ion chromatography revealed that the onset of tertiary oil production occurred only after the preceding brine had been displaced from the core. This indicates that chemical-front propagation, in situ mixing, and fluid accessibility govern when the tertiary response becomes observable. The data also confirmed transient formation-water banks ahead of the injected brine front. These findings indicate that tertiary low-salinity performance is controlled not only by brine composition, but also by the fluid occupancy and chemical accessibility inherited from prior flooding at the moment of brine introduction. More broadly, the results support viewing secondary, early tertiary, and conventional tertiary flooding as successive stages of flood maturity, each probing a different displacement state of the reservoir. Conventional tertiary corefloods may therefore underestimate the observable low-salinity response by introducing the modified brine only after extensive prior brine invasion and oil displacement. This highlights injection timing as a key mechanistic variable in chalk waterflooding.
Abstract Coke oven gas (COG) is a promising byproduct gas generated in steelmaking processes because of its high heating value and large production volume. The large amount of hydrogen in COG contributes to combustion reactivity, flame stability, and decarbonization. Recently, a strategy for recycling COG cofired with other fuels has been proposed to support continued utilization. Ammonia is an attractive carbon-free fuel, a suitable candidate for cofiring with COG. In this study, the combustion and emission characteristics of ammonia-blended COG were investigated using a coaxial-flow nonpremixed combustor. Experiments evaluated the flame length, blow-off limit, and OH radical and NOx emissions. 2D simulation using ANSYS Fluent analyzed flame temperature and NO mole fraction. As a result, it was found that the flame length decreased with increasing ammonia blending ratio because of the reduced heat release rate and fuel reactivity. The normalized correlation based on Roper’s equation accurately predicts the flame length of COG, implying that COG can subsequently be interpreted as a general-purpose fuel. In addition, despite decreased blow-off limit of the ammonia-blended COG, it still maintained a significantly higher stability limit than methane due to the high hydrogen content of COG. OH-PLIF measurements revealed that the flame structure and reaction intensity were only slightly affected by ammonia blending, demonstrating the feasibility of ammonia-blended COG for stable combustion. NOx emissions increased substantially because of enhanced fuel-NO formation. This study provides a fundamental database for ammonia-blended COG under nonpremixed conditions and can contribute to the development of low-carbon industrial combustion systems.
