Fuels

Methane gas (CH₄) leakage and gas extraction efficiency in drillholes present persistent challenges in coal mine gas management. To address these issues, a novel gas leakage detection device and a precision secondary grouting and thickening system were developed and field-tested at the Li YaZhuang Coal Mine, China. The system enables accurate identification of leakage zones and provides adjustable sealing length and depth, withstanding grouting pressures up to 2.0 MPa to achieve the full-section sealing of drillholes. Field application on 23 drillholes demonstrated a significant improvement in gas extraction performance. The average methane concentration and pure gas flow rate increased by more than 2-fold (2.61 and 3.05, respectively) compared with the pregrouting values, indicating substantial increases in gas extraction stability and duration. This study validates the effectiveness and practicality of the proposed secondary grouting technology for restoring failed drillholes, mitigating gas leakage, and improving methane recovery. The results provide a technical reference for advancing gas control strategies in high-gas coal seams.

To address the challenges of strong heterogeneity and poor crude oil mobility in tight conglomerate reservoirs of the Mahu Oilfield, this study systematically evaluated the effects of different surfactants on wettability alteration, spontaneous imbibition, and relative permeability through high-temperature/high-pressure spontaneous imbibition experiments, online Nuclear Magnetic Resonance (NMR) monitoring, and relative permeability measurements. Core samples from the Jinlong and Madong areas (porosity: 5.98–17.55%; permeability: 0.005–0.148 mD) were characterized alongside X-Ray Diffraction (XRD) data (clay mineral content: 22–35.7%) to compare the performance of anionic, cationic, nonionic, and biosurfactants. The results indicated that the nonionic surfactant AEO-2 (Fatty Alcohol Polyoxyethylene Ether) (0.2% concentration) at 80 °C exhibited optimal performance, achieving the following results: 1. a reduction in wettability contact angles by 80–90° (transitioning from oil-wet to water-wet); 2. a decrease in interfacial tension to 0.64 mN/m; 3. an imbibition recovery rate of 40.14%—5 to 10 percentage points higher than conventional fracturing fluids. NMR data revealed that nanopores (<50 nm) contributed 75.36% of the total recovery, serving as the primary channels for oil mobilization. Relative permeability tests confirmed that AEO-2 reduced residual oil saturation by 6.21–6.38%, significantly improving fluid flow in highly heterogeneous reservoirs. Mechanistic analysis highlighted that the synergy between wettability reversal and interfacial tension reduction was the key driver of recovery enhancement. This study provides a theoretical foundation and practical solutions for the efficient development of tight conglomerate reservoirs.

The urgent need to address climate change has driven the exploration of sustainable energy solutions, with wave energy and green hydrogen emerging as prominent alternatives to traditional fossil fuels. This study examines the potential synergy between wave energy and hydrogen production, with a focus on the economic viability of integrating these technologies. Through a detailed analysis of the levelised cost of electricity (LCOE) and the levelised cost of hydrogen (LCOH), this paper examines how coastal regions in Portugal and across Western Europe can harness wave energy to produce green hydrogen, a crucial component in the global energy transition. The techno-economic assessment accounts for capital and operational costs, energy efficiency, and lifetime performance to determine how design and location affect economic feasibility. Preliminary analysis indicates that regions with significant wave power potential present opportunities for competitive LCOE values, with some coastal areas achieving LCOE figures as low as 0.10 €/kWh. Additionally, the LCOH analysis reveals that among various storage methods, compressed gas hydrogen at 350 bar stands out as the most cost-effective option. This research highlights the transformative potential of wave energy-driven hydrogen production as a crucial solution for decarbonising the maritime sector. Future technological advancements and cost efficiencies are poised to overcome current economic barriers and accelerate the transition to a sustainable, low-carbon energy landscape.