Fuels

Pili nutshell (PS), an abundant agro-industrial byproduct in the Bicol Region, Philippines, demonstrates substantial potential as a solid biofuel and bioenergy feedstock. Proximate and ultimate analyses revealed high volatile matter (72.00 ± 0.20 wt%), low ash content (4.33 ± 0.76 wt%), and a higher heating value of 20.60 MJ/kg, indicating strong suitability as a solid fuel for thermochemical conversion and biofuel production. Thermogravimetric analysis (TGA) was conducted from 30 °C to 900 °C at heating rates of 10, 15, and 20 °C/min under nitrogen to examine its thermal decomposition behavior. The process followed three stages: initial moisture loss, active devolatilization, and lignin-rich char formation. The resulting kinetic and thermodynamic parameters are directly relevant for designing fast pyrolysis processes aimed at liquid biofuel production and optimizing downstream fuel utilization of the derived bio-oil and char. Kinetic analysis using the Coats–Redfern method identified third-order reaction (CR03) and diffusion-controlled (DM6) models as best-fitting, with activation energies ranging from 64.03–96.21 kJ/mol (CR03) and 66.98–104.72 kJ/mol (DM6). Corresponding thermodynamic parameters—ΔH (58.67–90.95 kJ/mol), ΔG (201.51–231.46 kJ/mol), and ΔS (−174.57 to −255.08 kJ/mol·K)—indicated an endothermic, non-spontaneous, entropy-reducing reaction pathway. Model-free methods confirmed a highly reactive zone at α = 0.3–0.6, with consistent E_a values (~130–190 kJ/mol). These findings affirm the viability of PS for fast pyrolysis, offering data-driven insights for optimizing advanced fuel and bioenergy systems in line with circular economy objectives.

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.