No abstract

The adsorption characteristics of sodium dodecylbenzene sulfonate (SDBS) on the surface of montmorillonite can lay a foundation for obtaining the optimum concentration of the anionic surfactant. The best absorption wavelength of SDBS was determined using an ultraviolet spectrophotometer. The standard curves of concentration and absorbance of SDBS were established. The amount of SDBS adsorbed on the surface of montmorillonite at various concentrations was calculated by stirring adsorption method. Scanning electron microscopy–energy dispersive X-ray spectrometry (SEM-EDS), X-ray diffraction (XRD), zeta potentiometer, and Fourier transform infrared (FTIR) spectroscopy were used to observe the changes of the structure, main ions, interlayer spacing, potential, and main functional groups on the montmorillonite surface before, and after, adsorption. The test results of SEM with EDS (SEM–EDS) showed that the surface of the montmorillonite after SDBS adsorption was rougher, and the adsorption capacity of the surface was enhanced as the SDBS concentration increased. The XRD results indicated that SDBS adsorbed on the interlayer of montmorillonite repulsed interlayer water and reduced the interlayer water content. With the increase of SDBS concentration, the interlayer spacing of the montmorillonite available for adsorbing SDBS decreased further. Additionally, interlayer adsorption and surface adsorption exist simultaneously in montmorillonite in SDBS solution. The distribution of total adsorption capacity of SDBS in the layers and on the surface of montmorillonite accords with the adsorption result simulated by a pseudo-second-order kinetic model. The increase in concentration of SDBS adsorbed by montmorillonite is the main reason for the decreased initial adsorption rate. The zeta potential test showed that the addition of H+ to the SDBS solution could reduce electrostatic repulsion and promote the adsorption of SDBS on montmorillonite. The results of this study provide an experimental basis for the study of the mechanism of SDBS adsorption on montmorillonite.

No abstract

Fracture and cleats development controls the permeability of coal reservoirs, while the migration of coal fines can block fractures and affect coalbed methane (CBM) production performance. To reveal the migration, agglomeration, and settlement of coal fines within fractures, and also to investigate permeability variations, an experimental simulation was conducted. Factors like coal fine particle sizes (<48, 48−75, 75−96, 96−120, and 120−180 μm), fracture width (0.05, 0.10, 0.15, and 0.20 mm), coal fines suspension concentration (0.5‰, 1.0‰, 1.5‰, 2.0‰, and 2.5‰), and injection flow rates (2.5, 5.0, 7.5, and 10.0 mL/min) were considered, and the deposited and output coal fines qualities were recorded. The results showed that by controlling stable injection flow rates, the injection pressures increased with the extension of time, indicating fractures were blocked gradually by coal fines. The pressure variation curves could be divided into three types: (1) steady slow rise type, (2) stable to sharp rise type, and (3) fluctuating type. The quality of deposited coal fines in fractures varied between 0.0068 and 0.917 g, and the quality of output coal fines was between 0 and 0.1028 g. With fracture width incrementation, the deposited and output values of coal fines of different sizes all increased. As coal fines concentration increased, the output values first increased and then decreased, and vice versa for deposited values. When the injection flow rate increased, the deposited coal fines values initially increased and then diminished. In the largest coal fines deposition, an injection flow rate of 5.0 mL/min was observed, while larger and stable coal fines migration and production were observed at 2.5 and 7.5 mL/min. Under most of the circumstances (except for 120−180 μm coal fines), permeability losses were concentrated between 70% and 95%, and the permeability loss with time was concentrated between 0.15 and 0.178 mD/h. Thus, the induced damages of coal fines to fractures were similar and could damage most of the flow channels. The quality of deposited coal fines was positively correlated with permeability reduction. For better coal fines output during CBM production, the flow rate should be controlled at certain rates for stable coal fines migration (e.g., 7.5 mL/min in this study). Also, further research should be focused on the dispersion of coal fines and their precise control.