Soil salinization poses a significant ecological challenge, emerging as a critical constraint to agricultural development in the arid and semi-arid regions of China, especially in southern Xinjiang. In particular, Yuepuhu County, situated in Kashgar, faces a distinctive issue. Impermeable thin clay layers within the vadose zone impede year-round leaching of salts, significantly impacting the growth of cotton. Through a combination of indoor testing, experiments, and statistical analyses, this study elucidated the varying permeability of soil layers at different depths and explored the forms and accumulation characteristics of soil salts in Yuepuhu County. It unveiled patterns of water and salt movement in soils with variable permeability layers, identifying key influencing factors. The research also proposed an irrigation regime suitable for cultivating vadose zone soils in the local context. The findings revealed a progression of increasing soil complexity and decreasing burial depth of clay layers from northwest to southeast, aligned with the direction of groundwater flow. With increasing depth, a noticeable reduction in soil saturated hydraulic conductivity was observed, indicating significant variability in permeability. Predominantly chloride-sulfate type saline soils in Yuepuhu County contained potassium (K⁺) and sodium (Na⁺) as the main cations in surface soils. Salinity strongly correlated with calcium (Ca²⁺) and magnesium (Mg²⁺). Chloride (Cl⁻), sulfate (SO₄²⁻), K⁺, Na⁺, and bicarbonate (HCO₃⁻) reflected the degree of soil salinization in Yuepuhu County. The clay interlayers in variable permeability zones significantly impeded water and salt movement in the vadose zone. Moving from west to east, thicker and shallower clay interlayers hindered downward water movement, increasing the difficulty of salt leaching. Additionally, the irrigation regime influenced water and salt movement in the vadose zone. Under the same soil structure, flood irrigation with a higher water flux resulted in more significant salt leaching, and lower total dissolved solids (TDS) in irrigation water were more favorable for effective salt leaching. Collectively, our findings provided a theoretical foundation for improving and managing local saline soils, as well as guiding the implementation of rational agricultural irrigation practices.

The analysis of water-soluble salts in the soil is an important basic work for the development and research of the salinity monitoring and salinization control of saline soils, aiming at the complexity of the development of soil salinization in oases in arid and semi-arid areas. Based on the regionalization theory, GPS positioning technology was adopted in this paper to conduct fixed point sampling of the Weigan River Basin oasis from April to May 2020. Soil sampling levels were between 0 m and 0.25 m, between 1 m and 2 m, and between 2 m and 3 m, respectively, and soil physical and chemical properties were analyzed and tested from May to June 2022. The spatial variability of soil salinity at different depths in the Weigan River Basin oasis was quantitatively studied by GIS and geostatistics, and the results show that: (1) the soil salinity of each layer in the Weigan River Basin oasis was generally high, with an average value of 1.27%, 0.87%, and 0.79%, respectively, and a variation coefficient between 1.023 and 1.265, showing strong variability. (2) A reasonable number of soil sampling should be based on the 95% confidence level and 20% relative error. Therefore, the number of soil samples in the corresponding layers should not be less than 89, 70, and 91. (3) Optimal fitting models of soil salinity at the layers between 0 m and 0.25 m and between 1 m and 2 m were both spherical models, while the optimal fitting model of soil salinity at the layer between 2 m and 3 m was an exponential model. Soil salinity at different depths is affected by random factors and structural factors. Soil salinity at the layer between 0 m and 0.25 m showed moderate spatial correlation, while soil salinity at the layers between 1 m and 2 m and between 2 m and 3 m showed strong spatial correlation. (4) Three layers of soil salinity had obvious anisotropy, and the maximum variation direction was northwest–southeast. The nested model can overcome the influence of directionality on the fitting of soil salinity variation function in the layer between 0 m and 0.25 m and improve the spatial interpolation accuracy. (5) In terms of spatial pattern, the area of high soil salinity was located along the Tarim River and at the edge of oasis (i.e., desert–oasis ecotone). On the whole, the salinity shows a gradual increasing trend from the inner part of the oasis (i.e., cultivation area) to the edge of the oasis, and from the northwest to the southeast. (6) The spatial distribution pattern of soil salinity in the study area was mainly affected by the differences in topography, groundwater level, and water quality, while agricultural activities intensified the formation of the distribution pattern, reflecting the complexity of the development of soil physical and chemical properties in arid and semi-arid areas. This study provided a reference for the improvement, management, and rational utilization of saline soil in the Weigan River Basin oasis.

Microwave heating of water-bearing coal can promote pore water evaporation. The pores are broken under the action of steam pressure, increasing the permeability of the coal. This study is aimed at investigating the mechanism of permeability improvement of water-bearing coal rock by microwave steam explosion. First, a microwave oven was used to irradiate and heat five groups of coal rock with different water contents; the NMR test was then conducted on the heated sample. Second, the internal vapor pressure and temperature changes during the heating process were obtained through the T-connector for samples with different water contents. Finally, a numerical experiment was used to explore the deformation characteristics of pores under three filling conditions. The experimental results showed that the total porosity increased significantly when the water content of coal increased from 0% to 8%, while the permeability increased by nearly 4.78 times. The extreme value of gas pressure inside the sample showed an increasing trend. The gas pressure and temperature were in line with the equation of state for an ideal gas during the rising phase. Numerical experiments showed that the pore boundary shrunk inward under vacuum conditions, and compressive stress appeared at the tip. The saturated humid air and liquid water conditions expanded the pore boundaries outward and caused tensile stress at the tip, with the latter being nearly 2.3 times larger than the former, making it more conducive to the development of pores. The findings of this study can be used as a reference value for the expansion of coalbed methane extraction technology.

Coalbed water participates in the whole process of coalbed gas generation, migration, accumulation, and exploitation, and its hydrogeochemical characteristics play a crucial role in the exploration and development of coalbed gas in mining areas. Taking the Fukang mining area in Xinjiang as the research object, this study tested the conventional cations, anions, trace elements, pH value, and TDS of its aquifer and analyzed the hydrochemical characteristics and evolution process of coalbed gas drainage water. The results show that the drainage water of coalbed gas is generally weakly alkaline, with significant changes in TDS and ion concentrations over time. Among the cations, Na⁺ occupies the absolute position, while among the anions, HCO₃ ^- dominates. Sixteen trace elements were detected in the drainage water of coalbed gas, each with varying concentrations. The concentrations of Al, Ti, V, Mn, Cu, As, Mo, Ba, Sb, and other elements exceeded the standard. In the early stages of the drainage process, the concentrations of Na⁺, Cl^-, and HCO₃ ^-, as well as TDS, were higher near the drainage well but gradually decreased and became more uniformly distributed outward along the wellbore. The distribution trends of Mg²⁺, Ca²⁺, and SO₄ ^2- concentrations were opposite to the former. Vertically, in groundwater within 1000 m, TDS, Na⁺, Ca²⁺, Cl^-, and HCO₃ ^- gradually increased with depth, while SO₄ ^2- and Mg²⁺ showed an increasing trend followed by a decrease with depth. After reaching a burial depth of 1200 m, the TDS, Mg²⁺, and Na⁺ of the reservoir water gradually stabilized, while Ca²⁺ and Cl^- decreased with depth, and HCO₃ ^- increased with depth. The hydrochemical characteristics indicate the influence of external fresh water or upper strata water inflow on the groundwater environment with increasing depth; the drainage activities worsen the closure degree of the groundwater environment, accepting infiltration replenishment and mixing from atmospheric precipitation. The reservoir drainage activities enhance the circulation of groundwater, and during the infiltration process, water-rock interactions such as salt dissolution, cation sorption exchange, and desulfurization occur between groundwater and reservoir. By analyzing the ions, trace elements, and hydrogeochemical characteristics of coalbed gas drainage water, the dynamic characteristics of coalbed reservoir water drainage and the hydrochemical evolution laws were clarified, providing theoretical guidance for coalbed gas exploration and development in the Fukang mining area.