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Clarifying the geochemical characteristics of formation water and its origin is conducive to clarifying the gas migration path, elaborating the law of gas migration and accumulation, and further predicting the favourable area of gas accumulation. Taking Quaternary formation water from the Tainan-Sebei area of the Sanhu Depression as the research object, the chemical characteristics and origin of the region are clarified using anion analysis, cation analysis, hydrogen isotope analysis, oxygen isotope analysis and so on. The results are as follows. (1) The formation water in the study area has a high total dissolved solids (TDS) content and is mainly type IV and V of CaCl2. (2) Low r(Na+)/r(Cl−), low desulfurization coefficient, high r(Ca2+)/r(Mg2+) and high indices of base exchange indicate that the Qigequan Formation is in a stagnant zone, which is beneficial for the accumulation and preservation of biogenic gas. (3) Due to albitization and water–rock reactions, the formation water is rich in Ca2+, poor in Na+ and poor in Mg2+. (4) The formation water in the study area originates from the glacial meltwater of the Kunlun Mountains, which converts into groundwater and seeps into the formation along the piedmont slope zone. In the process of groundwater infiltration and convergence, many salt substances in the formation are dissolved, resulting in a gradual increase in TDS. Then, the formation water with a high TDS migrates to the anticline in the northern part of the depression and is finally trapped in the formation. [ABSTRACT FROM AUTHOR]

The bedrock weathered crust in front of the Altun Mountains in the Qaidam Basin, western China, is different from others because this is a salt‐lake basin, where saline water fluid infiltrates and is deposited in the overlying strata. A large amount of gypsum infills the bedrock weathered crust, and this has changed the pore structure. Using core observation, polarized light microscopy, electron probe, physical property analysis and field emission scanning electron microscopy experiments, the characteristics of the weathered bedrock have been studied. There are cracks and a small number of dissolved pores in the interior of the weathered crust. Matrix micropores are widely developed, especially the various matrix cracks formed by tectonics and weathering, as well as the stress characteristics of small dissolved pores, and physical properties such as porosity and permeability. This 'dual structure' developed in the bedrock is important for guiding the exploration of the lake basin bedrock for natural gas. [ABSTRACT FROM AUTHOR]

In this paper, well-defined Mg-Al LDHs nanosheets with high yield are prepared by the following sequential procedures: hydrothermal preparation of Mg-Al-CO 3 2 − LDHs, followed by expanding interlayer spacing by NH4NO3 treatment. The results show that the concentration of the layer expansion agent (NH4NO 3) and the exfoliation solvent play a key role in the exfoliation result. The basal spacing changed from 0.758 nm to the range of 0.758–0.895 nm when the concentration of NH4NO3 was increased up to 5 M, which infers that the increase of layer space is caused by the synergy of NH 4 + and NO 3 − . Among the three exfoliation solvents (formamide, N-methyl pyrrolidone and isopropyl alcohol), formamide showed the highest exfoliation effect. From the characteristic XRD patterns, the as-obtained colloidal aggregates of the exfoliated nanosheets do not show the characteristic diffractions of LDHs, while the typical peaks at 10.562 ∘ , 20.032 ∘ and 21.185 ∘ assigned to LDHs are observed after drying of the colloidal aggregates. Moreover, a transparent LDH film is also successfully prepared by coating colloidal aggregates of nanosheets on a glass substrate without using any adhesive. The stable film exhibits the strong adsorption ability of Methyl Orange. The success in obtaining well-defined Mg-Al LDHs nanosheets through the following sequential procedures was described: hydrothermal preparation of Mg-Al LDHs, expanded interlayer spacing by NH4NO3 treatment, and stable, transparent colloidal suspension with no solid residues after standing in formamide for 2 days. The product had strong adsorption ability. [ABSTRACT FROM AUTHOR]