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The phase equilibria for the quaternary system Li + , Rb + , Mg 2+ // SO 4 2− − H 2 O at 273.2 K were studied by the isothermal dissolution equilibrium method. Based on the measured data, the space diagram, stable phase diagram, water content diagram, and the diagram of density vs composition are plotted. The stable phase diagram in the system consists of four quaternary invariant points, nine univariate curves, and six crystallization zones. For the invariant points, E 1 and E 4 belong to the commensurate type, and E 2 and E 3 belong to the incommensurate type. The order of the crystallization area is RbThe density of the equilibrium liquid changed regularly with the content of Rb 2 SO 4 in the solution. By comparing the stable phase diagram of the partial ternary subsystems at T = 273.2 K and T = 298.2 K, it is found that the crystallization regions of Rb 2 SO 4 increases with the decrease in temperature, which indicates that cooling is conducive to the crystallization of Rb 2 SO 4 . By comparing the stable phase diagram of the system at T = 273.2 K and T = 308.2 K, it was found that the system was composed of four invariant points, nine univariate curves, and six crystal regions. The double salt 3Li 2 SO 4 •Rb 2 SO 4 •2H 2 O is converted to 3Li 2 SO 4 •Rb 2 SO 4 . The crystallization region of single salt MgSO 4 •7H 2 O, Rb 2 SO 4 and double salt Li 2 SO 4 •Rb 2 SO 4 decreased obviously.

A set of marine carbonates was deposited in the Palaeozoic of the North China Craton, which is the dominant sequence for buried hill hydrocarbon exploration. This study focuses on the lithofacies and reservoirs developed in the sequence. Based on the data of cores, thin sections, drilling, and logging, the characteristics of the sequence stratigraphic framework and its control on lithofacies and reservoirs of the Lower Palaeozoic buried hills in the offshore Bohai Bay Basin are discussed.The results show that there developed 4 second-order sequences and 21 third-order sequences in the study area. Due to the deep burial depth, the dolomite is more likely to form high-quality reservoirs than limestone in the study area, and we define the dolomitic tidal flat-dominant sequences as 'favorable reservoir sequences'. There developed unconformity-related reservoirs and inner reservoirs in the buried hill, and the 'favourable reservoir sequences' present obvious control on both reservoirs, showing: (i) 'favourable reservoir sequences' and weathering interface control on the scale of the unconformity-related reservoir jointly, and (ii) the inner reservoirs developed within 'favourable reservoir sequences' as well, and the top and bottom of the high-frequency sequences are the predominant areas for the bedding karst reservoir distribution.

The stable phase equilibria of ternary systems Li+,Rb+//SO4 2––H2O and Li+,Cs+//SO4 2––H2O at 273.2 K are studied herein by the isothermal dissolution equilibrium method. The solubility and density of the systems are measured experimentally, and the related phase diagrams, density versus composition diagrams, are plotted. Results show that the ternary systems Li+,Rb+//SO4 2––H2O and Li+,Cs+//SO4 2––H2O are both complex systems with two kinds of double salts formed at 273.2 K. The stable phase diagrams of these two ternary systems all consist of one unsaturated solution region, three co-crystallization regions, three invariant points, four invariant curves, and four crystallization regions. By comparing the phase diagrams of the ternary system Li+,Rb+//SO4 2––H2O at 273.2 and 298.2 K, it is found that the crystallization regions of the two double salts (3Li2SO4·Rb2SO4·2H2O and Li2SO4·Rb2SO4) and the single salt Li2SO4·H2O all decrease, while that of Rb2SO4 increases when the temperature drops. Also, it can be seen from the phase diagram of the ternary system Li+,Cs+//SO4 2––H2O at 273.2 and 298.2 K that the crystallization regions of the double salt 3Li2SO4·Cs2SO4·2H2O and the single salt Cs2SO4 increase, while those of the double salt Li2SO4·Cs2SO4 and the single salt Li2SO4·H2O decrease as the temperature drops.

The phase equilibria of the quaternary system Li + , Rb + , Cs + //SO 4 2− -H 2 O at T = 273.2 K was investigated by the isothermal dissolution method. The solubility and density of the system were measured and the related phase diagram, water content diagram, and density vs composition diagram were plotted. The solid phase of the quaternary invariant point was identified by the Xray diffraction method and the solid solution morphology was analyzed by scanning electron microscopy. Results show that the stable phase diagram consists of 6 invariant points, 13 uninvariant curves, and 8 crystallization regions (corresponding to single salts Li 2 SO 4 •H 2 O, Rb 2 SO 4 , and Cs 2 SO 4 ; double salts 3Li 2 SO 4 •Rb 2 SO 4 •2H 2 O, 3Li 2 SO 4 •Cs 2 SO 4 •2H 2 O, Li 2 SO 4 •Rb 2 SO 4 , and Li 2 SO 4 • Cs 2 SO 4 ; and solid solution [(Rb, Cs) 2 SO 4 ]). Also, the crystallization region of double salt 3Li 2 SO 4 •Rb 2 SO 4 •2H 2 O is the largest, which means that it is easiest to precipitate from this system. Meanwhile, rubidium and cesium easily form a solid solution in the sulfate system, which increases the difficulty of separating the two elements. Comparing the stable phase diagram of the ternary subsystems at T = 273.2 K and T = 298.2 K, it is found that the crystallization regions of Rb 2 SO 4 , Cs 2 SO 4 , [(Rb, Cs) 2 SO 4 ], and 3Li 2 SO 4 •Cs 2 SO 4 •2H 2 O increase with the decrease of temperature, indicating that cooling is conducive to the crystallization of Rb 2 SO 4 , Cs 2 SO 4 , [(Rb, Cs) 2 SO 4 ], and 3Li 2 SO 4 •Cs 2 SO 4 •2H 2 O.