The effect of the density difference between supercritical CO_(2) and supercritical CH_(4) on their adsorption capacities: An experimental study on anthracite in the Qinshui Basin

Deep unmineable coals are considered as economic and effective geological media for CO_(2) storage and CO_(2) enhanced coalbed methane(CO_(2)-ECBM) recovery is the key technology to realize CO_(2) geological sequestration in coals. Anthracite samples were collected from the Qinshui Basin and subjected to mercury intrusion porosimetry, low-pressure CO_(2) adsorption, and high-pressure CH_(4)/CO_(2) isothermal adsorption experiments. The average number of layers of adsorbed molecules(ANLAM) and the CH_(4)/CO_(2) absolute adsorption amounts and their ratio at experimental temperatures and pressures were calculated. Based on a comparison of the density of supercritical CO_(2) and supercritical CH_(4), it is proposed that the higher adsorption capacity of supercritical CO_(2) over supercritical CH_(4) is the result of their density differences at the same temperature. Lastly, the optimal depth for CO_(2)-ECBM in the Qinshui Basin is recommended. The results show that:(1) the adsorption capacity and the ANLAM of CO_(2) are about twice that of CH_(4) on SH-3 anthracite. The effect of pressure on the CO_(2)/CH_(4) absolute adsorption ratio decreases with the increase of pressure and tends to be consistent.(2) A parameter(the density ratio between gas free and adsorbed phase(DRFA)) is proposed to assess the absolute adsorption amount according to the supercritical CO_(2)/CH_(4) attributes. The DRFA of CO_(2) and CH_(4) both show a highly positive correlation with their absolute adsorption amounts, and therefore, the higher DRFA of CO_(2) is the significant cause of its higher adsorption capacity over CH_(4) under the same temperature and pressure.(3) CO_(2) adsorption on coal shows micropore filling with multilayer adsorption in the macro-mesopore, while methane exhibits monolayer surface coverage.(4) Based on the ideal CO_(2)/CH_(4) competitive adsorption ratio, CO_(2) storage capacity, and permeability variation with depth, it is recommended that the optimal depth for CO_(2)-ECBM in the Qinshui Basin ranges from 1000 m to 1500 m.

Non-resistivity-based saturation evaluation methods in shale gas reservoirs

Free gas saturation is a key parameter for calculating shale gas reserves.The complex conductivity mechanism of shale reservoirs restricts the application of Archie's formula and its extended form for the evaluation of free gas saturation.Instead,a number of non-resistivity-based saturation evaluation methods suitable for shale gas reservoirs have been established,including core calibration(TOC method,clay content method),gas porosity cutoff,excavation effect and four-pore modeling.These methods,together with adsorbed phase porosity correction,are used to calculate the free gas saturation.These methods are applied to shale reservoirs of the Upper Ordovician Wufeng Formation and the Lower Silurian Longmaxi Formation in the Sichuan Basin,southwestern China to test their applicability and accuracy.The results,when compared with measured data from core samples,show that the TOC-based core calibration is more accurate in evaluating free gas saturation in the entire shale gas interval,which is of great significance to the calculation of shale gas reserves.

Synthesis and modification of spherical/hollow metal-organic frameworks for efficient extraction of sulfonamides in aqueous environments

In this study,two novel spherical/hollow metal-organic frameworks were successfully synthesized,and further modified by a mild non-covalent modification strategy with dopamine and 1,4-benzenedithiol(BDT)as polymeric monomers to obtain pB DT@PDA-Ni-MOF and p BDT@PDA-Ni/Co-MOF,respectively.The results showed that the above MOFs possessed extremely fast adsorption rates and ideal adsorption capacities for sulfonamides(SAs)and the modified MOFs exhibited enhanced adsorption capacities for SAs owing to a large number of additional functional groups.Then,benefit of their regular morphology and size,a facile syringe-assisted dispersive solid phase extraction(S-DSPE)method was developed for efficient detection of SAs,which will provide a powerful tool for monitoring trace level of SAs in aqueous environment.