Pore-Scale Water Vapor Condensation Behaviors in Shales: An Experimental Study

Water Adsorption and Its Pore Structure Dependence in Shale Gas Reservoirs

Investigating the occurrence characteristics of water molecules in shale is of great resource, economic, and environmental significance. In this work, the adsorption behavior of water vapor on Longmaxi shale samples is tested, and several isothermal adsorption models are employed to fit the experimental data and primary and secondary adsorption processes. Furthermore, the influence of organic matter content, mineralogical composition, and pore structure on the adsorption process is discussed, and their special combination relationship is revealed correspondingly. The results indicate that the Dent model is suitable for the experimental data with excellent goodness of fit, and the Langmuir and Freundlich models are suitable for the primary and secondary adsorption processes, respectively. The adsorption of water vapor is controlled by the pore volume and specific surface area (SSA) of shale. Mesopore structure parameters mostly determine the water adsorption amount. Massive micropores developed in organic matter with a huge SSA contribute strongly to the primary adsorption process. In general, the combination of organic matter and clay minerals controls the pore structure of shale, which further controls the primary and secondary adsorption processes of water vapor. These findings contribute to a better understanding of water adsorption in different adsorption carriers and in microscopic pores of different sizes occurring in shale gas reservoirs.

Moisture Retention and Multi-mechanistic Transport Behavior in Nanoporous Coal

Coal-water interactions induced by water retention in coals control the performance of coalbed methane reservoirs and coal utilizations. Experimental measurements on Illinois coal samples using X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, low-temperature N₂ adsorption, low-pressure CO₂ adsorption, and dynamic water vapor sorption were carried out. A mechanism-based isothermal model of water vapor sorption was proposed to estimate the water adsorption capacity at varied relative humidity, which implicitly considered both monolayer and multilayer adsorptions and capillary condensation. The analytical models for quantifying the stage-based diffusion coefficients as well as the apparent diffusion coefficients at different relative humidities were proposed and well validated. The contributions of different diffusion regimes to the total mass flow were discussed. At the first stage, both free water vapor diffusion and surface diffusion of adsorbed water molecules contribute to the total mass flow whereas the apparent diffusion at this stage is dominated by latter flow regime; during the second stage, the contribution of free water vapor flow to the apparent flow can be neglected and the mass transfer at this stage is still dominated by the surface diffusion flow; upon reaching the critical relative humidity, the flow in capillary condensation will dominate the total mass flow.

CENTAUR-The small- and wide-angle neutron scattering diffractometer/spectrometer for the Second Target Station of the Spallation Neutron Source

CENTAUR has been selected as one of the eight initial instruments to be built at the Second Target Station (STS) of the Spallation Neutron Source at Oak Ridge National Laboratory. It is a small-angle neutron scattering (SANS) and wide-angle neutron scattering (WANS) instrument with diffraction and spectroscopic capabilities. This instrument will maximally leverage the high brightness of the STS source, the state-of-the-art neutron optics, and a suite of detectors to deliver unprecedented capabilities that enable measurements over a wide range of length scales with excellent resolution, measurements on smaller samples, and time-resolved investigations of evolving structures. Notably, the simultaneous WANS and diffraction capability will be unique among neutron scattering instruments in the United States. This instrument will provide much needed capabilities for soft matter and polymer sciences, geology, biology, quantum condensed matter, and other materials sciences that need in situ and operando experiments for kinetic and/or out-of-equilibrium studies. Beam polarization and a high-resolution chopper will enable detailed structural and dynamical investigations of magnetic and quantum materials. CENTAUR's excellent resolution makes it ideal for low-angle diffraction studies of highly ordered large-scale structures, such as skyrmions, shear-induced ordering in colloids, and biomembranes. Additionally, the spectroscopic mode of this instrument extends to lower momentum transfers than are currently possible with existing spectrometers, thereby providing a unique capability for inelastic SANS studies.

In Situ Small-Angle Neutron Scattering Analysis of Water Evaporation from Porous Exhaust-Gas-Catalyst Supports

Porous media as catalyst supports are key to developing automotive exhaust purification systems. In particular, the water content of these porous media is attracting research attention because catalyst supports containing condensed water vapor at the early stage of cold start require a longer warm-up period. In this regard, water isotherms and evaporation in porous Al₂O₃ were investigated in this study using in situ small-angle neutron scattering (SANS) experiments. Unlike conventional evaluation methods, such as weighing and X-ray tomography, SANS distinguishes water in the primary and secondary pores using a contrast-matching method. Time-resolved measurements showed that water started to evaporate from the secondary pores in tens of seconds and subsequently from the primary pores in a hundred seconds. Exhaustive experiments conducted using nine alumina-based samples revealed that the drying rate depended on the secondary pore size of the porous Al₂O₃. The proposed approach can enable the evaluation of controlling factors to additionally optimize the performance of automotive exhaust gas catalysts, especially during cold start.