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Characteristics of sorption and distribution of water in nanoporous shale are topics of great interest to evaluate unconventional reservoirs. Also, a study of surface force of water/solid interaction at nanoscale is significant for understanding the storage of initial water and the fate of residual treatment liquid in shale systems. In this work, the thickness and stability of water film were investigated by vapor sorption experiments on clay and shale samples. Meanwhile, an approach based on surface forces (disjoining pressure), which resulted in the instability of adsorbed film transition into condensed bulk liquid, was developed to describe molecule/pore wall interactions. Our experimental results directly demonstrated the occurrence of capillary condensation in hydrophilic clay minerals; however, water would not entirely fill in shale nanopores even under high-moisture conditions. This remarkable finding is mainly due to the inaccessibility of water molecules to micropores of hydrophobic organic matter. In addition, the water distribution characteristics are also significantly influenced by pore scale. Under a moist condition with certain relative humidity (e.g., RH = 0.98), the water distributed in hydrophilic inorganic pores with different sizes was mainly classified as (i) capillary water in small pores (e.g., <6–7 nm) and (ii) water film in large pores (e.g., >6–7 nm). In contrast, the surface repulsion prevents water condensing and likely results in a monolayer water film sorption in hydrophobic organic pores (e.g., θ = 100°). Therefore, in an actual shale system with initial moisture content, the inorganic microporosity totally blocked by water might be incapable of gas transport or storage, while the hydrophobic organic pores mainly provide effective space for gas accumulation.

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The transport mechanism of gas moving through matrix pores is the bottleneck of conquering the difficulties in shale gas development. The matrix pores can be divided into organic and inorganic matrix pores. The transport mechanism of shale gas in organic and inorganic matrix pores is different. However, the present gas transport model only focused on the gas transport in organic matrix pores, in addition, the impact of organic and inorganic mass ratio has been largely neglected by shale gas transport models in the literature, leading to an unclear recognition of shale gas production discipline and large derivation between prediction results by the present models and actual performance of shale gas wells. In this paper, both the pore size distribution and water distribution in shale matrix pores are investigated. Furthermore, a new diffusion-slippage-flow model in combination with the gas transport mechanism is proposed. Also, the organic content effect is considered and the range of Knudsen number is quantified. Finally, a gas production model based on this gas transport mechanism is derived and employed to reveal the discipline of shale gas production. The preliminary results illustrate that Knudsen diffusion is not suitable for shale gas reservoirs. This is because Knudsen number is generally less than 10, especially for such shale gas reservoirs with higher initial reservoir pressure. Gas moving through shale matrix pores to fractures is mainly divided into two forms: in organic matrix pores, both slip effect and transition diffusion mechanism are dominant; in inorganic matrix pores, the gas-water two-phase flow controls the gas transport mechanism because of the presence of water in these pores. The efforts of this work will provide a more accurate technique for forecasting shale gas production, and also give some insights into scientific evidence to the rational development of shale gas reservoirs.

Previous attempts to characterize the gas transport through inorganic nanopores were not fully successful. The presence of an adsorption water film within nanopores is generally overlooked. Moreover, the compound influences of moisture content and confinement effect on critical properties of the gas phase have not been considered before. With the intent of overcoming these deficiencies, a fully coupled analytical model has been developed, in which complex bulk-gas transport mechanisms, moisture content, confinement effect, and various cross-section shapes of nanopores are incorporated. Results show that the confinement effect will significantly enhance the apparent gas permeability when the pore radius is smaller than 5 nm, and the real-gas effect can achieve an average increase of 4.38% when the pore radius falls in the range 1−2 nm. The stress dependence will greatly decrease the apparent gas permeability and the corresponding degree for slitlike inorganic nanopores will slightly increase with the increasing aspect ratio.

PREdiction of NOn-LINear soil behavior (PRENOLIN) is an international benchmark aiming to test multiple numerical simulation codes that are capable of predicting nonlinear seismic site response with various constitutive models. One of the objectives of this project is the assessment of the uncertainties associated with nonlinear simulation of 1D site effects. A first verification phase (i.e., comparison between numerical codes on simple idealistic cases) will be followed by a validation phase, comparing the predictions of such numerical estimations with actual strongmotion recordings obtained at well-known sites. The benchmark presently involves 21 teams and 23 different computational codes.We present here the main results of the verification phase dealing with simple cases. Three different idealized soil profiles were tested over a wide range of shear strains with different input motions and different boundary conditions at the sediment/bedrock interface. A first iteration focusing on the elastic and viscoelastic cases was proved to be useful to ensure a common understanding and to identify numerical issues before pursuing the nonlinear modeling. Besides minor mistakes in the implementation of input parameters and output units, the initial discrepancies between the numerical results can be attributed to (1) different understanding of the expression "input motion" in different communities, and (2) different implementations of material damping and possible numerical energy dissipation. The second round of computations thus allowed a convergence of all teams to the Haskell-Thomson analytical solution in elastic and viscoelastic cases. For nonlinear computations, we investigate the epistemic uncertainties related only to wave propagation modeling using different nonlinear constitutive models. Such epistemic uncertainties are shown to increase with the strain level and to reach values around 0.2 (log 10 scale) for a peak ground acceleration of 5 m=s 2 at the base of the soil column, which may be reduced by almost 50% when the various constitutive models used the same shear strength and damping implementation.

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