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The study on shale gas transport mechanisms plays an important role in shale gas production simulation. The majority of previous works neglected the body gas diffusion mechanism, and the multiple effects of stress sensitivity and multi-component of gas mixture system. In this paper, first, a model is built considering the multiple transport mechanisms of continuum flow, slippage flow, body gas diffusion and Knudsen diffusion. Then, the multiple effects of stress sensitivity and multi-component of gas mixture system are coupled into the model. Results show that: (a). For the body gas flow, both of the two weighted coefficients for items of body gas diffusion and slippage flow should be equal to one. And the ratio of one to Knudsen number is belong to the equation of body gas diffusion. (b). For a nanoscale pore of shale, the contribution of body gas diffusion on total mass flux cannot be neglected. The conductivities of continuum flow, slippage flow, modified slippage flow, Knudsen diffusion and weighted average flow decrease with decreasing of pressure due to shrinkage of nanopore radii and decrease in molecular concentration. (c). The decreasing of effective radii leads to the increase of the value of Knudsen number. The dominant transport mechanism is converting from modified slippage flow to Knudsen diffusion when the increase of stress sensitivity. (d). For methane confined in nanopores with extremely small effective transport radii, the injection of CO 2 can increase the mobility of methane. After a period of CO 2 injection, the methane molecules stored in nanopores can be flooded to fractures and then produced to the ground. • Multiple transport mechanisms, including body gas diffusion, are considered. • Multiple effect of stress sensitivity and multi-component are considered. • The injection of CO 2 can increase the mobility of methane confined in nanopores. [ABSTRACT FROM AUTHOR]

Abstract The modeling of shale gas transport through nanopores is the basis for shale gas production simulation. The real shale gas always consists of a series of gases, including ethane, propane and hydrogen sulfide etc. Previous models neglected the multi-component effect on the shale gas transport mechanisms. In this paper, a novel model is presented for simulating the real gas mixture transport through nanopores of shale formation. Firstly, a model is presented for ideal shale gas transport through nanopores considering the multi-component effect, then, the real gas effect is coupled into the model. Simulation results show that: (a) When it is under low pressure level condition, the conductivities of slippage flow and Knudsen diffusion increase with decreasing methane fraction. (b) When it is under medium pressure level condition, the conductivities of slippage flow and Knudsen diffusion increase with decreasing methane fraction. (c) Under high pressure condition, the conductivities of different flow patterns increase with decreasing methane fraction. Highlights • A novel model is proposed for real gas mixture transport through nanopores. • Both of the multi-component and real gas effects are considered. • The conductivity of real gas mixture increase with decreasing of methane content. [ABSTRACT FROM AUTHOR]

It is crucial to precisely estimate the water transport behaviors in shale formation. However, the present study on this subject is quite limited. A comprehensive literature review is conducted and some improvements are proposed. In this paper, an improved model is proposed to investigate the flow of water in nanopores of shale formation. First, a quadratic equation is proposed to build the relationship between water viscosity and contact angle. Then, the effect of critical thickness on water transport behaviors is discussed. Results show that: (a) the flow enhancement is smaller than 1 when the contact angle is smaller than 100° due to energy barrier induced by strong hydrophilicity of the nanopore wall; (b) the flow enhancement becomes infinite when the contact angle is approaching 180°; and (c) the flow enhancement increases with decreasing of critical thickness, especially for hydrophilic nanopores (the contact angle is smaller than 120°) and nanopores with a relatively small diameter (smaller than 50 nm). [ABSTRACT FROM AUTHOR]

Huge amount of works was done on modeling of gas transport in nanopores (both organic and inorganic) of shale formation. However, the study on oil transport behaviors is quite limited. Based on the study on water transport in carbon nanotubes, an analytical model is developed for oil transport in nanopores of shale formation. The new model takes the effect of oil-wall interaction on the oil viscosity in the adsorption region into consideration. Results show that: (1) the oil-wall interaction on oil viscosity in the adsorption region plays an important role in oil transport behaviors and cannot be neglected; (2) when the critical thickness is smaller than 1 nm, the volume flux increases slowly with increasing contact angle; (3) when the critical thickness increases to 2 nm, the volume flux increases rapidly to infinity when the contact angle is larger than 140°. [ABSTRACT FROM AUTHOR]

Abstract Shale oil reserves are becoming more important with the development of oil & gas industry. However, the transport mechanisms of oil in nanopores of kerogen remain a mystery. The understanding of the multiple transport mechanisms of oil in nanopores is crucial in the successful development of shale oil reservoirs. In this paper, a new model for flow enhancement of oil transport in nanopores of kerogen is proposed. Both boundary slip and physical adsorption are taken into consideration in the analytical model. Based on the previous experimental and theoretical studies, the model is validated. Results show that: (a) Covering the Hagen–Poiseuille flow, specific oil flow and the water flow, the new model is more universal in practice; (b) When the radius of the nanotube is equal to 1 nm, the value of slip factor is between 24081 and 48161 (the corresponding correction factor is between 0.7 and 1.4); (c) the flow enhancement is negligible when the radius is larger than 10 nm under various values of correction factor conditions. Besides, the flow enhancement increases with the increasing of the correction factor; (d) when the correction factor is small, the section of the curve higher than zero is characterized with short and low; (e) when the correction factor is smaller than 0.007, the normalized velocity increases slowly with increasing of the correction factor. When the correction factor is higher than 0.07, the normalized velocity increases rapidly when the transport length in nanopores is increased from 10 nm to 200 nm. Highlights • A model is proposed for oil trasport in nanopores of kerogen. • Boundary slip and physical adsorption is taken into consideration. • The relationship between water flow and oil flow in nanopores is revealed. • The new model is more universal in practice. [ABSTRACT FROM AUTHOR]