Simulation of real gas mixture transport through aqueous nanopores during the depressurization process considering stress sensitivity

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 CO2 can increase the mobility of methane. After a period of CO2 injection, the methane molecules stored in nanopores can be flooded to fractures and then produced to the ground.