Characterization of Gas Flow Ability and Contribution of Diffusion to Total Mass Flux in the Shale

Rui Wang,Xiaojuan Liu,Jian Yan,Xinmin Wu,Ningsheng Zhang

doi:10.19026/rjaset.6.3887

Abstract

The aim of this study is to search a parameter which characterize the flow ability and analyze the contribution of diffusion to total mass flux of gas flow in pore of shale whose size is as low as nanoscale. The diffusion coefficient of the flow region which was determined by Kundsen number was taken as the diffusion coefficient of system, then it was substituted into the equation which describes gas diffusive and flow in nano- porous media, the apparent permeability and mass flux were calculated and the impacts of the pore radius and gas type were analyzed finally. The result showed that the diffusion of gas in shale was mainly in the transition diffusion or Fick diffusion region; The ratio of the apparent permeability of considering the diffusion and slippage effect to Darcy permeability and the ratio of diffusion mass flux to total mass flux increased with the decreasing of the pore radius; The diffusion ability of the methane was stronger than ethane's. The present study implied that the calculated results of the diffusion coefficient which considers three kind of diffusion was less than that one considering Knudsen diffusion only; Considering diffusion and slippage effect, the apparent permeability of nanoscale pore of shale was 10 -6 μm 2 level, not 10 -9 μm 2 level in general temperature and pressure of shale reservoir.

Highlights

The minimum diameter of pores in shale reservoir is nanoscale, which is close to the diameter of the methane molecule (Javadpour et al, 2007; Javadpour, 2009)
It was found that the gas flow in shale reservoirs is in slippage and transition flow region by calculating Kundsen number, so considering the slippage and diffusion effects were needed (Sondergeld et al, 2010b)
The parameters which involved in the calculations and their range of value: The system of productive shale gas included four porous Medias, inorganic matter, organic matter, natural fractures and artificial fractures

Summary

Introduction

The minimum diameter of pores in shale reservoir is nanoscale, which is close to the diameter of the methane molecule (Javadpour et al, 2007; Javadpour, 2009). It was found that the gas flow in shale reservoirs is in slippage and transition flow region by calculating Kundsen number, so considering the slippage and diffusion effects were needed (Sondergeld et al, 2010b). Roy et al (2003) established a mathematical model which describes gas diffuse in nanopores, it was based on gas mass transfer experiment that Ar, N2 and O2 flow in alumina filtration membrane whose aperture is 200 nm. Javadpour (2009) and Roy et al (2003) model to describe gas diffuse and flow in shale (Javadpour et al, 2007). Sigal and Qin (2008) analyzed the importance of self-diffusion in process of gas mass transfer in shale by introducing an effective transfer coefficient. Javadpour (2009) established an equation which considers Kundsen diffusion and slipping and introduced a concept of apparent permeability (Javadpour, 2009). Javadpour (2009) established an equation which considers Kundsen diffusion and slipping and introduced a concept of apparent permeability (Javadpour, 2009). Sigal and Qin (2008) built a finite difference model about that

Objectives

Methods

Results