Study on Flow Model and Flow Equation of Shale Gas Based on Micro Flow Mechanism

Abstract Shale flow has microscale effects, and the flow is more complex. In this paper, the flow model and flow equation which can be used in the analysis of shale gas flow is established,which is based on the single nanotube model and combined with pore throat test results of the shale core by high-pressure mercury injection, and calculated the contributions of seepage, diffusion, transition flow and free molecular flow to shale gas flow. The contributions of seepage and diffusion were over 95%, and seepage and diffusion were the main flow patterns. Then, a coupled flow model and the coupled flow equation of shale gas with seepage and diffusion were established, which proposed a calculation method of shale permeability and diffusion by relationship between flow pressure and shale gas flow rate, and finally shale gas flow experiments were carried out and analyzed. The results show that the shale gas flow model and the flow equation established in this paper can describe shale gas flow very well. The shale gas flow rate is composed of seepage flow rate and diffusion flow rate, and the seepage flow rate is proportional to the pseudo pressure difference and is proportional to the pressure square difference at low pressure. The diffusion flow rate is proportional to the difference in shale gas density and is proportional to the pressure difference at low pressure. With shale gas reservoir pressure drops, the proportion of diffusion flow increases. The research results enrich the understanding of shale gas flow; they also have certain reference significance to the development of shale gas reservoirs.