Study On Mechanism And Model Of Shale Gas Flow In Micro-nano Pores

As a new energy resource, shale gas is becoming more and more attractive around the world. But the low porosity, low permeability and high adsorption impact the shale gas reservoir a lot, the classical percolation theory don’t fit this situation well. So a new theory which consider the slip effect and adsorption effect on the permeability of shale gas in micro-nano scale is significant. It has important theoretical and practical significance to the shale gas percolation mechanism and shale gas development.Based on the literature research at home and abroad, we analyzed the occurrence and percolation mechanism of shale gas. Introducing the Langmuir isothermal adsorption model into the shale gas percolation mechanism to describe the gas adsorption on pore wall in Micro-nano scale, and discuss the impact of adsorption on shale gas permeability. Introducing the gas molecular diffusion theory into shale gas percolation mechanism, analyze the impact of diffusion occurred in the adsorbed layer of pore wall on shale gas permeability. Build a modified shale gas permeability which consider both adsorption and diffusion. Based on the permeability model, build a shale gas percolation model that considered both adsorption and diffusion. Then obtain the numerical solution using the finite difference method. By the numerical simulation model of one-dimensional core, more in-depth shale gas percolation mechanism are discussed. Get the following conclusion:(1)Build the permeability model which consider the adsorption effect, and compare this model to the Klinkenberg model and Beskok-Karniadakis model, the adsorption considered model take the inter effect of the gas molecular into account, so the gas flow in shale gas reservoir is described more comprehensive and this model is more adaptable. adsorbed gas inthe shale pores is the key factor influencing the apparent permeability of shale gas.(2)The adsorption effect and diffusion effect is the key factor influencing the shale gas apparent permeability. In the micro-nano pores, the larger the pore size is, the smaller the effect of adsorption on permeability is. When reach micron scale, the influence of adsorption can be ignored. While the absorbed layer on the pore wall also has the diffusion effect, which can impact the apparent permeability a bit under micro-nano scale. When the pore size reach micron scale, the diffusion effect can be ignored.(3)Build a mathematical model of shale gas seepage flow and discuss the effect of different parameters. The adsorption amount not only determine the medium permeability but also decide the reserves of shale gas, it has a significant effect on the shale gas production. The bottom flowing pressure not only determines the range of gas pressure reduction, but also determines the desorption amount of shale gas, it has a significant effect on the shale gas production. The pore scale affects the shale reservoir apparent permeability, and have an obvious effect on gas production rate of shale gas.