Shale Gas Slippage Dynamic Characteristics in Nano-Scale Pores

Abstract

There are two important features on microstructure of shale.Firstly, Shale rocks are composed of rather fine grained particles, and their pores are very small, at the scale of nanometers.Gas slippage is complicate because its pore diameter is typically less than 10 nm. Secondly, a large amount of shale gas are absorbed in shale the same as coal-bed methane. Adsorbed gas desorption changes the structure. Permeability of shale is dynamic because of Nano-pore structure and desorption of absorbed gas during production. Shale gas slippage dynamic characteristics is researched in Nano-scale pores,based on capillary bundle medle and solid deformation theory. Mathematical model results show that pore diameter and pressure have important effect on permeability. Permeability increases firstly then reduces because of pressure drawdown when pore diameter is less than 10 nm. The lager pore diameter is, the lower pressure point of permeability Inflection and the faster permeability decline rate is. Gas molecular diffusion has less influence on flow when pore diameter is lager than 20 nm and when pressure is lager than 10 MPa. This model can be used for shale gas evaluation and production optimization.