Multi-field Coupling Permeability Model in Shale Gas Reservoir

Abstract

Abstract In order to characterize the influence of diffusion effect, stress sensitivity, matrix shrinkage and adsorption layer on shale gas permeability, weighted coefficient is used to establishdiffusion permeability model by couple transition diffusion and Knudsen diffusion. And the effect of matrix shrink, stress sensitivity and adsorption layer are considered into shale gas permeability model. The shale gas permeability model is verified by permeability experiment result of shale core in Ordos basin and discussing the effect of each parameter. The results showed that: (1) When the weighted coefficient- Km, n and m is 7, 4 and 16 respectively, the proposed diffusion permeability highly agrees with Fick diffusion, transient diffusion and Knudsen diffusion, that can represent diffusion of the whole flow stage.(2) Under the conditions of low pressure and small pores, diffusion flow is the main control factors of shale gas transmission; and under the condition of high pressure and large pores, viscous flow mainly controlling shale gas transmission.(3) The influence of stress sensitivity and adsorption layer on shale gas permeability is bigger, and the influence of the matrix shrink can be ignored.(4) Adsorption layer have a significant impact on the shale gas permeability under the conditions of high pressure and small pores. The proposed shale gas permeability model can eliminate the deviation result from describing the shale gas diffusion only by using Knudsen diffusion model, and also can describe the shale gas transmission under a multi-physic field, and thus it is significantly enlighten the development of shale gas.