Temporal scale analysis of shale gas dynamic coupling flow

Abstract

Shale gas is one of the world’s strategic energy reserves. The microscopic pores and the fracture structure of the shale rocks play an important role in shale gas flow. An effective reservoir simulation must account for the heterogeneity and anisotropy of the microscopic pore structure as well as the dynamics between the gas flow and the gas diffusion processes. In this study, the time lag effect, the dynamic coupling of gas flow and diffusion as well as the heterogeneity and anisotropy of the pores are taken into account in order to properly model shale gas production on a large scale. The effect of these variables on the temporal scale analysis of the wellbore gas pressure is presented, as the reliable estimate of wellbore pressure would allow better prediction of the duration of well shut-in periods. Gas production under the intermittent operation scheme at different temporal scales is discussed. The results showed that the well startup is composed of five stages, while the well shut-in is composed of only three stages. The crossflow stage is prolonged by the dynamic coupling. The heterogeneity, anisotropy and dynamic coupling phenomena are accurately presented on the temporal scale diagram. Moreover, the impact of time lag on the gas pressure is better captured by the dynamic coupling between the gas flow and the gas diffusion. The proposed model better simulates actual shale reservoirs and, hence, would be helpful in selecting suitable production rates.