Impact of water saturation on gas permeability in shale: Experimental and modelling

Shale gas is becoming more important in clean energy supply. There is original water content in shale pores under reservoir condition. In addition, the introduction of water-based fracturing fluid during hydraulic fracturing process also changes the shale reservoir water saturation. Water saturation has a profound impact on the gas effective permeability and its anisotropy, thus on shale gas production. Previous experimental studies on gas effective permeability were mostly on dry samples. Due to the great difficulty in gas-water two-phase flow experiment, there are very few experiments to study the impact of shale water saturation on gas permeability. How water content affects gas effective permeability is not well understood. This work proposes an experimental method to investigate the effect of water saturation on stress-dependent gas permeability. Moreover, the experimental method and gas permeability results are compared between this work and literature. An integrated permeability model considering the impact of water saturation is proposed. It is found that the water content has significant impact on gas effective permeability and the impact is more significant for low permeability samples.

Automated summary

Water saturation has a significant impact on gas effective permeability in shale formations, especially for low permeability samples. The proposed experimental method and integrated permeability model provide new insights into studying the effect of water saturation on gas permeability.