Effect of Water Imbibition on Shale Permeability and Its Influence on Gas Production

Large volume water filtrates into the shale formation during multi-stage fracturing. The influence of water imbibition to shale permeability, which still needs further investigation, is crucial to gas production. This paper presents a series of experiments to investigate the shale permeability change during water imbibition in comparison to typical sandstone and volcanic samples using the pulse-decay permeability technique. The permeability greatly fluctuates with the water imbibed into the shale, which is far different from that of sandstone and volcanic rock. Factors such as water blocking, stres's sensitivity, and clay swelling are discussed. Five typical permeability changes are put forward, which are conducive to understand the effect of water imbibition on gas flow post- fracturing. The work indicates that the shale permeability enhancement by water imbibition may be one of the reasons of obtaining shale gas well productivity to increase by soaking after fracturing. The results and conclusions are fundamentally important to guide the industry practice, especially for the determination of the soaking time after fracturing in a shale gas reservoir.