Implication of Water-Rock Interaction for Enhancing Shale Gas Production

Horizontal well drilling and multi-stage hydraulic fracturing technologies are at the root of commercial shale gas development and exploitation. During these processes, typically, a large amount of working fluid enters the formation, resulting in widespread water-rock interaction. Deeply understanding such effects is required to optimize the production system. In this study, the mechanisms of water-rock interaction and the associated responses of shale fabric are systematically reviewed for working fluids such as neutral fluids, acid fluids, alkali fluids and oxidative fluids. It is shown that shale is generally rich in water-sensitive components such as clay minerals, acidsensitive components (like carbonate minerals), alkali-sensitive components (like quartz), oxidative-sensitive components (like organic matter and pyrite), which easily lead to change of rock fabric and mechanical properties owing to water-rock interaction. According to the results, oxidizing acid fluids and oxidizing fracturing fluids should be used to enhance shale gas recovery. This study also indicates that an aspect playing an important role in increasing cumulative gas production is the optimization of the maximum shut-in time based on the change point of the wellhead pressure drop rate. Another important influential factor to be considered is the control of the wellhead pressure considering the stress sensitivity and creep characteristics of the fracture network.