Abstract:

The production of shale gas is a complex and multiscale process that spans a variety of scales and goes through a variety of mass transfer mode. The stress sensitivity of each path has an important influence on the mass transfer of shale gas. Especially when a large amount of fracturing fluid retained in shale reservoir, water-rock interactions will inevitably affect shale stress sensitivity. Taking Longmaxi Formation shale in the southeast area of Chongqing as the research object, stress sensitivity experiments of shale before and after water-rock interactions are carried out, which characterize the change characteristics of fracture surface properties before and after stress sensitivity experiments, and analyze the action mechanisms of water-rock interaction on the fracture surface. It is found that, the stress sensitivity of fractured shale containing proppants is weak, and the existence of proppants reduce the stress sensitivity of shale. The wider the crack width is, the stronger the stress sensitivity will be. The stress sensitivity of shale after water-rock interaction is from high to low in the following order: alkali sensitivity>salt sensitivity with reduced salinity>water sensitivity. In the process of salt sensitivity and water sensitivity with reduced salinity, clay minerals hydrate and expand, and particles migrate, resulting in smoother fracture surfaces. However, the alkali-sensitive process, the fluid not only hydrates with the fracture surface, but also causes the alkali erosion, which strengthens the shale stress sensitivity. The stress sensitivity of fracture shale containing proppant is weakened, and the embedding and crushing of propelling agent is the main cause of stress sensitivity. The optimal selection and reasonable laying of propelling agent is the key to reduce the stress sensitivity.

Key words: pore structure, nature of fracture surface, water-rock interaction, stress sensitivity, shale