Slickwater residues in shale multi-scale pore structures

Slickwater fracturing can significantly enhance shale gas production. However, following fracturing operations, a portion of the slickwater will inevitably remain in the reservoir, thereby altering the pore structure of the shale reservoir and impacting shale gas output. By slickwater, we mean a fluid mixture composed of water, friction reducers, and various additives, typically used in hydraulic fracturing to facilitate the creation of fractures in the reservoir. This study focuses on investigating the influence of slickwater on the multi-scale pore structure of shale reservoirs through various experimental techniques, including high-pressure mercury intrusion, low-temperature nitrogen adsorption, and low-temperature carbon dioxide adsorption experiments. The findings reveal that under pressure, slickwater infiltrates shale pores, with higher concentrations accumulating in macropores and mesopores. Additionally, increased pressure or slickwater concentration exacerbates damage to the pore structure. Fractal analysis further demonstrates that slickwater obstructs the pore structure and diminishes the complexity of the pore network, while adhering to rough surfaces to reduce shale surface roughness. Consequently, slickwater trapped in shale obstructs shale gas diffusion and thus reduces shale gas production.