Fracture Initiation and Morphology of Tight Sandstone by Liquid Nitrogen Fracturing

Hydraulic fracturing is a commonly used stimulation method in developing tight sandstone reservoirs. Creation of complex fracture networks to enlarge stimulated reservoir volume plays an increasingly significant role. However, planar fracture patterns are generally generated by water-based fluid fracturing. Besides, the water consumption and environmental burden of water-based fluid fracturing cannot be ignored. To solve the above issues, we investigated the liquid nitrogen (LN2) fracturing performance on tight sandstone with respect to breakdown pressures and fracture network patterns, and also compared the results with water fracturing in this paper. A comprehensive quantitative analysis was made for the fracture network induced by LN2 fracturing so as to enhance understandings of the fracturing mechanisms. Based on laboratory fracturing experiments and computed tomography (CT) scanning, we find that the breakdown pressure of LN2 fracturing can be reduced by 12.4–51.5% compared with water fracturing. Besides, LN2 fracturing can lead to volumetric fracturing patterns rather than planar fractures compared with water fracturing. The average tortuosity of LN2 fracturing was increased by 5.9% compared with water fracturing. Furthermore, the major fracture tends to traverse the bedding plane with an angle of around 45–80 degrees under lower horizontal stress difference. This study, for the first time, shows potential benefits of high-pressure LN2 fracturing in tight sandstone under triaxial in situ stress. It is expected to provide a viable alternative for the efficient development of tight sandstone reservoirs in a clean and waterless way.