Hydraulic Fracturing Fracture Propagation in Tight Sandstone Reservoir

The tight sandstone reservoir of Shaximiao Formation of Middle Jurassic in Qiulin block of central Sichuan Basin, with a burial depth about 2200 to 2300 m, is characterized by undeveloped natural fractures. It is difficult to form complex fracture network during the implementation of traditional volume fracturing technology, affecting the benefit of tight sandstone gas development. A series of true triaxial hydraulic fracturing tests were conducted on the sandstone outcrop (dimensions: 300 mm × 300 mm × 300 mm), collected from this block, to investigate the initiation and propagation law of hydraulic fracture in tight sandstone reservoir under different conditions. Experimental results indicate that the peak value disturbance and increasing stress shadow in the back section of the pump pressure curve of staged multi-cluster fracturing in horizontal wells of sandstone reservoir will dominate the fracture morphology. The small interval leads to the increase in dynamic hydrostatic pressure on the fracture wall and increase in the deflection angle and degree of multi-cluster fractures, and it is easy to form crosscut fractures. The symmetrical middle segment perforation cluster inhibits the initiation and expansion of fractures, and the fractures will extend perpendicular to the maximum horizontal in situ stress direction and gradually approach the fractures on both sides and finally stop expanding. High-viscosity fracturing fluid is easy to form high hydrostatic pressure in the perforated section, reducing the difficulty of fracture initiation. The angle between the borehole and the minimum horizontal in situ stress (σh) will affect the propagation direction of hydraulic fractures. When the angle is large, the propagation direction of fractures is easily affected by the natural weak surface and induced stress field, resulting in fracture diversion. This study has mastered the initiation and propagation mechanism of artificial hydraulic fractures in tight sandstone reservoir, established the optimization chart of fracturing parameters in sandstone reservoir, and has certain guiding significance for the establishment of on-site fine optimization fracturing scheme design.