Experimental Research on Fracture Propagation of Multi-Well Pad Fracturing Based on Distributed Strain Sensing

The conventional fracturing mode faces some problems, such as the low complexity of artificial fracture and rapid production decline after fracturing. The multi-well pad fracturing is a crucial technology for effectively developing unconventional reservoirs such as shale and tight sandstone. However, serious interaction exists between fractures when multiple horizontal wells are fractured. Therefore, it is crucial to determine the fracture propagation mechanism in the multi-well pad fracturing. Additionally, the propagation of complex fractures makes it difficult for traditional fracturing monitoring and diagnosis methods to evaluate the hydraulic fracturing operation promptly and effectively. The distributed strain sensing (DSS) technology can evaluate the fracturing effect in real time, which is a hot monitoring technology with an extensive application prospect in horizontal well fracturing. This study combined the DSS with a large-scale (400 mm × 400 mm × 400 mm) true triaxial fracturing device to carry out a three horizontal well preliminary fracturing experiment for the heterogeneous sandstone. Results show that the hydraulic fracture (HF) mainly forms the transverse fracture perpendicular to the direction of the minimum horizontal principal stress (σh). The HF near the well usually crosses the gravel, while the HF tends to bypass the gravel or even be inhibited by the gravel far away from the well. The waterfall diagram of the optic fiber strain can monitor the HF propagation dynamics in real time. Once the HF hits the fiber, the apparent tensile strain can be generated. If the HF deviates from the σh direction, the tension strain will spread to both sides. Under the stress shadow, the later fracturing fracture is prone to extend outside the stress shadow region of the earlier fracturing fracture. The preferential fracturing of intermediate fracture is conducive to exploiting the reservoir resource between the two sides of fractures, so the middle-near-far fracturing method is superior to the far-near-middle fracturing method. This study can provide the reference and guidance for the design of multi-well pad fracturing in oil fields.