Experimental Study on Initiation and Propagation of Multi-cluster Fractures in Tight Sandstone

Horizontal well segmented multi cluster fracturing technology is commonly used in tight sandstone reservoirs to increase the volume of transformation. However, due to the stress shadow effect between cracks, it is necessary to optimize fracturing parameters to avoid the occurrence of ineffective perforation clusters. To understand the initiation and propagation of multi cluster fractures in tight sandstone, multi cluster fracturing experiments were conducted based on a large-scale true triaxial multi cluster hydraulic fracturing physical simulation test system. A comprehensive analysis of the factors affecting the initiation and propagation of multi cluster cracks reveals that as the spacing between clusters increases, the stress interference between cracks gradually weakens, and the fracture pressure of cracks is reduced, the number of cracks opened increases, cracks tend to expand laterally, and the area of crack propagation increases. Under low displacement, the crack propagation of each cluster is relatively balanced. After increasing the displacement to 30 mL/min, the subsequent cluster initiation and propagation are easy to communicate with neighboring clusters near the wellbore and cannot form independent initiation cracks. As the viscosity of the fracturing fluid increases, the net pressure inside the crack increases, and the fracture pressure of each cluster of fractures increases. The stress shadow between cracks is more pronounced, and subsequent cracks tend to expand longitudinally, reducing the range of crack propagation. The research results provide guidance for understanding the propagation of multiple clusters of fractures in tight sand-stone.