Perforation spacing optimization for multi-stage hydraulic fracturing in Xujiahe formation: a tight sandstone formation in Sichuan Basin of China

Tight reservoir is characterized with low porosity and ultra-low permeability. Horizontal well with multi-stage fracturing is the key technique to maximize stimulated reservoir volume and achieve commercial production. The spacing between perforations has a significant impact on well production. Perforation spacing is currently optimized from the aspects of reservoir simulation. The methods ignore the fact that fracture will generate induced stress field, which may significantly affect the geometry of subsequent fracture. Based on the displacement discontinuity method, this paper established a multi-fracture stress interference model which is able to simulate non-isometric half-length, unequal fracture spacing and arbitrary angle between fracture and wellbore. Data from a tight sandstone reservoir in Sichuan Basin of China are used to analyze the stress field changes and verify the model. The results show that the induced stress creates the maximum compressive stress on both sides of the fracture, and the maximum tensile stress at the fracture tip by stress concentration. The fracture will change the differential horizontal stress ratio in the surrounding area. Position where the differential horizontal stress ratio is lower than 0.3 will be the optimal site to create the complex fractures. Multi-stage fracturing with multiple perforation clusters in one stage is more favorable for complex fracture formation than single perforation cluster in each stage. Data from field verified the proposed perforation optimization method.