Optimization of multiple hydraulic fracture initiation and propagation in deep tight reservoirs considering fracture macro/micro characteristics

In deep reservoirs, high pressure and horizontal stress difference lead to elevated breakdown pressure and reduced stimulation efficiency during multi-cluster hydraulic fracturing. To address these challenges, we carry out experimental studies to reveal the effects of fluid viscosity and flow rate, perforation cluster density, and flow control methods on the initiation and propagation of hydraulic fractures. The RA-AF method and SEM (Scanning Electron Microscope) + EDS (Energy Dispersive Spectrometer) + XRD (X-ray Diffraction) analyses were employed to evaluate the micro-fracture characteristics, including morphology, fracture types, and surface roughness. The results indicate that adjusting the fluid viscosity and flow rate is difficult to improve the initiation efficiency of perforating clusters, but the optimization effect on a single perforating cluster is significant. Low viscosity and flow rate promote the formation of multiple shear fractures around the perforation cluster, while high viscosity and flow rate will form a single through fracture. Dense perforation clusters induce multi-cluster fracture initiation, but also raise the peak pump pressure. Compared to multi-cluster synchronous injection, innovative intelligent injection methods (multi-stage synchronous injection and multi-stage asynchronous injection) achieved 100 % perforation clusters initiation. Multi-stage synchronous injection led to the formation of multiple shear fractures in some clusters but was prone to fracture deviation due to the stress shadow effect. Multi-stage asynchronous injection was less affected by stress shadow but exhibited higher peak pump pressure throughout the fracturing process. The test results reveal that there is a certain correlation between pump pressure fluctuation and hydraulic fracture macro/micro characteristics. These findings provide valuable data and theoretical guidance for fracturing design in deep tight reservoirs.