Optimal design and field test of volume fracturing for shale oil well A in Sichuan Basin

• Shale brittleness and quartz content drive complex fracture network formation. • Step-like and ╪ fracture shapes controlled by fluid viscosity and laminae. • Fracturing process can penetrate interlayers up to 4 m thick. • Layer-penetrating + differentiated close-cutting strategy validated in field. . To accelerate the exploration and development of Jurassic shale oil in the Sichuan Basin and to establish an effective volumetric fracturing technology, the mechanical properties of reservoir rocks, fracture propagation behavior, and proppant distribution characteristics were investigated through core mechanical testing and true triaxial hydraulic fracturing experiments. These results were used to propose a targeted fracturing strategy suitable for Jurassic shale reservoirs characterized by multi-lithology combinations and abundant natural fractures. Geological model simulations were further employed to optimize critical design parameters, including cluster spacing, injection parameters, stimulation scale, and the selection of fracturing fluids and proppants. The final design adopted a cluster spacing of 6–10 m in shale intervals and 8–12 m in sandstone intervals. A proppant intensity of 2.0 m³/m and a fluid intensity of 30 m³/m were determined to be optimal. A mixed-proppant system was selected, consisting of 70/140-mesh fine proppant for supporting bedding-plane fractures and 30/50-mesh ceramic proppant for enhancing the conductivity of the main hydraulic fractures, applied at a ratio of 7:3. Slickwater was used as the fracturing fluid. Based on these results, a volumetric fracturing technology characterized by “full-length horizontal penetration and differentiated close-cutting” was developed. Field test results show that post-fracturing daily oil and gas production reached 112.8 m³ and 1.145×10⁵ m³, respectively, demonstrating significant productivity enhancement and achieving a breakthrough in Jurassic shale oil exploration in the Sichuan Basin. The findings provide an important engineering reference for volumetric fracturing in similar shale reservoirs in future development areas.