Abstract: The Huazhuang area in the Gaoyou Sag of the Subei Basin is a key block for shale oil exploration in the Jiangsu Oilfield. The shale in the Huazhuang II block is buried at depths exceeding 4 000 m, accounting for 42% of the total shale oil resources in the Huazhuang area. Therefore, achieving efficient development of this block is of great significance to the Jiangsu Oilfield. However, with increasing burial depth, shale oil fracturing faces challenges such as high operational pressure and difficulty in sand addition. To address these issues, the research team conducted hydraulic fracturing physical simulation experiments with the goals of increasing fracture complexity, expanding supported fracture area, and improving fracture conductivity. The influence of different injection rates and fracturing fluid viscosity on fracture morphology was analyzed, and numerical simulations were used to optimize multi-stage cluster design, ball-throwing temporary plugging techniques, and proppant combinations. The results showed that injecting medium- to high- viscosity fracturing fluid at high displacement improved fracture penetration capability but reduced the number and area of opened bedding planes. Using low-viscosity fracturing fluid with conventional displacement injection facilitated the connection and formation of bedding fractures. A single-stage design with fewer clusters was beneficial to improve the energy of each cluster, promoting more balanced fluid and sand injection among fractures. Simulation results showed that having 5-6 clusters per stage could achieve balanced fracture propagation and proppant support. At the same time, simulations were conducted to examine the impact of temporary plugging balls under different injection rates, quantities, and diameters. The optimized parameters for the temporary plugging of ball throwing were determined as follows: injection rate of 12-14 m³/min, ball diameter of 15 mm, and ball quantity of 50%-60% of the number of perforation holes. Combined with simulations of complex fracture proppant transport and placement, the optimal proppant combination and pumping parameters were determined to improve the transformation effect. This technology was successfully implemented in well HY7, yielding a peak daily oil production of 52.3 t and a single well estimated ultimate recovery of 4.6×10⁴ t. The results represent a major breakthrough in deep shale oil exploration in the Huzhuang II block of the Jiangsu Oilfield and provide important reference for the development of similar shale oil reservoirs.

Key words: Subei Basin, deep shale oil, ultra-dense fracturing, ball-throwing temporary plugging, composite particle size