Abstract: The Bohai Oilfield possesses abundant low-permeability reserves. However, their economic development has been constrained by offshore operational limitations that hinder the application of large-scale network fracturing techniques. With the recent deployment of large fracturing vessels, large-scale network fracturing is poised to become a key trend for developing offshore low-permeability reservoirs. The study focuses on a low-permeability reservoir in the Bohai Sea. We characterizes rough fracture surfaces by splitting and scanning core samples from the target layer, establish a complex fracture model based on the operational capacity of fracturing vessels, and carry out physical experiments and numerical simulation analysis of proppant transport. Key findings include: rough fracture walls increase transport resistance, making it necessary to use slug flow to polish fracture surfaces; the transport mechanism of sand-carrying slickwater follows a dynamic equilibrium under the influence of gravity settling and fluid drag. Therefore, to improve placement efficiency, the strategy should focus on enhancing the proppant$'$s ability to migrate into the deeper sections of the fracture; through optimized parameter design, slickwater injection at 12 m$^3$/min with a staged proppant blend 40/70 + 30/50 + 20/40 mesh can significantly enhance intra-fracture proppant placement. These results provide scientific guidance for fracturing parameter design and hold critical implications for the efficient development of offshore low-permeability oilfields.

Key words: Bohai low-permeability reservoirs, fracturing vessel, large-scale fracturing, rough and complex fractures, proppant transport and placement