Abstract: The Bohai Sea oilfield has abundant low-permeability reserves, which are important replacement resources for increasing reserves and production. Among them, the C Oilfield in the Bohai Sea has well-developed natural fractures in the buried hill reservoirs. Volume fracturing to create complex fracture networks is a key technical means for development. To address the issue that the influence law of single-layer proppant placement of secondary fractures on conductivity is still unclear during network fracturing, a prediction model for the conductivity of secondary fractures with multi-size distribution was established based on the plane contact theory. The correctness of the model was verified through model degradation and experimental analysis, and the influencing factors were analyzed. The research results show that increasing the proportion of large-sized proppants is beneficial to maintaining the width of secondary fractures; the permeability of secondary fractures is approximately linearly and positively correlated with the proportion of large-sized proppants; in the case of multi-size proppant combinations, as the proportion of large-sized proppants increases, the conductivity of secondary fractures improves, and large-sized proppants play a key role in conductivity. The research conclusions provide theoretical guidance for the selection of proppant sizes in the fracture network fracturing design process in the Bohai Sea.

Key words: complex fracture network, flow conductivity, single-layer placement, particle size combination, proppant embedment