Abstract: To investigate the fracture characteristics and layer-crossing propagation law of CO₂-hybrid fracturing in laminated shale, CO₂-hybrid fracturing experiments were conducted with the full-diameter Jiyang Sag Shale, and the Cohesive unit model was used to simulate the effect of pre-CO₂ injection rate on layer-crossing propagation. The results show that: 1) CO₂ fracturing is easy to activate beddings and natural fractures, which provides conditions for the formation of complex cross fractures in subsequent hydraulic fracturing, and the fracture volume increased by 24.0% with doubled pre-CO₂ injection rate; 2) The low viscosity and high permeability of CO₂ easily induce fractures to propagate along weak surfaces (beddings, natural fractures), mineral grain boundaries, and pore directions, resulting in the roughness of CO₂ fracturing fractures about 50.0% higher than hydraulic fractures; 3) With the increase of CO₂ injection rate, the ability of fracture to pass through beddings is enhanced. At low CO₂ injection rate, fracture propagation is dominated by bedding, while fracture propagation is dominated by in-situ stress at high injection rate. The research results provide the mechanism and theoretical understanding of the fracture propagation law of CO₂-hybrid fracturing of shale oil reservoir in Jiyang Sag. Compared with conventional fracturing in the field, the stimulation volume of CO₂-hybrid fracturing increased by 12.2%, capacity by 33%, and decline rate of oil production decreased by 6.8%.

Key words: CO₂-hybrid fracturing, laminated shale, fracture spatial morphology, roughness, injection rate