Hydraulic fracture cross-layer propagation characteristics in the interlayered sand-shale reservoir

China's continental shale oil reserves face geological challenges from complex, weak structural planes (i.e., lithology interfaces and bedding planes) and discontinuous interlayers (i.e., shale and sandstone), which limit the effective stimulation of multiple pay layers. This study investigates hydraulic fracture (HF) cross-layer propagation behaviors in the Chang 7 Member sand-shale reservoirs, integrating fracturing experiments and numerical simulations to analyze impact of vertical stress difference (KV), interlayer stress contrast (Δσh), injection rate (Q), fluid viscosity (μ), weak plane shear strength (IS), weak plane tensile strength (IT), and cyclic injection. Results reveal that HF height extension is governed by interlayer obstruction and weak plane activation, forming three fracture propagation patterns: activated bedding planes, passivated fractures, and cross-layer fractures. Enhanced HF penetration occurs with higher KV, Q, μ, IS, IT, and reduced Δσh. Conversely, fractures become passivated with the weak plane activation. The dominant factor of fracture height is Δσh, followed by the IS, IT, KV, Q, and μ. Compared with conventional injection, cyclic injection improves fracture height and fracture area by 200% and 23%, respectively. Reduced cyclic amplitude or extended cycle duration promotes bedding activation. To achieve vertical connection of multiple pay layers, it is recommended to perform hydraulic fracturing with 30 mPa s guar gum at a flow rate above 8.3 m3/min. These findings are expected to provide hydraulic fracturing guidance for the interlayered shale oil reservoirs.