Hydraulic fracture height growth in thin sandstone–mudstone interbeds is often limited by bedding interface failure and multi-cluster stress interference. In this study, a coupled fracture–matrix interface finite element model was developed for the He-8 sandstone–mudstone interbeds in the Sulige Gas Field and validated against previously published true triaxial hydraulic fracturing experiments. The simulations indicate that vertical–horizontal stress difference (VSD; the difference between overburden stress and minimum horizontal stress within a layer) promotes fracture-height growth, whereas interlayer stress difference (ISD; the minimum horizontal stress contrast between adjacent layers) acts as a stress barrier that promotes bedding interface shear failure and arrests vertical growth. For the investigated reservoir configuration, each 4 MPa increase in VSD increased fracture height by approximately 1.5 m in the three-cluster case and 1.8 m in the four-cluster case, whereas each 2 MPa increase in ISD reduced the average fracture height by approximately 4.0 m in the three-cluster case and 3.5 m in the four-cluster case. Under moderate ISD, increasing the fluid viscosity was more effective than increasing the injection rate alone, although the benefit depended on cluster number and interface failure state. These results clarify how stress contrast, interface strength, and multi-cluster stress shadows jointly control cross-layer fracture propagation in thin interbedded reservoirs.

The SP Gas Storage is situated in the SP-Xingcheng structural belt, where volcanic gas reservoirs are widely distributed and characterized by abundant primary microfractures and pore structures. The developed pores and fractures degrade the petrophysical properties of reservoirs and render volcanic basement rocks highly abrasive. In addition, pore-fracture systems alter the internal stress field of formations, which substantially increases the risk of wellbore instability and the collapse of injection and production wells. This poses great challenges to drilling operations and the safe running of the gas storage in this block. To systematically clarify the wellbore instability mechanism of large-diameter wellbores and address the drilling engineering problems in the study area, a dedicated experimental scheme for large-diameter wellbore stability was designed in this work. Laboratory true triaxial tests were conducted on wellbore stability with different borehole sizes, and basic mechanical parameter tests of reservoir rocks were also completed. This study systematically investigates the evolution of rock mechanical parameters and the surrounding stress-reconstruction mechanism induced by pore-forming unloading and identifies the dominant internal mechanism of wellbore instability under large-diameter conditions. A clear distinction is made between the formation stress redistribution caused by stratum exposure and unloading during drilling and formation stress evolution during the subsequent injection and production of the gas storage. On this basis, the fracture initiation threshold, propagation paths, and morphological evolution in thin interbedded sandstone–mudstone reservoirs are further analyzed. Combined with rock mechanical parameters and in situ stress balance conditions, criteria and quantitative evaluation methods for wellbore instability discrimination are finally established.