Cementing interfaces debonding during methane deflagration fracturing based on measured bond strength and pressure data

This is the authors' abstract. We don't add key points for this paper.

The expansion of shale gas exploration into deeper reservoirs introduces increasing cementing challenges, primarily caused by cement sheath integrity failure through interfacial debonding. This study performed mechanical property characterization and interfacial bond strength evaluation of composite-toughened oil well cement to quantify the mechanical behavior of cement sheaths and cementing interfaces. Cavity pressure experiments were performed to obtain pressure-time curves of methane deflagration fracturing under different filling pressures. A whole-life-cycle well integrity model was established using a phased modeling approach, with the measured pressure data as input loads, and the cohesive zone model (CZM) was applied to simulate interfacial debonding evolution. Parametric analysis focused on the effects of perforation section length, deflagration parameters (peak pressure, duration), and cement formulations on interfacial debonding. Numerical results reveal that the casing-cement interface exhibits longer axial debonding lengths than the cement-formation interface, while the latter experiences faster debonding propagation. Sensitivity analysis highlights that composite toughened cement sheaths with reduced elastic modulus and enhanced bond strength significantly enhance wellbore integrity under methane deflagration. Interfacial debonding can be mitigated by optimizing perforation section length in staged fracturing operations and carefully controlling deflagration peak pressure and duration. This work enables predictive analysis of cement sheath debonding development and integrity evaluation, offering practical strategies for optimizing methane deflagration fracturing operations.