Study on Bonding Quality of Cement-Casing Interfacial Transition Zone Based on Acoustic Impedance Testing: Influence of Microstructural Characteristics

Investigating the interfacial transition zone (ITZ) between cement and casing, along with its bonding quality, holds significant importance for enhancing downhole cementing integrity. This study employed acoustic impedance testing to characterize interfacial bonding quality, while utilizing X-ray diffraction (XRD), scanning electron microscopy (SEM), and backscattered electron spectroscopy-energy dispersive spectroscopy (BSE-EDS) to elucidate cement-casing interfacial bonding mechanisms. The research methodology for ITZ microstructure analysis was optimized, establishing intrinsic correlations between ITZ microstructural characteristics and interfacial bonding performance. Results demonstrate that elevated free water content at the cement-casing interface promotes cement clinker accumulation within ITZ, forming a porous microstructure that compromises interfacial bonding. Enhanced hydration reaction efficiency and controlled cement sheath deformation characteristics effectively improved interfacial bonding quality, with gel phase content exhibiting a more pronounced strengthening effect than volumetric deformation factors. Specifically, gel phase content showed a negative correlation with ITZ thickness - increased gel phase proportion reduced ITZ thickness to 10-30 μm, achieving optimal interfacial bonding performance.