Nano-indentation and nano-scratch approach for precise measurements of the mechanical properties of gas hydrates

The micro-mechanical properties of gas hydrates fundamentally govern the stability of hydrate-bearing sediments. However, owing to the technical challenge of maintaining the thermodynamic stability of gas hydrates, their mechanical characteristics at the microscale to nanoscale still lack a systematic understanding. To address this issue, this study developed an integrated nano-indentation and nano-scratch device capable of preserving hydrate thermodynamic stability during testing. This device combines the indentation and scratch functionalities, enabling the acquisition of key micro-mechanical parameters such as hardness, modulus, and friction force on a single sample. To meet the surface roughness requirements for nanoscale testing, we established a standardized protocol for hydrate sample preparation and transfer, ensuring smooth and flat sample surfaces. Additionally, we developed a standardized experimental operation procedure covering various testing modes for nano-indentation and nano-scratch. The aforementioned device and method provide technical support for in-depth analysis of the micro-mechanical properties of gas hydrates. Applying this methodology to pure methane hydrate, primary tests revealed that the hardness and modulus are load-independent but exhibit significant temperature dependence, and their frictional characteristics are significantly correlated with normal load. This study provides the first quantitative measurements of methane hydrate micro-mechanical parameters, establishing a key foundation for explaining the macroscopic mechanical mechanism of hydrate-bearing sediments.