Initiation and expansion of layered fracture in sediments due to thermal-induced hydrate dissociation

• Layered fracture is caused by gas expansion during hydrate dissociation.
• The physical mechanisms are presented containing heat transfer, gas seepage and soil deformation.
• Decoupling method fits the initiation condition and expansion analysis.
• Layered fracture may lead to marine hazards in hydrate exploitation.

Methane hydrate dissociation in sediment may lead to geological hazards such as marine landslide, collapse of wellbore. The physical mechanisms, especially on the evolution of sediment damage, are not very clear sediment though some numerical simulations were presented based on conventional landslide. A failure form, namely layered fracture in sediment, was observed in experiments during hydrate dissociation. It was a gap filled with gas and water formed from continuous sediment by the gas and water expansion. A large laterally distributed layered fracture in seabed is a potential mechanism for marine landslide formation due to the very small shear strength in the fracture. This issue was analyzed based on dimensionless method and a two-phase mathematical model. The extension of the method and results to relate the engineering problem were discussed also. A mathematical model for studying the initiation and expansion of layered fracture was presented first by decoupling the expansion of hydrate dissociation front, gas seepage, and the movement of soil layer. Then the critical condition for the initiation of layered fracture was obtained and the thickness expansion of the layered fracture was numerically analyzed. The results could be used to evaluate the development of layered fractures under the condition of different hydrate recovery methods and geo-mechanical properties of hydrate formations in the future and will be extended to the study on the mechanism of marine landslide.