Microstructure and Mechanical Properties of Methane Hydrate-Bearing Sand

Methane hydrates (MHs), solid ice-like compounds of methane gas and water, form naturally at high pressure and low temperature in marine or permafrost settings. They represent a great alternative energy resource but also a source of geo-hazards and climate change. Knowledge of physical/mechanical properties of sediments containing MHs, depending considerably on methane hydrate morphologies and distribution at the pore scale, is of major importance to be able to minimize the environmental impacts of future exploitation of methane gas from methane hydrate-bearing sands (MHBS). Much of the reported experimental work consists in laboratory tests on synthetic samples due to the extreme difficulty to get intact cored natural methane hydrate-bearing sediment samples. Various methods have been proposed to form methane hydrates in sandy sediments to mimic natural MHBS, but with limited success. This paper discusses the morphologies and pore habits of MHs formed in synthetic MHBS, considered as model materials for real MHBS and their effects on the mechanical properties of MHBS, at various scales and via different methods mainly as synchrotron X-ray computed tomography, magnetic resonance imaging and triaxial tests. An alternative MH formation method is proposed to better mimic natural MHBS and the validity of existing idealized models used to describe MH pore habits is discussed.