Experimental Investigation and Modeling of Geomechanical Behavior for Methane Hydrate-Bearing Sediments

Alternative energy sources, such as methane gas hydrates, lie between renewable energy and conventional hydro-carbon fuels in terms of clean energy resources. The global abundance of methane hydrate reserves has generated interest in harnessing the energy without affecting the environment. The mechanical response of hydrate-bearing sediments depends on hydrate morphology, which exerts a profound influence on sediment behavior under various loading conditions. The present study experimentally investigates the mechanical characteristics such as stiffness, peak stress, and dilative behavior of methane hydrate-bearing specimen (MHBS), with a specific focus on the influence of densification caused by hydrate formation by comparing it with the host sand. It is observed that for MHBS, there is an increase in stiffness and a higher dilative response when compared with host sand. Additionally, this study utilizes one of the advanced critical state-based constitutive models, i.e., the Hierarchical Single-Surface Methane Hydrate (HISS-MH) model, to evaluate the model's performance in predicting the densification effect caused due to the presence of hydrates. After obtaining the model parameters, a comparison is made between the single-point integrated model predictions and experimental results. The deviatoric stress with axial strain predictions are in good agreement with the experimental results, while the dilative response is slightly underpredicted. This comparative study will offer vital insights into the mechanics of gas hydrate sediments. 1 INTRODUCTION Methane gas hydrates are translucent crystalline compounds formed by entrapping methane gas within a cage-like structure formed by water molecules (Li et al., 2023; Wani et al., 2023a). They are predominantly found in deep marine sediments and permafrost regions, where high pressure and low temperatures facilitate stable conditions for their formation. One cubic meter of gas hydrate decomposition yields 164 cubic meters of methane gas and 0.8 cubic meters of water (Demirbas, 2010; Makogon and Omelchenko, 2013). Typically, the methane hydrate has high energy density i.e., nearly twice the carbon atoms compared to conventional fossil fuel (Wani et al., 2023b, 2022). Furthermore, methane gas hydrates are characterized by a relatively low carbon footprint, contributing less to the greenhouse gas emissions and global warming compared to conventional fossil fuels (Ma and Xu, 2021). Thus, it represents a promising source of relatively clean and efficient unconventional fossil energy. With larger reserves and wider distribution around the world, the natural gas hydrates have the potential to mitigate the global energy shortage.