In this paper, we conducted simulations of hydrate with different saturation under different confining pressure based on a series of trial compression experiments. M-C and D-P models were applied respectively to calculate hydrate sediment yield stress. After comparing simulation results with experimental results, it was found that Mohr-Coulomb model is suitable for hydrate sediments with high saturation while Drucker-Prager model is suitable for lower saturation.
Natural gas hydrate is a new type of clean energy with huge reserves and wide distribution which is considered as a strategic energy. 1m3 of natural gas hydrate can release 164m3 of natural gas and 0.87m3 of water during the decomposition of hydrate. Natural gas hydrate is an ice-like crystal formed by methane and water under high pressure and low temperature. Currently, there are four main methods for hydrate extraction: depressurization, heat injection, chemical reagent and CO2 injection method. Depressurization is recognized as the method with the lowest cost. Natural gas hydrate will decompose when the phase equilibrium condition is broken during depressurization, which will cause the sediment soil become less dense or unbonded. The decrease of shear resistance and increase of pore space may lead to some geomechanical problems. For example, the hydrate dissociates during the depressurization process, releasing large amounts of methane gas. As a result, the effective stress decreases significantly with the increase in pore pressure and the mechanical properties of hydrate sediments may change, which may cause potential geomechanical disasters, such as subsea landslides, drilling platform failures, casing deformation, and so on (Huang, 2017). Therefore, it is of great significance to study the mechanical properties of natural gas hydrate sediments and determine the collapse of hydrate reservoir to ensure safe and efficient production. Due to the special properties of hydrate sediments, the methods for oil and conventional gas are not suitable for hydrates. Currently, there are four main methods for hydrate extraction: depressurization, heat injection, chemical reagent and CO2 injection method. Depressurization is recognized as the method with the lowest cost.
