Mechanical Characteristics of the Hydrate-Bearing Sediments in the South China Sea Using a Multistage Triaxial Loading Test

Abstract

Methane hydrate is being widely considered as an energy source by countries worldwide due to its to environmentally friendly and large reserves. However, during the exploitation process, a series of geological engineering disasters can be induced. Therefore, it is necessary to comprehensively study the mechanical characteristics of methane hydrate before commencing with commercial development. Many researchers have used conventional single-stage triaxial loading tests to study the mechanical characteristics of hydrate-bearing sediments, and these have the disadvantages of being time-consuming and labor-intensive. A multistage triaxial loading test can shear a single specimen under different effective confining pressures to obtain a series of mechanical parameters (strength, cohesion, internal frictional angle, etc.). In this study, a high-pressure and low-temperature triaxial apparatus was used to perform multistage and single-stage triaxial loading tests under effective confining pressures of 0.25, 0.5, and 1 MPa, and the specimens were remolded from the South China Sea had porosities of approximately 40% and a hydrate saturation of approximately 30%. The results show that under the relatively low effective confining pressure (0.25 and 0.5 MPa) the stress−strain and volumetric strain− axial strain curves between multistage and single-stage triaxial loading tests are highly coincident, and stress accumulation and compaction seem to have little effect on the strength and volumetric strain in the multistage triaxial loading test. However, under a relatively high effective confining pressure (1 MPa), the stress−strain and volumetric strain−axial strain curves of the two methods present a certain difference. In addition, the elastic modulus obtained by the multistage triaxial loading tests was larger than that from the single-stage triaxial loading tests due to stress accumulation and compaction.

Temperature Effect on Undrained Mechanical Properties of Hydrate-Bearing Clayey Silts in the South China Sea

“…Li et al performed single-stage and multistage consolidated drained (CD) triaxial shear experiments on hydrate-bearing clayey silts. 21 The conclusions demonstrate that the volumetric strain and stress−strain relationships obtained by these two ways are consistent at low effective stresses, while there are inconsistencies in the curves at high effective stresses. Luo et al generated CO 2 and CH 4 hydrates in silty soils and carried out isotropic consolidation and CD triaxial shear tests of CO 2 and CH 4 hydrate-bearing soils.…”

Virtual Special Issue of Recent Research Advances in China: Unconventional Gas

“…There are six reviews covering a wide range of aspects related to methane hydrates targeting resource potential, production methods (depressurization and CH 4 /CO 2 exchange), exploration activities, sand management, and hydrate properties . The original research articles pertaining to the topic of hydrates cover a wide spectrum of areas, from numerical modeling, ,,, hydrate properties and characterization, ,,,, hydrate equipment ,,, to fluid production analysis, ,− ,, etc.…”

Experimental Study on the Gas Permeability of Marine Sediments with Various Hydrate Saturations and Effective Stresses

“…The decomposition of hydrate in sediments will significantly reduce the strength and affect the stability of the whole reservoir. On the one hand, it may cause sediment collapse, wellbore collapse, submarine landslides, and other geological disasters. , On the other hand, it may cause methane to leak into the ocean and atmosphere, which will destroy the marine ecosystems and exacerbate the greenhouse effect. , In addition, permeability can affect the distribution of hydrate in the reservoir and the methane flux to the ocean and atmosphere . Thus, the study of the permeability of hydrate-bearing sediments (HBSs) plays a crucial role in investigating hydrate reservoirs as a potential energy resource and evaluating the impact of hydrate decomposition on marine ecosystems and global climate change. , …”