Study on the Micro-Mechanical Mechanism of Fine-Grained Marine Sediments Subjected to Shallow Gas Invasion

Marine sediment is an important channel for methane leakage from the earth interior to the atmosphere. The investigation of gas invasion in fine-grained marine sediments is of great theoretical and practical significance in marine science and engineering. To study the mechanical mechanisms of fine-grained marine sediments subjected to shallow gas invasion, a gas injection test with a self-developed experimental apparatus was performed, and the gas invasion behavior was investigated. The results showed that the behavior of gas invasion in fine-grained sediments can be divided into different phases; the fracturing direction beta gradually changes from vertical to horizontal, and finally fractures along the roof. Based on the 2D undrained elliptical cavity model and the tensile strength of sediments, considering both tensile and shear failure modes, a discrimination criteria of gas invasion was proposed. It revealed that gas invasion gradually changes from shear failure to tensile failure, and the fracturing angle theta predicted by the criteria is consistent with the experimental phenomenon.

Automated summary

Marine sediment serves as a significant pathway for methane leakage from the earth's interior to the atmosphere. Investigating gas invasion in fine-grained marine sediments is crucial in marine science and engineering. Through a gas injection test using a self-developed experimental apparatus, the behavior of gas invasion was studied. The results revealed that gas invasion in fine-grained sediments can be divided into different phases, with the fracturing direction changing from vertical to horizontal before fracturing along the roof. A discrimination criteria of gas invasion considering both tensile and shear failure modes was proposed based on the 2D undrained elliptical cavity model and sediment tensile strength, which showed good agreement with experimental observations.