Gas Hydrates in Permafrost: Distinctive Effect of Gas Hydrates and Ice on the Geomechanical Properties of Simulated Hydrate‐Bearing Permafrost Sediments

Abstract

The geomechanical stability of the permafrost formations containing gas hydrates in the Arctic is extremely vulnerable to global warming and the drilling of wells for oil and gas exploration purposes. In this work the effect of gas hydrate and ice on the geomechanical properties of sediments was compared by triaxial compression tests for typical sediment conditions: unfrozen hydrate‐free sediments at 0.3 °C, hydrate‐free sediments frozen at −10 °C, unfrozen sediments containing about 22 vol% methane hydrate at 0.3 °C, and hydrate‐bearing sediments frozen at −10 °C. The effect of hydrate saturation on the geomechanical properties of simulated permafrost sediments was also investigated at predefined temperatures and confining pressures. Results show that ice and gas hydrates distinctively influence the shearing characteristics and deformation behavior. The presence of around 22 vol% methane hydrate in the unfrozen sediments led to a shear strength as strong as those of the frozen hydrate‐free specimens with 85 vol% of ice in the pores. The frozen hydrate‐free sediments experienced brittle‐like failure, while the hydrate‐bearing sediments showed large dilatation without rapid failure. Hydrate formation in the sediments resulted in a measurable reduction in the internal friction, while freezing did not. In contrast to ice, gas hydrate plays a dominant role in reinforcement of the simulated permafrost sediments. Finally, a new physical model was developed, based on formation of hydrate networks or frame structures to interpret the observed strengthening in the shear strength and the ductile deformation.

Cementation Failure Behavior of Consolidated Gas Hydrate‐Bearing Sand

“…However, it should be noted that the shedded hydrates will not enter the pores immediately to accomplish filling but instead will support the sand particles near the original position. The retention of hydrates between the sand particles hinders the rearrangement of the sand particles during shearing, and the sand particles have to climb over the adjacent sand particles to attain rearrangement, which could result in dilatancy in the hydrate‐bearing specimen (Choi et al, ; Yang et al, ).…”

“…Natural gas hydrates (NGHs) are ice-like compounds consisting of methane molecules within a water framework (Englezos, 1993), which is stable under high-pressure and low-temperature conditions, typically naturally occurring in submarine continental margins, permafrost, and Arctic regions (Koh et al, 2012;Yang et al, 2019). The gross NGH reserves are estimated to be 1-150×10 15 m 3 (Boswell & Collett, 2011;Lee & Holder, 2001;Makogon et al, 2007), which are twice as much as all known conventional fossil fuels and more than 10 times the total reserve of conventional natural gas resources on Earth.…”

Microstructure Evolution of Hydrate‐Bearing Sands During Thermal Dissociation and Ensued Impacts on the Mechanical and Seepage Characteristics

“…However, when the specimen void ratio has increased to a certain extent, some sand particles have to roll over the adjacent sand particles with continued axial loading. And hydrate would encapsulate the sand particle surface forming large‐scale cementation structures (Yang et al, 2019), as shown in Figure 14, making sand particles rearrangement more difficult to accommodate the axial loading. As a result, a failure pattern with a clear shear band has been formed rather than drum‐like failure patterns.…”

An Experimental Investigation on the Kinetics of Integrated Methane Recovery and CO2 Sequestration by Injection of Flue Gas into Permafrost Methane Hydrate Reservoirs

“…At this point, hydrate, gas, water, and ice saturation were calculated as shown in Table 1. The same formulation as our previous work 35 was used for the calculation of the saturation. For purging the remaining methane gas and reducing the proportion of remaining free methane in the gas phase without dissociation of methane hydrate, flue gas composed of 85.4 mol % N 2 and 14.6 mol % CO 2 was injected to the cell at a pressure approximately 10 times the equilibrium pressure of methane hydrate at the target temperature after hydrate formation.…”