Strain Rate Dependency of Sediment Containing Synthetic Methane Hydrate in Triaxial Compression Test

Abstract

Methane hydrate is anticipated to be a promising energy resource of natural gas, since a large amount of reservoir exists in marine sediments or in permafrost regions worldwide. In order to evaluate a productivity of methane gas from methane hydrate reservoirs, it is necessary to develop a gas production numeric simulator. And, for precise assessment of long-term gas productivity, it is important to consider time-dependent properties of sediments containing methane hydrate. In this study, loading rate dependency, one of important time-dependent properties, of artificial sediment containing methane hydrate was experimentally examined. Results of triaxial compression tests of water-saturated Toyoura sand (saturated-sand specimen) and Toyoura sand containing synthetic methane hydrate (hydrate-sand specimen), at conditions of confining pressure 9MPa, pore water pressure 8MPa and temperature 278K, were presented. Loading was conducted at a constant strain rate or alternating strain rate. In constant strain rate test, specimen was loaded at strain rate of 0.1%/min, 0.05%/min and 0.01%/min. In alternating strain rate test, one specimen was loaded at a strain rate alternated between the lower rate C 1 and the higher rate C 2 at strain intervals Δε. The conditions of C 1 , C 2 and Δε were briefly examined in this study. Experimental results indicate that saturated-sand specimen shows very weak strain rate dependency suggesting that, in most cases, time-dependency is negligible small. Strain rate dependency of the peak strength for hydratesand specimen was considerably stronger than that of saturated-sand specimen. Referring to earlier works, the timedependency of hydrate-sand specimen seemed to be weaker than that of ice or methane hydrate and comparable with that of frozen sand.

Effect of Confining Pressure on Triaxial Compressive Properties of Artificial Methane Hydrate Bearing Sediments

“…4. Miyazaki et al (2009) reported that those specimens produced in the same manner with this study appeared to be consolidated in an early stage of axial loading before it started to expand by dilatancy effect. 4 are concave upward.…”

Creep of Sediment Containing Synthetic Methane Hydrate

“…，天然 MH は砂質 堆積層中の孔隙内に胚胎していることが多く，その観点からする と実用上重要であるのは MH と砂との混合物の力学特性 9-16) と いえる。例えば，著者ら14,15) は，MH を含む模擬砂質堆積物の…”

Gas Production from Offshore Methane Hydrate Layer and Seabed Subsidence by Depressurization Method

“…As shown in Figure 4, Masui et al (2005) [12] and Miyazaki et al (2005) [13] have presented the relationship between MH saturation and elastic modulus, E by the tri-axial compression test using the MH cores. It means that E value is increased linearly with increasing MH saturation in MH cores.…”