メタンハイドレートを含む模擬堆積物の三軸圧縮特性におよぼすひずみ速度の影響

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 C1 and the higher rate C2 at strain intervals Δe. The conditions of C1, C2 and Δe 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 hydrate-sand specimen was considerably stronger than that of saturated-sand specimen. Referring to earlier works, the time-dependency of hydrate-sand specimen seemed to be weaker than that of ice or methane hydrate and comparable with that of frozen sand.