ABSTRACT:

In this study, the applicability of variable-compliance-type constitutive model to triaxial compression test of Toyoura sand containing synthetic methane hydrate was examined as the first step towards formulation of mechanical properties of methane hydrate reservoirs. Parameters used in the constitutive model were determined by alternating strain rate triaxial compression tests. The calculated results by the model were compared with the previously experimental results.

INTRODUCTION

Methane hydrate is speculated to be a promising energy resource replacing conventional fossil fuel resources, since a large amount of reservoir exists in marine sediments or in permafrost regions worldwide (Kvenvolden, 1988; Kvenvolden et al., 1993; Okuda, 1993). In purpose of efficient extraction of natural gas from the reservoirs, some methods for in-situ dissociation of methane hydrate has been proposed; depressurization, thermal stimulation and inhibitor injection. Therefore, it is important to develop a model representing the constitutive relationship (stress-strain relationship) of hydrate bearing sediments and to introduce it into the simulator predicting gas production. In this study, experimental results obtained from triaxial compression tests of Toyoura sand containing synthetic methane hydrate (Masui et al., 2005) have been reviewed and the stress-strain relationship has been formulated using variable-compliance-type constitutive model which can be applicable to various time-dependent behaviors of rock (Okubo et al., 2002; Okubo et al., 2003).

REVIEW OF TRIAXIAL COMPRESSION TESTS
Host Specimen

A host specimen, in which synthetic methane hydrate was formed afterward, was produced by compacting water-saturated Toyoura sand densely in a mold on a vibration table. The initial water content which had a great influence on methane hydrate saturation of the specimen was adjusted by draining excess water with a syringe pump. The size of produced specimen was 50 mm in diameter and 100 mm in length and its porosity ranged from 36 % to 39 %.

This content is only available via PDF.
You can access this article if you purchase or spend a download.