Volume 35, Issue 5 (September 2012)
Testing Methane-Hydrate-Saturated Soil Using a Line Dissociation Apparatus
The combination of energy source and geohazardous potential of natural gas hydrate has raised the need to understand the processes related to hydrate dissociation within the sediment. In this article, several existing methane hydrate dissociation apparatuses are listed and their sample size capabilities given. A new design for line dissociation tests by combined electrical heating and pressure reduction from a miniature wellbore is presented. The 180-mm-diameter × 225-mm-length hydrate-bearing soil samples can be tested over a wide range of near in situ conditions, with pore pressures of up to 15 MPa, temperatures as low as −5°C and a maximum effective stress of 5.5 MPa. During testing, the pore pressure, local temperature changes, vertical strain, the extracted gas and water volumes, and radial density changes are measured. The devices used are shown and described in detail. The sample formation steps by the water excess method are described, and the dissociation behaviour of a typical 40 % hydrate-saturated sand sample during local heating and pressure reduction are illustrated.