ABSTRACT

A core holder was installed in a High-Speed X-ray CT scanner to observe the dissociation behavior of methane hydrate-bearing sediment. Artificial methane hydrate-bearing sediment was made and dissociated by the depressurization method. As a result, pore pressure in the sediment decreased immediately and the sediment temperature decreased proportionally to dissociation pressure. The CT luminance value decreased with the decomposition because hydrates in the sediment pore space replaced by methane gases.

INTRODUCTION

In order to use methane hydrate as an energy resource, it is necessary to establish decomposition methods for efficiently extracting methane gas from the methane hydrate-bearing layer. As a representative gas production method, there are depressurization method and thermal recovery method.

Artificial methane hydrate-bearing sediment was made in a core holder type pressure vessel as reported in a previous study (Chuvilin et al., 2003), and a decomposition experiment was conducted by the above methods. These experiments demonstrated that the permeability of gas and water through the methane hydrate sediment largely influenced gas production rate. It is therefore important to know how the dissociated methane gas and water flow through the methane hydrate-bearing sediments.

An X-ray Computed Tomography (CT) scanner, which can examine samples nondestructively, can be a powerful tool in such applications. There are several studies about investing natural gas hydrate sediments using medical X-ray CT equipment (Uchida et al., 1997; Uchida et al., 2004). Jin et al. (2004) studied the structure of gas hydrate sediments using a microfocus X-ray CT. However, it is difficult to apply standard medical X-ray CT to natural gas hydrate dissociation because it usually takes a long time to scan one image.

Sato et al. (2005) developed a high-speed X-ray CT device and related imaging techniques.

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