Micro X-Ray computed tomography imaging and ultrasonic velocity measurements in tetrahydrofuran-hydrate-bearing sediments

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Naturally occurring gas hydrates contain significant amounts of natural gas that might be produced as an energy resource in the foreseeable future. Thus, it is necessary to understand the pore-space characteristics of hydrate reservoirs, particularly the pore-scale distribution of the hydrate and its interaction with the sediment. Four end-member models for hydrate distribution in the pore space are pore filling, sediment-frame component, envelope cementing, and contact cementing. The goal of this study is to compare the models with pore-scale hydrate distributions obtained in laboratory-formed hydrates. Our results verify hydrate pore-scale distributions by direct, visual observations that were previously implied by indirect, elastic property measurements.

Laboratory measurements were conducted using tetrahydrofuran as a guest molecule since tetrahydrofuran hydrate can be used as a proxy for naturally occurring hydrates. We performed micro X-ray computed tomography to obtain information about the distribution of hydrate in the pore space of synthetic sediment (glass beads). We also made ultrasonic velocity measurements on the same samples. Micro X-ray computed tomography images and ultrasonic velocity measurements both indicate that the tetrahydrofuran hydrate forms in the pore space with a part of the hydrate bridging the grains without touching the grain surfaces. These hydrate-bearing sediments appear to follow a pore-filling model with a portion of the hydrate becoming a load-bearing part of the sediment frame.

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