Abstract
Dielectric constants can be used to detect hydrates in permafrost regions. Therefore, this study investigated the relationships between the dielectric constant characteristics of sandstone reservoir hydrate and the hydrate saturation degree through physical simulation experiments, as well as the granularity of the surrounding rock. Methane and tetrahydrofuran (THF) hydrates with quartz sands were prepared, and their dielectric constants were analyzed. With different granularities of quartz sands, the dielectric constants of two different methane hydrate sediments decreased with increasing saturation degrees. At a given saturation degree, the dielectric constant of methane hydrate sediments with small granularity was larger than that with medium granularity, a result attributed to the unreacted water in the larger pores of the latter. In addition, the dielectric constant of methane hydrate sediments was larger than that of THF hydrates, which was also attributed to gas-phase factors and the presence of unreacted water. At a given granularity and saturation, the dielectric constants of both the THF and methane hydrates decreased with increasing saturation degrees. We conclude that at low temperature and under normal pressure, THF hydrates cannot be used as a substitute for methane hydrates in laboratory experiments investigating geophysical phenomena.
Highlights
As a potentially vast source of energy, gas hydrate reserves have drawn increasing attention around the world
The Geological Survey of China has carried out geophysical exploration works and effectiveness experiments in the Muli area of Qilian Mountain, such as audio-frequency magnetotellurics, low frequency ground penetrating radar (GPR), surface nuclear magnetic resonance (NMR) method, and electromagnetic well logging technique[5].after drilling, it is found that many identification marks are not completely related to natural gas hydrate deposits
saturation in the model (Sh) where Vh is the volume of synthesized hydrates, the volume of synthetic methane hydrate in the reactor is fixed at 1 L, Vs is the volume of the quartz sand, and Φs is the porosity of quartz sand
Summary
As a potentially vast source of energy, gas hydrate reserves have drawn increasing attention around the world. Many geophysical and electromagnetic logging technologies were investigated for gas hydrate mineral deposits in the Mackenzie Delta in Canada and Alaska North Slope in the USA [3,4]. The Geological Survey of China has carried out geophysical exploration works and effectiveness experiments in the Muli area of Qilian Mountain, such as audio-frequency magnetotellurics, low frequency ground penetrating radar (GPR), surface nuclear magnetic resonance (NMR) method, and electromagnetic well logging technique[5].after drilling, it is found that many identification marks are not completely related to natural gas hydrate deposits. Data from the natural gas hydrate well logging in Alaska North Slope was analyzed by Collett et al, and the energy potential of natural gas hydrates in the studied area was determined. The main research objectives are: (1) to elucidate whether there are distinct dielectric properties of methane hydrate in sandstone; (2) to check whether artificially synthesized sandstone-methane hydrate has regular electromagnetic wave response characteristics, and, if yes, the influencing factors, and (3) to analyze the difference in electromagnetic responses from THF hydrate (a substitute of methane hydrate in laboratory) and methane hydrate itself
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