Phase speed in water-saturated sand and glass beads at MHz frequencies

Choosing the site for a new water well in rural southern Malawi is essentially a political process with competing priorities and stakeholders. For a new well (or borehole) to be sustainably used and maintained, the relevant stakeholders must be fully engaged in the siting process and given meaningful responsibility for the final siting decision. However, without sound technical information, a siting decision based solely on stakeholder priorities such as proximity to the headmans compound or accessibility to the center of population, may not result in a satisfactory borehole. Instead, in addition to stakeholder interests, we used a process that includes electrical resistivity tomography (ERT) as a tool to guide and constrain the local decision-making process. Within the region of the crystalline-basement aquifer, ERT profiles indicate variations in weathering thickness, hence aquifer storage. In a lacustrine setting, the ERT profile delineated a zone of moderately large resistivity associated with a deposit of fresh-water saturated sand. This ERT-derived technical information becomes one element in a comprehensive sociotechnical approach to the location of sustainable water resources. We used this sociotechnical approach to complete boreholes for all four villages in our project and have a high confidence that the villagers will be motivated to use and maintain these resources.

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Monitoring gas hydrate formation with magnetic resonance imaging in a metallic core holder

E3S Web of Conferences ◽

10.1051/e3sconf/20198902008 ◽

2019 ◽

Vol 89 ◽

pp. 02008

Author(s):

Mojtaba Shakerian ◽

Armin Afrough ◽

Sarah Vashaee ◽

Florin Marica ◽

Yuechao Zhao ◽

...

Keyword(s):

Magnetic Resonance Imaging ◽

Methane Hydrate ◽

Hydrate Formation ◽

Residual Water ◽

Saturated Sand ◽

Resonance Imaging ◽

The Core ◽

T2 Distribution ◽

Core Holder ◽

Water Saturated

Methane hydrate deposits world-wide are promising sources of natural gas. Magnetic Resonance Imaging (MRI) has proven useful in previous studies of hydrate formation. In the present work, methane hydrate formation in a water saturated sand pack was investigated employing an MRI-compatible metallic core holder at low magnetic ﬁeld with a suite of advanced MRI methods developed at the UNB MRI Centre. The new MRI methods are intended to permit observation and quantiﬁcation of residual ﬂuids in the pore space as hydrate forms. Hydrate formation occurred in the water-saturated sand at 1500 psi and 4 °C. The core holder has a maximum working pressure of 4000 psi between -28 and 80 °C. The heat-exchange jacket enclosing the core holder enabled very precise control of the sample temperature. A pure phase encode MRI technique, SPRITE, and a bulk T1-T2 MR method provided high quality measurements of pore ﬂuid saturation. Rapid 1D SPRITE MRI measurements time resolved the disappearance of pore water and hence the growth of hydrate in the sand pack. 3D π-EPI images conﬁrmed that the residual water was inhomogeneously distributed along the sand pack. Bulk T1-T2 measurements discriminated residual water from the pore gas during the hydrate formation. A recently published local T1-T2 method helped discriminate bulk gas from the residual ﬂuids in the sample. Hydrate formation commenced within two hours of gas supply. Hydrate formed throughout the sand pack, but maximum hydrate was observed at the interface between the gas pressure head and the sand pack. This irregular pattern of hydrate formation became more uniform over 24 hours. The rate of hydrate formation was greatest in the ﬁrst two hours of reaction. An SE-SPI T2 map showed the T2 distribution changed considerably in space and time as hydrate formation continued. Changes in the T2 distribution are interpreted as pore level changes in residual water content and environment.

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