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Gas bubble dynamics during methane hydrate formation and its influence on geophysical properties of sediment using high-resolution synchrotron imaging and rock physics modeling

Gas bubble dynamics during methane hydrate formation and its influence on geophysical properties of sediment using high-resolution synchrotron imaging and rock physics modeling
Gas bubble dynamics during methane hydrate formation and its influence on geophysical properties of sediment using high-resolution synchrotron imaging and rock physics modeling
Gas bubble in aquatic sediments has a significant effect on its geophysical and geomechanical properties. Recent studies have shown that methane gas and hydrate can coexist in gas hydrate–bearing sediments. Accurate calibration and understanding of the fundamental processes regarding such coexisting gas bubble dynamics is essential for geophysical characterization and hazard mitigation. We conducted high-resolution synchrotron imaging of methane hydrate formation from methane gas in water-saturated sand. While previous hydrate synchrotron imaging has focused on hydrate evolution, here we focus on the gas bubble dynamics. We used a novel semantic segmentation technique based on convolutional neural networks to observe bubble dynamics before and during hydrate formation. Our results show that bubbles change shape and size even before hydrate formation. Hydrate forms on the outer surface of the bubbles, leading to reduction in bubble size, connectivity of bubbles, and the development of nano-to micro-sized bubbles. Interestingly, methane gas bubble size does not monotonously decrease with hydrate formation; rather, we observe some bubbles being completely used up during hydrate formation, while bubbles originate from hydrates in other parts. This indicates the dynamic nature of gas and hydrate formation. We also used an effective medium model including gas bubble resonance effects to study how these bubble sizes affect the geophysical properties. Gas bubble resonance modeling for field or experimental data generally considers an average or equivalent bubble size. We use synchrotron imaging data to extract individual gas bubble volumes and equivalent spherical radii from the segmented images and implement this into the rock physics model. Our modeling results show that using actual bubble size distribution has a different effect on the geophysical properties compared to the using mean and median bubble size distributions. Our imaging and modeling studies show that the existence of these small gas bubbles of a specific size range, compared to a bigger bubble of equivalent volume, may give rise to significant uncertainties in the geophysical inversion of gas quantification.
gas bubble, gas hydrate, rock physics model, synchrotron X-ray imaging, wave velocity
Bangalore Narasimha Murthy, Madhusudhan
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Sahoo, Sourav K.
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Alvarez Borges, Fernando
5512cdfd-6ad3-475f-8aec-2fc767607314
Ahmed, Sharif
ddc6bab1-9d76-4391-b7ea-ae68d6f3924d
North, Laurence J.
9dc2779f-0a6f-4619-8473-7f2eea6a83fc
Best, Angus I.
cad03726-10f8-4f90-a3ba-5031665234c9
Bangalore Narasimha Murthy, Madhusudhan
e139e3d3-2992-4579-b3f0-4eec3ddae98c
Sahoo, Sourav K.
4c4db3a0-8fa2-4b7c-b09e-176b9c0343ae
Alvarez Borges, Fernando
5512cdfd-6ad3-475f-8aec-2fc767607314
Ahmed, Sharif
ddc6bab1-9d76-4391-b7ea-ae68d6f3924d
North, Laurence J.
9dc2779f-0a6f-4619-8473-7f2eea6a83fc
Best, Angus I.
cad03726-10f8-4f90-a3ba-5031665234c9

Bangalore Narasimha Murthy, Madhusudhan, Sahoo, Sourav K., Alvarez Borges, Fernando, Ahmed, Sharif, North, Laurence J. and Best, Angus I. (2022) Gas bubble dynamics during methane hydrate formation and its influence on geophysical properties of sediment using high-resolution synchrotron imaging and rock physics modeling. Frontiers in Earth Science, 10, [877641]. (doi:10.3389/feart.2022.877641).

Record type: Article

Abstract

Gas bubble in aquatic sediments has a significant effect on its geophysical and geomechanical properties. Recent studies have shown that methane gas and hydrate can coexist in gas hydrate–bearing sediments. Accurate calibration and understanding of the fundamental processes regarding such coexisting gas bubble dynamics is essential for geophysical characterization and hazard mitigation. We conducted high-resolution synchrotron imaging of methane hydrate formation from methane gas in water-saturated sand. While previous hydrate synchrotron imaging has focused on hydrate evolution, here we focus on the gas bubble dynamics. We used a novel semantic segmentation technique based on convolutional neural networks to observe bubble dynamics before and during hydrate formation. Our results show that bubbles change shape and size even before hydrate formation. Hydrate forms on the outer surface of the bubbles, leading to reduction in bubble size, connectivity of bubbles, and the development of nano-to micro-sized bubbles. Interestingly, methane gas bubble size does not monotonously decrease with hydrate formation; rather, we observe some bubbles being completely used up during hydrate formation, while bubbles originate from hydrates in other parts. This indicates the dynamic nature of gas and hydrate formation. We also used an effective medium model including gas bubble resonance effects to study how these bubble sizes affect the geophysical properties. Gas bubble resonance modeling for field or experimental data generally considers an average or equivalent bubble size. We use synchrotron imaging data to extract individual gas bubble volumes and equivalent spherical radii from the segmented images and implement this into the rock physics model. Our modeling results show that using actual bubble size distribution has a different effect on the geophysical properties compared to the using mean and median bubble size distributions. Our imaging and modeling studies show that the existence of these small gas bubbles of a specific size range, compared to a bigger bubble of equivalent volume, may give rise to significant uncertainties in the geophysical inversion of gas quantification.

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Accepted/In Press date: 19 April 2022
Published date: 8 June 2022
Additional Information: Funding Information: We acknowledge funding from the United Kingdom Natural Environment Research Council (Grant NE/J020753/1 and NE/R000123/1). BNM was supported by the SMMI HIEF internal grant from the University of Southampton. The experimental data are available at the National Geoscience Data Centre, United Kingdom under the Grant NE/J020753/1. Funding Information: FA-B and SA are employed by Diamond Light Source Ltd. Diamond Light Source Ltd ("Diamond"), is UK's national synchrotron facility and is a not-for-profit limited company funded as a joint venture by the UK Government as part of UK Research and Innovation (UKRI) through the Science & Technology Facilities Council (STFC) in collaboration with the Wellcome Trust. Publisher Copyright: Copyright © 2022 Madhusudhan, Sahoo, Alvarez-Borges, Ahmed, North and Best.
Keywords: gas bubble, gas hydrate, rock physics model, synchrotron X-ray imaging, wave velocity

Identifiers

Local EPrints ID: 469908
URI: http://eprints.soton.ac.uk/id/eprint/469908
PURE UUID: e45cad24-e031-490b-bc78-38bbe7e5c031
ORCID for Madhusudhan Bangalore Narasimha Murthy: ORCID iD orcid.org/0000-0002-2570-5934
ORCID for Fernando Alvarez Borges: ORCID iD orcid.org/0000-0002-6940-9918

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Date deposited: 28 Sep 2022 16:53
Last modified: 31 Jan 2023 03:06

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Contributors

Author: Sourav K. Sahoo
Author: Fernando Alvarez Borges ORCID iD
Author: Sharif Ahmed
Author: Laurence J. North
Author: Angus I. Best

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