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Seismic Characterisation of Gas Hydrates in the Luderitz Basin, Offshore Namibia: Investigating Shallow Heat Flow and Fluid Flow Phenomena

Campbell, Benedict Louis

[Thesis]. Manchester, UK: The University of Manchester; 2018.

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Abstract

The identification of gas hydrate accumulations and their associated fluid flow phenomena is important to both petroleum exploration and climatic scientists. They provide insight into the thermal regime of sedimentary basins where there is a lack of direct temperature measurements, as well as identify areas of potential shallow geohazards. Previous studies have developed a workflow to estimate shallow geothermal gradients using the depth of the base hydrate stability zone (BHSZ), often indicated in seismic data by a bottom simulating reflector (BSR). In this thesis, the workflow is applied to a high-quality seismic reflection dataset from the Luderitz Basin, offshore Namibia. Through seismic interpretation two BSRs were identified covering 1000 and 500 km2, respectively. Assuming a thermal conductivity of 0.67 W m-1 K-1, measured at the nearby ODP Site 1084, BSR derived heat flow estimations range from 28-56 mW m-2 (BSRN mean = 46 mW m- 2, BSRS mean = 48 mW m-2). Analysis and mapping of the BSR and the seafloor uncovered multiple seafloor (300-730 m water depth) and shallow subsurface anomalies. These are interpreted as the first cold-water coral reefs and gas hydrate pingoes in offshore Namibia and proposes the first global discovery of buried gas hydrate pingoes. The total volume of hydrate within mounds and buried anomalies is as great as 13 x 106 m3 (individual mound volume 4.2 x 103- 2.3 x 106 m3). This can be used to further world estimates of gas hydrate along continental margins and improve the understanding of the implications of gas hydrates on climate change and the potential of gas hydrates as a reserve. This case study provides another example that BSRs can successfully be used to estimate heat flow and proves a cost-effective method when direct temperature measurements are not present or are widely spaced across a margin.

Bibliographic metadata

Type of resource:
Content type:
Administered thesis
Form of thesis:
Alternative format
Type of submission:
Doctoral level ETD - final
Thesis title:
Seismic Characterisation of Gas Hydrates in the Luderitz Basin, Offshore Namibia: Investigating Shallow Heat Flow and Fluid Flow Phenomena
Degree type:
Master of Science by Research
Degree programme:
MSc by Research Earth, Atmospheric and Environmental Sciences
Publication date:
2018-01-24T09:27:02
Institution:
The University of Manchester
Location:
Manchester, UK
Total pages:
79
Abstract:
The identification of gas hydrate accumulations and their associated fluid flow phenomena is important to both petroleum exploration and climatic scientists. They provide insight into the thermal regime of sedimentary basins where there is a lack of direct temperature measurements, as well as identify areas of potential shallow geohazards. Previous studies have developed a workflow to estimate shallow geothermal gradients using the depth of the base hydrate stability zone (BHSZ), often indicated in seismic data by a bottom simulating reflector (BSR). In this thesis, the workflow is applied to a high-quality seismic reflection dataset from the Luderitz Basin, offshore Namibia. Through seismic interpretation two BSRs were identified covering 1000 and 500 km2, respectively. Assuming a thermal conductivity of 0.67 W m-1 K-1, measured at the nearby ODP Site 1084, BSR derived heat flow estimations range from 28-56 mW m-2 (BSRN mean = 46 mW m- 2, BSRS mean = 48 mW m-2). Analysis and mapping of the BSR and the seafloor uncovered multiple seafloor (300-730 m water depth) and shallow subsurface anomalies. These are interpreted as the first cold-water coral reefs and gas hydrate pingoes in offshore Namibia and proposes the first global discovery of buried gas hydrate pingoes. The total volume of hydrate within mounds and buried anomalies is as great as 13 x 106 m3 (individual mound volume 4.2 x 103- 2.3 x 106 m3). This can be used to further world estimates of gas hydrate along continental margins and improve the understanding of the implications of gas hydrates on climate change and the potential of gas hydrates as a reserve. This case study provides another example that BSRs can successfully be used to estimate heat flow and proves a cost-effective method when direct temperature measurements are not present or are widely spaced across a margin.
Keyword(s):
Thesis main supervisor(s):
Thesis co-supervisor(s):
Degree grantor:
Language:
en

Record metadata

Manchester eScholar ID:
uk-ac-man-scw:313126
Created by:
Campbell, Benedict
Created:
24th January, 2018, 09:27:02
Last modified by:
Campbell, Benedict
Last modified:
8th February, 2019, 13:32:06

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