Qiliang, Sun, Alves, Tiago  ORCID: https://orcid.org/0000-0002-2765-3760, Xie, Xinong, He, Jiaxiong, Li, Wei and Ni, Xianglong
2017.
Free gas accumulations in basal shear zones of mass-transport deposits (Pearl River Mouth Basin, South China Sea): An important geohazard on continental slope basins.
Marine and Petroleum Geology
81
, pp. 17-32.
10.1016/j.marpetgeo.2016.12.029
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Abstract
Free gas is an important trigger of instability on continental slopes, and resulting mass-wasting strata can potentially form competent seals to hydrocarbon accumulations. This work uses two high-quality 3D seismic volumes to investigate fluid accumulations at the base of mass-transport deposits in the Pearl River Mouth Basin, South China Sea. In parallel, IODP/ODP borehole data are used to document the petrophysical character of mass-transport deposits formed in similar continental-slope environments to the South China Sea. The interpreted data show gas accumulations as comprising enhanced seismic reflections that are discordant, or vertically stacked, below mass-transport deposits with chaotic seismic facies. Gas was accumulated in basal shear zones of mass-transport deposits in response to differences in capillary pressure and porosity. Free gas in Zone A covers an area of at least 18 km2. In Zone B, the free gas is sub-circular in plan view and covers an area of 30.58 km2 for a volume of sediment approaching 1.5 km3. This work is important as it shows that vertical migration of gas is not significant in mass-transport deposits from the Pearl River Mouth Basin, but up-dip migration along their basal shear zones is suggested in multiple locations. As a result, free gas can pinch-out laterally to extend 1–2 km beyond these same basal shear zones. As a corollary, we show that free gas accumulations below mass-transport deposits comprise an important geohazard and should be taken into account when drilling continental-slope successions in both the South China Sea and continental margins recording important mass wasting. Strata charged with free gas form weak layers, hinting at a novel trigger of retrogressive slope failures on continental slopes worldwide.
| Item Type: | Article |
|---|---|
| Date Type: | Publication |
| Status: | Published |
| Schools: | Schools > Earth and Environmental Sciences |
| Subjects: | Q Science > QE Geology |
| Publisher: | Elsevier |
| ISSN: | 0264-8172 |
| Funders: | China Scholarship Council |
| Date of First Compliant Deposit: | 31 March 2017 |
| Date of Acceptance: | 30 December 2016 |
| Last Modified: | 27 Nov 2024 15:30 |
| URI: | https://orca.cardiff.ac.uk/id/eprint/96470 |
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