Characterization of the slope-destabilizing effects of gas-charged sediment via seismic surveys

Eugene Morgan, Maarten Vanneste, Mark Vardy

Research output: Chapter in Book/Report/Conference proceedingConference contribution

3 Scopus citations

Abstract

Finneidfjord, Norway has a history of submarine slope failure and hosts areas of buried, gas-charged sediment. Using shipboard seismic survey data from Finneidfjord, we illustrate how novel seismic data processing techniques can yield estimates of geotechnical properties of this gas-charged sediment: gas saturation (concentration) and excess pore pressure as well as their uncertainty. This data processing involves two steps: 1) estimate the amount of seismic attenuation that a gas-bearing layer creates, and 2) fit a wave attenuation model to the observed attenuation. We accomplish the first step using a waveletbased spectral ratio approach, and find the seismic quality factor (inversely related to attenuation) from the change in amplitude spectra across the gas layer. The novelty of this paper really comes in the second step, where we create a Bayesian hierarchical model that combines a wave attenuation model with a spatial random (Gaussian) process model. The advantage of this combination is that our estimates of the gas properties not only must conform to the observations of attenuation (quality factor), but must also smoothly vary over space, as one would expect of any natural process. Ultimately, we end up with posterior distributions of gas properties at points throughout our gas-bearing layer, which give us estimates of parameter values and a sense of uncertainty about these estimates. We find good performance and agreeable values for gas saturation, but the model shows weak sensitivity to pressure, leaving large uncertainty in any excess pore pressure estimates. Implications for slope stability at Finneidfjord are discussed.

Original languageEnglish (US)
Title of host publicationOffshore Technology Conference Asia, OTC ASIA 2014
Subtitle of host publicationMeeting the Challenges for Asia's Growth
PublisherOffshore Technology Conference
Pages1296-1306
Number of pages11
ISBN (Electronic)9781632665287
ISBN (Print)9781632663870
DOIs
StatePublished - 2014
EventOffshore Technology Conference 2014, OTC 2014 - Houston, United States
Duration: May 5 2014May 8 2014

Publication series

NameProceedings of the Annual Offshore Technology Conference
Volume2
ISSN (Print)0160-3663

Other

OtherOffshore Technology Conference 2014, OTC 2014
CountryUnited States
CityHouston
Period5/5/145/8/14

All Science Journal Classification (ASJC) codes

  • Safety, Risk, Reliability and Quality
  • Ocean Engineering
  • Energy Engineering and Power Technology
  • Mechanical Engineering

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  • Cite this

    Morgan, E., Vanneste, M., & Vardy, M. (2014). Characterization of the slope-destabilizing effects of gas-charged sediment via seismic surveys. In Offshore Technology Conference Asia, OTC ASIA 2014: Meeting the Challenges for Asia's Growth (pp. 1296-1306). (Proceedings of the Annual Offshore Technology Conference; Vol. 2). Offshore Technology Conference. https://doi.org/10.4043/25196-ms