The University of Southampton
University of Southampton Institutional Repository

A marine electromagnetic survey to detect gas hydrate at Hydrate Ridge, Oregon

A marine electromagnetic survey to detect gas hydrate at Hydrate Ridge, Oregon
A marine electromagnetic survey to detect gas hydrate at Hydrate Ridge, Oregon
Gas hydrates are a potential energy resource and hazard for drilling and infrastructure, yet estimates of global volume vary by over three orders of magnitude. Hydrates are electrically resistive compared to water saturated sediment and so electromagnetic methods provide an additional tool to seismic surveys and drilling for determining hydrate saturations. A marine electromagnetic survey was carried out at Hydrate Ridge, Oregon, USA, with the aim of testing the use of controlled source electromagnetic (CSEM) and magnetotelluric (MT) methods to map gas hydrate and free gas below the gas hydrate stability zone. A 2-D CSEM inversion supports the scenario deduced from previous seismic and drilling results, which indicate two mechanisms of hydrate emplacement: a transport-dominated and reaction-dominated regime. A prominent resistive region of 2.5–4 ?m at a depth of about 130 mbsf, near the seismic bottom simulating reflector (BSR), suggests that 27 to 46 per cent of the bulk volume is filled with hydrate, depending on whether Archie's Law or the Hashin-Strikman bounds are used. This is representative of a reaction-dominated regime for hydrate emplacement, and where a significant low velocity zone exists based on a seismic tomography inversion, suggests large quantities of free gas below the BSR. Electrical resistivity logging while drilling (LWD) data show general agreement with the CSEM inversion model except for a CSEM-derived resistive region at seismic horizon A, known to transport free gas into the gas hydrate stability zone. Inversion of MT data collected simultaneously during the CSEM survey provides a complimentary low-resolution image of the shallow sediments and shows folding in the accretionary complex sediments similar to that imaged by a tomographic seismic velocity model.
Magnetotelluric, Marine electromagnetics, Gas and hydrate systems, Continental margins: convergent
0956-540X
45-62
Weitemeyer, K.A.
22c524f6-b24d-4d2a-a46d-16b06c70a5d1
Constable, S.
b931c7b4-33b8-4c2b-8b10-f6502a433413
Tréhu, A.M.
83b5aede-2c1d-4a03-a117-e45391147325
Weitemeyer, K.A.
22c524f6-b24d-4d2a-a46d-16b06c70a5d1
Constable, S.
b931c7b4-33b8-4c2b-8b10-f6502a433413
Tréhu, A.M.
83b5aede-2c1d-4a03-a117-e45391147325

Weitemeyer, K.A., Constable, S. and Tréhu, A.M. (2011) A marine electromagnetic survey to detect gas hydrate at Hydrate Ridge, Oregon. Geophysical Journal International, 187 (1), 45-62. (doi:10.1111/j.1365-246X.2011.05105.x).

Record type: Article

Abstract

Gas hydrates are a potential energy resource and hazard for drilling and infrastructure, yet estimates of global volume vary by over three orders of magnitude. Hydrates are electrically resistive compared to water saturated sediment and so electromagnetic methods provide an additional tool to seismic surveys and drilling for determining hydrate saturations. A marine electromagnetic survey was carried out at Hydrate Ridge, Oregon, USA, with the aim of testing the use of controlled source electromagnetic (CSEM) and magnetotelluric (MT) methods to map gas hydrate and free gas below the gas hydrate stability zone. A 2-D CSEM inversion supports the scenario deduced from previous seismic and drilling results, which indicate two mechanisms of hydrate emplacement: a transport-dominated and reaction-dominated regime. A prominent resistive region of 2.5–4 ?m at a depth of about 130 mbsf, near the seismic bottom simulating reflector (BSR), suggests that 27 to 46 per cent of the bulk volume is filled with hydrate, depending on whether Archie's Law or the Hashin-Strikman bounds are used. This is representative of a reaction-dominated regime for hydrate emplacement, and where a significant low velocity zone exists based on a seismic tomography inversion, suggests large quantities of free gas below the BSR. Electrical resistivity logging while drilling (LWD) data show general agreement with the CSEM inversion model except for a CSEM-derived resistive region at seismic horizon A, known to transport free gas into the gas hydrate stability zone. Inversion of MT data collected simultaneously during the CSEM survey provides a complimentary low-resolution image of the shallow sediments and shows folding in the accretionary complex sediments similar to that imaged by a tomographic seismic velocity model.

Text
abstract - Version of Record
Restricted to Repository staff only
Request a copy

More information

Published date: October 2011
Keywords: Magnetotelluric, Marine electromagnetics, Gas and hydrate systems, Continental margins: convergent
Organisations: Ocean and Earth Science

Identifiers

Local EPrints ID: 340171
URI: https://eprints.soton.ac.uk/id/eprint/340171
ISSN: 0956-540X
PURE UUID: facdb735-9c42-476b-b1ce-404234cb5cb0

Catalogue record

Date deposited: 14 Jun 2012 08:33
Last modified: 02 Dec 2019 20:57

Export record

Altmetrics

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of https://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×