Controlled-source electromagnetic and seismic delineation of subseafloor fluid flow structures in a gas hydrate province, offshore Norway

Abstract

SUMMARYDeep sea pockmarks underlain by chimney-like or pipe structures that contain methane hydrate are abundant along the Norwegian continental margin. In such hydrate provinces the interaction between hydrate formation and fluid flow has significance for benthic ecosystems and possibly climate change. The Nyegga region, situated on the western Norwegian continental slope, is characterized by an extensive pockmark field known to accommodate substantial methane gas hydrate deposits. The aim of this study is to detect and delineate both the gas hydrate and free gas reservoirs at one of Nyegga's pockmarks.In 2012, a marine controlled-source electromagnetic (CSEM) survey was performed at a pockmark in this region, where high-resolution three-dimensional seismic data were previously collected in 2006. Two-dimensional CSEM inversions were computed using the data acquired by ocean bottom electrical field receivers. Our results, derived from un- constrained and seismically constrained CSEM inversions, suggest the presence of two distinctive resistivity anomalies beneath the pockmark: a shallow vertical anomaly at the underlying pipe structure, likely due to gas hydrate accumulation, and a laterally extensive anomaly attributed to a free gas zone below the base of the gas hydrate stability zone. This work contributes to a robust characterization of gas hydrate deposits within sub-seafloor fluid flow pipe structures.

Marine‐controlled source electromagnetic study of methane seeps and gas hydrates at Opouawe Bank, Hikurangi Margin, New Zealand

“…Based on their high resistivities, Edwards [1997] suggested the use of time domain CSEM data for the detection of submarine gas hydrates. Several gas hydrate exploration case studies followed using CSEM systems in time domain [Yuan and Edwards, 2000;Schwalenberg et al, 2005Schwalenberg et al, , 2010aSchwalenberg et al, , 2010b, frequency domain [Weitemeyer et al, 2006[Weitemeyer et al, , 2011Weitemeyer and Constable, 2010;Ellis et al, 2008;Constable et al, 2016;Goswami et al, 2015, Attias et al, 2016, and a DC resistivity system [Goto et al, 2008].…”

Laboratory Insights Into the Effect of Sediment‐Hosted Methane Hydrate Morphology on Elastic Wave Velocity From Time‐Lapse 4‐D Synchrotron X‐Ray Computed Tomography

“…Notable insights have been gained from laboratory studies to date (e.g., Handa, 1990;Kerkar et al, 2014;Priegnitz et al, 2015;Priest et al, 2009;Tohidi et al, 2001), but further research is needed into the following areas: (i) the causes of the commonly observed discrepancy between hydrate saturation estimates from seismo-acoustic and electrical resistivity methods (Attias et al, 2016;Goswami et al, 2015;Lee & Collett, 2006;Miyakawa et al, 2014;Sahoo et al, 2018) (referred to here as the seismicelectrical discrepancy); and (ii) the effect of methane hydrate saturation and its spatial distribution in the host sediment on the seismo-acoustic velocity of hydrate-bearing sediments. Some studies associate the seismic-electrical discrepancy to the coexistence of gas and hydrate, as the presence of gas can reduce the seismic velocity but not the electrical resistivity of the sediment (e.g., Goswami et al, 2015;Lee & Collett, 2006;Miyakawa et al, 2014;Sahoo et al, 2018).…”

Presence and Consequences of Coexisting Methane Gas With Hydrate Under Two Phase Water‐Hydrate Stability Conditions

“… Note . References: 1, Schnurle et al (); 2, Hsu et al (); 3, Fohrmann and Pecher (); 4, Schwalenberg et al (); 5, Lee and Collett (); 6, Miyakawa et al (); 7, Attias et al (); 8, Plaza‐Faverola et al (); 9, Goswami et al (); 10, Hustoft et al ().…”