scholarly journals Authigenic Greigite as an Indicator of Methane Diffusion in Gas Hydrate-Bearing Sediments of the Hikurangi Margin, New Zealand

2021 ◽  
Vol 9 ◽  
Author(s):  
Myriam Kars ◽  
Annika Greve ◽  
Lilly Zerbst
Keyword(s):  
New Zealand ◽  
Microbial Activity ◽  
Fault Zone ◽  
Gas Hydrate ◽  
Methane Hydrate ◽  
Hanging Wall ◽  
Accretionary Wedge ◽  
Iron Sulfides ◽  
Stratigraphic Sequence ◽  
Methane Diffusion

Authigenic ferrimagnetic iron sulfides, essentially greigite (Fe3S4), are commonly found in gas hydrate-bearing marine sediments of active accretionary prisms. Greigite is a by-product, either intracellular or extracellular, of microbial activity, and therefore provides good indication of microbial processes which are closely related to the occurrence of gas hydrate. A high-resolution rock magnetic study was conducted at Site U1518 of International Ocean Discovery Program Expedition 375, located in the frontal accretionary wedge of the Hikurangi Margin, offshore New Zealand. Samples were collected throughout the entire recovered stratigraphic sequence, from the surface to ∼492 m below seafloor (mbsf) which includes the Pāpaku fault zone. This study aims to document the rock magnetic properties and the composition of the magnetic mineral assemblage at Site U1518. Based on downhole magnetic coercivity variations, the studied interval is divided into five consecutive zones. Most of the samples have high remanent coercivity (above 50 mT) and first-order reversal curves (FORC) diagrams typical of single-domain greigite. The top of the hanging wall has intervals that display a lower remanent coercivity, similar to lower coercivities measured on samples from the fault zone and footwall. The widespread distribution of greigite at Site U1518 is linked to methane diffusion and methane hydrate which is mainly disseminated within sediments. In three footwall gas hydrate-bearing intervals, investigated at higher resolution, an improved magnetic signal, especially a stronger FORC signature, is likely related to enhanced microbial activity which favors the formation and preservation of greigite. Our findings at the Hikurangi Margin show a close linkage between greigite, methane hydrate and microbial activity.

Distribution and fractionation of light hydrocarbons related to gas hydrate occurrence and biogenic production at Hikurangi Margin (IODP Site U1517), New Zealand

2020 ◽  
Author(s):  
Katja Heeschen ◽  
Stefan Schloemer ◽  
Marta Torres ◽  
Ann E Cook ◽  
Liz Screation ◽  
...  
Keyword(s):  
New Zealand ◽  
High Resolution ◽  
Gas Hydrates ◽  
Gas Hydrate ◽  
Isotopic Fractionation ◽  
Close Relation ◽  
Coarse Grained ◽  
Accretionary Wedge ◽  
Light Hydrocarbons ◽  
Slide Mass

<p>The investigation of the gas hydrate system and hydrocarbon distribution were targets of IODP expeditions 372 and 375 on the Hikurangi Margin offshore New Zealand. Isotopic and molecular signatures clearly indicate a biogenic signature of methane at all sites drilled along a section crossing the accretionary wedge and basin sediments. The gas void and headspace samples from depth of a few meters up to 600 m below the seafloor have varying amounts of light hydrocarbons with high amounts of methane and changing ratios of C<sub>2</sub>:C<sub>3</sub>. The best example is the high-resolution profile gained from gas voids collected at Site U1517. Drilling at U1517 reached through the creeping part of the Tuaheni Landslide Complex (TLC), the base of the slide mass, and the Bottom Simulation Reflector (BSR) just above the base of the hole. Whereas gas hydrates could not be observed macroscopically, the distribution of gas hydrates was determined by logging while drilling (LWD) and pore water data revealing the occurrence of gas hydrates at roughly 105 – 160 mbsf with elevated saturations in thin coarse-grained sediments. The application of cryo-Scanning Electric Microscopy (cryo-SEM) on samples preserved in liquid nitrogen enabled the visualization of gas hydrates.</p><p> </p><p>At Site U1517 the high-resolution void sampling reveals molecular and isotopic fractionation of hydrocarbons in close relation to the gas hydrate occurrences and allows for drawing conclusions on the recent history of the gas hydrate system and absence of free gas transport from below at the site. The molecular and isotopic composition further indicates ongoing propanogenesis.</p>

Methane hydrate saturations at the Southern Hikurangi margin (New Zealand) estimated from seismic and rock physics inversion

2020 ◽  
Author(s):  
Francesco Turco ◽  
Andrew Gorman ◽  
Gareth Crutchley ◽  
Leonardo Azevedo ◽  
Dario Grana ◽  
...  
Keyword(s):  
New Zealand ◽  
Gas Hydrate ◽  
Methane Hydrate ◽  
Waveform Inversion ◽  
Hydrate Formation ◽  
Rock Physics ◽  
Stability Zone ◽  
Hydrate Saturation ◽  
Physics Model ◽  
Hydrate Stability

<p>Geophysical data indicate that the Hikurangi subduction margin on New Zealand’s East Coast contains a large gas hydrate province. Gas hydrates are widespread in shallow sediments across the margin, and locally intense fluid seepage associated with methane hydrate is observed in several areas. Glendhu and Honeycomb ridges lie at the toe of the Hikurangi deformation wedge at depths ranging from 2100 to 2800 m. These two parallel four-way closure systems host concentrated methane hydrate deposits. The control on hydrate formation at these ridges is governed by steeply dipping permeable strata and fractures, which allow methane to flow upwards into the gas hydrate stability zone. Hydrate recycling at the base of the hydrate stability zone may contribute to the accumulation of highly concentrated hydrate in porous layers.<br>To improve the characterisation of the hydrate systems at Glendhu and Honeycomb ridges, we estimate hydrate saturation and porosity of the concentrated hydrate deposits. We first estimate elastic properties (density, compressional and shear-wave velocities) of the gas hydrate stability zone through full-waveform inversion and <span>iterative geostatistical seismic amplitude versus angle (AVA) inversion</span>. We then perform a petrophysical inversion based on a rock physics model to predict gas hydrate saturation and porosity of the hydrate bearing sediments along the two ridges.<br>Our results indicate that the high seismic amplitudes correspond to the top interface of highly concentrated hydrate deposit, with peak saturations around 35%. Because of the resolution of the seismic data we assume that the estimated properties are averaged over layers of 10 to 20 meters thickness. These saturation values are in agreement with studies conducted in other areas of concentrated hydrate accumulations in similar geologic settings.</p>

scholarly journals The last 2 Myr of accretionary wedge construction in the central Hikurangi margin (North Island, New Zealand): Insights from structural modeling

2016 ◽  
Vol 17 (7) ◽  
pp. 2661-2686 ◽  
Author(s):  
Francesca C. Ghisetti ◽  
Philip M. Barnes ◽  
Susan Ellis ◽  
Andreia A. Plaza-Faverola ◽  
Daniel H. N. Barker
Keyword(s):  
New Zealand ◽  
Structural Modeling ◽  
Accretionary Wedge

SS - Gas Hydrate: Gas production from methane hydrate sediment layer by thermal stimulation with hot water injection

2010 ◽  
Author(s):  
Kyuro Sasaki ◽  
Shinzi Ono ◽  
Yuichi Sugai ◽  
Norio Tenma ◽  
Takao Ebinuma ◽  
...  
Keyword(s):  
Gas Hydrate ◽  
Methane Hydrate ◽  
Water Injection ◽  
Gas Production ◽  
Hot Water ◽  
Thermal Stimulation ◽  
Sediment Layer

Influence of a Combined Low Dosage Gas Hydrate Inhibitor on Methane Hydrate Surface

2014 ◽  
Vol 1008-1009 ◽  
pp. 300-306
Author(s):  
Cui Ping Tang ◽  
Dong Liang Li ◽  
De Qing Liang
Keyword(s):  
Molecular Dynamics ◽  
Hydrogen Bond ◽  
Hydrogen Bonds ◽  
Gas Hydrate ◽  
Methane Hydrate ◽  
Md Simulation ◽  
Side Group ◽  
Large Space ◽  
Surface Molecules ◽  
Low Dosage

According to analysis of the gas hydrate cage and structure of the inhibitor and simulation of molecular dynamics, the interaction between GHI1 and hydrates was discussed. The structure analysis indicated the side group of PVP can insert into the open hydrate cage, and force the hydrate growing along the polymer chain, which results in a large space resistance and inhibits gas hydrate agglomerating. The results of MD simulation show GHI1 can damage the surface cage in hydrate lattice; the hydrogen and oxygen in GHI1 can form hydrogen bonds respectively with oxygen and hydrogen in hydrates, which makes the surface molecules of the cages unstable and distorts the cages; Synergist diethylene glycol ether increases strength and range of length of hydrogen bond.

scholarly journals Numerical Investigation into the Development Performance of Gas Hydrate by Depressurization Based on Heat Transfer and Entropy Generation Analyses

Entropy ◽  
2020 ◽  
Vol 22 (11) ◽  
pp. 1212 ◽  
Author(s):  
Bo Li ◽  
Wen-Na Wei ◽  
Qing-Cui Wan ◽  
Kang Peng ◽  
Ling-Ling Chen
Keyword(s):  
Heat Transfer ◽  
Energy Loss ◽  
Entropy Production ◽  
Entropy Generation ◽  
Gas Hydrate ◽  
Methane Hydrate ◽  
Dynamic Properties ◽  
Entropy Production Rate ◽  
Entropy Flow ◽  
Hydrate Reservoir

The purpose of this study is to analyze the dynamic properties of gas hydrate development from a large hydrate simulator through numerical simulation. A mathematical model of heat transfer and entropy production of methane hydrate dissociation by depressurization has been established, and the change behaviors of various heat flows and entropy generations have been evaluated. Simulation results show that most of the heat supplied from outside is assimilated by methane hydrate. The energy loss caused by the fluid production is insignificant in comparison to the heat assimilation of the hydrate reservoir. The entropy generation of gas hydrate can be considered as the entropy flow from the ambient environment to the hydrate particles, and it is favorable from the perspective of efficient hydrate exploitation. On the contrary, the undesirable entropy generations of water, gas and quartz sand are induced by the irreversible heat conduction and thermal convection under notable temperature gradient in the deposit. Although lower production pressure will lead to larger entropy production of the whole system, the irreversible energy loss is always extremely limited when compared with the amount of thermal energy utilized by methane hydrate. The production pressure should be set as low as possible for the purpose of enhancing exploitation efficiency, as the entropy production rate is not sensitive to the energy recovery rate under depressurization.

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