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

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 C2:C3. 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 &#8211; 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.&#160;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.

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Formation of submarine gas hydrates

Bulletin of the Geological Society of Denmark ◽

10.37570/bgsd-1995-41-09 ◽

1994 ◽

Vol 41 ◽

pp. 86-94

Author(s):

V. Soloviev ◽

G. D. Ginsburg

Keyword(s):

Gas Hydrates ◽

Gas Hydrate ◽

Deep Sea ◽

Hydrate Formation ◽

Coarse Grained ◽

Necessary Condition ◽

Dissolved Gas ◽

Scale Levels ◽

Bottom Sampling ◽

Gas Bearing

Submarine gas hydrates have been discovered in the course of deep-sea drilling (DSDP and ODP) and bottom sampling in many offshore regions. This paper reports on expeditions carried out in the Black, Caspian and Okhotsk Seas. Gas hydrate accumulations were discovered and investigated in all these areas. The data and an analysis of the results of the deep-sea drilling programme suggest that the infiltration of gas-bearing fluids is a necessary condition for gas hydrate accumulation. This is confirmed by geological observations at three scale levels. Firstly, hydrates in cores are usually associated with comparatively coarse-grained, permeable sediments as well as voids and fractures. Secondly, hydrate accumulations are controlled by permeable geological structures, i.e. faults, diapirs, mud volcanos as well as layered sequences. Thirdly, in the worldwide scale, hydrate accumulations are characteristic of continental slopes and rises and intra-continental seas where submarine seepages also are widespread. Both biogenic and catagenic gas may occur, and the gas sources may be located at various distances from the accumulation. Gas hydrates presumably originate from water-dissolved gas. The possibility of a transition from dissolved gas into hydrate is confirmed by experimental data. Shallow gas hydrate accumulations associated with gas-bearing fluid plumes are the most convenient features for the study of submarine hydrate formation in general. These accumulations are known from the Black, Caspian and Okhotsk Seas, the Gulf of Mexico and off northern California.

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

Frontiers in Earth Science ◽

10.3389/feart.2021.603363 ◽

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.

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Seismic attribute enhancement of weak and discontinuous gas hydrate bottom-simulating reflectors in the Pegasus Basin, New Zealand

Interpretation ◽

10.1190/int-2018-0222.1 ◽

2019 ◽

Vol 7 (3) ◽

pp. SG11-SG22 ◽

Cited By ~ 2

Author(s):

Heather Bedle

Keyword(s):

New Zealand ◽

Gas Hydrates ◽

Gas Hydrate ◽

Seismic Data ◽

Rock Physics ◽

Stability Zone ◽

Seismic Attribute ◽

Rock Physics Modeling ◽

Physics Modeling ◽

Hydrate Stability

Gas hydrates in the oceanic subsurface are often difficult to image with reflection seismic data, particularly when the strata run parallel to the seafloor and in regions that lack the presence of a bottom-simulating reflector (BSR). To address and understand these imaging complications, rock-physics modeling and seismic attribute analysis are performed on modern 2D lines in the Pegasus Basin in New Zealand, where the BSR is not continuously imaged. Based on rock-physics and seismic analyses, several seismic attribute methods identify weak BSR reflections, with the far-angle stack data being particularly effective. Rock modeling results demonstrate that far-offset seismic data are critical in improving the imaging and interpretation of the base of the gas hydrate stability zone. The rock-physics modeling results are applied to the Pegasus 2009 2D data set that reveals a very weak seismic reflection at the base of the hydrates in the far-angle stack. This often-discontinuous reflection is significantly weaker in amplitude than typical BSRs associated with hydrates. These weak far-angle stack BSRs often do not appear clearly in full stack data, the most commonly interpreted seismic data type. Additional amplitude variation with angle (AVA) attribute analyses provide insight into identifying the presence of gas hydrates in regions lacking a strong BSR. Although dozens of seismic attributes were investigated for their ability to reveal weak reflections at the base of the gas hydrate stability zone, those that enhance class 2 AVA anomalies were most effective, particularly the seismic fluid factor attribute.

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High-resolution seismic velocity analysis as a tool for exploring gas hydrate systems: An example from New Zealand’s southern Hikurangi margin

Interpretation ◽

10.1190/int-2015-0042.1 ◽

2016 ◽

Vol 4 (1) ◽

pp. SA1-SA12 ◽

Cited By ~ 14

Author(s):

Gareth J. Crutchley ◽

Guy Maslen ◽

Ingo A. Pecher ◽

Joshu J. Mountjoy

Keyword(s):

High Resolution ◽

Marine Sediments ◽

Gas Hydrate ◽

Seismic Data ◽

Seismic Velocity ◽

Coarse Grained ◽

Velocity Analysis ◽

Low Velocity ◽

Free Gas ◽

Velocity Models

The existence of free gas and gas hydrate in the pore spaces of marine sediments causes changes in acoustic velocities that overprint the background lithological velocities of the sediments themselves. Much previous work has determined that such velocity overprinting, if sufficiently pronounced, can be resolved with conventional velocity analysis from long-offset, multichannel seismic data. We used 2D seismic data from a gas hydrate province at the southern end of New Zealand’s Hikurangi subduction margin to describe a workflow for high-resolution velocity analysis that delivered detailed velocity models of shallow marine sediments and their coincident gas hydrate systems. The results showed examples of pronounced low-velocity zones caused by free gas ponding beneath the hydrate layer, as well as high-velocity zones related to gas hydrate deposits. For the seismic interpreter of a gas hydrate system, the velocity results represent an extra “layer” for interpretation that provides important information about the distribution of free gas and gas hydrate. By combining the velocity information from the seismic transect with geologic samples of the seafloor and an understanding of sedimentary processes, we have determined that high gas hydrate concentrations preferentially form within coarse-grained sediments at the proximal end of the Hikurangi Channel. Finer grained sediments expected elsewhere along the seismic transect might preclude the deposition of similarly high gas hydrate concentrations away from the channel.

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Characterisation of focused gas hydrate accumulations from the Pegasus Basin, New Zealand, using high-resolution and conventional seismic data

ASEG Extended Abstracts ◽

10.1071/aseg2018abt7_2a ◽

2018 ◽

Vol 2018 (1) ◽

pp. 1-4

Author(s):

Andrew R. Gorman ◽

Patrick T. Fletcher ◽

Dylan Baker ◽

Douglas R.A. Fraser ◽

Gareth J. Crutchley ◽

...

Keyword(s):

New Zealand ◽

High Resolution ◽

Gas Hydrate ◽

Seismic Data

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Gas hydrate and free gas detection using seismic quality factor estimates from high-resolution P-cable 3D seismic data

Interpretation ◽

10.1190/int-2015-0023.1 ◽

2016 ◽

Vol 4 (1) ◽

pp. SA39-SA54 ◽

Cited By ~ 6

Author(s):

Sunny Singhroha ◽

Stefan Bünz ◽

Andreia Plaza-Faverola ◽

Shyam Chand

Keyword(s):

High Resolution ◽

Frequency Shift ◽

Gas Hydrates ◽

Gas Hydrate ◽

Seismic Data ◽

Seismic Attenuation ◽

3D Seismic ◽

Free Gas ◽

Centroid Frequency ◽

3D Seismic Data

We have estimated the seismic attenuation in gas hydrate and free-gas-bearing sediments from high-resolution P-cable 3D seismic data from the Vestnesa Ridge on the Arctic continental margin of Svalbard. P-cable data have a broad bandwidth (20–300 Hz), which is extremely advantageous in estimating seismic attenuation in a medium. The seismic quality factor (Q), the inverse of seismic attenuation, is estimated from the seismic data set using the centroid frequency shift and spectral ratio (SR) methods. The centroid frequency shift method establishes a relationship between the change in the centroid frequency of an amplitude spectrum and the Q value of a medium. The SR method estimates the Q value of a medium by studying the differential decay of different frequencies. The broad bandwidth and short offset characteristics of the P-cable data set are useful to continuously map the Q for different layers throughout the 3D seismic volume. The centroid frequency shift method is found to be relatively more stable than the SR method. Q values estimated using these two methods are in concordance with each other. The Q data document attenuation anomalies in the layers in the gas hydrate stability zone above the bottom-simulating reflection (BSR) and in the free gas zone below. Changes in the attenuation anomalies correlate with small-scale fault systems in the Vestnesa Ridge suggesting a strong structural control on the distribution of free gas and gas hydrates in the region. We argued that high and spatially limited Q anomalies in the layer above the BSR indicate the presence of gas hydrates in marine sediments in this setting. Hence, our workflow to analyze Q using high-resolution P-cable 3D seismic data with a large bandwidth could be a potential technique to detect and directly map the distribution of gas hydrates in marine sediments.

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Thermodynamic Modelling of Gas Hydrate Formation in the Presence of Inhibitors and the Consideration of their Effect

ASEAN Journal of Chemical Engineering ◽

10.22146/ajche.49715 ◽

2014 ◽

Vol 14 (1) ◽

pp. 45

Author(s):

Peyman Sabzi ◽

Saheb Noroozi

Keyword(s):

Gas Hydrates ◽

Gas Hydrate ◽

Low Temperatures ◽

Hydrate Formation ◽

Transportation Systems ◽

Flow Lines ◽

Main Approach ◽

Efficient Inhibitor ◽

System A ◽

Gas Hydrate Formation

Gas hydrates formation is considered as one the greatest obstacles in gas transportation systems. Problems related to gas hydrate formation is more severe when dealing with transportation at low temperatures of deep water. In order to avoid formation of Gas hydrates, different inhibitors are used. Methanol is one of the most common and economically efficient inhibitor. Adding methanol to the flow lines, changes the thermodynamic equilibrium situation of the system. In order to predict these changes in thermodynamic behavior of the system, a series of modelings are performed using Matlab software in this paper. The main approach in this modeling is on the basis of Van der Waals and Plateau's thermodynamic approach. The obtained results of a system containing water, Methane and Methanol showed that hydrate formation pressure increases due to the increase of inhibitor amount in constant temperature and this increase is more in higher temperatures. Furthermore, these results were in harmony with the available empirical data.Keywords: Gas hydrates, thermodynamic inhibitor, modelling, pipeline blockage

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Rapid Gas Hydrate Formation—Evaluation of Three Reactor Concepts and Feasibility Study

Molecules ◽

10.3390/molecules26123615 ◽

2021 ◽

Vol 26 (12) ◽

pp. 3615

Author(s):

Florian Filarsky ◽

Julian Wieser ◽

Heyko Juergen Schultz

Keyword(s):

Gas Hydrates ◽

Gas Hydrate ◽

Hydrate Formation ◽

Synthetic Natural Gas ◽

Operation Conditions ◽

Gas Hydrate Formation ◽

Gas Conditioning ◽

And Storage ◽

Economic Considerations ◽

High Storage

Gas hydrates show great potential with regard to various technical applications, such as gas conditioning, separation and storage. Hence, there has been an increased interest in applied gas hydrate research worldwide in recent years. This paper describes the development of an energetically promising, highly attractive rapid gas hydrate production process that enables the instantaneous conditioning and storage of gases in the form of solid hydrates, as an alternative to costly established processes, such as, for example, cryogenic demethanization. In the first step of the investigations, three different reactor concepts for rapid hydrate formation were evaluated. It could be shown that coupled spraying with stirring provided the fastest hydrate formation and highest gas uptakes in the hydrate phase. In the second step, extensive experimental series were executed, using various different gas compositions on the example of synthetic natural gas mixtures containing methane, ethane and propane. Methane is eliminated from the gas phase and stored in gas hydrates. The experiments were conducted under moderate conditions (8 bar(g), 9–14 °C), using tetrahydrofuran as a thermodynamic promoter in a stoichiometric concentration of 5.56 mole%. High storage capacities, formation rates and separation efficiencies were achieved at moderate operation conditions supported by rough economic considerations, successfully showing the feasibility of this innovative concept. An adapted McCabe-Thiele diagram was created to approximately determine the necessary theoretical separation stage numbers for high purity gas separation requirements.

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