Report on range of long-term scenarios to be simulated

In order to proceed with speculative modelling of the impacts of potential leakage of geologically stored carbon, it is necessary to develop plausible scenarios. Here a range of such scenarios are developed based on a consensus of the possible geological mechanisms of leakage, namely abandoned wells, geological faults and operational blowouts. Whilst the resulting scenarios remain highly speculative, they do enable short term progress in modelling and provide a basis for further debate and refinement

Magnetic Resonance Imaging of Gas Hydrate Formation and Conversion at Sub-Seafloor Conditions

The production of natural gas from sub-seafloor gas hydrates is one possible strategy to meet the world’s growing demand for energy. On the other hand, climate warming scenarios call for the substitution of fossil energy resources by sustainable energy concepts. Burning natural gas from gas hydrates could be emission neutral if it was combined with a safe storage of the emitted CO2. Laboratory experiments, that address corresponding strategies, need to be performed under high pressures and low temperatures to meet the thermodynamic conditions of the sub-seafloor environment. In this paper, we present a high-pressure flow-through sample cell that is suitable for nuclear magnetic resonance (NMR) experiments at realistic marine environmental conditions, i.e. pressures up to 15 MPa and temperatures from 5 to 20 °C, and we demonstrate its suitability in applied gas hydrate research

Rising methane gas bubbles form massive hydrate layers at the seafloor

Extensive methane hydrate layers are formed in the near-surface sediments of the Cascadia margin. An undissociated section of such a layer was recovered at the base of a gravity core (i.e. at a sediment depth of 120 cm) at the southern summit of Hydrate Ridge. As a result of salt exclusion during methane hydrate formation, the associated pore waters show a highly elevated chloride concentration of 809 mM. In comparison, the average background value is 543 mM. A simple transport-reaction model was developed to reproduce the Cl- observations and quantify processes such as hydrate formation, methane demand, and fluid flow. From this first field observation of a positive Cl- anomaly, high hydrate formation rates (0.15–1.08 mol cm-2 a-1) were calculated. Our model results also suggest that the fluid flow rate at the Cascadia accretionary margin is constrained to 45–300 cm a-1. The amount of methane needed to build up enough methane hydrate to produce the observed chloride enrichment exceeds the methane solubility in pore water. Thus, most of the gas hydrate was most likely formed from ascending methane gas bubbles rather than solely from CH4 dissolved in the pore water

Mechanisches Tiefseesedimente-, marine Rohstofflagerstätten- und/oder Unterseehang- Stabilisierungsverfahren und/oder Regulierungs-/Konditionierungsverfahren der hydraulischen Eigenschaften von Tiefseesedimenten

Die Erfindung betrifft ein mechanisches Tiefseesedimente-, marine Rohstofflagerstätten- und/oder Unterseehang- Stabilisierungsverfahren und/oder Regulierungs-/Konditionierungs-verfahren der hydraulischen Eigenschaften von Tiefseesedimenten aufweisend ein Injizieren einer gashydratbildenden Substanz in marine oder submarine Sedimente, wobei Gashydrat-Sediment-Verbünde gebildet werden

Verfahren zur Erdgasförderung aus Kohlenwasserstoff-Hydraten bei gleichzeitiger Speicherung von Kohlendioxid in geologischen Formationen

Verfahren zur Gewinnung von Methan aus Methanhydraten, mit den Schritten: Zuleiten von Kohlendioxid zu Methanhydratvorkommen, Wirkenlassen des Kohlendioxids auf das Methanhydrat unter Freisetzen von Methan und Einlagern des Kohlendioxids als Kohlendioxidhydrat, Abführen des freigesetzten Methans, dadurch gekennzeichnet, dass das zugeleitete Kohlendioxid superkritisches Kohlendioxid ist

Geochemistry of cold seeps - Fluid sources and systematics

Emanation of fluids at cold seeps, mud volcanoes, and other types of submarine seepage structures is a typical phenomenon occurring at continental margins worldwide. They represent pathways along which volatiles and solutes are recycled from deeply buried sediments into the global ocean, and hence they may be considered as a potentially important link in global geochemical cycles. In this contribution we present geochemical data from various geological and tectonic settings such as the Gulf of Cadiz, the convergent margin off Central America, and/or the Black Sea and provide approaches how to systemize available data sets. Clay-mineral dewatering plays a central role in terms of fluid-mobilization from greater depth, however, resulting cold seep fluids are typically very different from each other and cover a large range of geochemical signatures. This is is due to variations in control parameters such as the type and thickness of the sediment cover, thermal conditions, extension of fluid pathways, and the potential for secondary overprinting. For example, freshened fluids emanating at cold seeps off Costa Rica indicate dewatering and related geochemical reactions in subducting sediments, while fluids sampled at mud volcanoes in the Gulf of Cadiz provide evidence for a high-temperature fluid source originating in the underlying oceanic basement. The latter finding provides evidence for a hydrological connection between buried oceanic crust and the water column even at old crustal ages. Varius geochemical tracers were proposed in the past to decipher relevant processes in the subsurface. In a recent systematic study, Scholz et al. [1] demonstrated the general use of Li, reflecting the temperature-dependent isotope fractionation during early diagenetic Li uptake and burial diagenetic Li release from sediments. However, additional approaches are required in order to provide robust geochmical interpretations of cold seep fluids

Paired Sr isotope (⁸⁷Sr/⁸⁶Sr, δ^88/86Sr) systematic of pore water profiles: A new perspective in marine weathering and seepage studies

The simultaneous and independent determination of the radiogenic (87Sr/86Sr) and the fractionation reflecting stable (!88/86Sr) Sr isotope ratio on pore waters, sediments and precipitates (e.g. carbonates and sulfates) opens a new perspective in the field of submarine weathering and Sr contribution to the ocean chemistry. Four initial case studies covering (1.) CO2 seeps of the Okinawa Trough (OT), (2.) mud volcanoes (MV) and mounds in the Gulf of Cadiz (GoC) and the (3.) Central American Fore Arc as well as first results from the (4.) Black Sea are conducted and reflect a stable Sr perspective on seeps from a broad range of geological settings. Referred to NIST-SRM-987, in this study the IAPSO seawater (SW) standard has a !88/86Sr of 0.39 ‰ (±0.03, 2SD). As a prominent systematic deviation the OT pore water (PW) data from a site with CO2 hydrate and liquid CO2 occurence show values ranging from 0.27 to 0.59 ‰ (286 to 64 cm sediment depth), accompanied by a weak inversely correlated trend from 0.2 to 0.15 ‰ for the corresponding bulk sediment (286 to 36 cm). In contradiction to a simple fluid/SW-mixing approach as driving mechanism for the PW stable Sr trend the 87Sr/86Sr signature stays within analytical uncertainty constant with depth (0.70980 (1)) and differs significantly from SW (0.70917 (1)) and the more radiogenic, slightly heterogeneous sediment (0.71892-0.71731). Potential explanation for the observed !88/86Sr trend and PW signatures heavier than SW are (a) strong fractionation processes enriching light isotopes in secondary precipitates and remineralisation products and heavier signatures in the remaining fluid and/or (b) preferential dissolution of heavier mineral phases. Examples for the latter kind of sediment component are determined in a detailed study of the Mercator MV (GoC) by high !88/86Sr ratios of 0.72 for authigenic and 0.92 ‰ for potentially extruded gypsum crystals. Combined with PW data from the other seep settings (0.2 to 0.52 ‰) a broad range of Sr contribution and fractionation processes becomes evident

SUGAR Site Gas Hydrates as a new energy source - Reconnaissance of a pilot location for the SUGAR project - Cruise No. MSM34, December 06, 2013 - January 16, 2014, Varna, Bulgaria - Varna, Bulgaria

Cruise MSM34 of R/V MARIA S. MERIAN aimed to investigate a possible test site location for the German SUGAR project. The well sealed gas hydrate deposit should be accessible by the mobile drilling device MeBo 200. During the two legs of cruise MSM34 of R/V MARIA S. MERIAN regional 2D seismic surveying, high resolution 2D and 3D seismic imaging, geo-chemical sampling, heatflow measurements and long-term piezometer installations were undertaken. A grid of 28 2D seismic profiles was collected across the palaeo Danube delta. A number of inactive and partly buried channel systems could be mapped. Most of them were underlain by one or more bottom simulation reflectors (BSR) indicating the existence of gas hydrates. Based on the seismic brute stack images and the limits of the MeBo drilling device a prospective channel system with indications for possible gas hydrate formation at shallow depth (BSR, inverted strong amplitudes) could be identified in about 1500 m water depth. High resolution 2D seismic and 3D P-Cable seismic were used together with OBS deployments in order to allow structural mapping and physical description of the channel infill. Heatflow measurements and geochemical analyses of gravity and multi corer samples accompany these investigations. Neither the multibeam water column images nor Parasound records show any evidence of flares (gas bubbles in the water column) in this working area suggesting a well sealed hydrate reservoir. Active gas expulsion from the seafloor was observed at about 200 m water depth circling around a slump area. The base plane of the failed sediment volume builds the current seafloor at about 600 m to 700 m water depth. On regional 2D seismic profiles a BSR has been mapped underneath the slope failure with unexpectedly strong upward bending. High resolution 2D and 3D P-Cable seismic investigations with complementary OBS deployment will allow imaging the BSR outline. Moreover velocity analyses, heatflow measurements and geo-chemical samples will be available for a detailed description of hydrate distribution and sediment parameters. In a third working area high resolution 2D seismic reflection profiles were acquired across a fully buried channel system. Together with the regional seismic lines slope failure of the channel fill material can be studied across the slope extension of the system. In summary cruise MSM34 achieved all proposed aims. Based on new regional seismic acquisition two working areas were selected for 3D high resolution studies. Investigations of a promising location for a SUGAR pilot site will be supported by a test location for slope stability and analyses of fluid migration pathways in a buried canyon site