Matthias Haeckel

METHANE BUDGET OF A LARGE GAS HYDRATE PROVINCE OFFSHORE GEORGIA, BLACK SEA

The Batumi Seep Area, offshore Georgia, Black Sea, has been intensively cored (gravity cores and TV-guided multi-cores) to investigate the methane turnover in the surface sediments. The seep area is characterized by vigorous methane gas bubble emanations. Geochemical analyses show a microbial origin of the methane and a shallow fluid source. Anaerobic methane oxidation rapidly consumes the SO4 within the top 5-20 cm, but significant upward fluid advection is not indicated by the porewater profiles. Hence, the Batumi Seep Area must be dominated by methane gas seepage in order to explain the required CH4 flux from below. 1-D transport-reaction modelling constrains the methane flux needed to support the observed SO4 flux as well as the rate of near-surface hydrate formation. The model results correlate well with the hydro-acoustic backscatter intensities recorded and mapped bubble release sites using the sonar of a ROV.

Best Practice Guidance for Environmental Risk Assessment for offshore CO2 geological storage

Carbon dioxide (CO2) separated from natural gas has been stored successfully below the seabed off Norway for almost two decades. Based on these experiences several demonstration projects supported by the EU and its member states are now setting out to store CO2 captured at power plants in offshore geological formations. The ECO2 project was triggered by these activities and funded by the EU to assess the environmental risks associated with the sub-seabed storage of CO2 and to provide guidance on environmental practices. ECO2 conducted a comprehensive offshore field programme at the Norwegian storage sites Sleipner and Snohvit and at several natural CO2 seepage sites in order to identify potential pathways for CO2 leakage through the overburden, monitor seep sites at the seabed, track and trace the spread of CO2 in ambient bottom waters, and study the response of benthic biota to CO2. ECO2 identified a rich variety of geological structures in the broader vicinity of the storage sites that may have served as conduits for gas release in the geological past and located a seabed fracture and several seeps and abandoned wells where natural gas and formation water are released into the marine environment. Even though leakage may occur if these structures are not avoided during site selection, observations at natural seeps, release experiments, and numerical modelling revealed that the footprint at the seabed where organisms would be impacted by CO2 is small for realistic leakage scenarios. ECO2 conducted additional studies to assess and evaluate the legal framework and the public perception of CO2 storage below the seabed. The following guidelines and recommendations for environmental practices are based on these experiences.

RV POSEIDON Fahrtbericht / Cruise Report POS518:Baseline Study for the Environmental Monitoringof Subseafloor CO2 Storage Operations, Leg 1: Bremerhaven – Bremerhaven (Germany)25.09.-11.10.2017, Leg 2: Bremerhaven – Kiel (Germany)12.10.-28.10.2017

Poseidon cruise 518 (leg 1 and 2) took place in the framework of the Horizon 2020 project STEMM-CCS of the EU. The project’s main goal is to develop and test strategies and technologies for the monitoring of subseafloor CO2 storage operations. In this context a small research-scale CO2 gas release experiment is planned for 2019 in the vicinity of the Goldeneye platform located in the British EEZ (central North Sea). Cruise POS518 aimed at collecting necessary oceanographic and biogeochemical baseline data for this release experiment. During Leg 1 ROV PHOCA was used to deploy MPI’s tool for high-precision measurements of O2, CO2 and pH in the bottom water at Goldeneye. In addition, ROV push cores and gravity cores were collected in the area for sediment biogeochemical analyses, and video-CTD casts were conducted to study the water column chemistry. The stereo-camera system and a horizontally looking multibeam echosounder, both, for determining gas bubble emissions at the seafloor were deployed at the Figge Maar blowout crater in the German Bight. Investigations were complemented by hydroacoustic surveys detecting gas bubble leakages at several abandoned wells in the North Sea as well as the Figge Maar. Surface water alkalinity as well as CH4, CO2, and water partial pressures in the air above the sea surface were measured continuously during the cruise. During Leg 2 three different benthic lander systems were deployed to obtain baseline data of oceanographic and biogeochemical parameters for a small research-scale CO2 gas release experiment planned for 2019. The first lander was equipped with an acoustic Doppler current profiler (ADCP), a CTD and an O2 optode. It was deployed for 6 days close to Goldeneye to obtain high resolution data which can be linked to the long-term measurements of the NOC-Lander. This lander is equipped with a suite of sensors to monitor temperature, conductivity, pressure, current speed and direction, hydro-acoustic, pH, pCO2, O2 and nutrients over a period of about 10 months with popup telemetry units for data transmission via IRIDIUM satellite telemetry every 3 months. Two short-term deployments of the Biogeochemical Observatory (BIGO) were conducted to study the molar ratio between oxygen and CO2-fluxes at the seafloor. Sediment cores obtained by gravity and multi corer were collected for sediment biogeochemical analyses and video-CTD casts were used to study the chemistry of the water column.

CCT2 Synthesis report on predicted impacts & uncertainties

The initial concept for this synthesis report was to follow a number of explicit leakage scenarios from the reservoir, assessing flow rates and environmental impact and ending with an economic analysis. However because at each stage of the trail the number of variables, scenarios and uncertainties multiply, this approach was replaced by a more pragmatic approach which addressed the primary scenario space at each stage. For example for any given reservoir leakage scenario there are multiple possible flow pathways through the overburden, a range of trapping and buffering possibilities within the overburden, multiple possibilities of CO2 bubble plume size and resultant water column plume dynamics, a wide range of hydrodynamic conditions which fundamentally change the size and shape of chemical perturbation in the natural environment and many different biological communities that may be impacted. On top of this a cost analysis must cope with a wide range of economic scenarios involving national and global responses (or the lack of) to climate change, energy generation and emissions reduction. Consequently, we initiated the exercise by identifying a small range of geologically plausible reservoir leakage scenarios, associated with Sleipner and Snøhvit, so that the following analysis was at least grounded in realism, rather than speculation. Hence 4 representative scenarios (table 1) were simulated addressing different potential leakage structures documented in the larger Sleipner and Snøhvit areas (see section 1.1).Whilst the leakage pathway modelling within the overburden and water column has taken the approach of using these specific scenarios (sections 1 & 2), the impact and economic analysis (sections 4 & 5) has taken a generic approach with the economic analysis taking a top-down approach.

FS MARIA S. MERIAN Fahrtbericht / Cruise ReportMSM34/1 & 2 - SUGAR Site ; Varna – Varna,06.12.13 – 16.01.14

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). 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.

Studies Towards the Development of a CH4 Production Technology By CO2 Sequestration into Submarine Hydrate Reservoirs

In the recent past, international research efforts towards exploitation of submarine and permafrost hydrate reservoirs have increased substantially. Emission neutral exploitation of CH4-hydrates could potentially be achieved in a combined process with CO2 injection and storage as CO2-hydrate. In the German gas hydrate initiative SUGAR, a combination of experimental and numerical studies is used to elucidate the process mechanisms and technical parameters on different scales. Among the parameters tested so far are the CO2 injection regime, the injection temperature and the reservoir pressure / temperature conditions. It was shown that CH4 production is optimal at intermediate reservoir temperatures (8 °C) compared to lower (2 °C) and higher temperatures (10 °C). The reservoir pressure, however, was of minor importance for the production efficiency. The injection of heated CO2 into the hydrate reservoir induces a variety of spatial and temporal processes which result in substantial bulk heterogeneity. Current numerical simulators are not able to predict these process dynamics and it is important to improve available transport-reaction models. Our results confirm that experimental studies are important to better understand the mechanisms of hydrate dissociation and conversion at CO2-injection conditions as a basis towards the development of a suitable hydrate conversion technology.

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.