ALBERT

Description: Highlights • There is direct and indirect evidence for hydrate occurrence in several areas around Europe. • Hydrate is particularly widespread offshore Norway and Svalbard and in the Black Sea. • Hydrate occurrence often coincides with conventional thermogenic hydrocarbon provinces. • The regional abundance of hydrate in Europe is poorly known. Abstract Large national programs in the United States and several Asian countries have defined and characterised their marine methane hydrate occurrences in some detail, but European hydrate occurrence has received less attention. The European Union-funded project “Marine gas hydrate – an indigenous resource of natural gas for Europe” (MIGRATE) aimed to determine the European potential inventory of exploitable gas hydrate, to assess current technologies for their production, and to evaluate the associated risks. We present a synthesis of results from a MIGRATE working group that focused on the definition and assessment of hydrate in Europe. Our review includes the western and eastern margins of Greenland, the Barents Sea and onshore and offshore Svalbard, the Atlantic margin of Europe, extending south to the northwestern margin of Morocco, the Mediterranean Sea, the Sea of Marmara, and the western and southern margins of the Black Sea. We have not attempted to cover the high Arctic, the Russian, Ukrainian and Georgian sectors of the Black Sea, or overseas territories of European nations. Following a formalised process, we defined a range of indicators of hydrate presence based on geophysical, geochemical and geological data. Our study was framed by the constraint of the hydrate stability field in European seas. Direct hydrate indicators included sampling of hydrate; the presence of bottom simulating reflectors in seismic reflection profiles; gas seepage into the ocean; and chlorinity anomalies in sediment cores. Indirect indicators included geophysical survey evidence for seismic velocity and/or resistivity anomalies, seismic reflectivity anomalies or subsurface gas escape structures; various seabed features associated with gas escape, and the presence of an underlying conventional petroleum system. We used these indicators to develop a database of hydrate occurrence across Europe. We identified a series of regions where there is substantial evidence for hydrate occurrence (some areas offshore Greenland, offshore west Svalbard, the Barents Sea, the mid-Norwegian margin, the Gulf of Cadiz, parts of the eastern Mediterranean, the Sea of Marmara and the Black Sea) and regions where the evidence is more tenuous (other areas offshore Greenland and of the eastern Mediterranean, onshore Svalbard, offshore Ireland and offshore northwest Iberia). We provide an overview of the evidence for hydrate occurrence in each of these regions. We conclude that around Europe, areas with strong evidence for the presence of hydrate commonly coincide with conventional thermogenic hydrocarbon provinces.

Description: Highlights • 4D studies of P-Cable HR3D data show good repeatability and a monitoring potential. • The P-Cable system can detect very small subsurface CO2 leaks (1.3–10.6 t). • We conclude that the system can be valuable in monitoring the (shallow) subsurface. The P-Cable technology is an acquisition principle for high-resolution and ultra-high-resolution 3D seismic data. Many 3D seismic datasets have been acquired over the last decade, but the application in time-lapse studies for monitoring of CO2 storage is a new and intriguing topic. High-resolution 3D (HR3D) seismic has the potential to detect and monitor CO2 leakage at carbon capture and storage sites with higher accuracy at depths ∼0−2 km below the seafloor compared to more traditional conventional seismic time-lapse data. Here, we synthesize and evaluate research on detection of subsurface CO2 movement using the P-Cable system and address the comparative advantages and disadvantages of conventional and HR3D technologies for subsurface fluid migration monitoring. Studies on P-Cable 4D seismic data show good repeatability (NRMS, 10–40 %), indicating a future monitoring potential. Analysis of detection limits of CO2 data from a CO2 storage site show the ability to detect very small amounts of CO2 (1.3–10.6 t; 3.3–27.4 % gas saturation) in the shallow subsurface. These detection limits are ∼30−300 times smaller than the detection limits of conventional seismic data at similar depths. We conclude that the P-Cable acquisition system can be a valuable monitoring tool in detecting small leakages and can complement conventional seismic data monitoring of the deeper interval.