Hydrate occurrence in Europe: A review of available evidence

Abstract Large national programs in the United States and several Asian countries have defined and characterised their marine methane hydrateoccurrences in some detail, but European hydrateoccurrence 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 hydratein Europe. Our review includes the western and eastern margins of Greenland, the Barents Sea and onshore and offshoreSvalbard, 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 Georgiansectors of the Black Sea, or overseas territories of European nations. Following a formalised process, we defined a range of indicators of hydratepresence based on geophysical, geochemical and geological data. Our study was framed by the constraint of the hydratestability field in European seas. Direct hydrateindicators 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 surveyevidence 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 hydrateoccurrence across Europe. We identified a series of regions where there is substantial evidence for hydrateoccurrence (some areas offshoreGreenland, offshorewest 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 offshoreGreenland and of the eastern Mediterranean, onshore Svalbard, offshoreIreland and offshorenorthwest Iberia). We provide an overview of the evidence for hydrateoccurrence in each of these regions. We conclude that around Europe, areas with strong evidence for the presence of hydratecommonly coincide with conventional thermogenichydrocarbon provinces.