Shallow gas transport and reservoirs in the vicinity of deeply rooted mud volcanoes in the central Black Sea

•We analyze the structure and the eruption reasons of six mud volcanoes.•Different types of pathways for gas and fluid migration and different types of gas reservoirs are recognized.•A clear BSR is observed firstly in the central Black Sea.•We infer the formation history of the gas reservoirs.

The principal objective of this paper is to understand the gas migration process and the structures of mud volcanoes in the central Black Sea. Multichannel seismic lines were acquired across 6 mud volcanoes in the central Black Sea: MSU, Yuzhmorgeologiya, Malyshev, Kornev, Goncharov and Vassoevitch. Based on a high resolution seismic processing, we analyzed acoustic anomalies and studied near-surface sediment structures of these mud volcanoes. Four types of pathways for gas and fluid migration and three types of gas reservoirs were recognized. A regional “Bottom Simulating Reflection” (BSR) seems to be absent in most parts of the study area, however a clear BSR was observed in one of the seismic profiles. The free gas migrating upwards along these pathways were sealed by gas hydrates or fine-grained sediments in the gas hydrate stability zone. Four seismic units were separated according to a suggested age model and identified seismic facies. Combining with the possible sedimentary processes of the central Black Sea, we try to reveal the active mechanism of these mud volcanoes. These mud volcanoes reveal two to three major active stages. These active stages might be related to distinct sea level falls, which seem to be one of the main trigger factors of the mud volcano eruptions in the central Black Sea. A structural model for the MSU mud volcano was presented with respect to mechanisms of gas migration and the origin of the gas.