Gas - escape features along the Trzebiatów Fault offshore Poland: evidence for a leaking petroleum system

Abstract

New 2D high resolution seismic and hydro-acoustic data demonstrate the presence of methane in the shallow sediments and its origin in the Pomeranian Bight, southern of the Baltic Sea area. Various shallow gas features were identified in the Gryfice block, along the inverted Trzebiatów fault zone, including chimneys, bright spots, acoustic blanking, pockmarks, and polarity reversal. Structural and stratigraphic interpretation with support of seismic attributes was carried out to show the potential of fluid migration pathways from the Upper Triassic formation reservoirs to shallow sediments below seabed and helps in explanation of how this natural gas escapes to the sea bottom. Amplitude-vs-offset (AVO) analysis verified remnants of free gas existence in the Upper Triassic potential reservoir and helped locating free gas deposits within sediments. Hydro-acoustic data illustrated the gas chimneys’ anomalies and corresponding free gas accumulation in Pleistocene to Quaternary successions. Leaking of gas to sea surface was also proved by exposure of pockmarks on multibeam (bathymetry) data. We combine seismic, hydro-acoustic data and information on petroleum system from previous studies to explain signatures of free gas and its migration from lower reservoirs to shallow sediments.