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, south of the Baltic Sea area. Various shallow gas features including chimneys, bright spots, acoustic blanking, pockmarks, and polarity reversal were identified in the Gryfice block, along the inverted Trzebiatów fault zone. Structural and stratigraphic interpretation with support of seismic attributes shows the potential of fluid migration pathways from the Upper Triassic formation reservoirs to shallow sediments below the seafloor. It also helps in the explanation of how this natural gas escapes to the sea bottom. Amplitude-vs-offset (AVO) analysis proved free gas existence in the potential Upper Triassic reservoir, and helped locate free gas deposits within sediments. Hydro-acoustic data illustrated the gas chimneys’ anomalies and the corresponding free gas accumulation in Pleistocene to Quaternary successions. Leaking of gas to the seafloor was also proved by the exposure of pockmarks on multibeam (bathymetry) data at the seafloor. We combine seismic, hydro-acoustic data, and information on petroleum system from previous studies to explain the signatures of free gas and its migration from lower reservoirs to shallow sediments.