Gas migration and sealing modelling in the Haapet Dome area, Norwegian Barents Sea - analysis of seismic anomalies and water column data

Abstract

Seismic interpretation, water column data, and well information have enabled a thorough review of shallow amplitude anomalies and subsurface faulting, in conjunction with possible migration pathways in the Haapet Dome area. The processed water column data from the MAREANO-program was presented and evaluated in accordance with potential gas leakage from the seafloor. Water column imaging illustrates that hydroacoustic signatures, which are representative of gas bubble leakage, are probably of non-existence in the Haapet Dome area. A correlation with subsurface stratigraphy illustrates that the possible gas accumulations are situated in the Stø and Nordmela formations, and the Early Cretaceous unit. Given that no apparent evidence of gas leakage is occurring suggests that a sealing lithology is constraining the assumed gas accumulations. Several models were introduced to discuss and evaluate the possible gas accumulations according to entrapment capability and the possibility of minor gas release. The analysed water column data did not indicate observable gas leakage, where acoustic distortion made detection of potential gas bubbles difficult. The Upper Regional Unconformity (URU) with overlying glacial sediments was assumed to act as a potential trapping mechanism for underlying zones of potential shallow gas accumulations. A gas hydrate stability model was established, which showed that gas hydrates could develop in the study area, dependent on the gas composition. Consequently, local zones of potential gas hydrates could act as hydrocarbon barriers. A possible Permian source rock was suggested to have generated and expelled gas, which is probably represented by its present-day shallow accumulations. The models presented suggest that no source rocks are generating and expelling hydrocarbons at present-day in the study area. The assumed shallow gas accumulations are thereby represented by a possible older working petroleum system. A shut-down petroleum system, with no or very little influx of hydrocarbons to the study area, combined with shallow sealing lithologies, might be one reason for lack of observed gas seepage in the water column.