Seismic interpretation of hydrocarbon seep features, Garden Banks, Gulf of Mexico

Abstract

The purpose of this study was to interpret and characterize hydrocarbon seeps using a 3D seismic data set. The information gained from this interpretation was then used to develop an understanding of the processes that resulted in the development of the seep features. The study of the hydrocarbons seeps was made using a 3D seismic survey of the study area aided with interpretation software. Side-scan sonar data was also used to assist in the interpretation. Three hydrocarbon seep features were identified and interpreted in Garden Banks lease blocks 424 and 425. The seep features consisted of two mud volcanoes and a mud in-filled depression. The hydrocarbon seep features were characterized by their rates and styles of seepage. All of the seep features are centered over normal faults created in response to the movement of a local salt diapir. Faults in the study area were interpreted and divided into two groups: Series A and B. Series A faults formed from the movement of a salt diapir directly underlying the faults. Series B developed on the flanks of the salt diapir and was the response to increased gravitational forces from an increasing slope angle. Seismic evidence showed the seep features developed from the upward movement of salt. Faults created from salt tectonics provided a pathway for fluid migration. Overpressured hydrocarbons and mud migrated along these faults to the seafloor. The seep features in Garden Banks 424 and 425 evolved into their present day appearance from continued venting episodes along these salt induced migration pathways. Seafloor amplitude maps were created to interpret anomalies associated with the style and rate of seepage for each of the features. Vents, authigenic carbonates, and gas hydrates locations were inferred from this map. The abundance and nature of these types of anomalies were used to characterize the seeps. The interpretation showed that the southern mud volcano exhibited evidence of active seepage, while the northern mud volcano showed seismic evidence of being a less active seep. The depression is characteristic of a low flux seep, which has not developed into the higher flux features exhibited by the mud volcanoes.