The Present is the Key to the Plio-Pleistocene: Seafloor Analogues at Shell's GB 516 Serrano Discovery

Dean, M.C., J.R. Booth, and K.M. King, Shell Offshore, Inc., New Orleans, LA

Abstract

Prospect Serrano is located approximately 220 miles southwest of New Orleans and 6 miles southeast of the Auger TLP in Garden Banks Block 516. Drilled in 1966, the Shell GB 516 #1 well has encountered 86 net feet of Pleistocene age (P. lacunosa) g as pay at the main objective horizon. The objective horizon occurs in the largely channelized Bypass Seismic Facies Assemblage, defined by Prather et. al. (1998), and can be mapped regionally as a highly continuous, draping seismic event. In offset penetrations, the objective horizon is sand lean and frequently associated with pyroclastic sediments. Mapping of 3D seismic data and comparisons to the present day seafloor, however, provide evidence for a sand-prone depositional setting at the Serrano prospect. Loop level attributes and interval isopachs indicate that several depositional systems are active at Serrano. In addition, present day seafloor bathymetry reveals the presence of a backstop setting within low-relief ponded accommodation space (e.g., Prather et al., 1998). Furthermore, images of the present day seafloor support the interpretation of multiple sediment entry points and offer clues to depositional and erosional relationships preserved in the subsurface. The seafloor analogue is instrumental to understanding the distribution of sheet sands, depositional and erosional bypass channel systems, debris flows, and large-scale erosional gorge systems at the Serrano prospect. The seafloor is a present-day analogue of Pleistoc ene depositional processes and is a valuable tool in reservoir prediction.