In recent years the search for hydrocarbon reservoirs has moved into deeper and more complex environments. In the Gulf of Mexico this has meant exploring below salt sheets, which distort the seismic raypaths and thus effectively mask the underlying geology. In northwest Europe subsalt plays face similar challenges and in the North Atlantic/Faroes imaging below basalt is a major issue.

Summary Seismic data have a key role to play in the process of reservoir characterisation which is a common problem to all phases of the Exploration and Production cycle. Here we present the application of impedance inversion to the Ewan field of the Niger Delta, offshore Nigeria. Key points of the study include: • The Ewan field is a roll-over anticline, fault bounded on three sides and comprises an alternating sand/shale sequence. • A unique, layered approach to acoustic impedance inversion yields high resolution identification of the main sand sequences without high constraints at well locations. • Visualisation and mapping of the spatial extent and quality of the main reservoir sands has enabled targeting of new horizontal wells.