Reservoir Characteristics of Turbidite Depositional Facies and Key Risks for Basin Floor Fan Turbidite Reservoirs

摘要

Exploration within the past ten years has resulted in the discovery of several very significant oil accumulations in deepwater turbidite reservoirs such as those in the Lower Tertiary Wilcox Formation of the Gulf of Mexico, and in the Cretaceous abrupt margin fans of the Jubilee turbidite complex, offshore Ghana, and the Zaedyus turbidite fans, offshore French Guiana. The first part of the talk presents a classification of turbidite reservoir deposits into three distinct depositional facies: (1) The upper fan, proximal channel canyon system characterized by amalgamated channels without levees, (2) the more confined, middle fan, amalgamated to layered channel levee complexes, and (3) the further downdip, distal outer fan, basin floor fans and sheet systems where most of the major discoveries have been made. Recent advances in seismic acquisition and processing has improved illumination of structure and stratigraphy of turbidite plays, and allowed a much better understanding of geologic risk of the important distal outer fan reservoir facies. The second part of the talk utilizes seismic datasets from the African Margin to assemble a geologic risk model for the basin floor fan play beginning with the deepwater Tano Basin, offshore Ghana, where the Jubilee and TEN complexes were discovered. Then a quick tour and review of the deepwater turbidite fan characteristics of fan discoveries and prospects in the deep-water environments of Morocco, Senegal, Angola, Namibia, and Mozambique is shown. Seismic data are used to identify key geologic risks and challenges that remain to be resolved regarding continued exploration of this important play that is attracting a lot of exploration interest and investment on both sides of the Atlantic Basin, and in the Gulf of Mexico. Key petroleum systems issues are discussed including sufficient overburden and adequate seal, fan volume continuity and connectivity, stratigraphic trapping, migration through turbidite muds, faults and stratigraphic compartmentalization, importance of adequate sediment influx, and application of seismic amplitude anomalies for prospect risking.