Seismic characterization and source rock evaluation of Lower Cretaceous organic-rich units on the Norwegian Continental Shelf

Abstract

Across the Norwegian Continental Shelf (NCS), the Upper Jurassic organic-rich shales are considered the main source rock unit charging most of the largest producing oil and gas fields. However, despite its extensive distribution across the NCS, this source rock unit is overmature and spent in the deep Cretaceous basins on the mid-Norwegian margin and the SW Barents Shelf. Documenting the presence of alternative source rock units at stratigraphic shallower intervals is therefore crucial for exploration success in these frontier areas. Such alternative source rock units may amongst others occur in the Lower Cretaceous or younger successions. The main objective of this study is thus to establish the presence, spatial variations, depositional conditions, and petroleum potential of Cretaceous organic-rich units on the NCS, particularly focusing on the deep Cretaceous basins along its rifted western margin. From south to north, the main study areas are confined to the mid-Norwegian margin (Paper II), the SW Barents Shelf (Paper I), and Svalbard (Paper III), the latter representing the exhumed NW corner of the NCS. This study utilizes high-quality regional 2D reflection seismic data, wireline logs, and an extensive geochemical database, all combined to assess and elucidate the petroleum potential of several organic-rich units recognized in the Lower Cretaceous of the study areas. This integrated dataset forms the basis for conceptual models made specifically for each region which host organic-rich units with generation potential. These models emphasize changing depositional conditions and factors that controlled the development and preservation of the various organic-rich units, including regional rift-related tectonics and global anoxic events. The lateral distribution of the organic-rich units is also discussed with respect to the regional tectonic evolution of the NCS during the Cretaceous, and their potential is established through traditional source rock evaluation.