A combined 3D seismic and sedimentological study of the Lower Cretaceous succession in the northeastern part of the Nordkapp Basin

Abstract

In this master’s thesis in geology, 3D seismic data and shallow stratigraphic cores were used to investigate the Lower Cretaceous succession in the central sub-basin of the Nordkapp Basin, Barents Shelf. The Lower Cretaceous is listed as a potential petroleum play model on the Barents Shelf, which makes the succession of interest for petroleum exploration. Recent studies of the have divided the Lower Cretaceous succession into seven genetic sequences, bounded by flooding surfaces. Out of these sequences, three were identified in the central sub-basin of the Nordkapp Basin. Salt diapirs are prominent in the Nordkapp Basin, including the study area, which affect the surrounding successions and are a challenge for seismic interpretation. The two 3D seismic surveys used were ST0624 and ST0811, which cover approximately 770 km2 and 1065 km2 respectively in the central Nordkapp Basin. Three shallow stratigraphic cores were used for sedimentological interpretation of the Lower Cretaceous succession: 7231/01-U-01, 7231/04-U-01 and 7230/05-U-09. The cores were taken in the vicinity of the seismic survey area. The Lower Cretaceous succession in the study area was divided into three sequences (S1–S3) based on seismic data interpretation, and correlation to other studies. An Upper Jurassic sequence was also interpreted (JS1), correlated to the Hekkingen Formation source rock. Depositional environments of the sequences were investigated in the shallow stratigraphic cores, and correlated to the seismic data. Time-thickness maps were generated to interpret the depocenters of each sequence, and their relation to each other. Seven salt diapirs were interpreted in the study area. Based on thinning towards the diapirs in sequences JS1 and S1, the diapirs are suggested to have been active during deposition of these sequences. A regressional trend was found in the Lower Cretaceous sequences in the cores, progressing from an outer marine to inner shelf and shoreface setting. This correlates well to the sequences observed in the seismic data, where the depocenters of each sequence migrates from the NE of the study area (S1), to the middle of the study area (S2), to SW of the study area (S3). Paleogeographic maps of the study area during the deposition of the Lower Cretaceous succession, were generated.