Abstract: Submarine fan reservoirs are a hotspot for oil and gas exploration and development in the world. The distribution pattern and genesis of sand bodies are complex. At present, there is a lack of research on the axial submarine fan sand bodies in deepwater grabens. Taking the B Formation of Upper Jurassic of the X Oilfield in the North Sea, UK as an example, this paper attempts to investigate the distribution patterns and controlling factors of axial submarine fan in the deep-water graben environment, by well and seismic data mining. The results show that submarine fan sand bodies are mainly of proximal bypass type, presenting banded, lobate or tongue shapes. Lobate sandbodies are thick and wide with a low length-width ratio of 5, which were formed by lateral migration or retrogradation superposition, commonly seen in B4 Oil Group. In contrast, banded sandbodies are relatively thin and narrow with a high length-width ratio of 10, which were formed by vertical superposition. This type of sandbodies is developed in the B2 Oil Group. The distribution of submarine fan sand bodies is mainly controlled by paleogeomorphology. The longitudinal steep slope (greater than 6°) driven by the differential subsidence of the graben, causes the submarine fan sand bodies to present proximal bypass type. The limitation of the internal graben affects the morphology and superposition style of the submarine fan. Compared with the thin mud-rich submarine fan sand bodies, the thick sand-rich submarine fan sand bodies are relatively less restricted, which are mostly lobate and tongue-shaped, and are lateral superposed. The lateral symmetry of the graben landform affects the lateral development position and migration direction of the submarine fan.

Key words: North Sea, submarine fan, paleogeomorphology, graben, distribution pattern