Formation of the Oil Pool of Stratum BV8 of the Samotlor Field

The BV 8 pool has a distinct zonality. See Fig. 1. At the crest there is a zone of relatively light (0.845) oil. In the next lower interval the oil is heavier; specific gravity is 0.855 to 0.865. Yet lower the oil is again lighter, the density being 0.834 to 0.849. Then along the margins of the pool the oil is heavier, having a density of 0.850-0.860. A zonality was also noted in the composition of the oils and in other physical properties. The amount of gas dissolved in the oil is at a maximum at the cr est of the pool; it then drops in the zone of occurrence of heavier oils from 92-96 m 3 /m 3 to 76-82 m 3 /m 3 . Toward the margins of the pool this tendency is reversed, and this parameter rises to 92-103 m 3 /m 3 . At the edge of the pool, however, it drops to 55 m 3 /m 3 . No relationship is found between the zonality in the pool and the distribution of formation temperature. It is concluded that the zonality is due to different stages of formation of the pool. The upper part formed and had its oil-water contact at the base of the upper zone of heavier oil. Subsequently a second phase of pool development took place and the two lo wer zones formed. © Petroleum Geology: A digest of Russian literature on Petroleum Geology, 2013