Sequence Stratigraphy of Jurassic Oil and Gas Reservoirs in the Barents Sea

Anna Suslova

The oil and gas potential of the Jurassic reservoirs in the Barents Sea is confirmed by many discoveries in both Russian and Norwegian sectors of the Barents Sea. Besides the large gas fields there are new oil fields on the Norwegian part of the Barents Sea. The structure of the Jurassic petroleum complex is practically uniform over the whole eastern part of the Barents Sea. The thickness of the complex is 700-1500 m; it regularly increases from south towards the central part of the South Barents depression. Jurassic reservoirs are accumulated in the deltaic and shallow marine environments under the general transgression with local regressive phases. The main regressions are represented by regional unconformities, which subdivide the Jurassic successions into several sequences (fig. 1). Each sequence contains the sandy reservoirs and seals. Sandy reservoirs accumulated during the local regressions, which indicates the gradual filling of the basin and its relevant shallowing.. These sandstones are promising for oil and gas discoveries. Regionally extended clayey beds, which were deposited during periods of fast transgression, are considered as a seal. The Jurassic reservoirs within the eastern part of the Barents Sea shelf are studied by wells in Ledovoe, Ludlovskoye, Shokmanovskoye, Arcticheskoye, Fersmanovskoe, Kurentsovskoe, Murmanskoe, Severo-Murmanskoe and Severo-Kildinskoe fields. They are represented by 20-80-m thick uniform sandstone units, alternating with 10-30-m thick shaly interbeds. Their regional seal is the Late Jurassic and partially Cretaceous shaly stratum. Sequence boundaries, maximum flooding surfaces and transgressive surfaces may be identified as relatively discrete events by the logs and core data. The important criterion to identify the separate sedimentation complex is the presence of an independent transgressive system tract of the deposits in its base. Transgressive system tracts were formed at the sharp rise of the sea level above the shelf edge. They characterize Jurassic transgressions of the marine basin into the drained shelf and into the littoral plain, when the shaly consolidated deposits were formed in a relatively submerged part of the shelf due to the deficit of sedimentations. The transgressive stages are short in terms of geological time. They are fixed in the wellbore data as sharp changes of lithology and in SP and gamma-ray logs.

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013