John C. Van Wagoner, Dave C. Jennette, Gyorgy Hamar, Inge Kaas
The giant Statfjord Field is located in the North Sea and has been on stream since 1979. Plateau production was from 1986 to 1992. As part of an improved oil recovery strategy initiated in 1993, sequence stratigraphy and stochastic modelling have been key elements in building a flow simulation model and mapping areas of potentially bypassed oil.
The main producing unit in the field is the middle Jurassic Brent Group. The Ness Formation, forming the middle part of the Brent Group, is composed of heterolithic delta-plain and lagoonal facies including a thick lagoonal shale at the base and the top. The former shale constitutes a fieldwide pressure barrier whereas the latter forms a pressure barrier in parts of the field. Biostratigraphic data and stacking patterns indicate that these shales each contain a 3rd order maximum flooding surface, between which 7 high-frequency sequences have been identified. The lower three form a highstand sequence set, the next two a braid sequence set and the upper two a transgressive sequence set.
Each high-frequency sequence shows a fairly regular facies distribution pattern. Braid deposits where present, consist of fluvial or tidal channel deposits at the base with increasing amounts of various overbank deposits toward the top. These are usually overlain by extensive coals along the transgressive surface. The parasequences of the transgressive and highstand systems tracts are typically coarsening-upward units composed of lagoonal mudstones, bayhead-delta and minor channel sandstones, and overbank deposits. Thus, the parasequence boundaries often form barriers to vertical fluid flow.
AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995