Forties Field (UK): Geological Modeling of a Turbidite Sequence for Reservoir Simulation

Alexander A. Kulpecz, Lucia C. Van Geuns

The Forties field is located in the United Kingdom sector of the Central North Sea straddling blocks 21/10 (BP) and 22/6a (Shell/Esso). The field represents one of the largest producing oil fields in the North Sea, with recoverable reserves exceeding 2.3 billion barrels. This paper highlights the improved understanding of the depositional history of the Forties submarine fan complex by the use of palynology and discusses some applications to three-dimensional modeling parameters.

The field was initially developed from four platforms in block 21/10 and production started in 1975. The sandstone reservoir of the field forms part of a large Paleocene submarine fan complex. Lithofacies associations were described by others in the past. However, in the absence of lithologic markers or reliable seismic, small shale breaks within large sandy units formed the basis of difficult and uncertain correlations. Development drilling in block 22/6a has brought a fifth platform onstream in 1987. Palynological sampling of seven cored wells in block 22/6a revealed a complex relationship between the shifting of submarine fan lobes. The study area was extended to include the entire field by analyzing seven additional main field cored wells and included additional micropaleontology ata from block 21/10.

A fivefold subdivision of the Forties reservoir produced a well-defined chronostratigraphic framework, which allowed reliable correlation within the submarine fan and highlighted the shifting nature of mid-fan channelled and lobed sequences in time. Thin-bedded turbidite sequences typically represent paleohighs or areas of relatively slow deposition, as is evidenced by the close spacing of chronostratigraphic markers. Adjacent to the interchannel paleohighs, the channeled lobe sequences may have been deposited along trends following existing paleotopography.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.