Sean Kelly¹, Simon Smith¹, Mike Ashton², Steve Coutts¹, Dhiren Jethwa¹

(1) Shell UK Expro, Aberdeen, United Kingdom
(2) Badley Ashton and Associates

ABSTRACT: Modelling Hierarchical Production Behaviour in Palaeocene Channel Complexes of the Schiehallion Field, West of Shetland

The Schiehallion field is located West of the Shetlands and consists of Palaeocene turbiditic sands containing black oil having a relatively low solution GOR. Production commenced in July 1998. 13 horizontal producers drain the field and the primary recovery mechanism for the field is waterflood via 11 high-angle or vertical water injectors. Although several production wells had high initial rates (>30 kb/d), major uncertainties relate to ultimate recovery of producers and sweep efficiency.

The bulk of production is from the T31 interval, comprising two sheet-like complexes (a and b), each 5-15 m thick, deposited in a base-of-slope to basin setting. These two complexes are separated over much of the field by a mudstone-dominated interval that is typically c.5 m thick. There is a 4-fold hierarchy within the T31 reservoir: (1) complexes (5-10+ km width), (2) fairways (2-5 km width), (3) channels (200-500 m width), and (4) architectural elements (10-300 m width). Flow behaviour at each of these levels of hierarchy has an impact on the connectivity and recovery.

Reservoir modelling reveals insight into the nature of multiphase flow within the Schiehallion reservoir. Inverted seismic has been successfully used to predict net-pay sand thickness. Mapping at various scales has defined the main complexes, fairways and channels. Sub-seismic detail has been added stochastically using amplitude derived N/G maps and volume-based seismic conditioning. Analogues were used to select aspect (width/thickness/bed length) ratios for various facies types. Following upscaling, sector and full-field simulation models were tested against production data and analysis of available 4D seismic.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado