Reservoir characterization of the Sherwood Formation in the Wytch Farm Field depended on control from 48 wells, approximately half of which had been cored. Lithotypes were denned by detailed study of a near-by outcrop, where photo mosaics were mapped to establish lithotype geometry for the reservoir model. Probe permeameter measurements were taken both at outcrop and in the laboratory to supplement existing core plug data. The key to achieving an optimum well trajectory through the reservoir is appropriate definition of the kv/kh ratio. Lithological data were assimilated to derive characteristics for input to flow simulation models. These models were developed at the single-well scale and reservoir characterizations then 'up-scaled' to full-field reservoir flow models. These studies indicated that lenses of mudstone and calcrete conglomerates have a significant effect on reservoir flow characteristics. Thus, to optimize individual well performance, a trajectory at 85 degrees to 87 degrees would be more effective than a horizontal well.

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