This paper illustrates the evolution of a sequence stratigraphic reservoir model for the Jurassic Hugin Formation in the Sleipner Ost field from a pre-development stage through to development drilling. In the pre-development work candidate Maximum Flooding Surfaces were used to build a semi-regional sequence stratigraphic model from which implications for the field were predicted. Development drilling significantly improved the data base and allowed a high resolution sequence stratigraphic model to be established for the Sleipner Ost field. In the pre-development work, detailed biostratigraphy enabled the identification of a series of candidate Maximum Flooding Surfaces within the Bathonian-Callovian interval. Sediments were divided into four main facies associations, each grouping together a number of broadly similar lithofacies. The pre-development model showed that a low-order overall north-to-south Middle Jurassic transgression strongly influenced deposition. The uppermost Hugin Formation beach-barrier sandstones backstep and are overlain by the offshore, fine-grained equivalents of the Heather Formation. Coastal plain deposits of the Sleipner Formation underlie and interfinger with the beach-barrier reservoir sandstones in Sleipner Vest but are absent in Sleipner Ost. Limited accommodation on Sleipner Ost resulted in stratigraphically incomplete sections and variable preservation of Jurassic sediments. The drilling of three development wells on the Sleipner Ost structure during 1995 tested the regional model and generally confirmed the reservoir predictions. In particular the existence of a Bow barrier of non-reservoir lagoonal mudstones and an overlying good reservoir quality shoreface sandstone were confirmed to be laterally persistent. Based on the new data a higher resolution, sedimentologically driven sequence stratigraphic model and a more detailed bed-to-bed reservoir facies correlation were established. The model shows that the Gamma High was initially flooded in a back-barrier/lagoonal setting. The stacking pattern shows a series of ravinement/flooding events followed by basinward stepping packages resulting in an aggradational to progradational pattern in the main part of the reservoir. In the uppermost part, this trend is reversed and a major landward movement brought shoreface deposition back across the area. Finally the whole area was flooded and only deeper marine mudstone accumulated.
