Ekofisk Field (in the Norweigian sector of the North sea) is a remarkable example of a strongly compacted chalk reservoir. Since the start of production in 1971, the water bottom has subsided by over 8 m as a result of reservoir compaction (Hermansen et al.). The field-wide waterflood, begun in 1989, was expected to halt pressure depletion and reservoir compaction. After a few years of waterflooding, Ekofisk reservoir pressure began increasing, but compaction and subsidence continued. Laboratory studies on chalk cores indicated that high-porosity, oil-filled chalk compacts strongly when flushed with seawater. These studies, along with reservoir flow simulation and...

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