The Njord Field is one of the most complex reservoirs in theNorwegian North Sea due to a large number of faults. Seismicquality in the heavily faulted areas is poor making seismicinterpretation difficult. Typically the uncertainty in topstructure is in the order of 10-100 m.The well design criteria on Njord are dependent on thestructural uncertainty and the availability of new technology.Njord started with relatively simple single-bore horizontalwells. This design was not suitable in the intensely faultedareas. High amplitude U-, S- and W-shaped wells have beeneffective to penetrate all reservoir units in uncertain areas, tominimize the risk of hole-instability and to drain oil frommultiple fault compartments.The need for placing a well in the best reservoir interval, topenetrate longer reservoir section and to drain oil fromsparsely located undrained compartments led to drill a treebranchedwell in the recent days. A new active visualizationassisted geo-steering technology coupled with biostratigraphyhas been tremendously successful to steer the well path in themost complicated area. Another well has been drilled inanother heavily faulted area where the pressure depletion insome of the compartments was in excess of 300 bar.The drive for a cheaper way of drilling sparsely locatedrelatively smaller undrained pockets led to initiate a newcampaign to find and drill low cost infill targets using theThrough Tubing Rotary Drilling technology. Intensiveresearch and development activities have been undertaken toresolve outstanding issues, such as, protection of X-mas treeand down hole safety valve, risk for mud loss and differentialsticking, zone isolation by swell packers, etc.This paper summarizes the reasons for adopting so manydifferent well types, and a comprehensive description on theirplanning, execution, challenges, successes and failures.
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