Several gas-influx events have occurred during drilling with oil-based mud on the Gullfaks field. These have usually started when hard chalk stringers were penetrated, and abnormal pressurized gas bearing zones were drilled into. These zones are often of low productivity ·and val ume.Based on all available data from the influxes in wells I and II, the events have been analyzed. The analysis has helped to explain the development of the influx events, and also the control phases have been evaluated.

This report is a case history of drilling well ClOin the Statfjord Field. The well is a world record in Extended Reach Drillingwith ahorizontal reach of5003 meters (16414 ft). This report will mainly concentrate on planning and executing the work; how torque, drag, holecleaning, welbore stability and surveying were handled through careful planning, follow-up and performance on the rig.

Several gas-influx events have occurred during drilling with oil-based mud on the Gullfaks field. These have usually started when hard chalk stringers were penetrated, and abnormal pressurized gas bearing zones were drilled into. These zones are often of low productivity ·and val ume.Based on all available data from the influxes in wells I and II, the events have been analyzed. The analysis has helped to explain the development of the influx events, and also the control phases have been evaluated.