Drilling through the over-pressured formations on Skarv field

Abstract

The main objective of this thesis was an investigation and of drilling operations in over-pressured formations on the J-4H/HT2 well on the Skarv field off the coast of mid-Norway. Abnormally high formation pressures on this well were the direct cause of a stuck pipe incident during drilling followed by consequences for the entire well construction process. Based on daily drilling reports the paper presents the sequence of events leading to the stuck pipe incident on well J-4H. It establishes a link between conditions in abnormally pressured zones and the causes of slow drilling process, as well as of the wellbore collapsing around the drill string. The ultimate goal was to understand the situation and suggest potential countermeasures. To achieve this, a wellbore stability evaluation was performed to analyze. The relationship between drilling fluids, drilling technology, well integrity and an offset well J-1H were taken into consideration to compare operations in the same environment. Further, looking for the most probable scenario and results, can give the clear picture of missteps which should have been done. Based on the results alternative approaches are discussed and suggestions are made to improve the quality of operations and avoid similar problems in the future. The wellbore stability analysis showed that more attention should be put on bottom hole assembly design and changes in wellbore conditions. The results of daily drilling reports analyses indicated that the most efficient solution for drilling challenges may be to change the setting deeper an intermediate casing and decrease the drilling mud density after drilling the over-pressured formations, to avoid overbalance.