Application of 3D visualization and VSP for horizontal well positioning – 9/13a-Nl case history, Nevis Field, UKCS

The Nevis Field, operated by Mobil North Sea Limited, came on stream in September 1996. This was achieved by completion of an existing vertical well in the Triassic and the drilling and completion of a horizontal well in the Middle Jurassic Beryl Formation. Horizontal wells are necessary for the economic development of the field. However, these wells are high risk because of the relatively thin and faulted reservoir interval. A multi-disciplinary team was formed to manage the risk of the crucial first horizontal well. 3D visualization was used to allow all disciplines the opportunity to understand the structure and difficulties associated with the well. A pilot well was planned to maximize the chance of penetrating the oil-water contact. A wide range of possible horizontal well trajectories, dependent on the results of the pilot, were constructed interactively in 3D. Using an iterative process, a well path was engineered that catered for the range of outcomes. An imaging vertical seismic profile (VSP) was acquired in the pilot well to help optimize the location of the final horizontal section. Thorough planning resulted in faults not apparent in the 3D dataset being identified on the VSP. Detailed structure maps were created based on the faults and bed dips interpreted from the VSP and fault trends observed from the 3D seismic data. The well design work in 3D meant that the required horizontal well trajectory could be drilled. The final horizontal section proved 610 m (2000 ft) of oil bearing section. The successful drilling of the well is considered to be largely as a result of extensive multi-disciplinary contingency planning.