Improving the Accuracy and Reliability of MWD/Magnetic-Wellbore-Directional Surveying in the Barents Sea

Abstract

Summary The years ahead will see increased petroleum-related activity in the Barents Sea, with operations far off the coast of Norway. The region is at high geomagnetic latitude in the auroral zone, and therefore, directional drilling by use of magnetic reference will experience enlarged azimuth uncertainty compared with operations in the Norwegian and North Seas. Two main contributors to azimuth uncertainty are magnetic disturbances from electric currents in the ionosphere and axial magnetic interference from the drillstring. The former is more frequent in the Barents Sea than farther south, and the effect of the latter is increased because of diminished value of the magnetic horizontal component. Wellbore directional surveying for operations on the continental shelf in the North Sea and the Norwegian Sea rely on well-established procedures for near-real-time magnetic monitoring by use of onshore magnetic-reference stations. The different land and sea configuration, distant offshore oil and gas fields, higher geomagnetic latitude, and different behavior of the magnetic field require the procedures to be reassessed before being applied to the Barents Sea. To reduce drilling delays, procedures must be implemented to enable efficient management of magnetic disturbances. In some areas of the Barents Sea, the management requires new equipment to be developed and tested before drilling, such as seabed magnetometer stations. One simple way to reduce drillstring interference is increasing the amount of nonmagnetic steel in the bottomhole assembly (BHA). To maintain azimuth uncertainty at an acceptable level in northern areas, it is crucial that wellbore-directional-surveying requirements are given high priority and considered early during well planning. During the development phase of an oil and gas field, the planned wells must be assigned adequate positional-uncertainty models and, if possible, be designed in a direction that minimizes the wellbore directional uncertainty.