Improving the Accuracy of Directional Wellbore Surveying in the Norwegian Sea

Abstract

Time-dependent current fluctuations in the Earth's ionosphere cause inaccuracies in wellbore directional surveying. These inaccuracies increase at higher latitudes and although monitoring and correction is possible, it becomes less valid as the distance between the monitoring site and the rigsite increases, a particular problem for offshore drill sites. The characteristics of the ionosphere currents indicate that the most favourable location for monitoring stations is on the same geomagnetic latitude as the drill site. Such an arrangement has been used to monitor and correct directional survey at the Haltenbanken area of the Norwegian Sea over a period of approximately two years. Haltenbanken is located about 200km west of the Norwegian coast at latitude 65° north, where magnetic storm activity can have a significant effect on directional surveying. A monitoring station was set up on the coast at the same geomagnetic latitude as Haltenbanken. To test the idea that magnetic disturbances are similar along constant magnetic latitude, an additional monitoring station was established 200km east of the main station. The data broadly confirmed the hypothesis, although isolated events were observed when this is not the case. The challenges of surveying at offshore sites north of 62° N latitude are probably greater than the oil and gas industry is accustomed to; challenges that will become more significant if the Arctic Ocean is opened to drilling operations. The technique described in this paper may contribute to safer and more productive offshore operations at high latitudes.

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

“…Torkildsen et al (1997) studied the declination variations along the Norwegian coast from 60 to 79 latitude and indicated that interpolation techniques can be applied up to 200 km with a time-dependent azimuth-uncertainty reduction of approximately 60%. A distance of 200 km from the rigsite to the onshore variometer station was confirmed as acceptable by the Norwegian Sea study by Edvardsen et al (2012), with a preferable setup of a variometer station on the same geomagnetic latitude as the rigsite. The total field and dip disturbances vary significantly with large distances in the north/south direction.…”

“…Usually, the axial component is the most significant contributor to errors in magnetic azimuth and the resulting wellbore position. The reasons include the fact that the axial magnetic interference in general is larger than the cross-axial components, and because of tool-face-independent-propagation behavior, it has a larger influence on the uncertainty of the calculated well position (Ekseth 1998). For uncorrected MWD magnetic surveys, which are used when algorithms for DSI correction are not applicable, the error DA in the magnetic azimuth A m caused by the axial magnetic interference Db z is given by (Ekseth 1998):…”

“…Such a device increases the accuracy of all geomagnetic reference parameters, which are vital for the accuracy of both multistation analysis (MSA) and single-station axial-magnetic-correction algorithms. During periods when the two variometer stations agree, a correction of the geomagnetic nominal field values can be derived as described by Edvardsen et al (2012).…”

Jim Dungey, The Open Magnetosphere, and Space Weather

“…The energy transferred into the magnetosphere by magnetic reconnection drives geomagnetic storms, during which the most rapid variations in the geomagnetic field cause strong geomagnetically induced currents that can degrade and damage power grids [ Kappenman , ], enhance corrosion of oil and gas pipelines [ Viljanen et al , ], and cause errors in magnetic guidance systems, such as those needed for safe oil and gas borehole drilling [ Edvardsen et al , ]. Magnetic reconnection also controls the near‐Earth energetic particle environment within which most satellites, astronauts and aircraft operate: it is central to the occurrence of solar flares and the release of coronal mass ejections (CMEs), and the shock fronts ahead of both these phenomena accelerate bursts of solar energetic particles [ Reames , ] that are damaging to both electronics systems and living organisms.…”