How To Manage Geomagnetic-Field Disturbances in the Northern Auroral Zone To Improve the Accuracy of Magnetic Measurement-While-Drilling Directional Surveys

Abstract

Summary The auroral zone is the region surrounding the geomagnetic North and South Poles, and it is where the largest and most frequent disturbances in the Earth's magnetic field are experienced. Because geomagnetic disturbances affect the accuracy of magnetic measurement-while-drilling (MWD) directional data, surveying wells in the auroral zone is challenging. Development of industry practices to enable accurate surveying and safe operations in these areas is important. The objective of this study was to investigate how magnetic disturbances in the auroral zone influence the geomagnetic-field parameters of declination, dip angle, and total magnetic-field intensity. This investigation analyzed the statistical properties of data from 20 land-based magnetic observatories and variometer stations in Scandinavia, Greenland, and Alaska—all located in the auroral zone. The results were used to estimate magnetic-field-disturbance covariations as a function of distance and direction. Additionally, methods to reduce azimuth uncertainty using data from distant monitoring stations were studied. Uncritical use of data obtained from monitoring stations can result in uncertain azimuth measurements. In cases where data from more than one nearby monitoring station are available, the challenge is often to identify which stations are providing the most-accurate corrections. Important criteria for the selection of monitoring stations are not limited to directions and distances, but also include the location of the ionospheric current relative to the rig location. Procedures and methods for predicting the location of ionospheric currents were tested. The data sets analyzed in this study contain measured deviations from the quiet mean for periods with low, moderate, and high geomagnetic activity. Station pairs with mutual distances ranging from 150 to 850 km were considered. The general trends of the magnetic data from station pairs located along the east/west direction are more correlated than in the north/south direction, and the differences in magnetic fluctuations between station pairs are lower in the east/west direction than in the north/south direction. This holds true for all distances, directions, and disturbance levels.