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Poedjono, Benny (Schlumberger) | Beck, Nathan (Schlumberger) | Buchanan, Andrew (Eni Petroleum Co.) | Brink, Jason (Eni Petroleum Co.) | Longo, Joseph (Eni Petroleum Co.) | Finn, Carol A. (U. S. Geological Survey) | Worthington, E. William (U. S. Geological Survey)
Abstract Geomagnetic referencing is becoming an increasingly attractive alternative to north-seeking gyroscopic surveys to achieve the precise wellbore positioning essential for success in today's complex drilling programs. However, the greater magnitude of variations in the geomagnetic environment at higher latitudes makes the application of geomagnetic referencing in those areas more challenging. Precise, real-time data on those variations from relatively nearby magnetic observatories can be crucial to achieving the required accuracy, but constructing and operating an observatory in these often harsh environments poses a number of significant challenges. Operational since March 2010, the Deadhorse Magnetic Observatory (DED), located in Deadhorse, Alaska, was created through collaboration between the United States Geological Survey (USGS) and a leading oilfield services supply company. DED was designed to produce real-time geomagnetic data at the required level of accuracy, and to do so reliably under the extreme temperatures and harsh weather conditions often experienced in the area. The observatory will serve a number of key scientific communities as well as the oilfield drilling industry, and has already played a vital role in the success of several commercial ventures in the area, providing essential, accurate data while offering significant cost and time savings, compared with traditional surveying techniques.
Seafloor observatories have been the important way to observe the ocean, but applying the magnetometers to it still remain technical problems. This paper presents a smart cheaper magnetometer which was designed as the sensor node for a small seafloor network for geomagnetic observation. System design was described in modules at first. The calibration method of the whole system so as to alleviate the intrinsic magnetism was introduced secondly. In order to orient the magnetometer when putted on seafloor, the azimuth arithmetic for IMU (Initial Measurement Unit) was demonstrated afterwards. Finally, the data from a sea trial was given and the assumption to construct a seafloor geomagnetic observatory network was promoted.
In 2016, the authors published evidence demonstrating that strong magnetic field perturbations resulting from Earth-directed solar events can adversely affect marine archaeological survey. Based on a 95% confidence level, it was estimated that 89.7 to 100 percent of geomagnetic storms occurring on days of Kp 5 or greater will generate marine magnetometer signatures that may be misinterpreted as archaeological sites. Aggressive processing, analysis, and comparison of single instrument, total field marine magnetometer datasets were unable to isolate and remove the storm sudden onset signature. These findings, however, only demonstrated the phenomena in data collected at mid-latitudes (Carrier et al. 2016). This paper builds on that work by presenting analysis of additional survey data collected from a low latitude region in the Gulf of Mexico. Although it is understood that geomagnetic storms affect Earth's magnetic field to a greater degree at high latitudes - that is, near the poles - and to a lesser degree at low latitudes - closer to the equator - the prevailing assumption that geomagnetic storms are not a problem in the Gulf of Mexico is unsubstantiated by the empirical evidence. Observatory datasets analyzed in this paper plainly reveal that geomagnetic storms affect Earth's magnetic field at low latitudes and external source artifacts remain in professionally-collected survey data, even after aggressive processing. Recommendations are made for marine magnetic data collection and processing methods that adequately account for geomagnetic storms, allowing for improved precision in analytical interpretation and thus improved identification of archaeological resources.
Acknowledgments We thank Fugro Airborne Surveys for supporting this research. The Geological Survey of Canada provided data from the Canadian Magnetic Observatories. The Institut für Geophysik, University of Göttingen, and the World Data Center, Kyoto provided the global indices.
Mitkus, Alexander (Helmerich & Payne Technologies) | Maus, Stefan (Helmerich & Payne Technologies) | Willerth, Marc (Helmerich & Payne Technologies) | Reetz, Andrew (Helmerich & Payne Technologies) | Oskarsen, Ray Tommy (Add Energy) | Emilsen, Morten Haug (Add Energy) | Gergerechi, Amir (Petroleumstilsynet)
Abstract As development of the Barents Sea continues with new plays such as the Castberg, accurate specification of the local magnetic field is important to reliably infer the orientation of the bottomhole assembly (BHA) in horizontal drilling. Since magnetic fields at high latitudes vary spatially and temporally, one requires both spatial models and a way to capture temporal changes. Large temporal changes in the magnetic field can severly distort measured azimuths and therefore must be corrected for. This study, based on a report written for Petroleumstilsynet (Maus et al., 2017), shows that in regions of the Barents Sea within 50 km of a magnetic observatory, either the nearest observatory, interpolated infield referencing (IIFR), or the disturbance function (DF) method may be used for corrections in wellbore surveying to meet accuracy requirements. IIFR and DF will give better error reduction but are slightly more complicated to implement. At distances between 50 km and 250 km, the disturbance field (DF) method best meets accuracy requirements. In remote regions beyond 250 km, a local observatory must be deployed to meet the highest accuracy specifications, but the DF will still far outperform the other interpolated methods at such large distances from an existing observatory. Despite having focused on the Barents Sea region, this comparison of the accuracy of different spatial and temporal magnetic field mitigation methods for wellbore surveying is applicable to high latitude northern and southern regions across the globe.