Using Hybrid Propulsions Autonomous Marine Vehicles to Better Characterized Geomagnetic Fields Offshore

Well placement by Measurement While Drilling (MWD) uses the direction of Earth’s geomagnetic field as a natural reference direction. It is critical to have an accurate knowledge of the geomagnetic reference field direction and strength in order to compute an accurate azimuth of the wellbore.

To develop new capabilities for offshore geomagnetic surveying, we equipped two (2) new generation autonomous marine vehicles (AMVs) with towed marine magnetometers. This abstract describes a validation study of the measurement system offshore between 2013 and 2015 by comparing a regular pattern with main lines and tie lines that was flawlessly repeated.

The 2015 measurement produce a highly accurate crustal magnetic anomaly map, which agreed with the previous campaign to within 15nT. The vehicles demonstrated an ability to move in a rectangular pattern around a fixed location in order to monitor the disturbance field, which was an issue in the previous campaign. Due to this movement, crustal field anomalies can leak into the measured disturbance field signals. By designing the measurement setup appropriately the leakage can be corrected. This method solves the problem of accurately mapping, a major contribution to the geomagnetic reference field in offshore locations, namely the crustal field.