Technical Paper: Geomagnetic Referencing Service - A Viable Alternative for Accurate Wellbore Surveying

Society: SPE
Paper Number: 127753
Presentation Date: 2010
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Wellbore positioning is a major challenge in eastern Canada because of the extensive faults in the Jeanne d'Arc basin. Accurate well placement is vital to the success of hydrocarbon production; accurate surveys are required in real time to drill 3D trajectories that penetrate multiple small geological targets and avoid costly subsurface collisions with adjacent wellbores.

Magnetic surveying has become increasingly accurate and now provides a cost-effective alternative to gyroscopic surveys in real-time drilling applications. Magnetic tools are subject to two main sources of error: variations in the local magnetic field and interference from magnetized elements in the drillstring. New techniques for identifying and compensating for these errors involve a better understanding of the natural variations in the earth's magnetic field, and new methods of mapping local variations improve magnetic modeling.

A key innovation is the ability to create an accurate and robust crustal model and integrate real-time diurnal measurements from nearby magnetic observatories. The addition of observatory data that improves positional uncertainty has made magnetic surveying a viable option, even at higher latitudes where more extreme variations in the local magnetic field would otherwise induce unacceptable positioning errors. Geomagnetic referencing services now offer a multitiered approach to achieve the requisite degree of positional accuracy within the economic restraints of a given drilling program.

Geomagnetic referencing can produce significant savings in overall project costs by providing accurate, real-time data on well position while corrections to trajectory are still possible. Real-time azimuth control can prevent the costly sidetracks that are often required when only a postdrilled survey is performed and reveals that the well has missed its target. Geomagnetic referencing also eliminates the cost of extra rig time required to run an accurate postdrilled gyroscopic survey, which can be a significant benefit when budget restraints are critical.

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