As an experienced supplier of the oil & gas downhole and completion tools team, Vigor will overview the definition, specifications, sizes, weight, and applications of Non-Magnetic Drill Collars.
Non Magnetic Drill Collar Definition
A non magnetic drill collar is a thick-walled drill string component made of non-magnetic alloys that minimize magnetic interference during downhole surveying [1]. Conventional carbon steel drill collars produce a magnetic field that can distort the measurements of sensitive wellbore surveying instruments that utilize magnetometers and gyroscopes [2]. By using specialty metals like monel, inconel, and titanium, non magnetic collars allow for precise wellbore placement.
Non Magnetic Drill Collar Specifications
- Length: 30-90 ft
- Diameter: 5-10 inches
- Wall thickness: 2-4 inches thicker than drill pipe
- Alloy material: Monel, Inconel, titanium
- Weight: 120-150 lbf/ft for optimal drilling performance
- Connections: Non-magnetic alloy welds or threads
The collars can be customized with different dimensions and configurations to suit specific drilling requirements. The thick walls provide crucial rigidity and strength downhole.
Non-Magnetic Drill Collar Sizes
- 5-inch collars - Typically 30-60 feet in length
- 6-inch collars - Typically 30-90 feet in length
- 8-inch collars - Typically 30-90 feet in length
- 9-inch collars - Typically 30-60 feet in length
Multiple joints are connected together to achieve the ideal total collar length for the drill string. Shorter, thicker collars can be used in curved or horizontal sections [4]. The optimal size depends on the well trajectory, torque and drag analysis, and hydraulic requirements.
Non Magnetic Drill Collar Weight
The weight of Non-Magnetic Drill Collar is a key specification. Heavier collars provide rigidity and put weight on the drill bit for improved drilling efficiency. Standard carbon steel collars typically weigh 300-600 lbs/ft. Non magnetic collars weigh slightly less due to lower material density:
- Monel - 275-300 lbs/ft
- Inconel- 250-350 lbs/ft
- Titanium - 120-240 lbs/ft [5]
Collar weight can be increased by having shorter joints or thicker walls where required. The total collar weight is carefully designed to match the drill bit, mud motor, and downhole conditions.
Non-Magnetic Drill Collars continue to enable smoother, faster drilling of complex directional and horizontal well paths. Their non-magnetic properties reduce interference with downhole survey tools for optimal wellbore placement. Understanding their specifications and applications allows drillers to maximize drilling performance.
References
[1] Non-Magnetic Drill Collar Reduces Interference for Directional Surveys.
[2] Loizou, N. (2002). Reduction of magnetic interference on directional surveys by using a non-magnetic drill collar. SPE 79971. doi:10.2118/79971-MS
[3] Drill Collars. files/002-drill-collars.pdf
[4] Mitchell, R.F. (1999). Non-Magnetic Drill Collar Selection. IADC/SPE 59164. doi:10.2118/59164-MS
[5] Non-Magnetic Drill Collar.
