The non-magnetic drill collar is made from specially treated steel alloys so that it does not affect magnetic surveying instruments. They aim to isolate directional survey instruments from magnetic distortion due to the steel drill string.
Non Magnetic Drill Collar Function
The magnetic survey instrument is influenced by the presence of a magnetic field around the tool: ferromagnetic material in the formation, drill pipe, drill collar, or other bottom hole assemblies. This influence can't be eliminated but can be reduced to minimize interference with the earth's magnetic field. The survey instrument is placed inside a non-magnetic drill collar so that the survey instrument can measure the earth's magnetic field. More than one non-magnetic drill collar may be used to minimize magnetic interference from the drill string and bottom hole assembly.
Material
Non-magnetic drill collars are manufactured from a material called Monel. This Monel contains a group of nickel alloys, mainly formed of nickel (ranging from 52 to 67%) and copper, with slight amounts of silicon, iron, carbon, and manganese. It is much stronger than pure nickel. In addition to being non-magnetic, Monel alloys have a high resistance to corrosion by highly aggressive agents, including rapidly flowing seawater. Hot- and cold-working, machining, and welding can readily be fabricated.
Non-magnetic drill collars play a crucial role in drilling operations, particularly in surveying the wellbore direction. These collars are made from specially treated steel alloys, such as Monel, which do not affect magnetic surveying instruments. The primary function of non-magnetic drill collars is to isolate directional survey instruments from magnetic distortion caused by the steel drill string and other bottom hole assemblies. By placing the survey instrument inside a non-magnetic drill collar, the instrument can accurately measure the earth's magnetic field without interference from the drill string. The selection of non-magnetic drill collars depends on various factors, including the geographical location, inclination, azimuth, and bottom-hole assembly.
Non-magnetic drill collars are typically manufactured from a material called Monel, which is a group of nickel alloys. Monel alloys are known for their non-magnetic properties and high resistance to corrosion, making them suitable for downhole applications. These alloys mainly consist of nickel and copper, with additional elements such as silicon, iron, carbon, and manganese. Monel alloys are not only non-magnetic but also strong and durable, allowing them to withstand the harsh conditions encountered during drilling operations.
The selection of non-magnetic drill collars is critical for accurate wellbore surveying. The number and length of the collars required depend on the geographical location and the earth's magnetic field intensity. The horizontal intensity of the earth's magnetic field varies depending on the magnetic dip angle, which is influenced by the location's proximity to the magnetic poles. Shell's zonal map provides a reference for determining the required length of non-magnetic drill collars based on the geographical zone. Additionally, the inclination and azimuth of the wellbore also dictate the number of collars needed. Wellbores with higher inclinations or orientations towards the East or West may require additional collars to minimize magnetic interference.
Vigor supplies specialized Non-Magnetic Drill Collars (NMDCs) engineered to maintain critical measurement accuracy in demanding drilling environments. Our range includes Monel, Inconel, and low-permeability alloy variants, all sourced via client partnerships to meet exact specifications-magnetic permeability (<1.005 μ), OD/ID tolerances (±0.125mm), and API connections (e.g., 6⅝" FH). Beyond procurement, Vigor's drilling engineers provide multidimensional support: analyzing formation magnetism, survey tool placement, and BHA dynamics to proactively optimize collar selection and placement. This collaboration eliminates magnetic interference risks that compromise MWD/LWD data accuracy.
Each NMDC undergoes rigorous validation: eddy current testing for permeability uniformity, Charpy V-notch impact tests, and full material traceability per API Spec 7-1. Leveraging our global network, Vigor secures competitive pricing and reduces lead times by 25–40%, while our engineering insights ensure rapid deployment of field-ready solutions. The result? Faster, error-free directional drilling, minimized sidetracks, and significant cost savings across complex well projects.
For more information, you can write to our mailbox info@vigorpetroleum.com & marketing@vigordrilling.com
