Non-magnetic Drill Collar

I. Definition and materials

Non magnetic drill collars are made of low-carbon high chromium manganese alloy steel, refined and forged through strict chemical composition ratios, and have good mechanical properties such as low magnetic permeability and high strength.

II. Performance characteristics

1. Low magnetic permeability: When the magnetic field strength is 1 × 105/4 π A/m, the relative magnetic permeability μ r of the non-magnetic drill collar is ≤ 1.010, and the magnetic induction gradient at any distance of 100mm along the inner hole is ≤ 0.05 μ T, which can provide a non-magnetic environment for magnetic measuring instruments.

2. High strength and wear resistance: Made of chromium manganese and austenitic alloys, processed by rotary hammer forging technology, non-magnetic drill collars have high strength and good wear resistance, which can prevent pressure corrosion cracking.

3. Corrosion resistance: Some non-magnetic drill collars, such as P550 non-magnetic drill collars, exhibit excellent corrosion resistance in seawater and saline media, and can adapt to harsh environments such as marine drilling.

III. Working principle

During the drilling process, the magnetism of ordinary drilling tools can interfere with the measurement of the geomagnetic field in the wellbore by magnetic measuring instruments, while non-magnetic drill collars do not produce such interference. The interference magnetic field lines above and below have no effect on the measuring instrument, ensuring that the data measured by the magnetic measuring instrument is true geomagnetic field information.

IV. Specification standards

There are various specifications for non-magnetic drill collars, with common outer diameters including 3 1/8 inches (79.4mm), 4 3/4 inches (120.7mm), 6 1/2 inches (165.1mm), etc. The length is usually 9.14m or 9.45m, and the connection types include NC23, NC35, etc. They comply with standards such as API Spec 7-1, API Spec 7-2, and SY/T 5144.

V. Application areas

Non magnetic drill collars are mainly used in the extraction of oil, natural gas, coalbed methane, and geological exploration, playing a key role in directional drilling, measurement while drilling, and other operations.