Several Types of Drill Collars

The drill collar is one of the main components of the drill string. Its role is to provide bit pressure while providing greater rigidity to the BHA assembly, thus keeping the bit stable and helping to overcome the well deviation problem.

The drill collar types are as follows:

1. Cylindrical type: made of ordinary alloy steel, the inside and outside of the cross section of the pipe are circular;

2. Spiral type: the drill collar made of ordinary alloy steel with spiral groove on the outer surface of the pipe body;

The function of spiral drill collar is to reduce the occurrence of sticking. Three right-handed spiral grooves are machined on the outer cylinder of the circular drill collar, and a section of 305-560mm round drill collar without groove is reserved in the external thread joint part and 475-610mm in the internal thread end joint part. Its weight is 4% less than that of the circular drill collar with the same size.

3. Non-magnetic type: it is made of stainless alloy steel with low permeability, and the inner and outer diameters of cross section of pipe body are circular.

The non-magnetic drill collar is mainly used for monitoring in the process of oil drilling. Its structure is the same as that of general drill collar, but its chemical composition and mechanical properties are different from ordinary drill collar. Non-magnetic drill collar is a special drilling tool in directional well engineering. When the magnetic inclinometer is used to measure the inclination angle and azimuth angle of the directional well, in order to make the compass not affected by the magnetic field of the drill string, a certain length of non-magnetic drill collar must be equipped in the drill string, so that the magnetic inclinometer can be located in the appropriate position in the non-magnetic drill collar for inclinometer measurement, otherwise the correct measurement results cannot be obtained.