What is a Drill Collar?

Drill Collar Definition

A drill collar is a device used at the lowest part of a drill string, an important part of the bottom hole assembly (BHA). It is always a very thick-walled tube to apply weight to the drill bit. Normally, a drill collar is threaded at both ends, male on one and female on the other. Except for thickness as a special characteristic, a drill collar owns other unique features, gravity, rigidity, etc.

Drill Collar Classification

Drill collars can be simply put into three categories according to their structure and material, namely the slick drill collar, the spiral grooved drill collar and the non-magnetic drill collar.

• The slick drill collar is normally a smooth thicked-wall tube, with a thickness in the range of 38 to 53, about 4 to 8 times of that of the drill pipes. It is machined into a uniform cylindrical shape and made up of plain alloy steel.
• The spiral grooved drill collar is also machined from plain alloy steel, but it is normally lighter by 4 to 6 percent than the slicker drill collar. This kind of drill collar is widely used nowadays because the special spiral design largely hold back of the possibility of sticking accidents by reducing the area of contact between the wall and the collar.
• The non-magnetic drill collar is manufactured from the non-magnetic alloy steel. As the magnetic measuring instruments can sense the geomagnetic field when measuring the direction of the borehole, the instruments must be kept working in a non-magnetic environment. However, in drilling process, the magnetic rigs always affect the accuracy of the measuring instrument. Therefore, the utilization of a non-magnetic drill collar can ensure a more reliable measuring result.

Drill Collars in Drilling Application

• Drill collars play a vital role in drilling process. Due to the structural features, drill collars can provide weight for drilling purpose, which is drill collar’s one and foremost specialty. Gravity works on a number of drill collars to offer enough downward force needed to break rocks with the drill bit.  
• Apart from providing weight on the bit (WOB), drill collars also work as a shock absorber to dampen the vibration and shaking when drilling takes place. In this way, the drilling process can be carried out in a much steadier state.
• Thirdly, the presence of the drill collars allows the pipelines to stay in the tensile state, while guarantees the rigidity of the drill string under great compression. Thus, the drill efficiency and quality are greatly improved.
• In addition to the above applications, drill collars can help to control the direction of the bottom hole assembly, avoiding the problem of hole deviation and enhancing the performance of drilling.

Anson Drill Collar

Henan Anson Steel Co., Ltd is a pioneer manufacturer and supplier in oil and gas products of high quality and at a competitive price. Anson mainly provides products such as tubing, casing, drill pipes, drill collars and so on.

We have drill collars from 5 to 32 feet, with a diameter from 3-1/8”to 11”. Our drill collars are made of AISI4145H premium alloy steel. These drill collars are fully heating quenched, tempered and water cooling measured to withstand high strength and compression. Strict mechanical inspection is applied to drill collars to make sure that all drill collars can meet the requirements of the API m7-1 specification.

We have been making drill collars for years so we are confident that our drill collars will satisfy or even beyond your demands. We are always here ready to offer you the top quality drill collars as well as our professional and all-embracing service.