Drill collar types and process characteristics

The drill collar is an important tool in drilling operations. It forms drilling pressure through its own weight to provide the necessary downward force during the drilling process. However, since the drilling pressure is mainly formed by the weight of the drill string, the compressive stress at the lower part of the drill string is relatively large. During the drilling process, the drilling pressure value is usually greater than the critical value of the compression rod stability of the drill string, which makes the compressed part of the lower part of the drill string easy to bend under the action of its own weight. The bent drill string will cause alternating stress when rotating, which will lead to fatigue damage of the drill string. In order to reduce the degree of fatigue damage, it is necessary to reduce the bending stress, which requires shortening the length of the compressed section as much as possible and increasing its rigidity. Based on this, the compressed part of the lower end of the drill string does not use a drill pipe but a drill collar.

Drill collars are usually made of thick-walled seamless steel pipes. According to different uses and process requirements, drill collars can be divided into round drill collars, spiral drill collars, non-magnetic drill collars and square drill collars.

At present, we have developed a series of drill collars with various specifications within 12 meters in length, and developed a new type of double-shoulder threaded oil drill collar to be suitable for deep well and high-pressure jet drilling under composite loads. These products are made of AISI4145H chromium-molybdenum steel, and the content of trace elements is effectively controlled to ensure the quality and performance of the products.

A spiral drill collar is a round drill collar with three spiral grooves machined on its outer cylindrical surface. This design leaves a 305 to 560 mm section of the round drill collar on the external thread end joint and a 457 to 610 mm section of the round drill collar on the internal thread end joint without spiral grooves, which is convenient for connection and disconnection operations and repair. Compared with round drill collars of the same size, the weight of the spiral drill collar is reduced by about 4%. In directional drilling, due to the large inclination of the well, the contact area between the drill collar and the well wall is also large, so it is more likely to cause sticking and drilling. Spiral drill collars reduce the risk of sticking and drilling by reducing the contact area with the well wall, so they are widely used.

Non-magnetic drill collars are made of low-chromium manganese alloy steel, which has undergone rigorous chemical composition analysis and forging process. The material has been tested for mechanical properties to ensure that its hardness, toughness, impact value and corrosion resistance meet the standards, while also having good low magnetic permeability and machinability. Non-magnetic drill collars have important application value in some specific drilling operations, especially when magnetic interference needs to be avoided.

Application of drill collar in drilling

Drill collars are widely used in drilling operations, especially in complex working conditions such as deep wells and high-pressure jet drilling. The performance of drill collars plays a key role in the success of the entire drilling operation. By rationally selecting the type and specifications of drill collars and adopting scientific process methods for manufacturing, drilling efficiency can be significantly improved, equipment failure rate can be reduced, and the safety and economy of drilling operations can be guaranteed.