The kelly is located at the top of the drill string, and its main function is to transmit the torque and bear the total weight of the drill string. The end face of the driving part of the kelly is divided into square and regular hexagonal. The square is the most used in oil drilling, and the water hole is regular hexagonal. Because the wall thickness is about three times larger than that of the drill pipe, it is made of high-strength alloy steel,so it has high tensile strength and torsional strength.
Drill pipe is a commonly used drilling tool, which is mainly used to transmit torque and transport drilling fluid. The pipe body and the joint of the existing drill pipe are connected together by butt welding. In order to increase the strength of the joint, the butt welding parts at both ends of the pipe body are thickened, and the thickening forms include inner thickening, outer thickening, and inner and outer thickening.
The inner thickening reduces the inner diameter of both ends of the pipe body to increase the thickness of the pipe wall. The outer diameter of this drill pipe is consistent, and the outer diameter of the joint is not too large. When rotating in the well, the joint has less contact with the well wall and wears less. Small, but because the inner diameter of the thickened part is smaller than the inner diameter of the pipe, the flow resistance during drilling fluid circulation is increased.
The inner diameter of the outer thickened drill pipe is the same, but the outer diameter at both ends of the pipe body is enlarged. The outer diameter of the drill pipe joint is larger than that of the same size drill pipe joint, and the joint is added to the well wall when rotating in the well. The contact friction is easy to wear; since the inner diameter of the drill pipe is consistent with the inner diameter of the pipe, the flow resistance is small when the drilling fluid is circulated.
The inner and outer thickened drill pipe is to reduce the inner diameter at both ends of the pipe body and increase the outer diameter to increase the wall thickness of the pipe body at both ends. The drill pipe of this structure combines the advantages of the above two structure drill pipes.
Heavy weight drill pipe
The feature of the heavy drill pipe is that the wall thickness is more than twice that of the ordinary drill pipe, the joint body is longer than the ordinary drill pipe, and there is a special wear-resistant roller in the middle of the pipe body. Heavy drill pipe is mainly used in the following aspects:
- It is used in the transition zone between the drill collar and the drill pipe to ease the change of the bending stress of the two to reduce the damage of the drill pipe;
- It replaces drill collars in slim hole drilling and is easy to operate;
- Replace most of the drill collars in directional wells to reduce the occurrence of torque and sticking pipe sticking, thereby reducing costs and helping to maintain the orientation of directional wells. Due to the large contact area between the drill collar and the tight seal, a large friction force occurs with the well wall when it rotates, so that the wellbore tends to deflect. When the drill collar is replaced by a heavy drill pipe, this possibility can be reduced, so there is It is beneficial to maintain the orientation of the directional well.
The drill collar is one of the main components of the drill string. Its function is to provide the drilling pressure for the drill bit, and at the same time make the lower drill tool assembly have greater rigidity, so that the drill bit works stably and helps to overcome the problem of well deviation. Drill Collar Classification:
- Cylindrical type: It is made of ordinary alloy steel, and the inside and outside of the cross section of the pipe body are circular drill collars;
- Spiral type: made of ordinary alloy steel, the outer surface of the pipe has a drill collar with spiral grooves;
- Non-magnetic type: It is made of stainless alloy steel with very low magnetic permeability, and the inner and outer diameters of the cross-section of the pipe body are circular drill collars. The types of drill collars include square drill collars and non-magnetic spiral drill collars.
Spiral drill collar
The role of the helical drill collar is to reduce sticking and sticking. Three right-handed helical grooves are processed on the outer cylinder of the round drill collar. There is a section of 305-560mm in the external thread joint part and 475-mm in the internal thread end joint part. The weight of the 610mm ungrooved round drill collar section is 4% less than that of the same size round drill collar. Spiral drill collars are not included in the API standard, but many foreign manufacturers have produced them. Domestic drill collars have also been officially put into production, and their specifications and dimensions are the same as those of foreign products.
Stabilizers are commonly known as centralizers. A certain number of stabilizers are placed at suitable positions in the drill string to form the lower drilling tool assembly of the drill string, which can prevent well deviation when drilling vertical wells and control the wellbore trajectory when drilling directional wells.
The use of a stabilizer can improve the working stability of the drill bit, thereby prolonging the service life of the drill bit, which is especially important for diamond drill bits.
Commonly used stabilizers are divided into four types: three-roller stabilizers, interchangeable sleeve stabilizers, integral helical stabilizers, and integral straight-edge stabilizers.
Non-magnetic drill collar
The structure of non-magnetic drill collars is the same as that of ordinary drill collars, but the chemical composition and mechanical properties are different from ordinary drill collars. Non-magnetic drill collar is a kind of drilling tool with special function in directional well engineering. When the magnetic clinometer is used to measure the inclination Angle and azimuth Angle of the hole in a directional well, in order to prevent the compass from being affected by the magnetic field of the drill string, the drill string must be equipped with a certain length of non-magnetic drill collar, so that the magnetic clinometer can be located in a suitable position in the non-magnetic drill collar to measure the inclination, otherwise the correct measurement results cannot be obtained.