The feature of the direct connection type premium connection is that the tubing and casing are not connected by coupling, and the internal and external threads are directly processed at the end of the tubing and casing. According to different structural dimensions, the direct connection type premium connection can be generally divided into two types: one is that the joint is more than the pipe body, and the outer diameter is exactly the same, that is, it is completely flush type; the other is that the joint is thicker than the pipe body and the outer diameter, that is, it is thickened type.
Because this premium connection does not use coupling connection, the outer diameter of the whole string is reduced, which means that the gap between the string and the wellbore is increased. It is precisely because of this advantage that the direct connection type premium connection has a special use in oil drilling, especially in deep well, ultra deep well drilling, small gap cementing, workover and other operations, which is of great significance to solve the problems of small hole, difficult casing running and poor cementing quality.