Coiled Tubing Drilling (CTD) is a technology that uses continuous tubes to complete drilling. Its development and application began in the early 1990s as a new technology. Continuous pipe drilling can be divided into two types: directional heavy drilling and vertical drilling. According to the process, it can be divided into three types: underbalanced drilling, near balanced drilling and overbalanced drilling.

Advantages of continuous tube drilling: 
1) The well site occupies a small area and is suitable for operation in areas with limited ground conditions or offshore platforms;
2) Particularly suitable for small well borehole drilling;
3) In the old well heavy drilling (drilling or sidetracking) operation, the oil pipe operation can be carried out, and the existing production equipment in the old well can be taken out, and the purpose of drilling while drilling can be realized;
4) The underbalanced drilling operation can be carried out safely. The biggest advantage is that it can ensure that the underground is always underbalanced, reduce mud loss and prevent formation damage;
5) Small borehole drilling can reduce hardware and labor requirements and reduce operating costs.
6) The continuous pipe does not need to be connected to a single root to realize continuous circulating mud, reduce the drilling time and operation cycle, improve the drilling speed and operation safety, and avoid the blowout and stuck drilling accidents caused by the single root;
7) After the built-in cable of the continuous pipe can improve the signal-driven transmission of the drill, and realize the logging while drilling, which is beneficial to the closed-loop drilling;
8) Minimize erosion of the formation, and good logging quality can be obtained (continuously, no take-over);

Disadvantages of continuous tube drilling:
1) The long-sleeve casing must be driven by means of a conventional rig or workover rig;
2) Before the drilling of the continuous pipe operation device, it is necessary to use the conventional drilling rig or workover rig to prepare for the downhole;
3) The continuous tube cannot be rotated, thus increasing the possibility of stuck drilling;
4) Frequent drilling is required to replace the downhole assembly or adjust the bending angle of the motor. The result is premature fatigue of the continuous tube and reduced service life;
5) Limiting the size of the wellbore and the displacement of the mud due to the small diameter;
6) The drilling pressure, torque, hydraulic parameters and the combination of downhole drilling tools are limited, and problems such as screw drilling failure, differential pressure stuck, drilling pressure transmission and bit mud pack may occur;
7) The huge roller is not easy to transport and lift.