Coiled tubing flexible drill rod ultra-short radius radial drilling string, system and method

A method for coiled tubing flexible drill rod ultra-short radius radial drilling for a system which is a coiled tubing flexible drill rod ultra-short radius radial drilling system, wherein the system comprises a plurality of operation modes, and the method comprises:

• when the coiled tubing flexible drill rod ultra-short radius radial drilling system is in a first operation mode, activating a screw motor and a flexible power drilling tool that are located at a lower part of a coiled tubing, wherein a drill bit is mounted at a lower end of a flexible drill rod, and both the screw motor and the flexible power drilling tool provide a torque and a weight on bit for the flexible drill rod and the drill bit;
• during operation, the screw motor remains in a main wellbore without entering a branch wellbore, so as to realize ultra-short radius radial drilling;
• when the coiled tubing flexible drill rod ultra-short radius radial drilling system is in a second operation mode, activating only the screw motor and deactivating the flexible power drilling tool, wherein a lower end of the screw motor is connected to the flexible drill rod, and the drill bit is mounted at the lower end of the flexible drill rod;
• during operation, the screw motor does not enter the branch wellbore, and provides a torque for the flexible drill rod and the drill bit;
• during drilling, a rotation speed of the flexible drill rod is controlled through a fluid flow from a pump, and an operating weight on bit is determined based on a rated torque of the screw motor;
• and
• when the coiled tubing flexible drill rod ultra-short radius radial drilling system is in a third operation mode, activating only the flexible power drilling tool connected to the drill bit below;
• during operation, the screw motor is deactivated, the flexible drill rod does not rotate, and the flexible power drilling tool enters the sidetrack drilling branch wellbore along with the drill bit to directly provide a torque for the drill bit to realize rotary drilling.