The development and application of coiled tubing drilling technology began in the early 1990s, and it is still in the primary stage of research and development. In 1991, the United States, Canada and France successively successfully tested and applied CT drilling technology. In recent years, the number of wells drilled with coiled tubing in the world has increased dramatically.
In recent years, with the further development of coiled tubing equipment and manufacturing technology, high-strength and large-diameter coiled tubing with high reliability, small-diameter positive displacement motor, advanced directional tools and measuring system and diamond bit have come out one after another, greatly promoting the development and application of coiled tubing drilling technology.
The advantages of coiled tubing are as follows:
1. It can realize underbalanced drilling safely, protect oil and gas reservoir and improve drilling speed.
2. It can realize the continuous circulation of drilling fluid without stopping the pump and connecting a single pipe, reduce the tripping time, shorten the drilling cycle, and improve the tripping speed and operation safety.
3. It is especially suitable for slim hole drilling, old well sidetracking, old well deepening, realizing the purpose of drilling while mining, and can significantly save drilling cost.
4. Less ground equipment and small floor area, especially suitable for the ground or offshore platform operation with limited conditions, which can reduce the impact on the surrounding environment, reduce the cost of well site construction and maintenance, and the equipment transportation and installation are fast, convenient and flexible.
5. Cable can be built in the coiled tubing, which is conducive to automatic control and MWD.
Coiled tubing also has its limitations.
1. Before drilling with coiled tubing, it is usually necessary to make preparations before drilling with conventional drilling or workover rig, such as tripping out tubing and packer, etc.
2. Although coiled tubing can be used to run short liner, if a longer casing string or liner string is to be run, it can only be completed with the help of a conventional drilling machine or workover rig. Therefore, the current coiled tubing unit can not complete all operations from drilling to completion.
3. Because the coiled tubing can not rotate like the conventional drill pipe, it can not stir the cuttings bed that may be formed, which increases the risk of sticking.
4. The inner diameter of CT is small, and the friction pressure consumption of mud in the pipe is too high, which limits the mud displacement.
5. WOB, torque, hydraulic parameters and BHA are limited.
6. The service life of coiled tubing is short.