Under the condition of under balanced pressure, coiled tubing drilling has shown great advantages, the main advantages are as follows:
1. Under balanced drilling with coiled tubing can reduce damage to formation or production layer
Under balanced drilling of coiled tubing requires that the negative pressure condition should be maintained during drilling, single connection, tripping and other operations, so as to effectively reduce the damage to the formation or production layer. When the conventional connecting drill string is used for underbalanced drilling, its advantages will be lost when the drill pipe is connected. However, the use of coiled tubing, because the drill pipe is not connected during drilling, can always maintain the underbalanced condition, thus fully showing the advantages of underbalanced drilling.
2. The efficiency of underbalanced drilling with coiled tubing is high.
The drilling speed of underbalanced drilling is higher than that of conventional drilling, while coiled tubing in underbalanced drilling does not need to connect a single, which saves the time of connecting a single, and the tripping speed in tripping is faster than that of conventional drill string, which can greatly save the time of occupying the drilling rig.
3. Underbalanced drilling with coiled tubing is safe and reliable
In underbalanced drilling, coiled tubing is used, which avoids the drilling personnel from unloading the drill pipe on the rig floor. In this way, casualties can be avoided when unloading the drill pipe. Another advantage is that coiled tubing can continuously circulate drilling fluid during tripping operation, eliminating blowout accidents caused by pressure pumping and pressure excitation during tripping.
4. Real time annulus pressure measurement can be carried out by underbalanced drilling with coiled tubing
In general, the drilling fluid pulse MWD tool cannot be used in the compressible drilling fluid used for underbalanced drilling, so it is impossible to measure. In this case, for example, the wired MWD tool is used for measurement, but the under balance condition is lost due to the need to stop drilling during measurement. In order to solve this problem, coiled tubing has its unique advantages in the current situation, because the cable installed in the coiled tubing can carry out real-time directional measurement, real-time annulus pressure measurement and real-time gamma logging, while maintaining the continuous under balance condition.
5. Save drilling cost
Due to the lack of large drilling equipment, the well pad needs less land and has strong adaptability, which is conducive to saving drilling costs.
Although underbalanced coiled tubing drilling has obvious advantages, it also has its limitations. Because of the flexibility of coiled tubing, it is easy to block, so the length that can reach the level is limited at present. In addition, it is difficult to control the direction of under balanced directional deviated well or horizontal drilling with coiled tubing. If there is a problem with wellbore stability during drilling, the coiled tubing cannot rotate. If vibration is needed to release the BHA stuck in the well, the coiled tubing string can not bear the bad mechanical operation conditions that conventional drill collars and drill pipes can bear.