Common Failure Types and Causes Analysis of Screw Drilling Tools

In recent years, the frequency and quantity of screw drilling tools have increased significantly, and the reasons for the failure of screw drilling tools have also changed significantly during use.

With the improvement of the manufacturer's manufacturing and processing level and the continuous improvement of products based on on-site feedback information, product quality has been greatly improved, and human operation factors have gradually become the main reason for the failure of screw drilling tools.

The main failure modes of screw drilling tools are broken drive shaft, degummed stator, bypass valve puncture, drive shaft stuck, casing tripping, etc.

If these situations are not accurately judged and decisive measures are not taken in time, it will cause more complicated situations downhole, and in severe cases, the screw drilling tool will be broken and the well will be broken or stuck.

1. The drive shaft of the screw drilling tool is broken

Due to the limitation of the structure of the screw drilling tool itself, the size of the drive shaft should not be too large, which affects its rigidity and strength and is the most prone to failure of the screw drilling tool.

The main reasons for the failure: in the case of compound drilling, the rotation and oscillation of the screw drilling tool is intensified, and the instantaneous load changes sharply; in the heterogeneous formation, the axial and radial impact loads of the screw drilling tool are suddenly large and small;

The drilling pressure is too large and the rotating speed of the turntable is too high, which exceeds the safe load of the general term of the drive shaft; the excessive drilling fluid displacement aggravates the erosion of the water hole of the drive shaft and causes its bearing capacity to decrease;

Intermittent drilling, slipping, and slugging make the drilling tools frequently stagnate and cause the drive shaft to break at weak points.

2. Puncture of the bypass valve of the screw drilling tool

In the process of drilling, sometimes the pump pressure drops and the drilling speed slows down. Except for the ground factors, it should be that the bypass valve is not closed or the bypass valve is damaged.

The main reason for the failure is that the sand content of the drilling fluid is too high or impurities such as plastic bags are mixed in the drilling fluid process, which causes the valve core and the valve seat to be stuck and cannot be closed.

3. The drive shaft of the screw drilling tool is stuck

The main reason for the sticking of the drive shaft in drilling is that the upper part of the drive shaft assembly is blocked by sand, and the drilling fluid cannot enter the bearing for lubrication and cooling, resulting in the burning of the drive shaft.

In this case, the pump pressure is often increased, the drilling tool is lifted up, the pump pressure is still high, the drilling speed is slowed down or there is no footage, and the turntable is reversed after stopping.

This is mainly due to the unsatisfactory performance of the drilling fluid, high sand content, fast drilling speed, failure of cuttings to return in time, slow connection of single rods or long pump down time, and mostly occurs in the first drilling of the second opening.

4. Stator degumming of screw drilling tools

The main manifestation of stator degumming is that the pump pressure increases during drilling, or even extremely high pump pressure causes the pump to suffocate. The reason is that the high hardness particles in the drilling fluid increase the rotational resistance of the interference fit between the stator and the rotor;

The increase of well temperature will change the stator rubber; the gas mixed in the drilling fluid will cause cavitation; the drilling and drilling will cause damage to the drilling tools.

5. The screw drilling tool shell is tripped

Generally, the screw drilling tool is easy to escape from the connection between the universal shaft casing and the transmission shaft casing, causing the rotor and the transmission shaft assembly to fall into the well.

The main reasons are: while the high-pressure drilling fluid exerts a forward torque on the rotor, the rotor exerts an equivalent reverse torque on the stator casing.

In the case of frequent stagnation of drilling tools and compound drilling, this counter torque increases significantly, which is easy to cause looseness, especially when the drive shaft string bearing is stuck or completely stuck, the risk of tripping is increased;

When the drilling speed is fast, the downhole is not clean, and when the well deviation is large, the whole screw drilling tool will accumulate a large amount of counter torque before the stop turntable is connected to a single one, and the sudden release and inversion will easily cause the thread to trip.