DTH hammer failure analysis and solution
According to the gas distribution method, the downhole hammer can be divided into two types: valve type hammer and valveless hammer. In addition to the different gas distribution methods, the structure is slightly different, but the working principle is basically similar, but the valve type and its anti-pollution ability are even worse.
There are many reasons for the failure of the down-the-hole hammer , but the manifestation is mainly the hammer without impact, impact force and intermittent impact. Analysis of the cause of the failure and subsequent improvements to the equipment will contribute to the improvement of the hammer structure and drilling process.
Inductive classification of its fault factors can be analyzed from the following five aspects:
1, processing defects
The dth hammer piston and the cylinder liner are tightly matched, and the mating length is long, and the processing precision and surface smoothness are required to be high, which requires a very high cylindricity of the piston and the cylinder liner. If the cylindricity is not guaranteed, the piston will be directional or intermittently stuck. In the end, it may not be right. Lift the drill pipe at the airport and repair the hammer.
In addition, the rigidity of the outer casing of the hammer is also an important factor that limits the service life of the hammer. If the outer casing is of poor hardness. During the drilling process, the inflating machine will be deformed due to frequent collision with the well wall; when the hammer is not working, it is often necessary to vibrate and disassemble and clean the hammer, which in turn will aggravate the deformation of the outer casing of the hammer; The deformation will cause each part of the hammer to become stuck and cause disassembly, which will eventually cause the hammer to be scrapped.
For the effective movement of the inner cylinder and piston of the hammer and the high-precision production of the product, Superman DTH Machinery Co., Ltd.has been working deeply for 20 years.
2, the hammer tail backstop seal is not reliable
At present, the tail of the hammer for geophysical exploration is provided with a check valve, and its structure is shown in Fig. 1. The sealing form is mainly based on the compression deformation of the spherical rubber cap or the O-ring attached to the metal cone to perform the backstop sealing. Its backstop function is achieved by an elastomer, and the elastomer generally has a guiding device.
This type of sealing has the following problems:
(1) The friction between the spring and the guide will affect the cutoff speed of the reverse stop valve;
(2) If the rubber seal material is compressed frequently for a long time, the friction will make it wear over;
(3) spring fatigue failure, resulting in reverse sealing failure;
(4) When the gas is stopped, the sudden decrease of the internal pressure of the hammer causes the rock powder or liquid-solid mixture to pour back into the inner cavity of the hammer, which will cause the piston to jam;
(5) More seriously, when water carries cuttings into the valve position (valve type hammer), the valve cannot normally close the valve, resulting in the failure of the hammer to discharge only debris without impacting work.
3, the hammer head is not sealed
The bit of the hammer head used in the geophysical drilling is provided with a vent hole communicating with the bottom of the well, and the bit and the hammer are connected by a spline, and the matching gap is large. In the case of encountering a diving surface during drilling or if it is necessary to fill the cementing fluid due to the difficulty of forming a well, there is a large amount of liquid and solid mixture in the gap between the bottom of the well and the wall of the well and the drill pipe. When connecting or replacing the drill pipe or adding When the well fluid is injected, the gas supply is stopped, so that the check valve at the tail of the hammer is quickly closed. Due to inertia, some liquids are instantaneously backflowed into the hammer through two ways: the venting hole of the bit, the gap between the bit and the spline sleeve. Subsequently, the hammer is like an empty water bottle that is buckled in the liquid, and the gas enclosed in the inner cavity of the hammer is bound to be compressed by the external liquid of the cup, as shown in Fig. 2.
When the air pressure in the inner chamber of the hammer is equal to the pressure of the external liquid, the equilibrium is reached. According to the internal and external balance, the air height h of the hammer chamber can be calculated as:
In the formula: po is the pressure after the inner cavity of the hammer is stopped; ho is the length of the inner cavity of the hammer; ρ is the density of the liquid at the bottom of the well; g is the acceleration of gravity; H is the height of the liquid level at the bottom of the well.
It can be seen from (1) in the formula that the higher the liquid level in the outside, the smaller the length of the sealing gas in the inner chamber of the hammer, that is, the more liquid entering the inner cavity of the hammer. If there is too much water in the inner cavity of the hammer, some cuttings will be brought into the movement of the inner piston, which increases the stuck frequency of the piston. At the same time, if the cuttings between the piston and the end face of the bit are delayed (see Figure 3), the impact energy of the piston will be mostly absorbed by the cuttings, which cannot be effectively transmitted, that is, the impact is weak.
4, the bit stuck
The bit and the hammer are splined (see Figure 4), the mating clearance is relatively large, and many types of hammer spline tails can be exposed to match the splined sleeve. If the cuttings are wet, it is easy to form a mud bag to adhere to the bit. If the state is not improved in time, the mud bag will enter the spline fit clearance, which will affect the effective impact of the hammer piston impact work; more seriously, the bit and the spline sleeve may be stuck together.
5. There are large solid phase particles in the cementing solution.
Under normal circumstances, in the case of easy collapsed formations that are difficult to form wells, it is necessary to use foam drilling, that is, frequently adding foaming agent to the well for cementing. However, in practice, during the construction of the squad, washing powder solution tends to be used in consideration of convenience and economy. Due to the quality of the washing powder or the quality of the water, there will be some insoluble particles. When the cementing fluid is filled from the drill pipe to the bottom of the well, the undissolved particles in the washing powder will directly enter the inner cavity of the hammer, affecting the normal operation of the valve (valve hammer), or increasing the piston stuck. Probability.