Reasons for sticking of rotary drilling rig and detailed countermeasures!

Rotary drilling rig is a kind of construction equipment introduced and developed in China in recent years. With the advantages of high concentration of mechanical, electrical and hydraulic integration, optimal design of working system, flexible field transfer and field displacement, the drilling rig makes the construction field, especially the field of cast-in-place piles, look new; At the same time, it occupies the market with its characteristics of high efficiency, high quality and no pollution, which is accepted by most owners and design units.

During the use of drilling rigs in recent years, all users have taken effective measures, with considerable economic and social benefits, but there are also some problems. This paper makes some analysis on the causes of drilling rig sticking in the construction process, and puts forward corresponding countermeasures to discuss with peers.

1. Causes of sticking

The so-called sticking means that during the drilling or lifting process of the rotary drilling rig, due to reasons other than the drilling rig itself, that is, when all systems of the drilling rig work normally, the forward and reverse movements cannot be carried out, and the main winch cannot lift the drill pipe, and then repeat the above actions repeatedly, and the normal operation cannot be restored.

According to the investigation and analysis of some sticking accidents in recent years, it is preliminarily considered that the main causes of sticking are as follows:

(1) In the process of drilling and lifting, the hole wall collapses in a large area, resulting in buried drilling, so that the bit can neither be reversed nor lifted. This situation is more likely to occur in sand egg layer or quicksand layer with low compactness.

(2) Due to the wrong operation of the operator during drilling, the one-time footage is too deep, resulting in the shrinkage of the hole wall, resulting in the disappearance of the gap between the drill barrel wall and the hole wall, resulting in the sticking of the drill. This situation is easy to occur when the clay layer or sand layer becomes clay layer.

(3) The side teeth and side teeth of the bit are seriously worn, and the hole diameter can not meet the size requirements, so that there is no gap between the outer wall of the drill barrel and the hole wall, and it is caused by drilling too deep at the same time.

(4) Due to accidental factors: for example, the steel wire rope is broken during drilling or lifting, the movable joint (universal joint) is disassembled, or some other faults of the machine itself (such as the engine can not work, the steel wire rope jumps out of the pulley groove, etc.) make the work stop suddenly, and the treatment is not timely. The bit stays at the bottom of the hole for too long, resulting in too much sediment around the barrel wall of the bit or shrinkage of the hole wall.

2. Measures to prevent sticking

Sticking is one of the most serious problems of rotary drilling rig during construction. Once it occurs, it is not easy to deal with. Even if the drill bit is finally taken out, it will take a lot of human and financial resources and a long time, resulting in great economic losses and adverse social impact. Therefore, we should focus on prevention. Prevention mainly starts from the following aspects:

(1) Before spud in, the geological report shall be fully studied to master the formation conditions, and pay close attention to the formation changes during construction. For the stratum that is easy to cause hole collapse, such as sand gravel layer and quicksand layer, countermeasures shall be formulated in advance, such as adjusting the performance of wall protection fluid and embedding long casing, so as to prevent large-area hole collapse.

(2) The operator shall control the footage during deep drilling and do not drill too much at one time. For example, when drilling at a depth of more than 15m, the one-time drilling depth shall not exceed 40cm. If drilling in clay layer, the diameter reduction factor shall be fully considered; In case of transition from sand pebble and other strata to clay layer, pay attention to the law of formation change, do not pressurize blindly, and control the one-time footage.

(3) Pay attention to the size of the drill barrel when making the drill bit. Generally, the diameter of the drill barrel shall be more than 6cm less than the hole diameter; During use, the drill bit shall be repaired in time. After the side teeth and side teeth of the drill bit are worn, they shall be replaced or repaired in time to ensure the hole size; At the same time, it shall be ensured that the bit hook is effective to avoid accidental tripping.

(4) Pay attention to the timely maintenance and repair of the drilling rig itself to avoid long-term shutdown due to the failure of the drilling rig.

① Pay attention to engine power. In case of insufficient power, the rotating speed of the equipment drops rapidly under normal load or stalls, it shall be repaired in time.

② Maintain the hydraulic system frequently to avoid the system pressure drop due to the blockage of the overflow valve and the cracking of the oil pipe, resulting in the failure of the power head to reach the rated torque and insufficient lifting tension.

③ Frequently check the steel wire rope, movable joint and other accessories to avoid the breakage of the steel wire rope and the disassembly of the movable joint, which will make the drill stay at the hole bottom for a long time.

④ The drill pin shall be assembled to avoid accidental separation between the drill pipe and the drill bit.

⑤ The construction site shall be equipped with mechanical professionals and necessary accessories. If the engine suddenly stalls, the steel wire rope is broken, and the movable joint is disassembled during drilling, it shall be repaired as soon as possible; If it cannot be repaired quickly, decisive measures shall be taken to lift the drill bit out of the hole as soon as possible with other auxiliary equipment (such as crane, etc.) to prevent sticking.

(5) Adjust the density and viscosity of the wall protection fluid so that there is no sediment at the hole bottom within a certain period of time, so as to ensure that there is sufficient time to eliminate the accidental failure of the equipment.

3. Treatment measures for sticking

(1) Analyze the causes of sticking, measure the sticking depth as soon as possible, analyze the formation and other factors, so as to take corresponding countermeasures.

(2) According to the reasons analyzed, corresponding countermeasures are taken.

① If the drilling is stuck due to hole collapse or equipment itself, and the sediment thickness is large, the hole shall be cleaned first, and then treated with drilling rig or auxiliary equipment.

② If the drill is stuck due to non collapse factors and there is not much sediment, self rescue measures should be taken first. For example, appropriately increase the pressure of the hydraulic system to increase the torque of the power head, and then rotate the drill pipe in the forward and reverse directions to make the drill pipe move as much as possible. As long as the drill bit can move, it can slowly rotate and lift, so as to solve the problem (but the wear degree of the steel wire rope and other factors should be fully considered in this method). In addition, the mast can be lifted appropriately to increase the lifting capacity of drill pipe (this method must be implemented in the presence of mechanical professionals and after full consideration of various factors). The above methods can only be used at the initial stage of sticking.

③ If the self rescue is invalid, use auxiliary equipment instead. At this time, measure the sediment thickness first. If there is little sediment, take measures quickly; If the sediment is too thick, the hole shall be cleaned before treatment. The methods mainly include direct lifting method, dredging around the drill bit and retaining wall excavation method.

Direct lifting method: use crane or hydraulic jacking machine to apply force directly upward. According to the practical experience in a construction site in Beijing, the problem can be solved by using four 45t cranes and the tension of the main winch of the drilling rig within 72h.

Dredging around the drill bit: use the reverse circulation or air lift reverse circulation principle (use the high-pressure air pump to produce gas water mixture in the pipe to form reverse circulation), underwater cutting and other methods to clean the sediment around the drill barrel, reduce the friction between the barrel wall and the hole wall, and then jack up with the drill rig and auxiliary equipment. This method is difficult to operate, but it has been successfully used in a construction site in Wuhan.

Wall protection excavation method: protect the wall with casing, cement or other articles, drain the wall protection fluid in the hole, directly excavate manually and clean the sediment around the drill barrel. This method is only used in formations where the sticking is not too deep.

4. Conclusion

Sticking is one of the most harmful accidents in the construction of rotary drilling rig. It should be prevented as far as possible. This requires managers and crew members to be aware of the hazards of drill sticking, formulate preventive measures in advance for various strata, and resolutely implement them in construction; At the same time, make appropriate preparations in terms of manpower and material resources for the handling of sticking accidents, and formulate a variety of rescue plans in advance according to various conditions to prepare for a rainy day.