Causes of DTH Drill Pipe drilling accidents
1) Geological factors

    The target of drilling is the formation, and the formation structure is hard or soft, the pressure system is high or low, and the pores are large or small. If you do not have enough understanding of these conditions, it is inevitable that unexpected problems will occur.

     First of all, we should understand the formation pore pressure, formation fracture pressure, formation collapse pressure and creep stress of some special formations (salt gypsum, ooze rock) of the designed well, as the main basis for well structure and drilling fluid design. Generally speaking, in the same open hole section, blowout and leakage layers cannot exist at the same time, and creep and leakage layers cannot exist at the same time. If the above requirements cannot be achieved on the well structure, and the high pressure layer and creep layer are below the leaky zone, then the leaky zone should be pre-processed and cannot blindly drill into the deep. If there is a low pressure layer or a leakage layer under the high pressure layer or creep layer, then the high pressure layer or creep layer has to be sealed with casing.

     Secondly, for some special formations, such as salt rock formations, gypsum salt formations, water-rich soft mud rocks, water-absorbing mudstone formations, mudstone formations that tend to collapse and spall, coal beds, and some These igneous rock intrusions should have a more detailed understanding, because these formations are the main reason for the downhole complexity. At the same time, some geological phenomena such as faults, fractures, karst caves, ultra-high permeability layers and the existence and content of hydrogen sulfide and carbon dioxide should also be understood.

      The above information is essential for making a well. However, the more detailed information provided by the geological department is oil and gas reservoir data, while the important information required for engineering is not provided much or detailed enough, and some data are even far away from the actual situation, even for the oil fields that have been developed. As a result of water injection development, the underground pressure system varies greatly, and it is difficult to use data from adjacent wells as the main basis. This makes the drilling process often have to fight encounters, so complicated situations occur frequently.

2) Engineering factors

     Drilling operations are concealed and complicated. Due to inaccurate geological data or inaccurate geological data, well structure design is not strictly carried out in accordance with scientific methods despite reliable geological data, so that blowout and leaky layers coexist in the same section of open hole. Leakage, spray when you cure it. Although the casing is installed, the parallel control equipment is not installed, or although the well control equipment is installed, the quality is not emphasized. Once a high-pressure layer is drilled, it will leak everywhere during emergency use, and even cause blowout out of control. The drilling fluid system and performance are not compatible with the formation characteristics, and even one-sided emphasis on saving drilling fluid treatment agent, which deteriorates the performance of the drilling fluid and causes the diameter reduction or collapse of certain formations in the open hole section.

      Improper drilling fluid density can also cause blowout, lost circulation or well collapse. Improper operation and too fast drilling speed will produce a lot of excitement pressure, which will easily suffocate the formation. Excessive tripping speed will produce a large suction force, which is easy to pump out the oil and gas layer or collapse the soft structure, especially in the case of drill bits or centralizer mud packs.

      Failure of drilling equipment and forced stop of drilling tool activity or drilling fluid circulation are the most common and common causes of downhole accidents. In addition, the management work is weak, there are rules that are not followed, there are tables (referring to weight meters, pump pressure meters, torque meters), do not look at things, do not think about things, make blind decisions, but seek to save effort, regardless of the consequences, lift off the drill, and drill down. Severe pressure, hard turning when stuck, and hard holding when leaking are common causes of underground accidents.

Common processing methods

1) Causes and treatment of stuck drill accidents

   Sticking and its causes: Sticking is caused by geological factors, poor drilling fluid performance, improper technical measures, etc., which prevent the drilling tool from moving freely in the well for a long time. This phenomenon is called stuck. Mainly include sticking stuck, heavy sand stuck, sand bridge stuck, well collapse stuck, reduced diameter stuck, mud pack stuck, falling object stuck, and drill tool falling down stuck stuck.

     Methods to deal with stuck drill accidents: (1) Soak oil to release the jam; (2) Use a jar to shake to release the jam; (3) Inverted sleeve milling; (4) Explosive release; (5) Explosive drill tool sidetrack New eyes and so on.

2) Causes and treatment of well collapse accident

Well collapse is the phenomenon of instability and collapse of the well wall during drilling. The reasons for the well collapse include: the pressure of the fluid column in the well cannot balance the formation pressure; the formation is soaked by the drilling fluid, which causes water-sensitive expansion, fragmentation, and stripping; the formation itself is broken and loose, and the suction phenomenon caused by the lifting of the drilling tool causes the lower wellbore pressure Decline; in the process of tripping, failure to recharge the drilling fluid in time causes the pressure of the fluid column in the well to drop; stop drilling for too long, and the performance of the drilling fluid will change; in the open hole section for a long time, large displacement circulation, etc. When the well collapse is severe, the wellbore situation will be complicated and cause accidents in the well.

(1) During the drilling process, if it is found that the drilling fluid does not return to the wellhead, or the drilling fluid is sprayed back in the drill pipe, this is a symbol of well collapse and the drilling should be stopped immediately. Open the pump to circulate through the well or mark the hole. After the downhole condition is normal, resume drilling.

(2) During the tripping process, if it is found that the liquid level at the wellhead does not drop, or the drilling fluid is sprayed back in the drill pipe, this is a symbol of well collapse, and tripping should be stopped immediately. Turn on the pump to circulate the drilling fluid. After the pump pressure is normal, the downhole is unobstructed, and the pressure inside and outside the pipe string is balanced, the drilling operation can be resumed.

(3) At any time, if a well collapse is found, the pump must be topped with a small displacement when starting. Then gradually increase the displacement without stopping the pump in the middle. If the small displacement fails, the pump pressure rises, and the drilling fluid does not return to the wellhead, it proves that the formation is leaking and the drilling fluid cannot be squeezed into it.

     
3) Drill bit accidents and preventive measures. Drill bit accidents that occur during the drilling process, including cone bit falling claws, cones, broken claws, teeth, cones; scraper bit broken blades, joints, and PDC bit falling off ; Or artificial polycrystalline diamond, natural diamond falling off, etc., collectively referred to as drill accidents.

   To prevent drill accidents, the following measures should be taken:

   (1) Choose a drill with qualified quality, the factory instruction manual requires the correct use of the drill
   (2) Carefully operate and evenly feed the drills to prevent accidents of slipping and stopping drills.
   (3) Operate correctly, construct according to design, pressurize according to requirements of drilling tool assembly and formation depth.

4) Top Hammer Drilling Tools lost circulation accident and treatment

Lost circulation is a phenomenon in which drilling fluid or other media (cement slurry, etc.) in the wellbore leaks into the pores and cracks of the formation during the drilling process. Lost circulation is a common complex situation in wells in drilling engineering, and most of the drilling processes have different degrees of leakage. Severe lost circulation will cause the pressure in the well to drop, affect normal drilling, cause well wall instability, and induce formation fluids to flow into the wellbore and blowout.

   Treatment measures for lost circulation:

  (1) Wells with complex downhole pressure systems and formations can only be treated by plugging;

  (2) For wells with a single downhole pressure system and strong formation structure, the method of reducing the density of the drilling fluid can be used.

 (3) Plugging materials such as sawdust, horse dung, shell powder, clay, etc. can be added to the drilling fluid.

  (4) Thick drilling fluid plus plugging materials such as sawdust, cotton shell, etc. should be used for crack leakage. The drilling speed should be slow and the pumping rate should be appropriate when dealing with lost circulation and technological measures.

5) Blowout accident and treatment

    Blowout is a phenomenon in which fluids in the formation spray out of the ground or flow into other formations in the well. Most of them occur at the site of oil and gas exploitation. There are many reasons for the blowout: inaccurate control of the formation pressure, low mud density, lower mud liquid column height in the well, tripping and suction, and other improper measures.

    The method of controlling the blowout is called killing the well. Killing the well mainly includes the driller kill method and the engineer kill method.

1) The driller kill method is to first discharge the gas or oil in the well, and then replace the original too light mud with heavy mud. This method takes a long time and is often used when the weighting equipment is insufficient.

2) The engineer kill method is a method of drilling into the wellbore at one time after calculating the amount of mud required. The blowout accident handling has been introduced in the previous section and will not be repeated here.