General repair methods for wellhead Christmas tree failures
1. Replacement of Christmas tree
With the continuous improvement of technological level, there are more and more Christmas tree models. Due to the different structural models of Christmas trees, the methods and steps of well repair are also different. In order to improve the development effect and realize the production policy of oil production under pressure, the oil field often replaces the Christmas tree without top screw flange with the Christmas tree with top screw flange. According to the different types and methods of on-site repair and replacement of Christmas trees, it is mainly divided into the following two methods:
1) Top screw flange Christmas tree repair method
(1) Make construction design. According to the specific conditions of the construction well and the content to be repaired, according to the purpose and requirements of the construction, write the specific content, methods and steps of the construction. At the same time, write technical safety measures.
(2) Drop the oil pipe plug. First, close the main gate of the Christmas tree, use the nozzle to drop the plug into the well, and use a high-pressure well washing truck to hold the pressure. When it is confirmed that the oil pipe channel has been blocked (sealed), the next process can be carried out.
(3) Lift the wellhead. After the plug is confirmed to be sealed, the overflow test is conducted. When there is no blowout at the wellhead, the screws at the wellhead of the Christmas tree should be removed as soon as possible and the Christmas tree should be removed.
(4) Repair or welding. Repair work should be carried out according to the construction requirements.
(5) Install the Christmas tree. After the wellhead components and equipment are repaired, the Christmas tree should be installed as soon as possible (if the Christmas tree cannot be installed temporarily, the wellhead should also be covered). Pay attention to tightening the top screw on the top screw flange to prevent the oil pipe from being pushed up due to the high pressure in the well, causing oil and gas to escape, etc.
(6) Salvage the plug. After the wellhead fault is repaired, use power equipment to salvage the plug in the well and resume production.
2) Repair method of Christmas tree without top screw flange
The main difference between the top screw flange Christmas tree and the Christmas tree without top screw flange is that the former can be combined with the no-kill and no-blowout wellhead device to form a no-kill facility and can be operated without killing the well, while the latter does not have a no-kill and no-blowout wellhead device and cannot be operated without killing the well. Therefore, the repair methods of the two Christmas trees are different.
The repair method of the Christmas tree without top screw flange is determined on site according to the specific conditions of the well and the material conditions of the equipment. Generally, the following two methods are often used.
(1) Well-killing and blowout prevention replacement method.
This method uses the effect of well killing to obtain smooth construction conditions. Its specific steps are: well killing, replacing the wellhead and the Christmas tree, replacing the blowout well to pass the well cleaning, and re-commissioning.
The advantage of this method is that due to the use of well killing hydraulic wells, the high-pressure liquid in the well is relatively stable during construction, safe and reliable, and blowout accidents are not likely to occur. However, its disadvantage is that the use of well-killing fluid (especially high-density well-killing fluid) not only causes a large amount of material consumption, but also easily injects pollutants into the oil layer, blocking the oil flow channel, and reducing the oil (water injection) production after the oil well (or water well) is repaired.
(2) Packer replacement method
The principle of replacing the Christmas tree by this method is to use the isolation effect of the packer, cooperate with the non-pressurization and non-spraying operation device in the wellbore (oil pipe working tube and plugger> and the wellhead (wellhead controller), so that the oil and gas in the wellbore can not be sprayed out temporarily, instead of the pressurization operation, to replace the wellhead Christmas tree.
The advantage of this repair method is that it does not require well-pressing operation, which not only avoids the damage of the well-pressing fluid to the oil layer during the well-pressing process, but also saves money. At the same time, there is no need to perform well-pressing work, so there is no rework and work delay due to the well being pressed or not being pressed, which can shorten the construction time and improve the construction efficiency. However, this method has disadvantages. First, once the packer or hydraulic anchor fails to work, it will cause the risk of blowout or personal accident. Second, the hydraulic anchor is stuck in the casing wall and it is easy to damage the casing. It needs to be installed and unloaded twice during construction without pressurization. The well does not have a blowout wellhead device, and the process is complicated.
2. Technology for handling casing four-way
The casing four-way of the oil well is located under the main gate of the oil tree. When it is damaged or needs to be replaced, the wellhead device alone cannot control the oil and gas flow in the well. Therefore, its treatment and repair method is basically the same as the treatment method for the flange wellhead device without top screws. There are two methods: one is to use the well killing and blowout prevention repair method; the other is to use the packer card sealing repair method. However, considering the potential unsafe and unreliable disadvantages of using the two methods, if this method is used to replace the four-way, if it is improperly handled, it will inevitably cause a major accident. Therefore, generally, one method is used when repairing and replacing the casing four-way, that is, the well killing and blowout prevention repair method. Especially for oil wells with high formation pressure and high production, this should be paid special attention to.
The specific construction steps for treating casing spools using the well-killing and blowout prevention repair method are:
(1) Well-killing, well-killing fluid and well-killing method should be determined according to the specific conditions of the well.
(2) Remove the wellhead controller flange screws and hang the production tree.
(3) Lift out the oil pipe in the well.
(4) Cut off the flange of the original casing spool installed with electric welding, and replace it with a new one or a flange with a top screw to install the new wellhead device.
(5) Install the casing spool with a top screw flange on the newly welded casing flange.
(6) Lower the completion string (this completion string cannot replace the replacement nozzle string, and a replacement nozzle string should be placed before this) to replace the well-killing fluid in the well. Then use the wellhead device without killing the well and without releasing the blowout to lift out the replacement nozzle string, and then lower the completion string.
(7) Set the production tree, tighten all screws, especially Especially the top screw on the top screw flange, to prevent the high-pressure oil and gas flow in the well after the replacement spraying_up the oil pipe string and cause a blowout.
(8) After the well string (or the replacement spraying pipe string) is used for replacement spraying and washing, it can be put into production again.
3. Matters to be noted when handling casing spools
(1) Wellhead electric welding must go through the wellhead fire procedures, prepare fire-fighting equipment and tools, and welding and cutting must be carried out when the fluid flow in the well is stable and there is no oil and gas overflow or oil and gas display at the wellhead.
(2) After disassembling the Christmas tree, pay attention to the storage of steel rings and other parts to prevent scratches, and pay attention to screws and small tools. Don't lose or fall into the well. When installing the Christmas tree, pay attention to the alignment and gentle placement to prevent the ring or other parts from being broken, causing leakage at the wellhead and rework.
(3) When lifting the Christmas tree, prevent it from falling and injuring personnel and wellhead equipment.
(4) If the part to be replaced or welded is too low, a circular pit should be dug in advance to facilitate the electric welding operation, so as to shorten the time of working with fire at the wellhead and ensure the quality.
(5) The dimensions should be carefully measured before welding the wellhead, and the oil filling distance should be accurately corrected after welding.
(6) For thicker casing, butt welding should be adopted; for thinner or severely corroded casing, a casing larger than the original casing diameter should be used for sleeve welding.
(7) The inner diameter of the casing selected for replacement of the wellhead should be the same as that of the original casing. If the rock is larger than the original casing, a slope should be made on the inner diameter of the top of the original casing to prevent obstruction, drilling and damage when lowering the wellbore pipe and tools, causing accidents. The inner diameter of the selected replacement casing shall not be smaller than the inner diameter of the original well casing.
(8) The welding quality must be ensured. The butt weld should be welded more than twice, and some reinforcing ribs should be appropriately welded around the weld to increase its strength. After welding, well-clearing and pressure testing are required, which requires that the welding is straight and not skewed, and must withstand the rated pressure without puncture or leakage to be qualified.