Fault and treatment of Christmas tree wellhead device

Fault and treatment of Christmas tree wellhead device

Wellhead equipment is the hub of oil well production and the surface part of the whole oil well. The main functions of both the blowout wellhead device and the pumping well device are to hang the tubing string and bear the weight of the whole tubing string in the well; seal the annular space of the tubing and casing to ensure the smooth operation of various downhole operations; control and adjust the production data and daily management. Therefore, the performance of wellhead equipment is closely related to oil well. With the growth of oilfield development time, due to natural conditions, external and human factors, wellhead equipment will be damaged to varying degrees. In order to maintain the normal production of oil wells, it is an important work to find out the causes of the damage of oil wellhead equipment, analyze the influencing factors and repair in time.

1、 Types of wellhead faults

Due to the different types of wellhead, there are many kinds of wellhead equipment, and the specific situation of each well is different, so there are many types of wellhead equipment failure. However, the wellhead fault can be summarized as "stab", "leakage", "bad" and "dead". The main phenomena are as follows:

1. Thorn

The performance of this kind of old phenomenon is that the gate, flange and connection point prick oil or water. Generally, it is less in oil wells than in wells, because the surface pump pressure is very high during water injection. Therefore, the performance of the equipment, pressure requirements are very strict. If some parts of wellhead equipment are not well sealed or the gasket is damaged, it is easy to cause wellhead stab. In some cases, because of the long-term high-pressure water injection, the equipment is corroded seriously, the sealing parts lose their function, and the phenomenon of pricking appears, which makes the oil and water wells unable to produce normally.

Leakage

This kind of fault is the phenomenon of leakage or oil leakage (or water drop) in wellhead components. It is due to the poor long-term performance of the equipment, or due to the damage of the screw thread during maintenance and no tightening, etc., the high-pressure liquid in the well is seeping or leaking out. This phenomenon not only pollutes the environment, is not easy to manage, affects the normal production of oil wells, but also is unsafe, easy to cause major accidents.

3. Bad

If the equipment or parts are damaged, the function of wellhead equipment will be reduced and failure will be reduced. The damage of wellhead equipment (or equipment) is mainly caused by careless production and maintenance at ordinary times, and also in the process of downhole operation and workover. Due to improper management system or violation of operation regulations, wellhead equipment will also be damaged.

4. Death

This kind of failure phenomenon is that the equipment is inflexible or necrotic, which is caused by bumping and knocking, or loss of maintenance and lubrication, and also due to the contamination of corrosive liquid is not removed. The operation of wellhead equipment is not flexible and even lost its function, which affects the smooth progress of production and operation. For example, the gate of the wellhead gate falls off, the screw thread is bent and rusted, etc., which can not be used normally.

2、 Causes of wellhead failure

There are many reasons for wellhead equipment, the main reasons are as follows:

(1) The quality of the equipment itself is poor.

(2) the maintenance is not timely.

(3) Damage due to violation of operating procedures.

(4) damage caused by improper measures.

3、 General repair method of wellhead fault

1. Replace Christmas tree

With the continuous improvement of technology level, there are more and more types of Christmas tree. Due to the different structure and model of Christmas tree, the methods and steps of workover are also different. In order to improve the development effect and realize the production policy of oil recovery under pressure, it is often carried out in the oil field to replace the Christmas tree with jack screw flange. According to the different types and methods of repairing and replacing Christmas trees on site, there are mainly two methods as follows:

1) repair method of jack screw flange Christmas tree

(1) Make construction design. According to the specific situation of the construction well and the contents to be repaired, the specific contents, methods and steps of the construction are compiled according to the purpose and requirements of the construction. At the same time, technical safety measures are compiled.

(2) Run in tubing plug. First, close the main gate of the Christmas tree, put the plug into the well with the help of the blowout nozzle, and hold the pressure with the high-pressure well washing truck. When it is confirmed that the oil pipe channel has been blocked (sealed), the next process can be carried out.

(3) Raise the wellhead. When it is confirmed that the plug is sealed, the test run overflow is used to observe. When there is no blowout at the wellhead, the screw at the wellhead of the Christmas tree should be removed as soon as possible to remove the Christmas tree.

(4) Repair or weld. Repair according to the construction requirements.

(5) Installation of Christmas tree. When 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 jack screw on the jack screw flange to prevent the tubing caused by high pressure in the well. The oil and gas will be channeled out.

(6) Fishing plug. When the wellhead fault is repaired, the plug in the well is fished out by power equipment and put into operation again.

2) Repair method of Christmas tree without top screw flange

The main difference between Jack wire flange and non jack screw flange Christmas tree is: the former can be combined with non killing and non blowout wellhead equipment to form a non killing operation; the latter can not be used without killing well and blowout wellhead equipment. Therefore, the repair methods of two kinds of Christmas tree are different.

The repair and replacement method of Christmas tree without top thread 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.

The specific steps are: kill the well, remove and replace the oil production tree at the wellhead, replace the spray well to be qualified, and put into production again.

The advantage of this method is that the high pressure liquid in the well is relatively stable, safe and reliable, and blowout accident is not easy to occur due to the use of killing hydraulic well. But its disadvantage is that the killing fluid (especially the high density killing fluid) is used to kill the well, which not only causes a large amount of material consumption, but also easily injects pollutants into the reservoir and blocks the oil flow channel, which reduces the oil production (water injection) after the oil well (or well) is repaired.

(2) Packer clamping replacement method.

The principle of using this method to replace the Christmas tree is to use the packer's packer's function, cooperate with the non killing and non blowout operation device in the Union (tubing work piece and plug) and wellhead (wellhead controller), so that the oil and gas in the well casing can not be ejected temporarily, so as to replace the pressure consolidation operation and replace the wellhead Christmas tree.

The advantage of this repair method is that it does not need well killing operation, which can avoid the flooding damage of medium pressure well fluid to reservoir during well killing process, and also save money. At the same time, there is no need to carry out well killing work, so there is no rework and delay phenomenon of pressing and unstoppable wells, which can shorten the construction time and improve the construction efficiency. However, this method has some disadvantages. One is that once the packer or hydraulic anchor fails to work, it will cause the risk of blowout or personal accident; the other is that the hydraulic anchor is stuck in the casing wall, which is easy to damage the casing. During the construction, the wellhead device should be loaded and unloaded twice without killing well and blowout, and the process is complex.

2. Technology of handling casing spool

The casing cross is located under the main gate of the Christmas tree. When it is damaged or needs to be replaced, the wellhead device alone can not control the oil and gas flow in the well. Therefore, the treatment and repair method is the same as that of the wellhead equipment without jacking thread flange, and there are two methods: one is to use well killing and blowout prevention repair method; the other is to use packer clamping repair method. However, considering the disadvantages of the latter method which is potentially unsafe and unreliable, if this method is used to replace the four-way pipe, in case of improper handling, it will cause a major accident. Therefore, the former method is usually used to repair and replace the casing spool, that is, the well killing and blowout prevention repair method. Especially for oil wells with high formation pressure and high production rate, this point should be paid more attention to.

The specific construction steps of casing spool treatment by well killing and blowout prevention repair method are as follows:

(1) Well killing, killing fluid and killing method should be determined according to the specific situation of the well.

(2) Remove the flange screw of wellhead controller and lift the Christmas tree.

(3) Pull out the tubing from the well.

(4) Cut off the flange of the original casing four-way by electric welding, and replace it with a new flange or with a jack screw, so as to install a new wellhead device.

(5) On the newly welded casing flange, install the casing cross with jacking screw flange.

(6) Run in the completion string (this completion string can not replace the nozzle string, it should be replaced once before) to replace the well killing fluid. Then use the wellhead device without killing and blowout to pull out the replacement nozzle string, and then run the completion string.

(7) Set up the Christmas tree and tighten all screws, especially the jack screw on the jack screw flange, to prevent the high pressure oil and gas flow in the well after replacing the blowout_ The tubing string was jacked up to cause blowout.

(8) The well can be put into production again after the well completion string (or special replacement nozzle string) is qualified.

3. Matters needing attention in handling casing spool

(1) The wellhead electric welding shall go through the procedures for using fire at the wellhead of the oil well, and the fire-fighting equipment and tools shall be prepared, and the welding and cutting can only be carried out when the fluid flow in the well is stable and there is no oil and gas gushing or oil and gas display at the wellhead.

(2) After removing the Christmas tree, pay attention to the storage of steel ring and other parts to prevent bumping. Pay attention to the screws and small tools that can not be lost and fall into the well. When installing the Christmas tree, attention should be paid to the alignment and light placement, so as to prevent the breakage of the ring or other components, resulting in wellhead leakage and rework.

(3) When lifting the Christmas tree, the personnel and wellhead equipment shall be prevented from falling.

(4) If the parts need to be replaced or cut and welded are too low, in order to facilitate the welding operation, the round pit should be dug in advance to shorten the working time of using fire at the wellhead and ensure the quality.

(5) Measure the size carefully before cutting and welding the wellhead, and correct the oil patching distance after cutting and welding.

(6) Butt welding should be adopted for the casing with thick wall thickness; for the casing with thin wall thickness or serious corrosion, the casing larger than the original casing diameter should be used for sleeve welding.

(7) The inner diameter of the casing to be replaced should be the same as that of the original well casing. When the rock is larger than the inner diameter of the original casing, a slope should be made on the inner diameter of the original casing top to prevent the string and tools from being blocked, stuck and damaged when running down the well. The inner diameter of the casing to be replaced shall not be less than that of the original well casing.

(8) The welding quality must be guaranteed. The butt weld should be welded twice or more, and some reinforcing ribs should be welded around the weld joint to increase its strength. After welding, it is necessary to carry out well drifting and pressure test inspection, that is to say, it is required to ensure the welding integrity without deflection, and to bear the rated pressure without penetration and leakage.