Corrosion Tubing Fishing Technology

Profile control technology of injection well refers to the technology of controlling the water absorption of high water absorption layer by mechanical or chemical method, increasing the water absorption of low water absorption layer accordingly, making the water injection advance evenly and improving the sweep coefficient of oil layer.

There are mechanical methods and chemical methods for profile control of injection Wells. The mechanical profile control method is mainly to adjust the water injection amount of each layer through stratified water injection, so as to achieve the purpose of adjusting the suction profile.

In the production process of oil and gas Wells, underground tubing is corroded and eroded by corrosive media such as hydrogen sulfide, carbon dioxide and formation water of gas field for a long time, resulting in tubing wall thinning, perforation and even fracture.

1. 1.    Corrosion Tubing Well Characteristics

(1) The formation pressure coefficient is low, most of them are between 0.5 and 0.7, and some are lower, so it is impossible to establish circulation, which brings great difficulties to grinding, milling and drilling.

(2)  The degree of tubing corrosion is serious, generally up to 30% to 60% (mass fraction), and the pipe wall is corroded inside and outside.

(3)  The strength of the pipe column is low, the pressure is easy to “shrink”, and the top of the fish often changes, so the lead printing is not useful;

(4)  It is difficult to make buckle inside and outside.

2.Corrosion Tubing Fishing Principle

In addition to the conventional fishing principles, corrosion tubing fishing should follow the following principles:

（1）The underground conditions are clear, the fishing tools are selected accurately, and the integrity of the fish top and the underground fish is maintained as far as possible;

（2）Well control safety must be ensured during fishing.

（3）Fishing operations can not complicate the underground situation, any measures must have a way out, can not blindly tentative fishing;

（4）Can not affect the original production capacity;

（5）Can not easily use the milling, but can not easily use the grinding shoe milling, to avoid the more complicated;

（6）Prevent damage to the casing.

3.Corrosion Tubing Fishing Measures

(1)The corrosion of tubing certainly also brings the corrosion of casing, so it is necessary to detect and judge the quality of wellbore casing, and try to avoid the damage of tubing and casing.

(2)Don’t rush it, plan and organize it in detail. Corroded tubing is obviously different from normal tubing and drill pipe fishing. Tubing can not be salvaged in the same way as drilling pipe fishing. If excessively forced fishing is adopted, tubing may be caught outside the casing. Therefore, once the tool selection is unreasonable, it may cause more complex underground, bringing incalculable difficulties to the later salvage. The choice of initial tools is best not to consider the tools with drilling, grinding and milling properties, because they are offensive and likely to destroy the fish and casing, bringing a lot of complexity.

(3)Equipment must be reliable and accurate. The brake system of the operation machine is sensitive and reliable, and the application of the lifting ring and elevator are bound firmly, and the quality of the rope pit is checked. The crane, turntable and wellhead should be handled properly. Kelly pipe should be straightened, after use can not be tilted on the edge of the drill floor; The weight indicator is sensitive, reliable and accurate. Tools should be carefully inspected and labeled (preferably with pictures) without quality problems. Carefully measure, calculate the “three square into” (fish top square into, salvage side into, maximum salvage side into), and mark

(4)Find out the inner and annular conditions of the tubing. The fishing priority principle should start from the outside of the oil pipe, check the outer annulus of the oil pipe, and generally do not use the inside fishing (for corroded oil pipe). The selection of tools can be optimized to back-off slip fishing cylinder, movable window fishing cylinder, sliding block window fishing cylinder and other tools that do not damage the fish, light pressure and slow turn when fishing, bit weight should not be too high.

(5)In addition to safety reasons, it is mainly technical control analysis, and the things that go down and out should be carefully analyzed, lined up, combined and restored, so as to analyze the possible conditions of the mine.

(6)If the drilling pressure of the fish head needs to be low (within 1t), the footage should not be too large (less than 10cm), and then the iron filings should be fished out in time and the shape of the fish head should be analyzed.

4.Corrosion Tubing Fishing Tools

1、Die Collars

The large range of female cone fishing thread taper can be set to 1:8, which is twice the taper of the conventional female cone fishing thread, and the length of the fishing thread is appropriately increased, and the fishing range is much larger than the fishing range of the conventional female cone. For example, the female cone MZ60×125 fishing thread length for 177.8mm casing is 520mm, the taper is 1:8, the maximum diameter is 125mm, and the fishing range is 60~125mm; After the 73mm tubing corrosion fracture, the tubing fracture is compressed and deformed, and its long axis diameter is usually 90~105mm, and the maximum is generally not more than 115mm. When fishing, rotate down, lead the shoe into the falling fish, the falling fish into a large range of female cones, and then continue to rotate down to complete the top of the fish dressing and holding.

The large range of Die Collars is used for fishing of corroded tubing with serious deformation of fish top but with certain strength, and can also salvage broken pieces and debris of tubing to clean up the top of the fish, and can also salvage the complete tubing, which is widely used and effectively protects the top of the fish.

2.Block Spears Fishing

The Block Spears is composed of a barrel body, a slider and a guide shoe. The upper end of the cylinder is an internal thread, which can be connected to the long cylinder. The inner cavity is a conical cavity with a “small upper part” and three chutes are symmetrically opened in the middle part. The slide block is installed in the chute, the end face of the slide block is processed with radial teeth, and the inner end face has a row of transverse internal teeth. During fishing operation, the shoe is led into the fish and the fishing cylinder is lowered, the fish top is pushed up along the chute, the fish top passes through the slide block, the fishing cylinder is lifted, and the slide block moves relative along the chute to hold the fish and achieve fishing.

The fishing part of the Block can be the oil pipe body or the oil pipe coupling. When fishing, the first coupling under the top of the fish can pass through the slider to realize fishing by lifting the coupling; It can also make the slider avoid the serious part of the oil pipe corrosion deformation and grasp the more complete part.

The Block Spears can not only realize the tubing fishing, but also realize the reverse buckle when the tubing is stuck. The reverse torque is transmitted through the radial teeth on the top of the slider or through the inner teeth of the slider, the slider and the chute. The sliding block dredge is suitable for tubing fishing where corrosion deformation is not very serious, and its fishing success rate is high.

3.Overshot With Slot

The overshot with slot is made of 8 to 10m scrap milling barrel or casing, as shown in Figure 1-1. The lower end of the fishing drum is made into a pen tip type and duck-bill type guide shoe, and the cylinder body is symmetrically opened with single or double lines, with good elasticity, easy to open to facilitate the introduction of falling fish, and easy to restore the original position of clamping falling fish. The hook is made of opening window in the cylinder, triangular or trapezoidal, staggered, with a certain strength and elasticity.

Fig1  Overshot With Slot Diagram

After the fish is exposed to the falling fish, the duck bill or pen tip guide shoe will open naturally and go down close to the casing wall. The falling fish will enter the fishing part of the fishing barrel through the guide shoe, squeeze the elasticity of the fishing hook, and at the same time, open the broken part, continue to lower the pipe string under pressure, and the falling fish will further enter the upper part of the fishing barrel, lift the fishing string, and the fishing hook will either cling to the pitting or penetrate into the corroded hole. Or support at the step of the collar and joint to achieve corrosion tubing fishing.

The overshot with slot can salvage the broken oil pipe and the side-by-side oil pipe, and can also salvage the broken oil pipe, debris and other debris, clean the fish top, and create conditions for the next salvage.

4.Composite Milling and Fishing Tool

The combination tool can complete the combined operation of milling and fishing. Milling shoes are combined with window dredging drum, steel wire dredging drum, sliding block dredging drum, female cone and other fishing tools, which can complete the milling, fish repair and fishing joint operations. In order to protect the top of the fish as far as possible, the milling shoes use large inner diameter milling shoes.

The large range casing cone is an effective tool for corroding tubing casing. It is composed of a large inner diameter casing mill and a large range casing cone. Large inside diameter overshoes have large inside diameter, easy to introduce the top of the fish, and the size of the milled fish is small; A large range of female cone fishing thread taper, the big end fishing thread diameter is large, and then quickly small, the top of the fish into the female cone soon after contact with the fishing part. Therefore, a large range of milled female cones can protect the top of the fish to a greater extent, and can also complete the fishing operation.