After the casing change well opens the channel and the fallen objects in the well are fished out, the casing pipe strength is reduced and reinforcement treatment is required. The commonly used method is supplementary reinforcement. The advantages of supplementary reinforcement are: first, it can reduce the reduction of the reset diameter of the casing damaged well section; second, it can prevent the casing damaged well section from entering the water and becoming a source of large-scale casing damage; third, the cost of supplementary reinforcement is low. The disadvantage is that after reinforcement and repair, the borehole diameter is still reduced to a certain extent.
- I. Unsealed reinforcement
- Process principle
The upper part of the reinforcement pipe is connected to the hand-release joint and the reinforcer. After the delivery string sends the reinforcement pipe and the reinforcer to the casing damaged well section with expanded diameter, the ball is dropped to pressurize, so that the anti-drop and anti-top slip in the reinforcer opens and tightly bites the inner wall of the casing. At the same time, the hand-release joint is disengaged under the action of pressure and can be lifted out together with the delivery string. The reinforcement pipe and the reinforcer remain in the well section to be reinforced, which plays a role in reinforcing the casing change point.
- Process
(1) Simulated well drilling: Run a 118mm × 3000m or 114mm × 8000m diameter well to simulate well drilling, ensuring that there is no clamping force on the damaged casing after shaping and expansion.
(2) Well logging: Perform X-Y well logging on the damaged casing section, select the upper and lower reinforcement points according to the logging curve, and determine the length of the reinforcement pipe.
(3) Use tubing to send the reinforcement device and reinforcement pipe to the reinforcement section, and then perform magnetic positioning logging to correct the position of the reinforcement point to ensure that the depth of the reinforcement pipe is accurate.
(4) Throw the ball to pressurize 12-15MPa to open the reinforcement device slip and tightly grip the inner wall of the casing. Pressurize to 20MPa, cut the pin, and pull out the hand-release joint and delivery pipe string.
- Common problems and solutions
(1) The reinforcement pipe cannot reach the predetermined position. The reason why the reinforcement pipe cannot be lowered to the predetermined position is mostly because the deformation point is not handled properly. Although the pear-shaped expander, lead mold and diameter gauge can pass through, the reinforcement pipe is longer than the above tools. If there is a large bend in the deformation section, the reinforcement pipe cannot be lowered to the predetermined position. In this case, the reinforcement pipe column should be pulled out, and the lower extended milling cone should be repeatedly cut and straightened at the deformation point until the reinforcement pipe can pass smoothly.
(2) The pump truck pressure is not enough, the pin cannot be cut, and the hand cannot be dropped. Due to the puncture of the pump truck pipeline, the pressure cannot meet the requirements, and the hand cannot be dropped. The solution to this problem is to test the pump truck pressure before construction, and then proceed with construction after confirming that the pump truck has no problems.
(3) Unsealed reinforcement Because there is a certain gap between the reinforcement pipe and the casing wall, the upper suspension device also plays a fixed role, and the annulus seal cannot be achieved. Therefore, it is mostly used for the reinforcement of oil well casing deformation, and cannot be used for water well casing misalignment, because the injected water will still leak from the reinforcement.
- II. Hydraulic sealing reinforcement
- Process principle
The pressure provided by the ground pump truck acts on the piston through the pressure guide hole in the reinforcement tool, causing the piston to move upward and the cylinder to move downward relatively, generating two forces of equal size and opposite direction, pushing the upper and lower expansion heads to work, squeezing the special expansion bodies at both ends of the reinforcement pipe to the perfect part of the casing, lifting the pipe column to cut off the connecting sleeve, so that the pipe column and the reinforcement pipe are separated, completing the release and achieving the purpose of sealing reinforcement.
- Process
(1) Simulated well clearance: Run into the 118mm × 3000mm or ³114mm × 8000mm diameter scale to simulate well clearance, ensuring that there is no clamping force on the casing damage part after shaping and expansion.
(2) Well logging: Perform X-Y wellbore logging on the casing damage section, select the upper and lower reinforcement points according to the logging curve, and determine the length of the reinforcement pipe.
(3) Use the reinforcement string to send the reinforcement device and reinforcement pipe to the reinforcement section, and then perform magnetic positioning logging to calibrate the position of the reinforcement point to ensure that the depth of the reinforcement pipe is accurate.
(4) Reinforcement: The pump truck slowly pressurizes to 13MPa, stabilizes the pressure for 10min, and then pulls off the connecting sleeve. Lower the string. If the string encounters resistance, it proves that the release is successful.
(5) Lower the pressure test string for pressure testing. The string structure is tubing + K344-95 packer + sandblaster + K344-95 packer + tail pipe + wire plug. Perform a clean water pressure test on the reinforcement section, the pressure is 15MPa, and the pressure is stabilized for 30min without pressure drop.
- Common problems and solutions
(1) The reinforcement pipe cannot reach the predetermined position. The reason why the reinforcement pipe cannot be lowered to the predetermined position is mostly because the deformation point is not handled properly. Although the pear-shaped expander, lead mold and diameter gauge can pass through, the reinforcement pipe is longer than the above tools. If there is a large bend in the deformation section, the reinforcement pipe cannot be lowered to the predetermined position. In this case, the reinforcement pipe column should be pulled out, and the lower extended milling cone should be repeatedly cut and straightened at the deformation point until the reinforcement pipe can pass smoothly.
(2) Hydraulic seal reinforcement can only reinforce wells with casing damage sections less than 10m. If the casing damage section exceeds 10m, other methods should be considered.
(3) The pressure test column cannot be tested. The main reasons for the failure to test pressure are as follows:
① The pump truck and the pump truck pipeline have punctures and leaks;
② The pressure test column has punctures and leaks;
③ There is no seal between the reinforcement pipe and the casing. If it is the first two reasons, just check the pump truck, pipeline and pressure test column to eliminate the hidden dangers. If it is the third case, the reinforcement pipe should be removed and re-construction should be carried out.
- Gas-powered reinforcement
- Process principle
Gas-powered sealing reinforcement uses the cone at the end of the reinforcement device to expand the diameter of the anchor body at the end of the reinforcement pipe to complete the sealing reinforcement, while the inner diameter of the reinforcement pipe itself remains unchanged. The principle is to use the high-temperature and high-pressure gas generated by the combustion of gunpowder in the cylinder as the power. The gas drives the piston to move, and the piston drives the central pull rod and the outer cylinder sleeve of the piston to move up and down relative to each other. The axial force of the pull rod and the cylinder sleeve is converted into the radial force of the anchor body. In a very short time, the anchor body changes from elastic deformation to permanent plastic deformation, achieving interference fit between the anchor body and the casing, and realizing sealing reinforcement. This technology is currently widely used in oil fields.
- Process
(1) Insert a 118mm×3000mm or 114mm×8000mm diameter scale to be used for well drilling, ensuring that there is no clamping force at the damaged part of the casing after shaping and expanding.
(2) Perform X-Y wellbore logging on the damaged casing section, select the upper and lower reinforcement points according to the logging curve, and determine the length of the reinforcement pipe.
(3) Use the delivery string to deliver the reinforcement device and reinforcement pipe to the reinforcement section, and then perform magnetic positioning logging to calibrate the position of the reinforcement point to ensure that the depth of the reinforcement pipe is accurate.
(4) Rod reinforcement.
(5) Measure the X-Y wellbore to check the reinforcement effect.
- Common problems and precautions
(1) The reinforcement pipe cannot be lowered to the predetermined position. The reinforcement pipe cannot be lowered to the predetermined position mostly because the deformation point is not handled properly. Although the pear-shaped expander, lead mold and diameter gauge can pass through, the reinforcement pipe is longer than the above tools. If there is a large section of bend in the deformation section, the reinforcement pipe cannot be lowered to the predetermined position. In this case, the reinforcement pipe string should be pulled out, and the deformation point should be repeatedly cut and straightened by the extended milling cone until the reinforcement pipe can pass smoothly.
(2) The explosives cannot explode after the rod is thrown. When the rod is detonated, the explosives at the bottom of the well explode, and there should be a reaction at the wellhead. Generally, a sound can be heard and the workover fluid can be seen rolling. If there is no display, it means that the explosives have not detonated. The reinforcement pipe string needs to be removed and a dedicated person needs to check the reinforcement device or replace the reinforcement device before re-reinforcement.
(3) When reinforcing in the oil layer, the reinforcement endpoint must be selected on the interlayer.
(4) For faulted wells with active fractures, reinforcement must be carried out first and then sand flushing to avoid losing the fracture.
(5) When pre-setting the reinforcement pipe, it must be placed above the fracture to avoid hanging upside down.
(6) Explosive sealing reinforcement is applicable to 439.7mm, 146mm, and 168mm casing. The casing damage section less than 15m can be reinforced, and the long well section can be reinforced in sections.
