Can Damaged Oil and Gas Well Casing Still be Used?

Can Damaged Oil and Gas Well Casing Still be Used? How Can it be Repaired?

Whether oil and gas well casing can still be used depends on the type and extent of the damage and the application scenario. Generally, damaged oil and gas well casing cannot be used, but in most cases, its integrity and pressure-bearing capacity can be restored through professional repair techniques.

Situations where it can continue to be used:

● Minor damage (such as localized corrosion, small holes) can be restored to function after repairs such as chemical plugging, expansion tube patching, and small casing cementing.

● The repaired casing passes pressure testing and does not affect the integrity of the wellbore.

Situations where it cannot be used and needs to be scrapped or replaced:

● Severe deformation, misalignment, cracking, or perforation that cannot be effectively repaired.
● Wall thickness reduction exceeding 12.5% of the standard wall thickness, or excessive internal wall corrosion, resulting in insufficient strength.
● Thread damage that cannot be repaired according to standards.

The hazards of continuing to use damaged casing:

1. Wellbore blockage: Deformation obstructs the passage of downhole tools;
2. Reduced production: Formation fluids cannot be effectively extracted;
3. Well control risks: High-pressure oil and gas may leak along the damaged area, causing a blowout;
4. Environmental pollution: Formation fluid leakage pollutes groundwater or the surface;
5. Well abandonment: In severe cases, it can lead to the abandonment of the entire well, resulting in huge economic losses.

Therefore, if any damage is found to the oil well casing (deformation, rupture, misalignment, corrosion perforation, etc.), its use must be stopped immediately and repaired.

Main causes of oil and gas casing damage:

1. Corrosion perforation: Formation water containing corrosive media such as H₂S, CO₂, and high mineralization;
2. Casing deformation/crushing: Geological movement, salt-gypsum layer creep, abnormal formation pressure;
3. Casing misalignment: Formation slippage, earthquakes, long-term stress fatigue;
4. Casing thread leakage: Improper threading torque, thread damage, seal failure;
5. Casing wear: Long-term friction of the drill string during drilling and workover.

General judgment principles:

Regardless of the type of oil casing, it is recommended to stop use and repair or replace it in the following situations:

1. Visible cracks, leaks, obvious deformation, or significant wall thinning;
2. Safety cannot be confirmed by pressure testing or non-destructive testing (such as ultrasonic or electromagnetic testing);
3. Operating in a high-pressure, high-temperature, or corrosive environment, requiring high safety redundancy.

Common Casing Repair Techniques:

Depending on the location, type, and severity of the damage, engineers will choose different repair solutions:

1. Surface Casing Repair
Applicable Scenarios: Casing corrosion and rupture near the wellhead.

Common Techniques:
Cut-off Replacement Method:The damaged section is cut off, a new casing section is welded, and a support frame is installed.
C-clamp Repair: Steel clamps are installed, and resin sealant is injected to form a barrier.

Case Study: In a South American oilfield, a 20-inch surface casing ruptured due to corrosion. By cutting off the corroded section, welding a new casing section, and installing a support frame, production was restored within 3 months, avoiding a large-scale well workover operation requiring wellhead replacement.

2. Shallow to Mid-Level Casing Damage

Applicable Scenarios: Shallow casing corrosion and leakage.

Commonly Used Technologies: Targeted Casing Removal Technology

Using a multi-stage torque converter, a fixed-point reversing device, and a coupling positioner; accurately reversing the coupling to be replaced in one go; in conjunction with a minor repair machine and top drive equipment.

Case Study: Daqing Oilfield in China has used this technology to treat 53 shallow casing leakage wells with a 100% success rate. The average construction period has been shortened to 8 days, saving over 300,000 yuan per well.

3. Deep Casing Repair (Hundreds of Meters to Kilometers)

Applicable Scenarios: Deep casing deformation and misalignment.

Typical Technology: Major Workover Casing Replacement Technology

Milling out the damaged casing, running in new casing and connecting it with the coupling, and cementing it in place.

Case Study: Xinjiang Oilfield in China successfully completed the repair of a 1008.22-meter deep casing misalignment in well B5010. After 32 days of continuous operation, this technology filled a gap in deep casing damage repair.

4. Chemical Plugging and Reinforcement

Applicable Scenarios: Casing corrosion perforation and micro-cracks.

Typical Technologies: High-Strength Resin Leak Sealing and Reinforcement
Resin material is extruded to the leak location.
A polymerization reaction occurs, forming a network solid structure.
Pressure resistance is greater than 45 MPa, suitable for acidic and alkaline environments.
The inner diameter of the casing remains unchanged after repair, without affecting subsequent production.

5. Casing Patching Technology

Applicable Scenarios: Localized perforations and cracks.
Principle: A thin-walled metal liner is inserted, and hydraulic expansion is used to make it tightly adhere to the inner wall of the original casing, forming a new sealing layer.

6. Integrated Exploration and Repair Intelligent Tool

Latest Development: Bohai Drilling has developed an integrated exploration and repair intelligent tool, equipped with high-precision sensors and a mechanical repair module. It can quickly locate the damaged location and simultaneously carry out repairs, significantly improving efficiency and reducing costs.

Acceptance Standards After Repair:

The repaired casing must meet the following requirements before it can be put back into use:

1. Pressure Test Passed: A hydrostatic pressure test is conducted at the design pressure, with stable pressure and no leakage.
2. Bore Inspection Passed: The bore gauge can pass smoothly through the entire casing string.
3. Wellbore integrity restored: capable of withstanding subsequent operations and production loads.

4. Meets corrosion resistance requirements: the repaired area possesses corrosion resistance equivalent to the original casing.

Read more: Specifications and Dimensions of Drilling Casing or Casing Pipe vs. Drill Pipe