Causes and types of oil casing damage

Oil casing pipe is a barrier that isolates the formation from the wellbore during drilling. In heavy oil thermal recovery wells, casing damage is particularly common. Its main damage is manifested in extrusion deformation, twisting, etc.

The mechanism of oil casing pipe damage is:

1. The influence of temperature: a. As the temperature rises, the strength of the casing itself decreases; b. As the temperature rises, the casing expands, causing compressive stress and bending stress in the casing, which reduces the strength; c. As the temperature rises, the annular fluid expands, causing the internal pressure to increase, thereby reducing the strength of the casing.

2. Fatigue damage: As the temperature rises, the casing stretches, generating tensile stress and compressive stress. This stress is periodic, causing fatigue damage to the casing.
3. Slip damage: As the temperature rises, the cement ring and the casing will slip, causing the casing to contact the bottom of the well and deform and damage.

4. Sand production: Heavy oil wells have serious sand production, and sand particles contribute greatly to casing wear.

Causes of oil casing pipe damage:

1. Mechanical wear: The casing moves up and down in the wellbore of the oil well, rubs against the well wall, and gradually wears out. In addition, the oil well contains hard objects such as sand and gravel, which will cause more obvious wear on the casing.
2. Corrosion damage: The casing in the oil well will be corroded by various chemicals such as acids, alkalis, and salts, and will be corroded over time.
3. External force damage: During the long-term operation of the casing in the oil well, it will inevitably be impacted by some external forces, such as drill bit impact, worker injury, etc.
4. Thermal expansion and contraction: The oil well will produce high and low temperatures during the production process, so the casing will expand and contract due to heat, which will cause casing damage over time.

5. Strategic damage: Casing damage caused by certain human factors, such as improper operation of mechanical equipment, worker errors, etc.

Types of oil casing pipe damage:

1. Scratches: Longitudinal or spiral grooves are scratched on the surface of the casing.
2. Wear: The surface of the casing is worn into a boss shape or an elliptical groove.
3. Corrosion: Chemical corrosion marks appear on the metal surface of the casing, and rust spots or holes appear on the surface of the casing.
4. Break: The metal surface of the casing is broken, and the inner wall shows cracks and fractures.
5. Distortion: The casing is subjected to external forces, resulting in bending and twisting deformation.
6. Fracture: Longitudinal or transverse cracks appear in the casing, resulting in casing fracture.

‌Preventive measures and detection methods‌:

‌1. Regularly check the operating conditions of the oil well and casing‌: Ensure the safe and stable production of the oil well‌.
‌2. Avoid mechanical wear and corrosion damage‌: Use corrosion-resistant materials and take appropriate protective measures.
‌3. Prevent external force damage‌: Strengthen equipment maintenance and operating specifications.
‌4. Deal with thermal expansion and contraction‌: Take appropriate insulation and cooling measures.

The above are the causes and types of OCTG casing damage. When maintaining and operating oil wells, oil workers should pay attention to avoid casing damage and repair and replace it in time. At the same time, they should regularly check the operating conditions of oil wells and casing to ensure safe and stable production of oil wells.

Read more: Casing pipe VS Drill pipe or API 5CT Steel Casing and Tubing Chart