How can you design casing connections and seals to prevent leaks and corrosion?

2 Seal types

The seal is the part of the connection that provides the pressure seal between the casing and the formation. There are different types of seals, such as metal-to-metal, elastomeric, or composite seals. Metal-to-metal seals rely on the interference fit between the mating surfaces of the connection, which creates a metal barrier that prevents fluid leakage. Elastomeric seals use rubber or plastic materials that deform under pressure and conform to the irregularities of the connection, which creates a flexible and resilient seal. Composite seals combine metal and elastomeric elements, which provide both the strength and the flexibility of the seal.

3 Design criteria

To design casing connections and seals that can prevent leaks and corrosion, you need to consider several factors, such as the well depth, pressure, temperature, fluid composition, load conditions, and environmental factors. These factors affect the performance and durability of the connection and seal, and determine the selection of the appropriate type, size, grade, and coating of the casing and the connection. For example, deeper wells require higher strength and fatigue resistance connections, such as integral or semi-flush connections, while shallow wells can use T&C connections. Similarly, higher pressure and temperature wells require metal-to-metal or composite seals, while lower pressure and temperature wells can use elastomeric seals. Furthermore, corrosive fluids or gases require special coatings or materials for the casing and the connection, such as stainless steel, alloy steel, or corrosion-resistant alloys.

4 Testing methods

To verify the quality and integrity of the casing connections and seals, you need to conduct various testing methods, such as hydrostatic, gas, or ultrasonic testing. Hydrostatic testing involves applying water pressure to the connection and seal, and measuring the leakage rate or the pressure drop. Gas testing involves applying gas pressure to the connection and seal, and detecting the gas leakage using a gas detector or a soap solution. Ultrasonic testing involves using sound waves to inspect the internal and external surfaces of the connection and seal, and identifying any defects or flaws.

5 Maintenance practices

To maintain the casing connections and seals in good condition, you need to follow some best practices, such as cleaning, lubricating, inspecting, and repairing the connections and seals. Cleaning involves removing any dirt, debris, or rust from the connection and seal, using brushes, solvents, or water jets. Lubricating involves applying a suitable lubricant to the connection and seal, to reduce friction, wear, and corrosion. Inspecting involves checking the connection and seal for any signs of damage, such as cracks, dents, or leaks, using visual or non-destructive methods. Repairing involves fixing or replacing any damaged or faulty connection or seal, using welding, machining, or cutting tools.

6 Common problems

Despite following the design criteria, testing methods, and maintenance practices, you may still encounter some common problems with the casing connections and seals, such as galling, make-up, or sealability problems. Galling is the abrasion or damage of the metal surfaces of the connection and seal, caused by excessive friction, torque, or pressure. Make-up problems are the improper alignment or engagement of the connection and seal, caused by misalignment, over-torque, or under-torque. Sealability problems are the failure of the connection and seal to provide an adequate pressure seal, caused by defects, corrosion, or wear. To prevent or solve these problems, you need to use the correct tools, procedures, and standards, and consult with the connection and seal manufacturers or experts.

7 Here’s what else to consider

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