Well Cementing: Primary and Remedial Operations for Well Integrity

Well Cementing: Primary and Remedial Operations

Primary Cementing

Primary cementing is the process of placing a cement sheath in the annulus between the casing and the formation. Its objectives include:

• Removing drilling fluid from the casing interior and borehole
• Placing a cement slurry in the annulus
• Filling the casing interior with a displacement fluid (e.g., drilling fluid, brine, water)

A bottom plug separates the cement slurry from the drilling fluid, while a top plug separates it from the displacement fluid. The bottom plug ruptures upon landing at the casing string's bottom, allowing the cement slurry to flow into the annulus.

Remedial Cementing

Remedial cementing occurs after primary cementing to inject cements into strategic well locations for purposes such as:

• Well repair
• Well abandonment

When logging operations indicate a defective cement job (e.g., poor bonding or communication between zones), squeeze cementing may be performed to establish zonal isolation. This involves perforating the casing at the defective interval and forcing cement slurry through the perforations into the annulus to fill voids.

Cement Properties and Additives

Well cements must perform over a wide temperature range and are exposed to conditions significantly different from those encountered in surface applications. Over 100 cement additives are available to adjust cement performance, allowing engineers to customize formulations for specific well environments.

The primary objective is to formulate a cement that is:

• Pumpable for a sufficient time for placement in the annulus
• Develops strength within a few hours after placement
• Durable throughout the well's lifetime

Testing and Evaluation

After cementing operations, engineers perform tests to confirm the cement sheath's integrity and performance meet design criteria. If the cement job is defective, remedial cementing techniques may be employed.