Workover Definition / Meaning

A workover is a remedial operation performed on an existing oil or gas well to restore, maintain, or enhance its production. Unlike a new well drill, which creates a new borehole, a workover intervenes in an already drilled and completed well. Workovers address mechanical failures, formation damage, changes in reservoir conditions, or the need to access different hydrocarbon zones. They are a critical part of production and operations, helping operators maximize recovery and extend the economic life of a well.

Reasons for Workover

Workovers become necessary for many reasons. Common causes include:

• Mechanical failure: Downhole equipment such as pumps, packers, or tubing may fail due to wear, corrosion, or pressure extremes.
• Formation damage: Scaling, paraffin buildup, fines migration, or clay swelling can block pore spaces and reduce permeability.
• Water or gas coning: Unwanted water or gas production can be controlled by isolating certain intervals or installing special completion equipment.
• Recompletion: The well may need to be completed in a different zone after the original zone is depleted or if new reserves are identified.
• Artificial lift changes: Switching from natural flow to gas lift, ESP, or rod pump to maintain economic rates.
• Well integrity issues: Casing leaks, cement squeeze failure, or damaged wellhead components require repair to prevent environmental harm.

Types of Workover Operations

Workovers are classified by the method used to access the well. The main types include:

• Rig workover: Uses a conventional drilling or workover rig to pull the entire tubing string and perform major repairs. Suitable for deep wells and complex jobs.
• Hydraulic workover (snubbing): Employs a hydraulic snubbing unit to run or pull tubing under pressure without killing the well. Ideal for high-pressure wells where killing could cause formation damage.
• Coiled tubing workover: Uses continuous coiled tubing for through-tubing interventions. Enables operations such as milling, cleanouts, and stimulation without removing the existing production string.
• Light workover: Performed with a service rig or hoist for simpler tasks like rod pulling or pump changeouts.

Typical Workover Procedures

Although every workover is tailored to the specific well issue, a typical sequence includes:

1. Well preparation: Secure the well, kill or control pressure (if needed), and install blowout preventers (BOPs).
2. Access the downhole assembly: Pull the production tubing and any downhole tools using the rig or snubbing unit.
3. Diagnostic and repair: Run logging tools to inspect casing and formation, then perform the needed operations (e.g., milling scale, washing sand, setting squeeze cement).
4. Reassembly: Install new or refurbished completion equipment (e.g., packers, safety valves, pumps).
5. Testing and commissioning: Pressure test the well, bring it back online, and monitor production.

Key Equipment Used in Workover

The following table outlines major equipment categories and their functions.

Comparison: Workover vs. Drilling

Understanding the difference between drilling and workover helps clarify scope and cost. The table below highlights key contrasts.

Usage Example

The operator scheduled a workover to replace a failed downhole pump and clean out sand fill that had accumulated in the wellbore. After pulling the old pump, a coiled tubing unit circulated fluids to remove sand, then a new electric submersible pump was installed. Post workover, production increased from 50 bbl/d to 180 bbl/d.

Conclusion

Workovers are a cost-effective way to maximize asset value. By extending well life, increasing production rates, and reducing the need for new drilling, workovers play a vital role in the petroleum industry. Operators must carefully plan each intervention, considering reservoir conditions, well integrity, and budgetary constraints. As technology advances, less invasive methods like coiled tubing and snubbing continue to make workovers safer and more efficient.