A workover is an extensive service on an oil or gas well, requiring interventions in the wellbore itself to correct a problem with the well. Some oil and gas companies may perform this work themselves, while others choose to contract it out to companies specializing in workovers. The length of time required can vary, and the well will not be productive during the servicing. Some planning is also necessary to prepare ahead of time, whether the event is a scheduled or emergency intervention.
A well may need a workover if it becomes unstable or unsuitable. Sometimes a safety issue develops, equipment fails, or a well needs renovations. Wells that are not producing may require a workover for the purpose of stimulating the well to see if it is possible to get more material before capping and abandoning it. Engineers can determine when a workover is necessary and provide recommendations on the most appropriate interventions to take.
The first step in the process is a well kill, where the workers pump heavy material into the well to stop production. The material's density prevents oil and gas from seeping up into the wellbore, clearing it for work. Next, personnel will remove material inside the wellbore so they can access it. Their work may require inserting and removing various equipment, cleaning and replacing components, and checking on the integrity of the wellbore to determine if issues like leaks or collapses could develop.
Once the personnel are finished, they can clear the wellbore for use again. Oil and gas production personnel will reinstall the regular well rig and start production again. Workovers are a very invasive form of well maintenance, and workers usually follow a careful protocol when bringing the well back up to production. This can include checklists for environmental health and occupational safety, to make sure the well will be safely operational.
Firms specializing in workovers travel around the world with teams and equipment. The cost for this procedure depends on the nature of the intervention required, and the oil and gas company must weigh this when considering whether to invest in rehabilitating a well. If a well is not likely to produce much more, it may be more sensible to kill it and cap it, moving on to another well. It can be difficult to accurately predict production, even with advanced engineering practices, and the process of evaluating a well before a workover can involve feedback from a variety of specialists.