903 Well Site Completion and Servicing Safety

Plug-Backs

Plug-back is used before abandoning a well or before sidetracking is done.

Plug-back is the process of placing a cement plug at one or more locations in a well to shut off flow from below the plug. Cement plugs are placed in the borehole to prevent migration of fluids between the different formations. This also prevents the migration of gas or fluids to the surface.

There are two methods for placing a cement plug in a well:

• plug-back using tubing
• plug-back using a dump bailer

Potential Hazard

• being struck by pressured lines when pumping cement

Possible Solution

• Instruct personnel to stand clear of pressurized lines.

Sidetracking

Sidetracking is the workover term for drilling a directional hole to bypass an obstruction in the well that cannot be removed or damage to the well, such as collapsed casing that cannot be repaired.

Sidetracking is also done to deepen a well or to relocate the bottom of the well in a more productive zone, which is horizontally removed from the original well.

To sidetrack, a hole (called a window) is made in the casing above the obstruction. The well is then plugged with cement below the window. Special drill tools, such as a whipstock, bent housing, or bent sub are used to drill off at an angle from the main well. This new hole is completed in the same manner as any well after a liner is set.

Potential Hazards and Solutions:

• The hazards and solutions associated with sidetracking are similar to drilling.

Knowledge Check Choose the best answer for the question.