Workover activities include one or more of a variety of remedial operations on a producing well to try to increase production. Four or more people will work on the workover rig site. The rig is used to complete and stimulates, repairs and maintains an existing well.
Sand cleanout operations are performed to remove buildup of sand in the wellbore. Potential hazards and solutions are similar to those for well servicing.
Liners and casing are essentially the same and repair procedures are the same for both. Casing can be damaged by corrosion, abrasion, pressure, or other forces that create holes or splits.
A packer is run down the well to locate the hole in the casing. Fluid, usually salt water or oil, but sometimes mud, is pumped into the casing above the packer. A packer is a piece of downhole equipment that consists of a sealing device, a holding or setting device, and an inside passage for fluids.
A loss of pressure indicates a hole in the casing.
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:
A well is abandoned when it reaches the end of its useful life or is a dry hole.
The rig is used to remove the casing and plug the well. The wellhead is removed. After the casing is cut off, it is removed..
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:
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