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A ''workover'' is any operation done on, within, or through the wellbore after the initial completion. Although proper drilling, cementing, and completion practices minimize the need, virtually every well will need several workovers during its lifetime to satisfactorily fulfill its purpose.

A ''workover'' is any operation done on, within, or through the wellbore after the initial completion. Although proper drilling, cementing, and completion practices minimize the need, virtually every well will need several workovers during its lifetime to satisfactorily fulfill its purpose.

To help understand why workovers are required, it is useful to visualize a wellbore. A typical wellbore schematic is shown in [[:file:workovers_fig1.png|Figure 1]]. The production casing is only 5 to [[length::9 in.]] in diameter, and it has been run into a corkscrew-shaped hole that is not entirely circular and may be substantially deviated from vertical. An attempt has been made to cement the casing centrally, at least across the productive intervals, to obtain a hydraulic seal and casing support. Inside the production casing, even smaller equipment is run for completion and production or injection purposes. [[:file:workovers_fig2.png|Figure 2]] illustrates the tight fit of these concentric strings. Although the diameters are small, the surface area of the equipment is significant and may be exposed to corrosive fluids and pressure for long periods of time.

To help understand why workovers are required, it is useful to visualize a wellbore. A typical wellbore schematic is shown in [[:file:workovers_fig1.png|Figure 1]]. The production casing is only 5 to [[length::9 in.]] in diameter, and it has been run into a corkscrew-shaped hole that is not entirely circular and may be substantially deviated from vertical. An attempt has been made to cement the casing centrally, at least across the productive intervals, to obtain a hydraulic seal and casing support. Inside the production casing, even smaller equipment is run for completion and production or injection purposes. [[:file:workovers_fig2.png|Figure 2]] illustrates the tight fit of these concentric strings. Although the diameters are small, the surface area of the equipment is significant and may be exposed to corrosive fluids and pressure for long periods of time.