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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.

==Reasons for workovers==

==Reasons for workovers==

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workovers_fig1.png|{{figure number|1}}Components of a well.

workovers_fig1.png|{{figure number|1}}Components of a well.

workovers_fig2.png|{{figure number|2}}Horizontal cross section of a well.

workovers_fig2.png|{{figure number|2}}Horizontal cross section of a well.

* The condition of the well equipment may be a major factor in what and how much is done in a particular workover. The toll taken by corrosion, erosion, and mechanical wear may be significant, particularly if the casing is involved. Extra funds and time may need to be allocated to cover potential squeeze cement jobs, fishing operations, and equipment replacement.

* The condition of the well equipment may be a major factor in what and how much is done in a particular workover. The toll taken by corrosion, erosion, and mechanical wear may be significant, particularly if the casing is involved. Extra funds and time may need to be allocated to cover potential squeeze cement jobs, fishing operations, and equipment replacement.

To some degree, workovers are classified on the basis of the reasons for them (discussed earlier). Another way to describe types of workovers is to divide them into (1) jobs performed primarily to influence the reservoir and (2) jobs applied to the wellbore (including the cement) and its associated equipment. Workovers done primarily to influence the reservoir can be subdivided into (1) work done for the zone already open and (2) work done to shut off the existing zone in favor of opening a new zone, termed a ''recompletion''.

To some degree, workovers are classified on the basis of the reasons for them (discussed earlier). Another way to describe types of workovers is to divide them into (1) jobs performed primarily to influence the reservoir and (2) jobs applied to the wellbore (including the cement) and its associated equipment. Workovers done primarily to influence the reservoir can be subdivided into (1) work done for the zone already open and (2) work done to shut off the existing zone in favor of opening a new zone, termed a ''recompletion''.

==Workover equipment==

==Workover equipment==

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file:workovers_fig5.png|{{figure number|5}}Wireline equipment, (a) Lubricator, (b) Typical string.

file:workovers_fig5.png|{{figure number|5}}Wireline equipment, (a) Lubricator, (b) Typical string.

file:workovers_fig6.jpg|{{figure number|6}}Coiled tubing unit.

file:workovers_fig6.jpg|{{figure number|6}}Coiled tubing unit.

[[Category:Production engineering methods]]

[[Category:Production engineering methods]]