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Workovers can be done with conventional rigs (smaller but similar to drilling rigs) or nonconventional systems. Conventional rigs can be equipped to handle almost all types of work that may be required (see [[Land rigs]]). Nonconventional systems allow specific types of work to be done without pulling the tubing, disassembling the Christmas tree, or even killing the well. This is accomplished by using lubricators and packoff equipment at the surface and by running the required equipment inside the production tubing. Common types of nonconventional systems are wireline units, coiled tubing units, and snubbing units. Generally, these systems are designed to do a relatively narrow scope of work.

Workovers can be done with conventional rigs (smaller but similar to drilling rigs) or nonconventional systems. Conventional rigs can be equipped to handle almost all types of work that may be required (see [[Land rigs]]). Nonconventional systems allow specific types of work to be done without pulling the tubing, disassembling the Christmas tree, or even killing the well. This is accomplished by using lubricators and packoff equipment at the surface and by running the required equipment inside the production tubing. Common types of nonconventional systems are wireline units, coiled tubing units, and snubbing units. Generally, these systems are designed to do a relatively narrow scope of work.

''Wireline units'' use special equipment (Figure 5) on a solid wireline to gather data (pressure, temperature, and depth) and to set, manipulate, and/or retrieve tubing plugs, sliding sleeves, flow regulators, gas lift valves, safety valves, and wireline fishing tools. Wireline equipment can also be used to cut paraffin and remove wellbore fill. Prior planning, good operators, good equipment, and reasonable well conditions are prerequisites to the success of this method.

''Wireline units'' use special equipment ([[:file:workovers_fig5.png|Figure 5]]) on a solid wireline to gather data (pressure, temperature, and depth) and to set, manipulate, and/or retrieve tubing plugs, sliding sleeves, flow regulators, gas lift valves, safety valves, and wireline fishing tools. Wireline equipment can also be used to cut paraffin and remove wellbore fill. Prior planning, good operators, good equipment, and reasonable well conditions are prerequisites to the success of this method.

''Coiled tubing units'' (Figure 6) find application in cleanout work, stimulation, plugback jobs, and unloading wells with nitrogen. Coiled tubing units can have 10,000 to [[depth::15,000 ft]] of pipe (usually 1-in. outside diameter) that can be reeled continuously into the wellbore. The pipe can be used to pump into the well and circulate fluids such as water, acid, or cement. The use of a dynadrill permits some drilling with coiled tubing. Limitations of coiled tubing include the reduced strength of the tubing and low pumping rates (high friction pressure because of the diameter and length). Coiled tubing can be run into wells against pressures up to 5000 psi.

''Coiled tubing units'' ([[:file:workovers_fig6.png|Figure 6]]) find application in cleanout work, stimulation, plugback jobs, and unloading wells with nitrogen. Coiled tubing units can have 10,000 to [[depth::15,000 ft]] of pipe (usually 1-in. outside diameter) that can be reeled continuously into the wellbore. The pipe can be used to pump into the well and circulate fluids such as water, acid, or cement. The use of a dynadrill permits some drilling with coiled tubing. Limitations of coiled tubing include the reduced strength of the tubing and low pumping rates (high friction pressure because of the diameter and length). Coiled tubing can be run into wells against pressures up to 5000 psi.

''Snubbing units'' (Figure 7) use hydraulic pressure and rams to introduce small, coupled tubing into the well, if necessary, against pressures above 5000 psi. The tubing is stronger and can be rotated so that tougher cleanout or fishing jobs can be accomplished. Snubbing units are used for the same type of jobs as are coiled tubing units, but their compactness is an advantage in offshore work. They are slow and expensive, but in the right applications, they are the more economical way to accomplish the task.

''Snubbing units'' ([[:file:workovers_fig7.png|Figure 7]]) use hydraulic pressure and rams to introduce small, coupled tubing into the well, if necessary, against pressures above 5000 psi. The tubing is stronger and can be rotated so that tougher cleanout or fishing jobs can be accomplished. Snubbing units are used for the same type of jobs as are coiled tubing units, but their compactness is an advantage in offshore work. They are slow and expensive, but in the right applications, they are the more economical way to accomplish the task.

==See also==

==See also==