Well Intervention / Servicing
A well intervention, or well work, is any operation carried out on an oil or gas well during, or at the end of, its productive life that alters the state of the well or well geometry, provides well diagnostics, or manages the production of the well. SBS Energy Services is an example of a company that specializes in snubbing/workover and coil tubing well intervention.
The term workover is used to refer to any kind of oil well intervention involving invasive techniques, such as wireline, coiled tubing or snubbing. More specifically, a workover refers to the expensive process of pulling and replacing completion or production hardware in order to extend the life of the well.
Pumping is the simplest form of intervention as it does not involve putting hardware into the well itself. Frequently it simply involves rigging up to the kill wing valve on the Christmas tree and pumping in a fluid determined necessary for the particular well.
In the context of oil wells, pumping is a routine operation involving injecting fluids into the well. Pumping may either be done by rigging up to the kill wing valve on the Xmas tree or, if an intervention rig up is present pumping into the riser through a T-piece (a small section of riser with a connection on the side). Pumping is most routinely done to protect the well against scale and hydrates through the pumping of scale inhibitors and methanol. Pumping of kill weight brine may be done for the purposes of well kills and more exotic chemicals may be pumped from surface for cleaning the lower completion or stimulating the reservoir (though these types are jobs are more frequently done with coiled tubing for extra precision)
Coiled tubing is used when it is desired to pump chemicals directly to the bottom of the well, such as in a circulating operation or a chemical wash. It can also be used for tasks normally done by wireline if the deviation[clarification needed] in the well is too severe for gravity to lower the toolstring and circumstances prevent the use of a wireline tractor
Braided line is more complex than slickline due to the need for a grease injection system in the rigup to ensure the blowout preventer (BOP) can seal around the braided contours of the wire. It also requires an additional shear-seal BOP as a tertiary barrier as the upper master valve on the Christmas tree can only cut slickline. Braided line includes both the core-less variety used for heaving fishing and electric-line used for well logging and perforating
Reasons to Perform a Workover
Workovers rank among the most complex, difficult and expensive types of wellwork. They are only performed if the completion of a well is terminally unsuitable for the job at hand. The production tubing may have become damaged due to operational factors like corrosion to the point where well integrity is threatened. Downhole components such as tubing, retrievable downhole safety valves, or electrical submersible pumps may have malfunctioned, needing replacement.
In other circumstances, the reason for a workover may not be that the completion itself is in a bad condition, but that changing reservoir conditions make the former completion unsuitable. For example, a high productivity well may have been completed with 5½” tubing to allow high flow rates (a narrower tubing would have unnecessarily choked the flow). Some years on, declining productivity means the reservoir can no longer support stable flow through this wide bore. This may lead to a workover to replace the 5½” tubing with 4½” tubing. The narrower bore makes for a more stable flow.
Well Servicing Operations
Before any workover, the well must first be killed. Since workovers are long planned in advance, there would be much time to plan the well kill and so the reverse circulation would be common. The intense nature of this operation often requires no less than the capabilities of a drilling rig.
The workover begins by killing the well then removing the wellhead and possibly the flow line, then installing a B.O.P commonly known as a blowout preventer, then lifting the tubing hanger from the casing head, thus beginning to pull the completion out of the well. The string will almost always be fixed in place by at least one production packer. If the packer is retrievable it can be released easily enough and pulled out with the completion string. If it is permanent, then it is common to cut the tubing just above it and pull out the upper portion of the string. If necessary, the packer and the tubing left in hole can be milled out, though more commonly, the new completion will make use of it by setting a new packer just above it and running new tubing down to the top of the old.
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