Drilling gets the headlines, but most of a well's life happens after the drilling rig leaves, and most of the money a well ever makes depends on the years of maintenance and repair that follow. That work belongs to the workover rig, the smaller unit the field calls a pulling unit or service rig: a telescoping mast on a truck carrier, a drawworks, a set of rod and tubing tools, and a crew that can rig up on a location in hours and give an old well its production back. This page explains the machine, the jobs, and the way a workover actually runs, in the same plain terms the rest of our knowledge library uses.
The rig itself
A workover rig is purpose-built for wells that already exist. The mast telescopes up from the carrier and is rated for pulling rods and tubing, not for the rotating loads of making new hole. The drawworks spools the fast line for trips; hydraulic rod tongs and tubing tongs make and break the connections; a rod basket and pipe racks catch what comes out of the hole. For jobs that need rotation, a power swivel rides along: milling, drilling out plugs, washing sand. The well control stack is a servicing BOP nippled up on the wellhead, and a pump and tanks keep kill fluid moving. Compared with a drilling rig it is small, fast, and cheap, which is the entire point: the economics of fixing a well only work when the fixing machine costs a fraction of what built it.
Why wells need intervention
Wells decline for reasons that have nothing to do with the reservoir running dry. Rod pumps wear out, and a worn pump shows up as falling production long before it quits entirely. Tubing develops leaks, from rod wear on the inside or corrosion on the outside, and a tubing leak can cut a well's lift efficiency in half while everything at surface looks normal. Paraffin and scale choke the flow path. Sand and fines fill the rathole and climb over the perforations. Water finds its way to the perfs as the field matures. Downhole equipment parts and falls. And sometimes nothing is broken at all: the zone is simply finished, and the value left in the wellbore is behind a different set of perforations. Every one of those stories ends with a rig on location.
The job families
Routine well servicing
The bread and butter: pulling rods to replace a worn downhole pump, swapping bad rods, pulling and rerunning tubing to fix a leak, wellhead and stuffing box maintenance. A day or two of rig time that buys back months of production.
Cleanouts
Sand, scale, and fill removed by bailing, washing with a workstring and power swivel, or milling. The gauge of success is simple: tag bottom where bottom belongs, and put the perforations back to work.
Recompletions
Changing what the well produces from: plugging back a depleted or watered-out zone and perforating a new one, or opening additional intervals. The cheapest new well an operator can buy is often hiding inside an old one.
Remedial cementing and casing repair
Squeeze jobs to shut off unwanted water or gas and repair channels, and patches or liners for corroded and split casing. Precision work where the diagnosis matters as much as the pumping.
Fishing
Recovering what the hole swallowed: parted rods, dropped tubing, stuck tools. A trade of patience, the right fishing tools, and knowing when continuing beats sidetracking or walking away.
Completions and P&A
On the front end, running tubing, packers, and pumps to put a new well on production. On the back end, plugging and abandonment done to state requirements: cement plugs placed and tagged, casing cut and capped, the location left right.
How a job actually runs
Nearly every rig job follows the same skeleton. First the well is killed: fluid heavy enough to hold the formation, usually a clean brine, pumped until the well stands dead. The arithmetic is the same 0.052 rule that governs drilling, covered in our mud weight guide, and the fluid choices, KCl and calcium chloride brines and the rest, are cousins of the systems in the drilling fluids guide. Then the BOP goes on, and pulling begins: rods first on a pumping well, then tubing, everything tallied and inspected as it comes.
With the well open, diagnostics tell the truth: tag for fill, pressure test the tubing, run the gauges the job calls for. The remedial work happens, whatever the job family, and the well goes back together the way it came apart. Last comes bringing it back to life. A well full of kill fluid won't flow, so the column gets lightened: swabbing, the old and still standard method, pulls fluid out with a sealing tool run on wireline until the formation takes over. Rig down, move off, and the pumper watches the numbers that justify the whole exercise.
One thing never comes off the checklist: well control. A dead well is only dead because the fluid column says so, and pulling pipe swabs the hole, fluid leaks away into the formation, and gas migrates. Service crews run BOPs, keep the hole full, and treat every well as live until the last plug proves otherwise, because the incidents that make the news are the ones where somebody trusted "dead" as a permanent condition.
Rig work and its rigless cousins
Not every intervention needs a mast. Wireline handles surveys, plugs, and perforating through the tubing. Coiled tubing washes, circulates, and stimulates without killing the well in some cases. Hydraulic workover and snubbing units work against live pressure for specialized jobs. The workover rig owns everything the others can't reach: any job that pulls rods or tubing, mechanical repairs, fishing, and the heavy remedial work. A good service company's answer to "rig or rigless" is whichever gets the well back cheapest per barrel restored, and an honest one will tell you when the answer isn't a rig.
The economics, plainly
Workover decisions are arithmetic. The job costs rig hours, services, and parts; it buys production restored or added, and it resets the clock on deferred failures. A pump change that recovers a hundred barrels a month pays for itself before the invoice clears. A marginal well's workover competes with shutting it in, and a recompletion competes with drilling. The operators who do best at this treat their well files like a portfolio, rank the candidates by barrels-per-dollar, and use pre-job diagnostics so the rig spends its hours fixing what is actually broken. Rig time is the expensive ingredient; certainty about the problem is the cheap one.
Common questions
What does a workover rig crew look like?
Typically a rig operator and a crew of two to four: floor hands working rods and tubing, a derrick worker when the job racks pipe. Small crews, long relationships: the crews that know a field's wells are worth more than any spec sheet shows.
What permits and rules apply?
State oil and gas regulators govern intervention and abandonment work; in Texas that's the Railroad Commission, with notification and plugging requirements per its rules. Operators of record handle the filings, and the service company works to the permit, the operator's program, and the safety standards the location demands, H2S contingency included where the field calls for it.
What information should an operator have ready before calling for a rig?
The wellbore diagram, last known bottom, tubing and rod details, recent production and fluid levels, and what changed. Ten minutes with a good well file saves a day of rig-time archaeology.
Where Vexon fits
Vexon provides workover rig services, along with mud sales, mud engineering, welding, and general oilfield labor, to qualified operators. If you run wells and have candidates on your list, get in touch and ask for our qualification form; it takes a day to get set up and the conversation after that is about your wells, not paperwork. For the rest of the library, start at the knowledge hub or the mud engineering guide.