All wells will need to be serviced at some point, either for maintenance or because there’s been a drop in production. To properly service a well, it’s necessary to have a broad understanding of the well’s history, the tools and techniques available, and a range of other information as well. Used well, that information can lead to an extended production life for a well. If wells are not serviced, or not serviced correctly, it can lead to the abandonment of a well that is still capable of producing. Servicing a well may require pulling rods or tubing and running tools downhole.
Well Records For Servicing
It’s a good idea to take a look at the records for the well before beginning service. These records will provide specific information about the well that will be important when pulling, servicing, and replacing a tubing or rod string, as well as for running tools down the well. Records can also help indicate any problems, as a look over the history of the well will show production levels, changes, and other factors that may have an impact on the well’s behavior.
Information about the well casing should be examined. The casing information sheet will indicate the distance from the wellhead to the perforations, the distance from the perforations to the bottom of the casing, and specifics about the perforations. The tubing tally sheet will have similar information for the tubing string. It will list elements that make up the tubing string, such as where the joints of pipe are, as well as information about the packer, the seating nipple, and the mud anchor. All of these will be listed in their order in the string from the tubing head to the bottom. It will also list whatever other equipment may be in the hole. The packer or holddown description will also have this information, but will generally include more detail. That record should include enough information to safely pull the piece of equipment if necessary.
A rod tally sheet will also have important information. The length and size of every rod is listed, as well as type of rod. For tapered rods, the number of each type of rod will also be listed.The tally sheet will also have instructions for releasing a safety joint, and any other special instructions. The pump description is useful if the pump has to be pulled, though a more complete record of the pump used should be included with the lease records.
Also we go into more depth on the recording and importance of proper well records here Well Records For Oil & Gas Production.
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Well Servicing Units
Specially equipped servicing units are required to pull rod and tubing string out of the well. This can be a lengthy process where the tubing and rod sections are brought up and disconnected from the string, which clears the way for the next section to be brought up, and so forth. There are three basic types of servicing units: single pole, double pole, and single mast. Some may have one or two wire drums. With a single drum, it’s possible to run only a single wire down into the well so these units are usually able to either pull rods or tubing, or swab the well, but not both. It is possible to do both by switching lines, though that can be complicated. A double drum unit can run two wires, and so is able to do a wider range of tasks. The smaller single or double pole unit may have either one or two drums, while the mast unit will always have 2 drums.
Servicing units are usually large pieces of machinery which are accompanied by at least one other truck. It’s possible that a whole caravan of support equipment may be necessary, depending on the service you’re performing. It’s important to follow some basic safety guidelines when bringing a service unit to the well site, as well as when operating the unit. Make sure everyone is aware of the plan and what’s going to happen. Have drivers discuss routes and potential problems before setting off, and take similar steps to prepare. A little common sense can prevent larger problems down the road.
These units have a single mast and a single drum and are used to service shallower wells. With a single pole unit, the rod or tubing sections will have to be laid out on a rack as they are brought to the surface. These units are small enough that it’s possible to run with them just a crew of two, an operator and somehow on the floor. However, an extra hand is usually a good idea, so getting a third crew member is probably wise.
The pole will most often be in two parts, with the higher section telescoping out of the lower section. The pole will also have to be secured with guy wires. The bottom section may have as many as 8 guy wires, while the upper section will most likely have fewer. The servicing unit base will most often also have guy wires to keep it securely on the ground.
Figure 1. Correctly securing guy lines. (courtesy of Williamsport Wirerope Works, Inc.)
When setting up the servicing unit, you’ll want to work from the bottom up, securing each section before moving on to the next. The base of the unit should be secured with guy wires before the lower section of the pole is raised. Likewise, the lower section should be secured before the last section is raised.
That upper section can often be raised to one of several different heights, depending on the type of service. Rods are generally around 25 feet long, so the mast only needs to be raised high enough for the rod to be lifted safely. Tubing section are generally longer, so the pole may need to be raised further. Single pole servicing units are popular with companies that have a number of shallow wells, as they can usually afford to buy one of these units themselves, reducing long term costs.
Generally more efficient than single pole units, double pole units are generally able to handle a wider range of tasks. Because of the second pole, rods can be setup and hung in doubles (with two rods being lowered at once), though tubing still can only be run in single lengths. These units can also perform some types of work-over. They do require a slightly larger crew than single pole units, needing three of four people to operate safely.
When you pull the pumping rods, they need to be unscrewed from the rod below in order to be removed. When pulling rods in doubles, either end of the rod may come unscrewed. This unscrewing process is referred to as ‘breaking the box,’ with the box being another name for the female side of the screw. Since either end of the rod may be the one that comes unscrewed, it’s important to return rods into the hole in the order they came out. Each rod has a specific place in the string, based on strength, size, and a number of other factors.
Pulling tubing is a similar process with a few differences. The tubing will be supported by a collar on the lower end, so it’s always the upper joint that is broken. Tubing should be run back in the same order as it was taken out, as mixing up tubing sections usually leads to a higher risk of leaks. Thread lubricant should be used, and the correct torque should be applied when tightening joints. The manufacturer or supplier of the rod will usually have some information, on a card or sheet, that lists how tightly the joints should be made up.
A double pole unit is about the same size as a mast servicing unit, but it’s better suited for shallow or medium depth wells. Many operators like these trucks as they can service most wells, and it’s not unusual for companies to own one of these units.
An example of a mast unit is shown in Figure 2. It’s able to pull more at once, taking tubing in doubles and rods in triples. Rods are racked by a crew member on the derrick, allowing the operation to go quite quickly. Mast units are usually required for deeper wells.
Figure 2. A mast style well servicing unit.