When using a gas lift system, mandrels are an integral part of the pumping system. Valves are installed in these pieces of hardware, which are an important part of regulating the flow of gas. Conventional mandrels are straightforward to use, but they have a significant downside. When one mandrel fails or needs maintenance, the entire tubing string has to be pulled.
Side pocket mandrels are an alternative that addresses this issue. Rather than pulling the entire tube string, side pocket mandrels can be pulled separately from the tubing string using a wireline machine. You won’t need a pulling unit and a whole crew, and wireline machines are useful to have around for a lot of reasons. Side pocket mandrels are particularly good choices for offshore rigs, having lesser requirements for crew and equipment.
Figure 1. A few different types of side pocket mandrels. (courtesy of CAMCO Products and Services Company)
Wireline Machines and Safety
Wireline machines can do more than simply pull side pocket mandrels. The tools used with a wireline machine can be used to do a variety of things, from removing sand to cleaning up scale. Paraffin can precipitate, for example, blocking tubing and slowing the flow of production oil. A wireline can cut through the paraffin and reduce the buildup.
Other types of maintenance are also possible with a wireline machine. Safety valves and other safety equipment could also be serviced and maintained. A wireline machine is useful for many reasons on an offshore well. One of the most important is that it allows the running of a second string of tubing into the well, in case of an emergency.
While it’s possible to add some safety equipment using a wireline machine, the machine itself can be dangerous. Fast moving wire cables are dangerous, and you should never approach or attempt to handle the wire while the machine is on.
Gas lift usually works best when the well is going to be continuously flowing. This is because the unloading sequence that is required to get a gas lift system flowing is complex and can be time consuming. For smaller wells, where the unloading sequence is easier to manage, running the well only intermittently could be prudent.
Figure 2. An example chart showing production from a gas lift system producing continuously. (courtesy of McMurry-Macco)
Figure 3. An example chart from a well producing intermittently using gas lift. (courtesy of McMurry-Macco)
Gas Lift Using The Annular Space
For most operations, the gas is injected through the annular space so that oil is produced up through the tubing. That’s the optimal arrangement for most wells, from those only producing a few dozen barrels a day to operations producing tens of thousands of barrels.
For high production wells, the standard system is actually reversed, with the gas being injected through the tubing and fluid produced through the casing. In that case, no packing is necessary in the casing, as it would be with the standard system. This is more common with wells producing more than 20,000 barrels daily. This is a particularly efficient in operations dependent on waterflood, as the amount of water pumped to the surface will tend to increase over time.
Is your appetite for oil & gas operating knowledge insatiable like ours? 😀 If so, check out these related articles, The Basics of Gas Lift Pumping in Oil & Gas Production and, Mandrels and Gas Lift Valves in Oil & Gas Production – they’ll be sure to pump you up!!!