A gas lift system normally requires valves in the production tubing down the well. These valves open in sequence, injecting the gas that forces fluid in the tubing to the surface. The hardware that connects the valve to the tubing is called a mandrel. There’s two general categories of mandrels, and whichever you choose can have an impact on how your well operates and is maintained. The first variety of mandrel is the conventional mandrel.
Conventional Gas Lifts and Mandrels
Valves are attached to the outside of the mandrels, which are then inserted into the tubing string at regular intervals. The entire assembly of tubing, mandrel, and the attached valves are all run into the well together. That means that when a valve needs maintenance or to be replaced, the entire thing needs to be pulled, which requires a crew of workers.
Another component to be aware of with a conventional gas lift system is the packer above the tubing perforations, which seals the annular space. That space is closed at the bottom as well, so that gas that is fed into that area from the compressor on the surface will activate the system.
Figure 1. Four different conventional mandrels. (courtesy of Camco Products and Services Company)
Installing Mandrel and Valves
The valves will need to be installed at a specific, regular interval along the tubing. It’s best to measure the intervals and assemble the mandrel and valve before transporting the tubing to the well. The first lengths of tubing to be lowered down are all loaded together and marked with a 1. The second group is marked 2 and also loaded together, and so forth. Each mandrel is similarly assembled and marked for the order it’s going to be installed. When the tubing reaches the well location, it can be assembled with the mandrels in order.
When the tubing has to be pulled for servicing, the same ordering and numbering can be used. It’s vital that each valve be used only in its correct place in sequence, as otherwise the lifting system will not work correctly.
Figure 2. A few different gas lift valves. (courtesy of Camco)
The Basics of the Gas Lift Valve
A valve will automatically open under a specific pressure, the opening operated by a bellows that is gas operated or occasionally through a spring loaded mechanism. The gas lift valve is divided into several different chambers.
The top most chamber is filled with a pressurized neutral gas. It has a fill valve that’s similar to one you’d find on a tire. The fill valve is set to a specific pressure and then it’s sealed up.
The second chamber is a bellows, one end of which is round. The bellows is forced up against its seat by the internal pressure.
The lower chamber of the valve is exposed to the annular pressure at the bottom of the well. The difference in pressure in the annular space opens the valve so that the gas is injected into the fluid.
Gas enters the tubing from the uppermost valve first. That valve then closes, and the one below it opens. This sequence continues until the entire column has been injected with gas and the fluid begins to flow. As long as gas continues to enter the tubing, fluid will continue to flow.
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, Using Side Pocket Mandrels in Oil & Gas Production – they’ll be sure to pump you up!!!