A sliding sleeve generally refers to a series of ports meant to regulate various reservoirs inside a gas well or oil well. These parts are generally installed during the final phases of the drilling process, sometimes called the completion stage by industry professionals. Most oil wells, for instance, have a structure of production tubing that is meant to take oil out of the natural reservoir and pump it to a storage facility. Oil wells are generally drilled directly into a highly pressurized chamber, so mechanical or hydraulic valves are necessary to control the flow of material out of the reservoir. A sliding sleeve is the device that enables this level of control.
One of the most important applications of a sliding sleeve is the regulation of flow pressure between different zones in a well. For instance, a well might have two main production chambers, but the combined flow from both would put too much strain on the well equipment. In this case, an installed sliding sleeve could help by shutting off the flow from one chamber while allowing the other chamber to produce oil unimpeded.
In most configurations, the sliding sleeve can be closed by a mechanical or hydraulic component controlled from the surface. The nonelectrical cable used to physically alter the configuration of components inside a productive well is called a wireline, and a sliding sleeve is the part connected to the wireline and controlled from the surface. The "sliding" of a sliding sleeve refers to the mechanical motion of sliding the ports shut when a wireline is activated.
The possible applications of a sliding sleeve configuration in any well can change based on the type of well, production methods such as hydraulic fracturing, well age, and many other factors. There are also various sliding sleeve configurations, including an open/close configuration that is typical of many wells. In these, the flow usually can only start or stop, whereas a choked configuration can be opened to a variable diameter.
Many well intervention activities also benefit from sliding sleeves because certain areas of a well can be constricted while maintenance is being performed in another area of the well. For example, a well with two main chambers may still be productive in one chamber while the other is primarily filled with water. A sliding sleeve would allow well technicians to close off the chamber producing water while still drawing oil from the other chamber.