A landing nipple is a tubing sub with a box, pin-threaded connection, and a precisely machined and configured internal bore. This internal bore, designed to accept a suitably sized mandrel with a matching external profile, functions as a guide for the mandrel as it is run down the inside of the tubing string using a wireline. The nipple normally provides two facilities:
- A facility will allow the mandrel to be latched within the nipple profile.
- a sealing capability for the mandrel within the bore of the nipple.
Therefore, the nipple must offer a landing/locking profile and a seal bore. The seal bore is generally located beneath the locking profile to avoid mechanical damage.
A variety of nipple/mandrel systems are available to offer the following capabilities:
- Isolation or plugging of the tubing string for well shut-in, workover, or for hydraulically setting packers.
- A ported device communicating between the tubing and the annulus.
- Emergency closure of the tubing or annular flow conduit by remote or direct control.
- Downhole regulation or throttling of the flow.
- Installation of downhole pressure and temperature recording gauges.
Two basic types of landing nipples are available: selective and nonselective.
Selective Landing Nipple System
There are three methods of obtaining selectivity in a landing nipple system:
- Firstly, Selectivity is based on a variable internal profile.
- Secondly, Selectivity is associated with the setting tool.
- Thirdly, Selectivity is based on pre-spaced magnets.
Selective Internal Profile
In this system, it is crucial to match the internal profile of the nipple to a set of locating keys on a lock mandrel. Nipples are available in 5 to 7 selective positions and must be run as part of the completion string in the sequence denoted by the selective location keys. The importance of running the nipples sequentially and noting the depth of each nipple cannot be overstated, as it assists mandrel placement during subsequent work.
Setting Tool Selective Nipple
With this system, the setting tool, which includes its removable locking and sealing device, is designed with fixed external profiles. Thus, the setting tool locates the nipple, positions the lock mandrel, and seals in the appropriate nipple. Using this system of selectivity, an unlimited number of this type of landing nipples of the same size can be installed in the string.
Prespaced Magnet Selectivity
This type of nipple system usually comprises a lower section, which contains the locking profile and sealing section, and an upper section, where two pre-spaced magnet rings are located. For a mandrel to be inserted and locked into such a nipple, two magnets also replaced on the running tool must correspond with the location of the rings within the nipple. The mandrel is locked in position by a mechanical locking mechanism actuated by a small explosive charge detonated by the electric circuit created when the mandrel lands in the nipple. Up to six of these nipples, of the same size, can be run in the same string.
For most applications, selectivity is preferred based on variable profile or setting tool actuation.
Nonselective Landing Nipple
This type of landing nipple is frequently referred to as a no-nipple. It operates such that the outside diameter of the mandrel will be slightly larger than the minimum inside diameter of the nipple, preventing its passage through the nipple. In a string with several nipples to be operated on this basis, they must be designed to sequentially reduce in diameter as their installation depth in the string increases. The clearance of a mandrel through the upper nipples should be based on the size of the locking section of the mandrel and, normally, the sealing bore of the nipple. The no-go profile of the nipple can be designed to be at the top or bottom of the nipple.
Available Nipple/Mandrel Systems
All the major completion equipment supply companies offer a wide range of nipple systems with varying internal profiles for various applications.
Common Baker Landing Nipple Systems
Two commonly used Baker nipple systems are the Model F and Model R seating nipples.
The Model F seating nipple features a top no-go shoulder, and a locking groove above the lower seal bore section. This type of nipple can be operated on a selective or top no-go landing lock system. This type of nipple is used for a range of tubing operations, including:
- Setting a blanking plug to isolate production
- Landing directly controlled sub-surface safety valves, check valves, and downhole chokes.
- To land off pressure and temperature recording gauges.
The Model R nipple is a bottom no-go seating nipple with a honed internal sealing bore and a locking groove/bottom no-go shoulder. It can be used for the same type of applications as the Model F nipple.
Common Halliburton Landing Nipple Systems
The type X and R nipples offered by Halliburton are commonly utilized in completion strings. Both types X and R run tool-selective nipple systems.
The type X nipple was originally designed for completions using standard-weight tubings, e.g., 3 1/2″ or 4 1/2″ dia. maximum, in wells where the pressures would not exceed 10,000 psi. The type R nipple was developed for heavier-weight or larger-bore tubing strings. Both nipples were designed to offer a maximum sealbore diameter and minimal flow resistance. For the X and R nipples, the seal bore is located beneath the locking profile.
The mandrels used with these nipples are designed to retract the locking keys, allowing passage through the nipple system with minimum resistance.
A no-go version is available for both the X and R type nipples, as are the type XN and RN, respectively. One of these is normally placed at the bottom of a series of type X or R selective nipples.
The mandrels for the type X and R equipment and their respective versions with the bottom no-go, figures 3 and 4, are designed to hold high differential pressure from above or below. Pulling could be difficult or hazardous when unseating the mandrel with a high differential pressure. In the event of a high differential pressure from below, the force on the mandrel could be sufficient to blow it up the tubing string. Conversely, if the pressure differential were reversed, it may require significant force to unseat the mandrel. In such cases, it is essential to equalize pressures across the mandrel prior to it being unseated. This is done by installing an equalizing sub at the base of the mandrel. The sub has a port normally closed off by an internal sleeve, but when engaged, a prong on the mandrel pulling tool will open the sub.
Other Halliburton Types
Halliburton offers two other nipple systems: the type S selective and the type N no-go, which is nonselective.
The type S nipples are a system based upon selectivity by the locating mandrel. They feature seven predetermined relative landing locations in a single tubing string into which a mandrel can be landed through selective locating keys. This system allows up to seven different nipple locations to be employed. The type S nipple offers a large bore and can handle differential pressures in either direction but is only available for tubing sizes up to 4 1/2″ O.D.
The type N no-go nipple is a nonselective landing nipple frequently employed as the bottom nipple on a string comprising several type S nipples.
Setting Mandrels Not Requiring A Nipple Profile
In a properly designed well completion, nipple locations are identified, which provides the capability for installing downhole equipment based on the landing and locking profile. However, occasionally, the need arises to be able to land off equipment in the tubing where a nipple is not available, e.g.
- where a nipple seat has been damaged or access to the locking profile is difficult
- where a mandrel cannot be retrieved from a nipple
- where a suitable nipple location has not been provided.
In these circumstances, mandrels are available for setting without the tubing or in some specific designs within the collar of tubular threaded couplings. Obviously, since the locking system will be based upon slips engaging the tubing wall or dogs entering the tubing coupling collar, the efficiency of the mechanical locking will not be as effective as a proper mandrel/nipple system. These mandrels are only suitable for differential pressures of less than 1500 psi. In addition, the mandrels are not recommended if the differential pressure is from above.
The type D mandrel is designed to lock in a tubing collar (for API thread couplings only), and subsequent upward jarring compresses the seal element within the tubing wall. Figure 27
The sliding plug (petroline) is an attentive system for correlating opposite slips and can withstand high differential pressures.
Ancillary Equipment For Nipples
Any wireline nipple installed within a tubing string, with or without the relevant mandrel system, will cause some restriction to flow. The convergence and divergence effects associated with entry to and exit from the nipple system will cause severe turbulence and eddying currents. This turbulence can lead to substantial abrasive action on the tubing wall and nipple system. To protect against this abrasion, flow couplings are installed above and below the nipple to act as flow straightening devices.
