Proper preparation of tubing before running serves two purposes. Firstly to ensure that the pipe body and threads are adequately protected from possible damage when being moved to the drill floor. Secondly, that handling of the tubing on the drill floor is kept to a minimum.

1 Identification and measurement

Electronic tagging will eliminate the need for casing length measurement at the wellsite. Numbering of each joint with paint will still be necessary, however, to enable quick visual identification.

2 Bucking units

These should be used in the pipe yard or at the wellsite to make up completion accessories such as packer seals, flow couplings etc. which are time consuming to install at the rotary table.

3 Cleaning of threads

Prior to inspection of the threads, the storage compound should be fully removed from the threads using fast drying solvents. The threads should then be blow dried, making sure no excess solvent is left on the threads.

Diesel should not be used as a cleaning agent. The subsequently applied dope may be contaminated and will have difficulty adhering to a surface cleaned by diesel. High pressure steam cleaners and air line dryers are recommended, wire brushes should be avoided.

Hybrid (i.e. multi-purpose) thread compounds eliminate the need for this cleaning process.

4 Inspection

With the tubing still on the pipe rack, the threads should be inspected for damage to the thread itself or to the sealing area.

While the tubing is being run, an inspector can check that the tubing is run according to approved practice, including whether the coupling has moved during make-up (by reference to a pre-marked scribe line) and whether the torque-turn graph is within specification.

All inspection could be performed by an independent quality control surveyor.

CRAs are particularly sensitive to galling during make-up, particular care should be exercised during the inspection to ensure the anti-galling treatment is present on all mating interfaces.

5 Thread compound application

5.1 General remarks

Thread compounds are used for three distinct purposes:

• to prevent corrosion of the connection parts during storage;
• to facilitate the running of connections during make-up/break-out;
• to seal the helical paths in the thread profile of tapered interference fit thread seals.

To serve the first purpose, storage compounds were developed. These compounds can only be used to protect against corrosion during the storage of the tubular, and should never be used as running compound.

To serve the second and third purposes, running compounds were developed to fulfil the following functions:

• during make-up: prevent metal-to-metal contact and thus protect the threads and seal areas from galling and wear;
• in made-up condition: seal the helical paths between mating threads to make the non-Premium connection leak tight;
• during break-out: ensure that the connection can be broken out, after having served for a long period, without galling and at torques which do not differ excessively with the applied make-up torque.

There has in the past been a definite distinction between the two sorts of compounds. However, some manufacturers claim to have developed running compounds which offer corrosion inhibition, equivalent to that of a good storage compound. These compounds are called hybrid or multipurpose compounds.

The use of running compounds conforming to API Bull. 5A2 is generally recommended. Although the API compounds were developed for API round and buttress thread connections for which the solid constituents have a sealing function, it is also used for connections with metal-to-metal seals.

5.2 Lubricating and sealing properties

Conventional thread compounds contain relatively weak, ductile, solid particles, suspended in heavy grease. Therefore the compound can be split up in grease base and suspended solid particles. Both of these components have a distinct function.

The functions of the grease are:

• to act as a carrier to hold the solid particles in a stable dispersion and permit even distribution over the surface of the connection;
• to act as an adhesive to ensure that the coating sticks to the metal surface under condition of application;
• to provide sufficient lubricity to overcome the initial friction between the connection thread and seal surfaces during make-up.

The solid particles have two functions:

• To provide reserves in lubrication in extreme operating conditions, where the boundary lubrication regime prevails and the grease component has leached out. If, after some time, the connection will have to be broken out, the solids will act as lubricants. They will then prevent excessive torque required for breaking out, by deforming when the thread surfaces move over them.
• To seal the helical leak paths of API type connections. These paths should be sealed by the compound. While being made up, the grease will tend to get forced into the leak paths of the particular thread. It has been suggested that over time the grease base will tend to disappear by leaching and evaporation of the volatile parts or fluidisation due to exposure to elevated temperatures. The solids will be left as sealers. The amount of pressure which can be withstood by the solids, seems to depend on their particle size and the amount of solids suspended in the grease. Sealers used are for instance lead powder, copper flake, zinc dust or chunks of Teflon. The latter is only to be used in combination with API buttress and round thread connections, for which it is reported that the "chunky" material performs better than the "flaky" material.

Each compound will have a characteristic friction correction factor, which depends on the compound composition. Grease, oil, high pressure additives, Teflon, copper flakes, graphite and certain sulphur compounds decrease the friction coefficient. Metal oxides and silicates increase the friction coefficient. The friction correction factor also depends on the hardness, the size and shape, and the number of particles suspended in the grease base.

However it is now thought that the effect of different types of thread compound on the make-up characteristics of connections may be smaller than would be suggested by the differences in the friction correction factors. Nevertheless, in the absence of specific recommendations to the contrary from the connection manufacturers, it is recommended that a compound with a quoted friction correction factor of 1.0 be used.

The use of too much compound on a Premium connection, in order to increase the lubrication, can have adverse effects. With certain connection types it has been shown that the pressure built up by the thread compound during make-up may have an adverse effect on the sealing performance of the connection. In such instances, more care should be taken in applying the right amount of compound, which should be applied to the thread surface of the pin end only (unless using an automated mechanism. Based on qualification testing, the manufacturer should provide a value for the amount of compound to be applied.

5.3 Environmental aspects

Conventional running compounds contain about 64% metal solids by weight. As an example the API Modified thread compound consists of (ref: API Bull. 5A2):

• grease;
• lead powder;
• zinc dust;
• copper flakes;
• powdered graphite.

However, thread compounds can contain a whole range of other chemicals which are harmful to the environment, like Arsenic, Antimony and Molybdenum disulphide.

Concern over the escape of these into the environment led to a second generation of compounds without lead. However, although several additives seal nearly as well as lead, they tend to create their own environmental problems.

Teflon based compounds should be avoided on metal-to-metal seals and joints with teflon rings as the hard deposits of teflon may adhere to the seals affecting the sealing performance.

Additionally, the use of biodegradable grease bases has been researched, however in general this type of grease is not stable at high temperatures, and therefore not applicable in deep wells.

Example of hybrid compounds:

• Mercasol 633SR Multimake White;
• Kendex Enviro Seal;
• Bestolife copperfree PTC;
• Shell Française SF 3646;
• Bestolife 2000 5% copper.

5.4 Dope applicators

Portable equipment can apply lubricant to the box thread of pipe ranging from 2 3/8in (0.0603 m) to 20 in (0.5080 m) OD. As well as saving time, such a method offers the following additional advantages:

• accurate control of the volume applied and thus reduction of downhole contamination by internal extrusion;
• uniformity of application (i.e. not operator dependent);
• improve the quality (and quantity) of its application
• can be used while the tubing is still on the pipe rack
• lubricant temperature can be controlled for colder climates, making it easier to apply;
• filtering mechanisms ensure lubricant consistency and cleanliness.

5.5 Thread running compounds

A storage compound is not to be used as running compound, and vice versa. The amount of compound to be applied is a function of connection sealing mechanism and geometry. The actual quantity should be acquired from the connection manufacturer. To much dope may end up in perforations and cause permanent near wellbore formation damage.

Typical running compounds, other than Hybrid compounds for threaded connections which conform to API Bull. 5A2, are listed below;

• Calcium hydroxy stearate grease base;
• Aluminium stearate grease base;
• Calcium stearate grease base;

No distinction is currently made between the type of connection (premium, buttress, API round) in selecting thread running compounds.