Preparation for Running Casing

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Preparation of casing before running serves two purposes. 1. ensure that the pipe body and threads are adequately protected from possible damage when being moved to the drill floor. 2. ensure that handling of the casing on the drill floor is kept to a minimum.

These goals can be achieved by use of the following equipment and procedures:

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 casing accessories such as float collars which are time consuming to install at the rotary table.

3 Cleaning of threads

Prior to inspection of the casing 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. Furthermore working with diesel can be detrimental to health by contact and inhalation of the fumes. Also, diesel should be disposed of in a controlled environmentally friendly way.

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

4 Inspection

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

While the casing is being run, an inspection party could be considered to check that the casing 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, often a third party.

5 Dope applicators

To eliminate the need to manually apply thread running/sealing compound (dope) at the drillfloor and to improve the quality (and quantity) of its application, automatic dope applicators can be used while the casing is still on the pipe rack.

Portable equipment, such as Weatherford's Accukote Applicator, can be used to apply lubricant to the box thread of pipe ranging from 23/8 in (0.0603 m) to 20 in (0.5080 m) O.D. 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);

·lubricant temperature can be controlled for colder climates, making it easier to apply;

·filtering mechanisms ensure lubricant consistency and cleanliness.

6 Thread running compounds

The recommended running compounds to be applied to the threaded connections are listed below. All conform to API Bull. 5A2 Section 1.3.2.2.

  • Calcium hydroxy stearate grease base
  • Aluminium stearate grease base
  • Calcium stearate grease base
  • Thread Kote No. 706

It should be noted that a running compound is not to be used as a storage compound and that a storage compound is not to be used as a running compound.

Hybrid compounds - which can be used for both storage and running - do exist.

The recommended Hybrid compounds are:

  • Kendex Enviro Seal
  • Mercasol 633 SR Multimake White
  • Cats Paw black 712 S
  • Bestolife copperfree PTC
  • Bestolife 2000 5% copper
  • Shell Française SF 3646

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

Most running compounds contain chemicals that are harmful to the environment such as lead, copper, zinc, arsenic, antimony and molybdenum disulphide. The Drilling Engineering Association (Europe) has carried out research into metal-free compounds, which can be used for both storage and running.

7 Thread protectors for handling casing

The basic function of a thread protector is to protect threads and seals against impact loading and corrosion.

Thread protectors can be divided into two types:

7.1 Threaded or transit protector

This type of protector, for both pin and box, can be used from the mill up to the moment the joint is laid down on the pipe rack, where it is taken off to allow removal of the storage compound. Most of these heavy-duty type of connectors are composed of a moulded polymer body reinforced with a cylindrical steel insert. However they can also consist of 100% polymers.

In general, the installation procedures for these protectors, as stated by the manufacturers, are poorly defined. A clear description is of particular importance since proper functioning of a protector is closely allied to the way it is fitted on the pipe end. Figures for the required installation torque, are available from some manufacturers, whilst from others no figures are available but simply definitions like:

"handtight followed by a sudden tightening with a steel bar".

Note that transit protectors are guaranteed to protect only individual lengths during movement. Protection is not guaranteed, when joints are bundled together, since the applied impact load experienced by the protector on a single protruding joint will be considerably greater.

7.2 Handling or non-threaded protector

The non-threaded protector, also called handling protector, is installed on the pin prior to lifting the joint up to the drillfloor. In most cases it is either a clamp-on type or an inflatable type.

Clamp-on style protectors designed for API connections can cause seal area damage when used for premium connections. The operating mechanism can contribute to seal area damage if the protector is incorrectly installed.

A recommended alternative protector which has been field proven is the Klepo Inflatable Thread protector. This protector, available in sizes from 23/8 in (0.0603 m) to 30 in (0.7620 m) pipe, is a solid circular ring manufactured from polyurethane. It is inflated using rig air supply once it has been installed over the pin end threads. The protector then provides a uniform 360 degrees grip and is independent of thread type. Once the joint is ready for stabbing, the protector is deflated and removed.

8 Centralisers

All centralisers must be qualified by test for the application in question.

Centralisers should be installed while the casing is on the pipe rack whenever possible.

A development by Weatherford in the area of casing centralisation are centralisers which can be activated once they are downhole. This can be achieved either by pressure, temperature or chemical activation. These centralisers will reduce drag forces while the casing is being run, will pass through casing spiders, will prevent damage to wellheads, but will still provide centralisation of the casing during cementing.

9 Float equipment

Float equipment should always be qualified by test prior to use.

For situations where tubulars can be run without a BOP, automatic-fill float equipment may be used. This equipment is available in casing sizes from 41/2 in to 20 in and allows the casing to be filled from below while being run. Conversion from the "open" configuration to conventional mode is achieved (depending on the type) either by dropping a ball or by circulating at a predetermined rate.

10 Magnetised casing joints

Magnetised joints of casing, placed at the shoe, have been identified as increasing the range of passive homing-in tools used in relief well drilling. For casing ODs from 41/2 in (0.1143 m) to 133/8 in (0.3397 m) detection ranges between 75 and 140 ft (23 to 42 m) can be obtained with regular electronic magnetic surveying tools. Especially for slimhole projects artificial magnetisation is required to keep the option of magnetostatic homing-in.

The magnetising procedure can be carried out by preparing the casing in a shop or on site before it is run. Tuboscope offer these services.

Tests have shown that the accuracy of neither logging tools nor surveying tools is adversely affected by running through one or two magnetised casing joints. However, the azimuth accuracy of some gyro tools may be affected when they perform their initial North-alignment downhole in close proximity of these joints. An along-hole distance of ±130 ft (±40 m) to the nearest pole is regarded a safe spacing.

 

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