Running and Testing Casing

casing_running2To ensure that the casing is run efficiently to the correct depth and in the desired condition, specific equipment and techniques should be considered in the design phase.

1 Rig hoisting capacity

The casing designer should be aware of the hoist capacity of the rig which is to drill the well. Where deep, heavy strings are required, it may be necessary to set a liner and tie-back instead of a complete string. Alternatively, the drilling sequence may be rearranged to allow the use of a larger rig for a particular well. Floating devices, different from the float shoe/collar, could be considered. However, thorough evaluation of these tools and their applications is required in the design phase.

2 Handling

Handling of casing between pipe deck and drillfloor should be carried out in accordance with Safety Handling Procedures.

Particular care should be taken when handling casing hangers and housings with pup joints above and below, that the lifting point is above the centre of gravity. This ensures that the load is stable when lifted.

Some service companies have developed in-house tubular handling and running manuals.

3 Safety clamp

The traditional type of safety clamp, mainly used when running extreme line casing, requires manual tightening of a torque nut - invariably using a sledge hammer. This technique inevitably leads to variations in the amount of "set" taken by the clamp and can be time consuming.

The Clamp Master from Bros Services uses a hydraulic piston instead of the torque nut which ensures that the clamp is always tightened to the same degree. It is also quicker, safer (since no hammering is required), requires fewer personnel and reduces the risk of dropping tools downhole.

4 Casing hand slips and casing spider

Poorly fitting slips or bushings could cause severe damage to the casing which may not be noticed while running. Make sure this is thoroughly checked at the early stages of the job.

Before use check whether:

  • the size of the slip assembly matches the casing OD;
  • there are sufficient segments to grip the casing all around;
  • all dies are present;
  • all segments are in full contact with the casing.

5 Single joint weight compensator

Positioning of the pin in the box during make-up is critical. If no weight is transferred to the box, make-up cannot take place. If too much weight is transferred, stabbing and alignment becomes difficult and galling may occur due to high contact loads. It is extremely difficult for the driller to achieve accurate weight transfer with the standard rig hoisting system. The same problems also apply to connection break-out.

Although the susceptibility of connections to stabbing damage and galling can be minimised in the connection design process, controlled and accurate weight transfer is the key to successful make-up.

By the installation of a compensating device between the rig's travelling block and the single joint elevator, the weight of the pipe is neutralised and controlled downward penetration of the pipe is possible during make-up.

This is highly recommended for both make-up and break-out of premium connections and/or corrosion resistant alloy (CRA) tubulars.

Casing service companies can supply single joint compensators in different weight ranges to cover all casing sizes.

6 Multi-size rig tongs

Automatic rig tongs are now available which can make up and break out drill pipe, drill collars, casing and tubing in one machine. The size range is 23/8 in (0.0603 m) to 21 in (0.5334 m), and torques of up to 140,000 ft.lbs (189,805 Nm) are possible. Associated computer equipment monitors and records each make-up.

One example is the Weatherford Torque Wrenching Machine.

7 Non-marking jaws

In corrosive operating environments where defects or stress concentrations in the casing may have catastrophic consequences, the use of non-marking jaws should be considered, not only on the rig floor (tongs, slips, elevators) but also in the threading plant.

Such jaws, based on elastomers, are available from Weatherford in sizes up to 7 in (0.1778 m) casing.

Frank's International and Weatherford can supply power tongs which grip the entire circumference of the pipe by means of fluid pressure applied to a non-metallic gripping surface. As a result, the tubular surface is not penetrated, and stress concentrations are avoided.

Low stress tong dies are available from, amongst others, Cousino (USA).

8 Connection make-up torque

Reference should be made to connection qualification tests for selection of optimum make-up torque to allow for adequate sealing capability. This torque is often significantly different from those quoted by manufacturers. It should also be noted that make-up torque will vary with different thread compounds and may also vary for different manufacturing batches of the same compound (see connections).

The correct make-up of any threaded connection cannot, however, be judged on torque alone. Correct make-up torque can be reached under a variety of unacceptable circumstances such as crossed, dirty, or galled threads. Surface finish variations may also influence the required torque. It is important that adequate pin penetration into the box is achieved to assure design stress levels are achieved in the connection. As a result, torque-turn data are published by the connection manufacturers and can be compared with that measured in the field using portable equipment (e.g. Weatherford JAM system). These data are usually based on the use of an API 5A2 formulated compound. The use of a thread compound other than this requires the use of a correction factor to accommodate the differences in friction coefficient. Critical on-site analysis of torque-turn graphs is, at present, seen as the best practical means of identifying potentially leaking connections before they are run into the hole.

Even with premium seal connections incorporating a torque shoulder, in which final torque is a reasonable indicator of adequate seal pressure, torque-turn measuring equipment is recommended because of the accuracy of the torque gauge.

Soft-torque tongs (from Camco/Bilco or Frank's International) and/or Weatherford's A-Q-Tork system are recommended to prevent overtorque due to the inertia of the rotating pipe/tong mass.

9 Connection leak testing

Field leak detection equipment is mainly used while running tubing, although it would also be highly applicable to production casing in gaslift wells. Evidence to date concludes that gas-based leak detection tools, which use a spectrometer to detect the leak, work better than the hydrostatic pressure leak detection tools.

Examples of such gas-based tools are the HOLD and Supra HOLD, both manufactured by Weatherford.

The HOLD system works with a gas mixture of 99% Nitrogen and 1% Helium. It requires a considerable amount of gas and strict safety measures. The SUPRA HOLD uses a small volume of pure Helium gas. Water is used to pre-pressure up the system, after which Helium is used to attain the required test pressure. The advantage of the SUPRA over the older HOLD system is that as less gas required, it is safer and more sensitive. A pressure test can be performed on the connection from both sides, i.e. from the inside to the outside, or from the outside to the inside.

Field leak detection equipment may not be capable of detecting all leaking connections within a reasonable period of time, since it may take a considerable amount of time for the gas to percolate through the running compound trapped between the threads. The response time can be improved by limiting the quantity of thread compound applied to the connections but this increases the risk of galling and may result in high shouldering torques.

The use of ultrasonic measurements of contact stresses to assess the sealing integrity of connections in the field is being investigated. A field trial on a prototype tool was successful, although further work is necessary. The tool was developed to be able to check Finite Element Analysis stress predictions.

It is based on the fact that the amplitude of an ultrasonic beam reflected from an interface is dependent on the contact pressure at that interface.

10 Polymeric seals

Connections that incorporate polymeric seals will require a high degree of on-site supervision of the installation procedures to ensure that the seal is present, clean and undamaged.

11 Mill-end leakages

The major cause of mill-end leakage appears to be improper make up at the mill as indicated by the movement of the mill-end during field connection make-up. This can be detected by observing a scribe line marked across the coupling/pipe body interface. The movement causes an unfavourable redistribution of the thread compound solids which were originally plated on the threads when the mill installed the couplings. Field tests indicate that floating on the coupling, with make-up occurring simultaneously at both ends of the coupling, eliminates the tendency for leakage to occur on the mill-end, provided fresh thread compound is used. This, however, necessitates the use of slip-type elevators and safety clamps rather than collar elevators when lowering the string for the next connection.

API Specification 5CT recognises the leakage problem encountered with mill-installed couplings, and states that cleaning and inspecting threads and applying fresh thread compound before using the pipe results in less chance of thread leakage. These standards make provision for ordering API tubular goods with couplings screwed on hand tight or shipped separately from the pipe. However, it is recommended that casing be ordered with mill-installed couplings; but if any movement of the coupling is observed during field make-up, the connection should be backed out, cleaned, re-doped and re-made.

12 Casing running speeds

Use should be made of swab/surge calculations to determine the maximum allowable running/pulling speeds. Note that swab and surge pressures are exerted upon the formation irrespective of the location of the casing being run relative to the previous shoe. This means that care should be taken even when still inside cased hole.

Since shock load calculations used in designing the string are based on typical running speeds, it may be necessary to run casing slowly to reduce these potential loads.

13 Drifting casing while running

Although not always recommended, when making up connections to torque values significantly greater than the manufacturers recommended figures, a check should be made for reduction of internal diameter at the connections. This can be achieved by vertically drifting the casing after (for example) every ten connections.

Since the API casing drift is short 6-12 in (0.1524-0.3048 m), relative to some downhole tools, it can be useful to construct a long dummy tool, 42 in (1.0668 m), in aluminium for drifting purposes.

14 Circulating devices

For rigs with top drive, the TAM or La Fleur casing circulating packers allow casing to be circulated through tight sections of open hole without the use of a circulating head. It is made up to the top drive via a drill pipe pup joint. As each casing joint is made up, the packer is stabbed into the top of the joint as the elevators are lowered. This casing is filled through the uninflated packer as the joint is lowered. At tight sections the packer is inflated to seal to internal diameter of the casing and circulation can then be established. The packer can later be returned to filling mode if desired.

For rigs without top drive, a Kwik Koupler circulating head is available from Baker Oil Tools which uses a seal pack-off unit to seal over the casing collar. (Similar equipment is available from other companies such as Halliburton and Dowell Schlumberger). This simplifies installation compared to threaded connection circulating heads and minimises stoppage time. This tool can also be used as a cement head. It is available in sizes ranging from 23/8 in (0.0603 m) to 133/8 in (0.3397 m).

15 One-way strings

Use should be made of torque and drag software to predict drag forces while running in or pulling back a casing string. In some instances, the load required to pull back the casing, once it reaches a certain depth, will exceed the tensile capacity of the casing at surface. Such a string is known as a "one-way" string.

Drag forces can be minimised by optimising the wellpath design. This will generally be achieved by use of the lowest possible dogleg severity in build and drop sections. Drilling equipment and practices should be implemented so as to accurately follow the desired wellpath and to eliminate severe localised doglegs.

16 Pressure testing

Pressure testing of a cemented casing string (either immediately after installation or during a workover) will be limited by a number of factors, namely:

  • the pressure rating of exposed cementing accessories;
  • the minimum burst rating of the casing (taking into account any suspected wall thickness reduction due to wear or corrosion);
  • the tensile load that results from the pressure test;
  • the possibility of damaging the cement bond during pressure testing as the casing expands radially;
  • the pressure rating of the surface equipment.

Pressure tests for combination strings, where the burst rating and tensile rating vary along the string, need to be carefully planned and usually require a retrievable packer to be used to isolate the weaker sections. Also damage to the cement sheath can be avoided by application of such tools.

17 Perforating

A significant part of the explosive energy of a shape charge is absorbed by the production casing. As a result damage may occur in the form of deformation and cracks or splits in the casing. Several authors have investigated casing damage caused by jet perforating, and their main findings and recommendations are summarised:

  • Hollow carrier steel shaped charges cause little casing deformation and no significant damage.
  • Large expendable guns of charge loads >20 gram are likely to cause damage if the casing is in poor condition and/or unsupported.
  • All types of shape charge guns can be used in well cemented casing with minimal damage.

In cases where it is suspected that the condition of the production casing is poor or the casing is unsupported, it is recommended to (re)perforate using hollow carrier guns.

 

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