Ditch Magnets

The metal worn away from the casing and tooljoint is carried by the mud to the shaker header box where it will be attracted to the ditch magnet. Not all the metal particles will be trapped and so the amount of metal cannot be used as an exact quantitative measurement of metal worn away.

Any metal removed by corrosion will not be collected by the magnet.

Regular recording of the weight of metal recovered should show changes in wear rate. There is no way of telling if the wear is from the whole string or aggressively from a small length. It should be borne in mind that the volume recovered by the ditch magnet may only be a fraction of the metal generated.

Mud loggers should include any metal in the cuttings description log and an estimate of the amount of metal generated.

Surface Torque

As the wear groove deepens, the contact area between the tooljoint and casing changes. This will tend to increase the friction between the two surfaces. This results in increased surface torque.

It is accepted that this is difficult to detect since surface torque fluctuates for a variety of reasons. If the surface torque and drag is seen to increase above the normal expected values, casing wear should be considered as a possible cause.

Polished Tooljoints

Shinyhardbandingand polished tooljoints indicate that the hardbanding is worn away and the tooljoints are taking load. Both the drillpipe tooljoint and the casing will wear away at different rates.

The tooljoint will become polished as the OD reduces and should be regularly calipered to ensure the OD does not drop below API tolerances.

During trips, the Drilling Contractor should make regular visual inspections for polishing and uneven wear as rapid changes could indicate casing wear.

Damaged DP Protectors

Drillpipe protectors run best on a smooth polished surface. A casing wear groove may form a distinct break in the internal casing surface. The protector will be forced to run in a wear groove formed by a smaller tooljoint. This may cause uneven loading and will tend to tear the protector surface.

Staggering the protectors will prevent the initial wear and the protectors will run smoothly on the inside of the casing.

During trips, the drillpipe protectors should be checked for damage.

Logging Tools

Nominal Remaining Thickness

Since all casing wear inspection logs can be affected by centralisation and calibration issues, nominal remaining thickness should be established by the difference between the maximum and minimum diameter indications.

Casing Wear in Directional Wells

Casing wear measurement in directional wells should be oriented on the high side in the upper section of the hole, then transitioning to the low-side orientation near the end of the build and throughout the long tangent section and horizontal sections.

Casing Wear Measuring Tools

Varioustools are available to measure casing wear. They are divided into mechanical and electrical tools.

The following measurement tools are available:

• multi-finger calliper tool
• acoustic calliper tool
• electromagnetic tools
• down hole video camera.