Down hole Reamer – Its Application in Directional Drilling

Not only are reamers important for directional drilling, but they can also be useful in straight hole applications. Reaming assemblies can straighten out and smooth over crooked holes, restore undergauge holes to gauge, and get rid of any irregularities or keyseats. They also help to prevent excessive hole curvature in short intervals, which may be experienced when entering and exiting a section of hole which forms a sharp curve. Finally, reamers can reduce the rotational torque in a wellbore, and may therefore be used as a substitute for a conventional string or near-bit stabilizer.

Reamers are made by almost all major downhole tool manufacturers, and have the same core features: sealed or open (mud lubricated) bearings, cutter types – either “nobbly” or “smooth”, and either one (so called “3-point”) or two (“6-point”) sets of cutters in a tool.

Reamer (Courtesy of NOV, 2017)

Reamer (Courtesy of NOV, 2017)

To regulate standards for roller reamer tools, BP created a set of rules that they should all adhere to. These are:

  1. Compression split lock pins and not screw-threaded bolts must primarily secure the bearing blocks. Any secondary bolts need to include anti-back-off implementations and preparation procedures. Other primary securing systems which don’t have parts that can come loose and fail due to vibrations from drilling may also be used- an example of this would be taper lock wedges.
  2. Any parts in the tool body, such as rollers, blocks, or shaft assemblies, must not be able to fall out if the primary securing system should fail. This necessitates specific geometry of bearing blocks, such as dove tailing or wedging.
  3. Bearing blocks must be flush with the tool body. Furthermore, they must be reinforced with tungsten carbide inserts, on both the bottom edge and outer face.
  4. The downhole leading edge shoulders of the roller reamer should be reinforced with hard facing and/or tungsten carbide inserts.
  5. There needs to be enough clearance between the roller and tool body cavity to allow for a significant amount of bearing wear without the roller coming into contact with the back of the cavity. The tools need to be full gauge, preferably on the generous side rather than slightly under-gauge. Gauge adjustability is not a requirement (the necessity for redressing is always because the bearings wear out well before the cutters wear down).
  6. It is necessary to use wear-resistant bearings, with the target being bearings that can rotate at 200rpm and accumulate a maximum of 1 million revolutions.
  7. Both near-bit roller reamers and a string must be used. The near-bit tools also need to be bored in order to accommodate float valves. A minimum ID is also needed to provide adequate access for surveying instruments, circulating sub and core barrel drop balls- these will depend on the individual requirements of the drilling operation.
  8. Tools need to be able to be fixed quickly and easily, with a minimum of manpower and equipment.
  9. It is necessary to work with a Q.A.-approved supplier, so that any rental tools and redress kits can be obtained at short notice in the necessary amount.


Inglis, T.A. (2010) Directional drilling. Dordrecht: Springer-Verlag New York.

Mitchell, R.F., Miska, S.Z. and Aadnoy, B.S. (2012) Fundamentals of drilling engineering. Richardson, TX: Society of Petroleum Engineers. (2018). National Oilwell Varco. [online] Available at: [Accessed 17 Jan. 2018].

Schlumberger Limited (2017) Schlumberger Drilling Services. Available at: (Accessed: 25 February 2017).

Short, J.J.A. (1993) Introduction to directional and horizontal drilling. Tulsa, OK: PennWell Books.

Technical, T., Astier, B., Baron, G., Boe, J.-C., Peuvedic, J.L.P. and French Oil & Gas Industry Association (1990) Directional drilling and deviation control technology. Paris: Editions

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