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Concave Reamer Blades

IP.com Disclosure Number: IPCOM000249100D
Publication Date: 2017-Feb-06
Document File: 6 page(s) / 828K

Publishing Venue

The IP.com Prior Art Database

Abstract

State of the art reamer blades for downhole tools feature a straight or convex drilling structure. This invention features a concave reamer blade design. The advantages of the new design will be: less torque generated, less risks of back-offs, less lateral and torsional vibrations, higher weight on reamer (WOR) capability. Furthermore Depth of cut (DOC) control measures can be applied with this new design, leading to an optimal aggressiveness of the blades, resulting in less stick slip.

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Concave Reamer Blades

Abstract:

State of the art reamer blades for downhole tools feature a straight or convex drilling structure. This invention features a concave reamer blade design. The advantages of the new design will be: less torque generated, less risks of back-offs, less lateral and torsional vibrations, higher weight on reamer (WOR) capability. Furthermore Depth of cut (DOC) control measures can be applied with this new design, leading to an optimal aggressiveness of the blades, resulting in less stick slip.

Goal of this proposal is to overthink the actual reamer blade design and aiming for a design which induces less vibrations and increases drilling stability. Therefore a new design for reamer blades is proposed as a foundation for this progress.

Description:

With reamers, there are two cutting structures in the drillstring – reamer and bit. Both will induce drilling dynamics into the drillstring. That’s why it is important to match those two drilling structures together. But this is difficult.

State of the art bits have a lot of flat angle cutters and just a few gauge cutters (outer most cutters). The reason for this is that the flat angle cutters are able to take a lot of weight, while the gauge cutters induce a lot of torque into the drillstring. Studies showed that “[…] long profile/cone shaped bits are more prone to stick-slip” (Jain, et al., 2011).

State of the Art reamers have long blades with a lot of gauge cutters. The reason behind this shape is, that the outer most part of a bit was taken, scaled up to the desired size and loaded with cutters. These cutters, mostly all of them, are placed on the gauge, which results in high torque values during reaming. The blades are shown on the left side of the following Figure 1, the bit that was reviewed in (Jain, et al., 2011) on the right. The shape of the blades of the unfavorable bit is looking nearly identical to the state of the art reamer blades.

Figure 1: left: State of the Art Reamer Blade; right: prone to stick-slip bit (Jain, et al., 2011)

The past showed that there were some incidents where high torque values on the reamer resulted in a stick slip of the reamer, while the pilot BHA (BHA below the reamer) was spinning freely. The bit outdrilled the reamer. Ultimately this lead to a back off of the drillstring below the reamer because of its rotational inertia.

Too aggressive drilling structures are also more prone to stick slip than less aggressive ones (Jain, et al., 2011). Knowing this, reamer blades should be designed to be less prone to stick slip due to the below hanging pilot BHA that can otherwise be backed off.

Furthermore new measurements showed that reamers induce high lateral vibrations into a drillstring. The result during reaming looked like shown in Figure 2 (vertical axis unit: [g]). Reducing those vibrations that are mainly a result from the drilling structure would be beneficial for the whole reaming-service.

Figure 2:  measurements during rea...