Downhole Tools

Game Changer in Horizontal Directional Drilling

Herrenknecht is an innovation driver in mechanized solutions for the construction of underground infrastructures. Together with leading industry specialists we have developed three innovative downhole tools for the fast, safe and cost-effective installation of pipelines with the HDD method (horizontal directional drilling): the Full Face Hole Opener, the Downhole Jet Pump and the Weeper Sub.


Optimizing HDD drilling processes

Used individually or in combination, the three patented new developments optimize the drilling process in HDD projects. Thus, for example, boreholes can be reamed and cleaned in one pass, while at the same time preventing unwanted drilling fluid leaks (frac-outs). With the innovation Herrenknecht is responding to long known challenges in the HDD business. The results of successful pilot projects have already confirmed the concept and the performance of the new downhole tools.

  • Innovative downhole tools to optimize the HDD process
  • Material flow optimization with Weeper Subs
  • Reaming of the pilot hole by the Full Face Hole Opener in a single pass
  • Efficient borehole cleaning with the Downhole Jet Pump
  • Tools can be used individually or in combination
  • Optimized cost-effectiveness of drilling with the HDD process
  • Lower risk of frac-outs
  • No multi-step reaming required
  • Drillings removal directly through the drill string

Weeper Sub: pilot drilling with optimized material flow

Weeper Subs significantly improve material flow when drilling HDD pilot holes. A nozzle removes part of the drilling fluid from the drill string and actively directs it into the flushing cycle in the annulus. This optimizes the material flow in the annulus and facilitates the removal of the sedimented drillings. The process is supported by the eccentric screw shape of the Weeper Sub. A clean pilot borehole without major deposits is the result.

Using multiple Weeper Subs gradually increases the volume flow in the borehole. The required amount of flushing fluid, on the other hand, decreases in the direction of the drill bit. This reduces the pressure level in the annulus and, in particular, the maximum pressure on the drill bit. The more balanced pressure level in the flushing cycle reduces the risk of frac-outs typical of the process.

  • Pilot hole diameter: 8 1/2” - 9 7/8” - 12 1/4“
  • Flexible jet volume: 20 – 105 gpm (75 - 400 l/min)
  • Reduced pressure level in the annulus reduces the risk of frac-outs
  • Axially arranged nozzles optimize the material flow and do not cut into the borehole wall
  • Various nozzle configurations available
  • Calculation tool for downhole pressure level available

Full Face Hole Opener: reaming in a single pass

Herrenknecht's new Full Face Hole Opener reams pilot holes to the required final diameter in a single pass. Multiple reaming passes typical of the HDD process are thus obsolete.

The Full Face Hole Opener can be equipped with different types of cutters depending on the requirements of the ground conditions. They are easy to change and budget-friendly to refurbish. The cutters have special wear protection and are equipped with pressure compensators. This prevents an unwanted intrusion of drilling fluid or the loss of bearing lubrication. In addition, the bearings are extra large and can absorb forces twice as high compared to conventional cutters. This means a higher pressure can be applied to the toolface to improve the excavation of material and thus the speed of the advance.

  • Excavation diameter: 30”–72”
  • Minimum pilot hole diameter: 12 ¼“
  • Application: soft to hard rock (up to 350 MPa)
  • Reaming of pilot holes in a single pass
  • Low required torque and smooth rotation through automatic toolface centering
  • Interior non-stick coating prevents "bit balling" (clogging) in cohesive soils
  • Front centering and wear protection plates can be replaced on site
  • Sprinkler system for larger drillings, higher ROP (rate of penetration) and less wear
  • Toolface scraper for optimal cleaning and material transport
  • Flexible use in soft and hard rock due to different types of cutters
  • Modular design for quick and economical cutter change
  • Multiple reference projects successfully completed

Downhole Jet Pump: borehole cleaning and material transport in one go

Herrenknecht's Downhole Jet Pump is the first HDD tool on the market that simultaneously cleans the borehole and efficiently removes the drillings inside the drill string.

To take up the material from the borehole, the Downhole Jet Pump has three laterally placed vanes with an integrated grid. The rod rotation moves the drillings to the inside of the pump. There, with the help of a jet pump system they are pumped into the drill string and transported away. Due to this major reduction in the cross section of the transport pipe, even larger drillings can be economically removed with simple drilling fluids without special additives. The drilling fluid's only function in the annulus remains the support and sealing of the borehole. The Downhole Jet Pump works without suction, which creates neither underpressure nor overpressure and reduces the risk of accidental drilling fluid leaks.

  • Borehole diameter: 20”–72”
  • Drive volume: 475 gpm (1800 l/min) at 65 bar
  • Cleans the borehole up to 98%
  • Removal of the drillings directly in the drill string
  • Significant reduction of the required bentonite and other additives
  • Frac-out risk is reduced to a minimum
  • Can be used autonomously or in combination with the Full Face Hole Opener
  • Can be used in stable soil even in dry, unfilled boreholes

Performance optimization through optimal tool combinations

For HDD projects, various combinations of Herrenknecht's newly developed downhole tools are possible. The advantages of the Full Face Hole Opener are especially apparent when it is used together with the Down Hole Jet Pump. For this, the Downhole Jet Pump is installed directly behind the Full Face Hole Opener. Thus a clean borehole can be created quickly in a single pass with reduced consumption of bentonite.


Successful premiere of the Downhole Jet Pump in Sweden:
Read the article on LinkedIn

Successful premiere of the Full Face Hole opener in Sweden:
Read the article on LinkedIn


Technical article of the Full Face Hole Opener

Downhole Tools – Reaming Diameter Table

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Steffen Dubé President and General Manager Herrenknecht Tunnelling Systems USA Inc.
Gerhard Goisser Commercial Manager Herrenknecht Tunnelling Systems USA, Inc.

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Steffen Dubé President and General Manager Herrenknecht Tunnelling Systems USA Inc.
Gerhard Goisser Commercial Manager Herrenknecht Tunnelling Systems USA, Inc.