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.
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.
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.
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.
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.
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Successful premiere of the Downhole Jet Pump in Sweden:
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Successful premiere of the Full Face Hole opener in Sweden:
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