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Tunnelling system makes tight turns

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An innovative CSIRO project to develop a new type of tunnelling system will receive additional personnel and funding in the new financial year.

Further development of the Microtunneller will include proofing of the various components that make up the over 1m long by 100mm diameter water-powered and electronically controlled drill.

The project has slowed recently because of several factors including the death of the CSIRO’s project director Michael Wendt midway through last year and the need to secure a number of intellectual property issues raised by the project.

Microtunneller is seen as a step change in drilling cost reduction and flexibility for applications in coal and minerals mining.

The design uses a downhole motor and propulsion system to allow tight turns of about 10m and to maintain thrust on the bit over long distances

Potentially the drill can use a range of cutting heads and be joined to surface by a flexible high-pressure hose.

From a single vertical hole, it is proposed to drill multiple horizontal holes in a direction perpendicular to the direction of lowest permeability.

In addition, without the need for drill string handling the process becomes easy to automate.

Among the roles envisaged for the Microtunneller in the coal industry for instance, are drainage holes.

The concept potentially allows faster, cheaper, longer and deeper holes to be drilled horizontally in coal seams. Alternatively, it may help improve the economics of coal seam methane production in low permeability coal seams, or in sequestration of carbon dioxide in deep unmineable seams.

In the minerals sector Microtunneller has potential to provide a highly capable deep drilling system for exploration under cover.

Drilling curved blast holes could also provide significant production advantages.

CSIRO spokesperson Andrew Beath tells Australian Mining that the system can produce more optimal drilling patterns than is possible with conventional drilling technologies and has significantly lower labour costs compared with conventional practices.

The prototype Microtunneller has a diamond cutting head attached via a shaft to a water-powered electronically controlled motor at its rear.

Two hydraulic clamps that grip the wall of the hole provide resistance to rotation and axial motion.

Clamping force for the rear clamp comes from a series of six hydraulic rams with the front set having another three rams actuated in sequence to provide the forward motion of the drill.

The thrust, propulsion and steering comes from three axial rams sat between the clamps.

Ram control, the motor control and steering is embedded within the drill with navigation and position information and condition monitoring information relayed to surface.

The primary advance of the Microtunneller is its ability to steer and navigate to produce tight radius holes of circa 10m in coal or rock.

With lower quantities of water and drilling fluids used over similar systems represents a potential environmental benefit.

The CSIRO has tested the prototype unit to date on coal, sandstone and granite.

It has included gas drainage modelling, cuttings transport modelling and geotechnical modelling of unsupported holes.

Innovative water-hydraulic systems for the drill head, clamping, motor and controls have also been developed and incorporated in the prototype.

These included an electro-hydraulic wobble plate motor that operates at high pressure on potable water, with variable torque and speed with full control from the embedded computer.

The CSIRO is also developing a novel high-performance cutting head using thermally stable diamond composite point, – attack picks, predicted to increase the rate of penetration over conventional cutting heads.

The next step in the evaluation later this year will be industry participation in mine site trials most probably in drilling horizontal holes into highwall seams of at least 100m in length.

Optimising drainage systems will also be completed using reservoir data obtained from the mines.

If these trials prove successful Microtunneller will undergo further trials of 1000m holes and surface to inseam holes in follow up projects.

More info: (07) 3327 4686

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