The Development of a Borehole Tool for Investigating Otherwise Inaccessible Areas in Underground Coalmines

This report deals with the fourth and final phase of a project.  The overall objective was to develop an investigation tool for use in sealed or inaccessible areas of underground coal mines.  The device would gather gas concentration data and visual information.  This would aid in the rapid identification and treatment of heatings and other incidents. The device may have application to other issues such as subsidence monitoring or shaft inspections.

The initial phase of the project evaluated the feasibility of developing such a device.  Included in this feasibility study was the clarification of the need for such a device, what these needs were and what the practical limitations were.  The next phase was the construction of a prototype device to demonstrate the practicality of full system development.  This focused on developing the basic cabling and deployment system, to be deployed via the borehole.  Non Intrinsically Safe (IS) video cameras were utilised in this phase to evaluate the value of vision to the probe.  The next phase, project C14017, sought to develop this tool further by refining the optical systems to improve underground visibility, include the ability to measure the underground atmospheric pressure, air velocity and develop an active inert shield to render the device effectively flameproof.  In addition the probe head was reduced in size in order so it could be deployed via a 100 mm borehole.  The smaller borehole diameter requirement offers significant savings in time and money for drilling the boreholes.

C14017 did achieve the majority of its objectives. The basic system was extensively successfully trialled at Newstan Colliery over a five week period accessing a total of fourteen boreholes.  The probe then underwent two revisions and these were successfully trialled at Newstan and two other locations in NSW.  In these latter instances the camera system was used to evaluate subsidence effects of underground coal mines.   Areas of mine roadway were clearly observed over 50 m away.  Gas samples were taken and temperatures and pressures monitored at these locations.  The vision enabled Newstan to quantify the state of seals around an old longwall goaf as well as identify a number of areas of roof fall.  In addition during the application of fly ash the camera was able to assess the quality of the sealing the flyash achieved.  The probe had a separate down-hole camera capability which has proven very useful for inspecting the walls of the unlined boreholes for cracks and effects of subsidence.

C14017 did not achieve all its project aims, due to a combination of technical difficulties and the associated time and cost increases incurred in overcoming them. In particular the complexity in building a probe capable of being deployed down a 100 mm diameter uncased borehole was underestimated.  Uncased boreholes often became much narrower due to swelling of the materials lining the borehole and some blocked completely.  As the borehole is usually uncased, material became attached to the probe and can cover the camera or lights.  In addition, the probe cable became damaged due to difficulties traversing these reduced diameter boreholes and had to be shortened to 380 m to remove the damaged sections.  The probe assembly was damaged on several occasions in attempting to traverse narrow boreholes.    Some elements of the probe, such as the rotation mechanism, proved to be less robust than desired.  

The current project was initiated to overcome these issues.  A commercial sewer pipe inspection system was modified for deployment down boreholes.  The system was developed to specifically address the issues outlined above.  It is portable - it was despatched by air charter to Moranbah in less than 8 hours from time of call.  It has 1000 m of cable, utilizes fibre optic technology for ease of application and high quality still and video signals.  It has onboard data acquisition systems that allow for continual monitoring of atmospheric pressure, temperature, surface temperature, air velocity and oxygen concentration.  Because it was based upon a commercial system the data and image handling systems were much more sophisticated and robust.  It was demonstrated at several coal mines and at the Newcastle Mines Rescue Station.  The system is also fitted with a microphone and speaker to enable communication with the base of the borehole.  It was displayed at the Longwall conference in the Hunter Valley in October 2008 and received much attention.

The principal researchers on this project were Associate Professor David Cliff, who has over ten years experience in dealing with mine environments and spontaneous combustion in particular and Mr John Lakeland, who has over twenty years experience in developing borehole equipment, including camera systems for inspecting boreholes.

An e-newsletter has also been published for this project, highlighting its significance for the industry.