Underground » Ventilation, Gas Drainage and Monitoring
This report describes the development, design and surface testing of a device designed to maintain pressure in a borehole during all phases of drilling. This borehole pressurisation device is designed to fit directly between the standpipe and the drill.
The purposes of maintaining fluid pressure in the borehole are to:
- provide support for the borehole wall against collapse
- provide improved operator safety
- permit the use of geophysical probes which need a water filled annulus for their operation permit the taking of un-degassed chip samples.
The borehole pressurisation device has been tested successfully in a surface trial involving high pressure waterjet drilling through concrete. The device operated for several hours of flow time much of which involved the passage of cuttings.
The main focus of the trial was on the performance of the regulator which had to regulate cuttings and water flow to a preset pressure and in addition had to shut down completely below that pressure. How the abrasive nature of the cuttings affected the life of the regulator was the main concern.
The tool had through flow for several hours a fair proportion of which was spent drilling. The regulator was shut down for several days under conditions of no flow. The only malfunction of the device was caused by blockage when water jet drilling produced large particles of greater than 10 mm diameter. The regulator element itself showed slight scoring but negligible wear.