The town of Augusta is one of WA's most picturesque towns and is a popular getaway spot for many people. Augusta has recently had a major communications upgrade along with other centres in the region, building up both the information capacity and backup routing should damage or failure occur. There were two options for the installation one being directional drilling and one for laying a cable on the river bed. The river bed option was discounted due to occasional dredging operations and continual natural repositioning of the river channel. The scope of our work was to cross the Blackwood River over 420m and install a 110mm PE conduit by directional drilling. Underground Services Australia took on this challenging project and although the geological formation was predominantly extremely hard granite there were also extremely soft materials in the drill path. Our drill path put the shot 27m below the river level and made conventional guidance systems unsuitable for the situation. The steering of the drill was carried out by using a gravitational field steering tool which is located in the head of the drill string and communication is transmitted back to the steerer by a wireline. Due to the sensitivity of the sensors and the interference to signals by steel objects two non magnetic rods had to be inserted into the drill string on either side of the steering tool.
Interpretation and steering control are assisted by a laptop computer running bore path software enabling the steerer to guide the head to its final destination. The presence of granite rock made the use of a "mud motor" essential which allows the drill to penetrate the hard material and maintain steering. The drill used to complete this shot was our Vermeer D80x100 with 80,000lb of thrust and pullback and 10,000ft.lb's of torque. Coupled with this rig was our drilling fluid mixing and reclaiming system which allows the cuttings to be processed and disposed of dry and the majority of the drilling fluids re-used.
The drilling fluids for this project were carefully selected by our drilling team in collaboration with the supplier, changing ground conditions throughout the length of the bore required constant monitoring, testing and alteration of the drilling fluid mixture. The pilot was successfully completed to a high degree of accuracy and once the steering assembly was removed the package was attached and pulled back with ease. The pipe installed was then roped and proved using a mandrel to confirm that no damage had been done or stretching had occurred in the installation process.
