Geotech Drilling is involved with Anglo American’s Metallurgical Coal Division at two sites: their Grasstree mine at Middlemount and their Moranbah North mine, both in the coal-mining region of central Queensland.
The Grasstree operation began in January 2012 and is ongoing. It was the first of Geotech Drilling’s contracts with Anglo American and its success led to the securing of the Moranbah North job.
At Grasstree, Geotech Drilling has completed the wells for gas drainage from the coal seams to ensure longwall mining can be carried out safely.
These Surface to In-Seam (SIS) wells are being drilled by Rig 1, the Gallagher 400, which has a push-pull capacity of 400,000 pounds. This rig has also drilled wells up to 2,500 metres in length. Rig 1 can drill at entry angles from 10 to 90 degrees, with the angled entry allowing us to target shallower seams. At Grasstree, Rig 1 also intersects a single vertical well which is drilled prior by Geotech Drilling’s Rig 6.
Rig 6 is a Bourne 2000THD drill rig. This rig has 100,000 pounds pull-back capacity and is used specifically for the drilling of vertical wells. Rig 6 has also worked in the Coal Seam Gas sector, drilling vertical wells for the extraction of gas.
Geotech Drilling is always looking at ways of refining processes and at Grasstree an experimental horizontal goaf hole was drilled in 2012. This process was implemented to provide the mine with a method of extracting gases generated during the long-wall mining process of the mine. Traditionally these wells are drilled as vertical wells to vent these gases; however in some instances a vertical rig cannot access the area on the surface due to swamps or water courses. When this circumstance arose Geotech Drilling was able to work with our client to drill a horizontal well under the difficult ground to achieve the same objectives. This technique may well have further applications in the longwall mining process and when refined could replace the practice of multiple vertical wells.
Recently, at the Grasstree site, Geotech Drilling scored their first-ever ‘hole-in-one’ when our 2,450m lateral well intersected our 408m deep vertical well on the first pass.
This was achieved by employs Integrated Directional Services’ (IDS) Rotating Magnet Ranging Service (RMRS), which uses the rotation of a magnetic bit sub-located directly behind the drill bit to create a time-varying magnetic field that can be detected up to 70m away in a second well, in this case the vertical target well which had a receiver on a wire-line.
The RMRS kit consists of a rotating-magnet sub that contains stacks of powerful rare earth magnets that create an A/C magnetic field when rotating with the bit. This magnetic field is monitored by a sensor probe and provides a distance and direction from the probe to the drill bit. Accurate positional information can be acquired at around 70m of lateral separation, allowing for significant trajectory correction prior to intersection.
Our successful driller was Divay Kumar, who maintained great consistency of angle and speed throughout the lateral well, so much so that at the 70m mark (from intersection) we were only 1m off target. The RMRS system then homed in on the vertical target and intersected on the first pass, thus eliminating to need to perform any ‘drive bys’. This ultimately led to a saving on metres-drilled of 80-120m.
Steering for IDS was their Operations Manager, Steve Wilson. Steve has been in the directional drilling and surveying business for almost 14 years.