Published in June 2006 Australian Longwall Magazine
Imagine a material that is up to 10 times stronger than your average steel, is lightweight and flexible, and most importantly is non-magnetic, non-conductive and non-corrosive. Now imagine the potential of that material being used in a drill rod – the improved sensing capabilities alone have the ability to enhance geophysical information and improve gas drainage.
All this is exactly what CSIRO research scientist Philip Teakle imagined when he was working with fibre composites and saw the huge potential for the underground coal mining and exploration sectors.
These thoughts led Teakle to an ACARP proposal this year, which will aim to develop a field-tested fibre composite drill rod that enables electronic logging while drilling (LWD) and measurement while drilling (MWD) in coal seams.
The metallic rods currently used to house sensors for drilling in coal seams interfere with electrical, magnetic, electromagnetic and gamma ray measurements of the material surrounding the borehole. The metals are also brittle or weak, difficult to machine and may be toxic, for example beryllium copper.
However, drill rods made from a fibre composite can offer improved sensing while drilling and have the potential to improve directional accuracy dramatically and provide geophysical information that is not presently available while drilling. This reduces non-productive time and improving gas drainage, according to Teakle.
Fibre composite is made from a plastic material, strengthened by glass, aramid or carbon fibres. The material is relatively transparent to radio waves, x-rays and gamma rays. It is as strong as high-strength metal alloys but is more flexible with better fatigue resistance and vibration-damping characteristics.
Electrodes, antennae, wires, sensors and other components used in downhole sensing can also be embedded in the material.
If successful, the benefits of the fibre composite are huge. It can offer a reduction of gas drainage costs and the maximisation of pre-mining gas recovery; development of advanced techniques to process and interpret geophysical data and the further development of geophysical tools. It also offers improved efficiency and effectiveness in characterising ground conditions using innovative methods of drilling and remote sensing.
Teakle said with minor modifications, the drill rods may also be adapted into specialised subs to reduce rod joint loads, absorb vibrations generated by the motor and bit, or electrically isolate drill string components.
The lightweight nature of the composite rod – estimated at half the weight of a steel rod – is also an advantage. Rods typically used in underground coal seams weigh around 23kg and are 3m long. Drillers have to handle the rods and this can be a major cause of shoulder injuries.
So what is the downside? According to Teakle, the major challenges will be wear and impact-resistant coatings or design, composite-metal joint design – increased wall thickness at the joint may be undesirable for some applications; and lower stiffness may cause problems with wear, buckling, hole directionality and vibration.
However, Teakle said these problems have apparently been successfully addressed in a US Department of Energy-funded project for fibre composite drill rods for oil and gas exploration
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Cost is also not an inhibiting factor. The new drill rods would be competing with expensive nonmagnetic drill rods, and typically only three rods would be used in a drill string.
There are cost benefits to the coal producer, with reduced coal production costs through faster and more accurate drainage holes.
“The cost of coal seam gas drainage has been estimated at 90c per tonne. If drilling costs can be halved through real-time electronic (rather than physical) sensing of the coal seam roof and floor, a reduction in the number of drainage holes through optimum placement of drainage holes within the seam and the reduced requirement for exploration drilling, savings for producers would amount to approximately $1 million per year per mine for a typical mine production rate of approximately 2 million tonnes per year,” Teakle said.
Teakle has proposed developing the rods with commercial success in mind by designing and testing prototypes with the help of drill rod manufacturer and drilling service provider Boart Longyear and downhole sensing hardware suppliers Surtron Technologies and Advanced Mining Technologies.
“If successful, composite rods could transform the drilling industry allowing the further
development of real-time logging, directional control and data collection. Significant
operational savings are probable, flowing through to production costs associated with the gas extraction process,” Boart Longyear technology manager Peter Kanck said.
“The probability of utilising natural resources that are deemed uneconomic or marginal could be possible due to the more efficient and accurate drilling that would stem from this product.”
If the project proved successful, AMT said it saw the potential for the composite rods to further other projects currently on hold.
“AMT is very interested and supports the development of non-metallic drill rods, subs or windowed metal rods to aid the completion of many research projects that are presently sitting on the shelf within CSIRO, CMTE and other research organisations,” technical director Henk Verhoef said.
“It is AMT’s belief that the sensors developed over the years will finally be completed and used to provide the coal mines with additional geophysical information or in the case of roof and floor detection, reduce the need for roof touches and therefore reduce the cost of drilling. However, this can only be done with the development of non-metallic drill rods/subs.”
Teakle is looking to have a prototype ready for field testing in 16 to 20 months and a product ready for commercialisation in 21 to 24 months.
