Rotary Steerable Systems (RSS) have been used successfully to assist with drilling high value offshore and onshore wells. But the use of RSS for mining related projects has historically been hampered by high cost, complex systems and the need for multiple specialists on site.
A new type of RSS, using “at bit” steering technology has been trialled in a mining environment in Australia as part of Lucas’s technology acceleration strategy.
The results of the trial showed that the RSS performed near perfectly, with some minor improvements to be incorporated ahead of a further test in the future.
Transition to full commercial use of this new type of RSS technology in a mining project would present a step change towards the adoption of reliable and repeatable RSS at a price point that is accessible to mining clients.
The project
Current technology deployed for directional drilling in mining operations is made up of a bent-sub positive displacement motor (PDM) driving the drill bit, measure whilst drilling (MWD) sensors and transmission equipment and suitable non-magnetic drill pipe to both measure and guide the drilled path towards the desired target.
The drilling team use a combination of “slide”, where the drill pipe is held at a set angle and pushed to produce a curved borehole trajectory change and rotate sections where the drill pipe is rotated at a moderate rate to produce a straight borehole section. Overall, the borehole trajectory is a mix of curved and straight sections along the entire well path and the resulting torque and drag effects limit the controllability of the steering at depth which in turn limits the ultimate drilled length that can be achieved.
RSS come in many different guises however they all contain a way to exert a force on the wall of the borehole in order to deviate the next part to be drilled. All RSS units also contain systems to measure borehole trajectory and transmission technology to send and receive data to and from the surface. The two-way link allows the drilling team to set a desired well trajectory, which the RSS will maintain via a series of small continuous changes to deviation as the well is drilled. Adjustments to the drilling trajectory can be made by a new downlink command.
The result is a smooth wellbore trajectory that extends the limit of drillable distance for a given hole size, whilst producing a cleaner well with less drill cuttings left in place thanks to the constant drill pipe rotation.
RSS systems, by design, are complicated with some brands incorporating high pressure hydraulics to operate the deviation mechanisms, electronics to measure report and receive the unit’s position and turbines to generate power for the overall system. The fine tolerances, high operating pressures and the rugged downhole environment means that RSS units are expensive to buy, operate and maintain.
As part of a technology acceleration strategy, Lucas has been trialling several new drilling tools in conjunction with key clients. An opportunity to trial RSS recently presented itself at a coal mine, where drilling in a relatively thin seam was required.
Testing involved placing the RSS in the drilling string behind existing PDM based equipment to test the RSS’s ability to collect data and exhibit suitable control output to memory in a live drilling environment.
After reaching target drilling depth the RSS was retrieved and the results analysed. The entire RSS was functioning correctly and disassembly went without issue. All required data was recorded and downloaded successfully with the RSS clearly working properly at the end of the well.
Operational learnings were gained, with the RSS displaying better control at certain combinations of operating parameters, however all were well within expected limits for the type of drilling undertaken.
Both the RSS manufacturer and Lucas considered the trial to be a success and plan to conduct another live drilling trial, this time with the RSS as the main directional drilling unit.
Continued success is expected and would lead to Lucas offering RSS services as a regular part of drilling operations for mining clients. According to a Lucas representative: “It’s exciting that RSS technology has evolved to a point where it can be attractive to a wider range of drilling requirements, thereby producing better results for the wellbore and reducing overall cost for the customer.”
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