Drilling faster is a big driver for technological development in every aspect of the subsurface industry, and the shallow geothermal sector is no exception.
“We can significantly increase the drilling rate compared to conventional rod-based drilling,” says Kate McRostie from CoilRig. “And with that statistic alone, we believe we have something that more drillers in the geothermal shallow loop market should be interested in.”
Based in Adelaide, Australia, and founded by Soren Soe and Kate, the team behind CoilRig™ has been leading the development of coiled tubing rigs because of a demand from the mining sector. Not having to attach or uncouple rods all the time not only saves a lot of time, the work can also be done with fewer people and is much safer at the same time.
“The proof is in the pudding, of course, but the first rig dedicated to geothermal drilling is now being manufactured in Australia and will soon find its way to our first customer in the USA,” says Kate. In the meantime, the team is trying to open up the European market as well.
“There is a degree of conservatism in the drilling industry,” Kate says, “so it is not a matter of one call and an order is in. But at the same time, I see that the geothermal sector employs more and more people from the oil and gas industry. These people have often been exposed to coiled tubing operations already, so there is some familiarity with the concept. That will surely make it easier to pave the way for this technology,” she concludes.
HOW DOES IT WORK?
The unique aspect of the CoilRig is that the reel that holds the continuous tubing is attached to the drilling mast. As such, it is placed straight on top of the borehole, ensuring that the number of bending events is strongly reduced compared to the conventional situation where the reel is fitted at the back of the drilling unit. This means a longer operational life, and it is expected that between 300 and 600 loop installations can be done with the same system.
The drilling itself is performed by a downhole motor attached to the end of the coiled tubing. This means that all the torque is delivered at the bit whilst the tubing is stationary.
The geothermal CoilRig drills 4¾” holes, which is generally classed as a slim hole. However, a conventional loop can still be lowered in these holes, reducing the amount of grout compared to wider holes.
Setting casing with coiled tubing technology is not as easy as with more conventional drilling methods, especially if a deeper casing is required. Part of the solution in this case is working with mud-based biofilms that can temporarily ensure hole stability whilst they are entirely biodegradable and don’t need removal from the borehole.
