The A-Z guide to geothermal drilling

Geothermal drilling is a relatively foreign concept to most people. However, with the rising popularity of geothermal energy projects, it’s a process that an increasing number of people are having to invest and be involved in, if only from the sidelines. 

Below, we go through some of the basic things to be aware of in geothermal drilling projects, to provide you with a general overview of some of the processes and terminologies involved. 

Boreholes

A borehole is the hole left by the drill in geothermal drilling projects. The borehole will often be drilled to a depth of around 50-150m, depending on the energy requirements of the project in question and the thermal energy stored in the ground.

The drilling rig

The drilling rig is the machinery that’s used to drill a borehole in a geothermal drilling project. These rigs can drill between 50 and 100 vertical metres per day, depending on the material that’s being drilled through. As a result, most domestic geothermal projects can be completed in 1-2 days. 

Geological surveys

Before a drilling project can get started, a geological survey will need to be completed. This will be used to assess the suitability of the ground that’s going to be drilled into, and inform the drilling team on what drill bits they need to use. 

Loop

In geothermal drilling projects, once the borehole has been drilled, a loop will typically be inserted into that hole. This loop will be filled with a water/antifreeze mix, which can be pumped through the loop to bring heat up from down below.

Casing

To ensure both the structural integrity of the borehole and the maximally efficient transfer of energy between the ground and the loop, a casing will need to be installed. At the top, this may include a steel casing, to prevent cave-ins. Lower down, it will consist of some type of cement or grout.

Heat exchange

When the liquid in the loop has been brought up to the surface at a relatively warmer temperature, it will need to be run through a heat exchange unit. This will be used to essentially ‘amplify’ the temperature of the liquid, rendering it usable for heating purposes.

Testing 

As the borehole is being drilled, ongoing tests will need to be carried out. These tests can be used to ensure that the drill doesn’t accidentally release trapped hazardous materials, or affect an ecologically sensitive water source. 

Drilling fluid

As the drill bores its way down further into the hole, a substance called drilling fluid will be pumped down. This fluid keeps the drill bit at a stable temperature, while also removing rock cuttings and stabilising the walls of the hole, preventing excessive cave-ins. 

These are likely the most common pieces of terminology that you’ll come across in the context of geothermal drilling projects. If there are any concepts that come up that you’re unfamiliar with, it’s worth giving a geothermal drilling company a call to ask for further explanation