Can you convert an existing water borehole to geothermal?

One of the main things that people struggle with when considering a geothermal energy solution is how substantial an investment it is to have geothermal boreholes drilled. 

As a result, if there’s any chance that existing infrastructure could be adapted to fulfil that same function, it’s an opportunity well worth looking into. 

Below, we investigate whether or not it’s possible to convert existing water boreholes into geothermal solutions, along with some complications and considerations that need to be kept in mind.

Is it possible?

In short, yes, it is sometimes possible to convert existing water boreholes into geothermal energy sources. Both kinds of boreholes are often a similar depth, and so long as a range of other factors line up, it can work out. 

Of course, you will need to have a geological survey conducted to determine whether it’s actually feasible or not. There are sometimes environmental considerations as well, which may require additional regulatory permits.

What to assess

There are a few critical parts of the system that will need to be assessed to determine whether the conversion will be possible.

Depth 

Exactly how deep a geothermal borehole needs to be will depend on two main factors. The first is how much heat is required; the second is how effectively the ground below can transfer heat into the fluid pipe. 

That being said, most geothermal boreholes will be between 50 and 200 m in depth. Water boreholes vary a lot more, as it depends on how close to the water table the ground is. In general, they’ll be anywhere between 10 and 200 m deep, which may or may not work for a geothermal project. 

Thermal tests

Not all boreholes will be capable of transferring the same amount of heat into the fluid loop. For example, harder ground types will typically transfer heat much more efficiently compared to drier, sandier ground types, and the type of ground the water borehole is drilled through will have an impact on how deep it needs to be. 

The presence of water around the borehole can actually be a good thing, as water is very good at transferring heat. However, it can also cause some complications, and will have to be factored into the planning process accordingly.

A second hole

Geothermal boreholes work by pumping liquid through a sealed loop. While the existing water borehole may work for one side of that loop, you’ll often still need to drill a second borehole next to it, to complete the loop. 

If the original borehole is wide enough, it’s possible that the full loop will fit in, but it will then require a lot of grout material to fill in the gaps and create an adequate seal. 

Converting an existing water borehole to a geothermal energy source can absolutely be possible, but it will take some testing to assess this possibility, and then some work to implement the conversion. It’s important to have a geothermal technician come and assess the site and conduct some tests, to see whether it will be worth it or not.