Distributed temperature sensing for geothermal boreholes and thermal response tests
What is the ground made of, layer by layer, and is the field slowly cooling?
What is the ground made of, layer by layer, and is the field slowly cooling?
A conventional thermal response test gives one conductivity for the whole borehole. A fibre in the U-pipe gives one for every half metre, so the field is sized on the layers that are actually down there, and the same fibre keeps watching once the heat pumps run.
- Thermal conductivity and borehole resistance per depth interval, with uncertainty, from one test.
- Groundwater-affected intervals flagged where apparent conductivity rises with time.
- For operating fields, the annual mean profile against the baseline year, drift in kelvin per year per depth, and an alarm when the field leaves its design envelope.
- A report per test, and a dashboard for the years after.
The event, and the signal
- The rig pushes heat into the borehole. The fibre in the U-pipe reads every half metre.
- Layers that conduct well carry the heat away; layers that do not heat up more.
- The temperature rise per depth becomes conductivity per layer, from the same hours of heating.
Setup
| Fibre | Any cable already in the U-pipe or grouted behind it, single-mode or multimode. No fibre yet? A slim borehole cable comes with the rental, terminated and cut to length. |
| Boreholes per instrument | Up to eight through the optical switch, so one box covers a test field. |
| Rig connection | The test rig's energy meter, flow meter and inlet and outlet sensors plug into the same box, so the heat input and the response sit in one file on one clock. |
| Power | Mains at the rig, or a battery and a panel for long-term monitoring at one profile an hour. |
| Term | A campaign of two to four weeks per test, or continuous monitoring on a service contract. |
The measurement
During heating and recovery the temperature profile is recorded every few minutes. The late-time slope at each depth gives the conductivity of that interval by the line-source method, and a layered inversion with the known heat input refines it. Recovery is fitted as well as heating, so a shortened test still gives a result. For monitoring, each year's mean profile is compared with the first.
Deliverables
- Conductivity versus depth with uncertainty band
- Table per interval, conductivity, borehole resistance, advective flag
- Monitoring dashboard with baseline and current profiles and the difference shaded
- netCDF and CSV of every profile, for your own analysis
On the dashboard, through the API, and as files. All three, always.
Asked before
- Can it replace the standard thermal response test?
- It extends it. The same rig and heating schedule give the standard effective value and, from the same hours of heating, the depth-resolved profile on top.
- How many boreholes can one instrument test at once?
- Up to eight through the optical switch, sequentially within each profile. Fields are covered from one cabinet.
- What if the borehole has no fibre?
- A slim sensing cable is pushed into the U-pipe or taped to it before grouting. It comes with the rental, terminated and cut to length.
Other things the same box does
- Wells
Where is the injected fluid going, and is the well behaving?
You get Time-lapse temperature profiles against the pre-injection baseline, with injection and shut-in periods marked.
Read more - Glaciers and permafrost
What is the borehole doing through the winter, when nobody can get there?
You get An hourly or four-hourly profile of the whole borehole, every day of the season.
Read more - Pipelines and district heating
Where is the leak, before the road sinks? Hot water, cold water or gas.
You get A per-metre temperature baseline for the route, with every persistent deviation located to the half metre.
Read more
Put your fibre to work.
Tell us about your fibre and your question. You get a call, a plan for your site and a monthly price.