Drilling the wells
Close to the surface the production well is 24” in diameter and the injection well 18”.
Both are initially vertical but as they get deeper they were steered towards the southwest to intersect the geological target while getting progressively narrower. Both wells are steel-lined for most of their length but open hole for the last few hundred metres, and finish up 8 ½” in diameter.
Drilling such deep wells in very hard rocks required a large drilling rig, similar to those normally used for oil, gas and conventional geothermal wells. Together with its ancillary equipment it filled most of the site. It took just under 8 months to drill the two wells, operating 24 hours a day.
Now that the wells have been completed, the drilling rig has been removed from the site and we will carry out various production, injection and circulation tests to characterise the geothermal system and determine how much heat and power it will be able to produce. This phase should be completed towards the end of spring 2020.
We selected a modern ‘new generation’ semi-automated hydraulic rig to drill the wells called the Innovarig. It is based in Germany and is one of the quietest rigs of its size in Europe. After drilling a deep geothermal well in Finland the rig was brought to the UK, assembled at the United Downs site, and started drilling in early November 2018. Following drilling it was demobilised during July 2019.
How deep are the wells?
(HAS Innovarig, image: GEL)