In November 2018 Geothermal Engineering Limited (GEL) announced that it had started drilling at the United Downs Industrial Estate near St Day in Cornwall, the first stage in the development of the UK's first deep geothermal electricity plant.
The project - United Downs Deep Geothermal Power (UDDGP) - once completed will demonstrate the potential of the geothermal resources within the UK to produce electricity and renewable heat. Working with GEL on the project is GeoScience Limited and its managing director has been talking to GDI about how the project, planned to supply up to 3MWe (Mega Watt electrical) of electricity, which is enough energy to power 3,000 homes, is progressing.
The project, which was made possible through funding of £10.6 million (US$13.8 million) from the European Regional Development Fund in addition to a grant of £2.4 million from Cornwall Council and private investment of £5 million, was initially planned to drill into the Cornish granite to a depth of 4.5km.
The first stage was the delivery of the dedicated deep drilling rig designed in co-operation with German tunnelling specialist Herrenknecht Vertical and the German Research Centre for Geosciences Potsdam, Innova rig is a modern ‘new generation' semi-automated hydraulic rig, which was previously used to drill a deep geothermal well in Finland. Similar in design to those normally used for oil and gas drilling, the first parts of the rig arrived in the UK in early October and it was operational within a month.
Close to the surface, the two wells will be 24in in diameter and vertical but as they get deeper they will be steered towards the southwest to intersect the geological target and will get progressively narrower. They will be steel-lined for most of their length but open hole for the last few hundred metres and finish up 8-1/2in in diameter. The current rate of drilling for the first hole is variable, but averaging 4m per hour. However, Ledingham notes that this figure is for actual drilling, not taking into account tripping times and so on.
When GDI spoke to Ledingham he said that drilling has reached 4,400m but that the deeper hole is expected to be up to 5,500m measured depth or 5,200m true vertical depth once drilling is completed. Once both holes have reached been drilled and the rig has been removed, water will be pumped from the deepest well at a temperature of approximately190°C, fed through a heat exchanger on the surface and then re-injected into the ground through the second hole to pick up more heat from the rock in a continuous cycle. The extracted heat will be converted into electricity and supplied to the UK's National Grid.
Pete Ledingham MD of GeoScience and Lucy Cotton the project geologist at United Downs
That stage of the project is still some way off though as tougher than expected drilling conditions and a slower rate of penetration than expected have occurred. Ledingham philosophically notes that there is "nothing much we can do about that, but we have very got experienced drilling contractors and supervisors so we are doing the best engineering job we can."
The current time scale will see the completion of the first well by the end of April at which point the team will run geophysical logs and do a short production test before moving the rig 8m to start the second hole. Drilling the second hole is expected to be finished by the end of June this year.
The development of the United Downs plant in Cornwall follows on from the success of similar operations in Insheim and Landau in Germany and it is hoped that the innovative approach should be repeatable at other suitable sites in Cornwall and Devon in the UK.
