- review of existing geological and geophysical data
- reprocessing of geological and geophysical data
- development of a preliminary geological model
- gathering of resolution data through geophysical surveys
- development of a 3D geological model
- drilling of first borehole
- testing of the reservoir to determine the reservoir characteristics
Construction and well completion
- drilling of the second borehole for re-injecting the geothermal fluid
- construction of the energy centre
Operation and maintenance
- geothermal energy centre begins operation
- geothermal fluid is harnessed and distributed to customers
1 Preliminary assessment
A location requires certain characteristics to be suitable for geothermal assessment and geological exploration such as:
- Temperature gradient
- Natural heat flow
- Aquifer characteristics
- Presence of fault structures
The preliminary assessment focuses on collecting and analysing all available geological and geophysical information on the chosen location.
The UK has extensive knowledge of deep geological conditions necessary to understand the potential for geothermal energy development in the UK. This information is available as a result of extensive oil and gas exploration completed since the 1970s.
Information on the deep geological conditions is obtained as part of this phase and is accessed through the British Geological Survey. This allows us to establish the suitability of an area for geothermal exploitation.
2 Geological exploration
Feasibility studies focus on determining the most favourable location for the drilling and harnessing of the geothermal resource. We:
- Obtain seismic, geophysical, borehole and structural data to compile a detailed 3D model. Using this, we identify data gaps and assess the best methodology for improving the quality of the 3D model.
- Carry out additional non-invasive geophysical survey work to further enhance the quality of the 3D model. This allows us to better understand the geological conditions and identify target locations for drilling the production and re-injection wells.
- Develop a drilling location map and a well construction design. The design of the wells ensures that local groundwater resources are protected. This is done through the use of steel casing and cement grout in the upper parts of the well. The lower section of the borehole maximises the flow of geothermal fluids to the well from the productive horizons.
The preliminary design of the energy plant and surface equipment can also be carried out at this stage.
3 Drilling and testing
The first borehole is drilled and tested as part of the initial phase of the drilling operations. The objective of this phase is to measure the geological formation temperatures and test the natural volumes of geothermal fluids that can be produced from the reservoir. This is done by carrying out a pumping test.
Once suitable flow rates and temperatures are established, we undertake a pumping and re-injection test using the information gathered in the completion of the first borehole. This assesses the production conditions of the geothermal well doublet system.
In this way, we can determine if geothermal heat can be extracted successfully before commencing the final construction phase and the completion of the second borehole.
4 Construction and well completion
We carry out a detailed design of the energy centre. Construction begins when purchase agreements, planning permission and financing is secured. The construction phase comprises the drilling of the second well based on the successful results of the tests carried out on the first borehole and the construction of the distribution network.
Once the second well is completed, the well infrastructure is connected to the energy centre in advance of the system entering into production.
5 Operation and maintenance
Finally, the energy centre commences operation and distributes geothermal energy to customers. Qualified professionals ensure it is maintained and managed effectively.
The geothermal plant will provide an uninterrupted source of renewable heat for at least 25 years but could be substantially longer.