Eden Deep Geothermal Magnetotelluric Survey
This excellent example of a collaboration between two Cornish business, EGS Energy (EGSE) and their delivery partner, Eden Geothermal Ltd. (EGL), the British Geological Survey (BGS) and Deep Digital Cornwall (DDC; University of Exeter) is a model for how a public-private partnership can be formed to develop a GeoResources project to better understand a renewable resource. In this way, this partnership will provide data about targeting the deep geothermal resource in Cornwall as well as public domain data for future research purposes.
In this Research and Innovation Project, the BGS have been employed by EGSE-EGL to use the magnetotelluric (MT) survey technique to identify the location at depth of the geological target fault structure for the Eden Deep Geothermal energy project, based at Boldelva, near St Austell, Cornwall. This involves using a line of electrodes to provide a cross-section across the extent of the St Austell Granite. This will assist the understanding of the geological and hydrogeological characteristics of the first deep geothermal well (EG-1) at the Eden Deep Geothermal energy project site and will help to evaluate the potential geothermal resource associated with large fault structures in Cornwall. One of the aims of the MT survey is to identify the location of the target fault structure at a depth of 4,000 – 5,000 m and to either verify that it has been intersected by the well or to locate its position in relation to the well.
MT is sensitive to the electrical resistivity signatures of the main components of a geothermal system (heat source and structures that conduct fluid flow). However, its use to identify steeply inclined fault structures within crystalline rock that have the potential to be targets for deep engineered geothermal systems (EGS), as proposed at the Eden Project, is less proven. One research aspect of this Project is to ascertain the suitability of a MT survey for specific application to identify large permeable fault structures in Cornish granite. The innovation aspect is to adapt the methodology, interpretation and modelling of the MT survey to best suit the requirements for deep geothermal exploration and development in Cornwall.
The results from this project will provide essential information not only to decide whether the next step in planning for a second deep well at the Eden Project site is justified but also to gain a better understanding of the deep structures underlying Cornwall and within the granites, where very little data are known. In this way, a public domain output of “cleaned” raw MT survey data will be made available for projection in the Deep Digital Cornwall Visualisation Suite for the purposes of further future digital research possibilities, which will assist all parties involved as well as other interested people and organisations.
Image shown. Map from Google EarthTM, with annotation, showing the proposed layout of the MT survey profile line to be used at the Eden Deep Geothermal site.
