Feeling the heat: exploring the potential for geothermal energy...by Chris Rochelle

The Los Azufres geothermal area. Steam swirls from a natural vent (fumarole)
in the valley bottom, and also from several geothermal wells amongst
the trees further up the valley sides.

Part One - Mexico

Swirls of steam and the deep ‘bloop, bloop’ sound of bubbling mud pools greeted me on my first visit to a geothermal prospect in Costa Rica during my PhD fieldwork in the mid 1980s. Heat energy was literally pouring out of the ground, and the visit opened my eyes to the potential of geothermal energy as a renewable energy resource. Now, some 30 years later, geothermal power produces some 15% of Costa Rica’s electricity, with 80% coming from the prospect I studied. This, together with power from other geothermal areas and a very large hydroelectric capacity, allows >99% of Costa Rica’s electricity generation to be from renewable sources, and the country aims for its power supply to be carbon neutral by 2021.

And Costa Rica is not the only country with high aims. I write the first part of this blog on the return leg of a long-haul flight from Mexico where I have attended a meeting of the GEMex project - a €20M EU-Mexico collaboration which aims to enhance understanding of two geothermal systems east of Mexico City. Over 100 scientists from across Europe and Mexico spent 4 days visiting working geothermal operations, discussing their latest data, and trying to combine many different strands of research into coherent models for the two study sites.

Our busy schedule started with a four-hour ride in the back of a minibus to the Los Azufres geothermal field. This geothermal field has an installed capacity of about 200 MW, and produces some 20% of Mexico’s geothermal power. The geothermal field covers many square kms, and is in a beautiful area of rolling countryside. We walked through pine tree-lined valleys to study natural features of hydrothermal areas, including fumaroles, bubbling pools and hydrothermally-altered rocks. We were also allowed to visit the surface infrastructure of a geothermal plant, including: production wells, injection wells, turbine halls and the control centre of the whole operation. Unfortunately, time did not allow us to visit the numerous geothermal spas in the area.

From L-R: GEMex project participants inspect the wellhead of a producing geothermal borehole; A similar image but this
 time taken with an infra-red camera, with white and yellow areas showing the hot steel of the wellhead (and the relatively
 cold people being barely visible left of centre). The steel of the wellhead had a temperature of approximately 150°C.
The following three days were spent in Morelia discussing progress on our investigations of the two study sites: at Los Humeros, a currently working geothermal field where its operators want to deepen boreholes, but where little is known about the hotter fluids below the currently exploited zone; and at Acoculco, a prospective, but poorly understood geothermal area where fluid flow rates have been unexpectedly low. BGS input to the programme includes:
  • Study of exhumed, ancient systems that may be analogous to what may lie below the currently active geothermal systems, and where we can investigate fluid-rock reaction processes in detail;
  • UAV-based thermal imaging of warm/hot vents at Los Humeros to identify features conducting warm fluids and to try to match their position with geological structures (i.e. faults);
  • Surface gas monitoring to also identify conductive features;
  • And lab experimental and mineralogical studies to fluid-rock reaction processes that may impact fluid flow with the deep, currently exploited geothermal reservoir.
Developing Los Humeros and Acoculco, and other systems, will help Mexico achieve its own target of 50% of its energy from ‘clean energy sources’ by 2050. The knowledge learned will also help in Europe’s geothermal development, which could provide an important contribution towards the European target of at least 20% of its total energy needs being via renewable sources by 2020, and 32% by 2030.

Whilst achieving 100% renewable energy generation is akin to the Holy Grail of national energy targets, any significant move in that direction would mark a huge shift away from our dependence on CO2-producing fossil fuels which have been the mainstay of our energy-generating technologies since the Industrial Revolution. However, we must make this transition, as climate change driven by release of greenhouse gasses to the atmosphere is one of the biggest challenges we currently face.

The drilling rig under construction at
United Downs in Cornwall.

Part Two - The UK

And the UK is also rising to the challenge of renewable energy generation. On returning to the UK I travelled to Cornwall where a large drilling rig is being erected at United Downs. Once assembled, it will spend some 7 months drilling two deep boreholes into the Carnmenellis Granite, one of which could be up to 4.5km deep (thereby becoming the deepest onshore borehole in the UK). This £18M United Downs Deep Geothermal Power Project aims to tap deep natural fractures filled with groundwater at 180-190°C and prove the feasibility of a fully working ‘engineered geothermal system’ (EGS) that can export electrical power to the national grid. This exciting project will utilise modern technologies to convert heat energy to electricity, and builds on expertise gained in the previous ‘Hot Dry Rock’ geothermal project which ran in Cornwall in the 1980s-1990s. If the United Downs Deep Geothermal Power Project succeeds, then it will open up the possibility of parts of the UK’s deep geosphere becoming a renewable energy resource for the future.

Since starting work on this blog, I found out that I have just won £1.8M from NERC for a Highlight Topic focussed on understanding the deep geothermal resources of Cornwall (project = GWatt). This study (which also involves Herriot Watt University, Camborne School of Mines, GeoScience, Geothermal Engineering Ltd, and the Cornwall and Isles Of Scilly Local Enterprise Partnership) aims to reduce the uncertainty associated with geothermal exploration through a detailed appraisal of existing and newly gathered data. Key to this will be the incorporation of new data coming from the United Downs Deep Geothermal Power project.

The European Union Horizon 2020 research programme for funding for the European half of GEMex under grant agreement 727550. Thanks go to the ComisiĆ³n Federal de Electricidad (CFE) for allowing the site visit and access to their facilities, and providing many explanations of the different parts of their powerplant.