Recovery Act funding recipient profile III: Berkeley Lab to focus $7 million on enhanced geothermal technologies

In California, Lawrence Berkeley National Laboratory has been awarded $7 million in recovery act funding for four projects that seek to advance Enhanced Geothermal Systems (EGS). EGS holds the promise of harnessing the Earth’s heat where conventional geothermal technologies cannot. The funding is part of an original package announced by the Department of Energy in May that included $350 million for geothermal and another $117 million for solar.

The funds will support studies in fluid imaging ($1.95 M), fracture surface area estimating (another $1.95 M), thermal-hydrological-mechanical-chemical (THMC) modeling (1.74 M) and the use of carbon dioxide as a fluid ($1.32 M). The knowledge developed will be critical in translating conventional geothermal technologies, where heat and water flow and permeability are easily measured, to deep heat sources, where they are not. And the use of CO2 in dry holes in place of water may contribute to efficiency and manage to sequester some of the carbon.

In the fluid imaging investigation, scientists will look to reliably predict fluid location, movement and concentration several kilometers below the surface. They will couple geophysical data from various sources, such as seismic and electromagnetic surveys. If successful, the data developed would reduce the number of wells drilled at a given site.

A central theme of EGS is the creature of a network of fractures deep in the earth for fluid to circulate. How much fracture surface is actually created needs to be accurately measured, as they determine the capacity and longevity of an EGS system. The fracture surface estimation study will use natural chemical and isotopic tracers to estimate changes in fracture surface area induced by well stimulation.

Rock mechanics and chemistry each play important roles in fluid flow in the subsurface, and the THMC modeling work aims to combine all three factors into a single model. If successful, the tool will allow for more effective strategies for heat extraction and reservoir sustainability.

Finally, the use of CO2 as the fluid of choice in EGS systems will be studied in collaboration with Idaho National Laboratory. In theory, CO2 may extract heat from fracture rock at about 50% higher rates than water. Assuming a dry well, the use of CO2 would have a number of additional advantages as well, including the use of waste CO2 generated by fossil fuel plants, the potential sequestration of some of the CO2 and the non-use of what are always critical local water resources.

The potential of carbon sequestration in the process raises some interesting questions. Does it reduce EGS efficiency? If carbon is held, what is returned? How are the fractures affected? There is a great deal of fundamental CO2 science and the deep crustal environment that is not understood as yet.