A team of researchers led by EEES Professor Larry Murdoch was recently awarded $4M by the Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy for a project entitled A Strain Sensing Array to Characterize Deformation at the FORGE Site. The goal of the project is to evaluate the use of strain data as a way to improve the performance of enhanced geothermal systems (EGS). By extracting heat from the subsurface, EGS holds promise as a virtually limitless carbon-free energy supply. However, there are some critical technical barriers that must be overcome before the promise can become a reality. One of the main barriers is that most hot rocks are virtually impermeable, so it is difficult to circulate water through the rocks to extract their heat. The EGS solution is to drill a horizontal well, and then create permeable zones along the well using hydraulic fracturing techniques. These hot, permeable zones are a newly created, enhanced geothermal reservoir from which heat can now be extracted. Geophysical techniques are used to characterize the location of the new reservoir, and a second well is then drilled to intersect it. With the second well in place, water can be circulated down one well, through the newly created, hot permeable zone, and back up the second well where it can be used to generate electricity.
Characterizing the enhanced geothermal reservoir is key to the success of EGS, and this is where strain sensing could help. Hydraulic fracturing deforms the enveloping rocks and this deformation creates a strain field that extends long distances from the new reservoir. Simulations of the FORGE site show that the strain field extends up to the ground surface where it could be detected by high resolution strainmeters deployed at shallow depths (Figure 1). Numerical models are then used to interpret the strain data and estimate the location and extent of the enhanced geothermal reservoir. These data are then used to help design the second well and the process of heat recovery. Strain sensing and interpretation would provide a new mechanism for characterizing and monitoring geothermal reservoirs, and these insights ultimately will improve EGS performance.
The DOE has invested heavily in EGS and their flagship research program is called Utah FORGE. A goal of the Utah FORGE project is to evaluate novel technologies at their field site in southern Utah in order to overcome technical barriers holding back EGS. The new EEES project was selected in the first round of funding for research projects at Utah FORGE.
Along with Dr. Murdoch, the Clemson team includes Drs. Scott DeWolf, Leonid Germanovich, Liwei Hua, and Hai Xiao (Chair of the Department of Electrical and Computer Engineering). EEES graduate students working on the project include Austin Smith-Jones, Clem Laffaille, Jess McDaniel, and Josh Parris. Also working on the Clemson project are Andy Barbour and Ole Kaven with the U.S. Geological Survey (USGS).
A centerpiece of the new project is the deployment of an array of optical fiber tensor strainmeters developed by EEES Associate Research Professor Scott DeWolf. Scott’s instruments are the current state-of-the-art in high resolution borehole strainmeters, and the Utah FORGE project will showcase the largest array of borehole strainmeters ever deployed. The first two strainmeters in the array were deployed in Utah during a blizzard in February 2022 (Figures 2-4), and deployment of the next two is scheduled for early October 2022. Dean’s Distinguished Research Professor Leonid Germanovich is developing a novel analytical solution for a pressurized poroelastic inclusion in a half-space, which will be used to create ultra-fast interpretations of strain data. Ole Kaven and Andy Barbour with the USGS are specialists in the analysis of strain and seismic data from geothermal sites, and they are collaborating with Scott and Leonid on data analysis. The project also includes developing a high temperature strainmeter that can survive under the scorching temperatures of a geothermal reservoir (200oC or hotter). Clem, Jess and Josh have been making good progress on developing and testing the high temperature strainmeter in the lab (Figure 5). The hope is that one day contributions from this new EEES research project will help bring down the cost of creating carbon-free geothermal energy.
