Temperatures at this level can reach beyond 200 ºC (392 ºF). Water pumped from one well to the other and back up to the surface area collects heat from the rock, generating steam that can drive a turbine for electrical power.
Improved geothermal systems could supply an estimated 100 gigawatts of electrical power– adequate to power 100 million houses. Such systems include pricey drilling, and they need better monitoring and forecast of underground modifications to reduce the uncertainty and danger associated with an offered project.
Like any underground environment, boosted geothermal systems change over time. Fractures in the rock close and open in response to stresses triggered by high-pressure fluid injections, altering the systems heat output. Seismic activity is one indicator of subsurface stress, however information from microseismic tracking is limited.
” In these deep, hot rocks, its too pricey to drill adequate monitoring wells to comprehend whats going on using direct tasting,” said Tim Johnson, a computational researcher at PNNL who co-authored the study. “The main focus of this task is to better comprehend, and ultimately to forecast, how fractures are going to act in a high-stress environment when you attempt to link them in between two wells.”
Getting a clearer underground picture
When an electrical current is sent between them, ert involves inserting metal electrodes into keeping an eye on boreholes and then imaging the conductivity of the rock. Conductivity increases in time show where fractures are opening; when fractures are smaller sized or closed, conductivity declines. Johnson developed software application called E4D which operates on supercomputers and turns all of this electrical information into a visual that looks like a heat map, displaying fluctuations in conductivity over time. In 2016, E4D was granted an R&D 100 Award.
Time-lapse electrical resistivity tomography. Credit: Tim Johnson, et al.
” What we were seeing with the modifications in conductivity didnt make sense in terms of fluid flow,” Johnson said. If the conductivity wasnt showing the motion of fluids, what was it showing?
Johnson discovered the answer after years of searching through scientific papers from the 1970s and 1960s. Scientists at the Massachusetts Institute of Technology and the Lawrence Berkeley National Laboratory had actually previously noticed variations in the conductivity of crystalline rocks in reaction to stress– in lab experiments, compressing the rock made it less conductive. This showed that the ERT wasnt simply following fluid underground.
” Once we made that link, whatever made good sense in regards to what the time-lapse images were doing,” Johnson said.
ERT offers a number of benefits. ERT can not be utilized with metal wellbore cases, which are common in deep subsurface jobs.
There are methods around this obstacle, such as utilizing fiberglass casing, coating the casing with a non-metallic epoxy, or using a various, nonmetallic product entirely. For now, Johnson and the team are continuing to improve and check the use of ERT at the Sanford facility.
Recommendation: “4D Proxy Imaging of Fracture Dilation and Stress Shadowing Using Electrical Resistivity Tomography During High Pressure Injections Into a Dense Rock Formation” by T. C. Johnson, J. Burghardt, C. Strickland, H. Knox, V. Vermeul, M. White, P. Schwering, D. Blankenship, T. Kneafsey and the EGS Collab Team, 08 October 2021, Journal of Geophysical Research: Solid Earth.DOI: 10.1029/ 2021JB022298.
Pacific Northwest National Laboratory
The flow of electrical current signals changes in fractures deep underneath the earth
Scorchingly hot granite deep underground can be tapped for energy by opening cracks in the rock. This potential resource, referred to as improved geothermal energy, requires a clear sense of modifications happening in the rock gradually– a complex image that can be challenging to catch.
A team led by researchers at Pacific Northwest National Laboratory (PNNL) has actually shown a brand-new method to monitor deep subsurface fractures. The method, electrical resistivity tomography (ERT), gauges underground changes by determining electrical conductivity in the rock. ERT produces 4D– that is, 3D plus time-lapse– pictures of the subsurface.
What is a boosted geothermal system?
Conventional geothermal systems depend on pre-existing water and circulation pathways that are currently inside hot rock. By injecting water and fractures, an improved geothermal system catches heat caught within dry rock. Operators drill two underground wells countless feet below the surface, then pump high-pressure fluid into the rock between the wells to fracture it. The fracturing procedure to acquire heat is equivalent to “fracking” shale rock to launch oil and gas.
Electrical resistivity tomography (ERT) evaluates underground changes by determining electrical conductivity in the rock. The strategy, electrical resistivity tomography (ERT), evaluates underground modifications by measuring electrical conductivity in the rock. Fractures in the rock open and close in response to stresses triggered by high-pressure fluid injections, altering the systems heat output. ERT involves placing metal electrodes into keeping an eye on boreholes and then imaging the conductivity of the rock when an electrical current is sent between them. Scientists at the Massachusetts Institute of Technology and the Lawrence Berkeley National Laboratory had actually formerly discovered variations in the conductivity of crystalline rocks in reaction to tension– in lab experiments, compressing the rock made it less conductive.
