This week I am attending the #stanford #geothermal workshop. SGW is a premier forum on all aspects of geothermal, from district heating to electric power generation.
After serving six years as #uark #geosciences department chair and two more as #fulbright college associate dean, I've chosen to rejoin regular faculty this summer. My plan is to focus on modern, utility-scale geothermal power generation for #arkansas, where 90% of electrical power is from fossil fuels and a mature nuclear power plant. In the coming decades, some other form of baseload power will be needed in my state and across much of the world. Geothermal is one of the few options that is everywhere, scalable, dispatchable, 24/7, and essentially carbon-free. My early research indicates geothermal power could be a viable option in Arkansas. I look forward to meeting and learning from experts this week.
Excellent keynote by Lauren Boyd on her first day as director of DOE Geothermal Technology Office.
Jack Norbeck of Fervo Energy gave a high level overview of thier Blue Mtn (B) and Cape (C) geothermal power projects, both sites have ig-met basement with thin sedimentary cover. Drilling performance: Well B1 took 70 days to drill and latest C well took only 20 days, a 35% learning rate. Bit durability: B1 used 9 bits on a 3500 ft lateral, latest C used 2 bits on a 5000 ft lateral. Fewer bit changes, fewer trips in/out of the well, faster drilling, lower cost.
Q: Great updates and look forward to more! What is "thin" here and how long was the lateral in the igneous?
Some terminology:
EGS: enhanced geothermal system usually with frac wells to create permeability.
Greenfield: EGS with new wells
Brownfield: EGS with reused wells
Binary plant: power plant driven by hot brine passing through a heat exchanger to flash working fluid with low boiling point.
Closed loop: no-frac EGS with working fluid circulating through boreholes and power plant.
Excellent talk by Phil Vardon describing the very impressive TU Delft on-campus geothermal project followed by Denis Voskov also of Delft reviewing modeling and simulation support for the project. Laudably, TU Delt is committed to open data and source code, impacting geothermal projects worldwide. How delightfully enlightened. Love this cool graphic:
Nice talk this morning on Utah FORGE stimulation by Mark McClure of ReFrac. Some points and phrases: no Digital Fracture Network (DFN) used in simulations but more data may show need for DFN; model used has 22 params, no layering; 'stress shadowing'; frac reach from well bore about 1800 ft lateral and 1500 ft vertical; simulated 20 yr behavior; sim 1 no thermal stress effects (TSE), 2-3 kbbl/d; sim 2 with TSE, 8 kbbl/d and thermal breakthrough (TB) in about 7 months; sim 3 with flow control, 8 kbbl/d, TB in 8 years; sim 4 with CO2, 37% more heat extraction than H2O.
Q: why do fracs propagate up not down from lateral?A: because SHmax increases faster with depth than the pressure gradient.
A couple of high-level thoughts come to mind after listening to so many experts on geothermal (GT). First, GT power plant efficiency is highest when ambient temperature is low and lowest when ambient temperature is high, whereas wind and solar are just the opposite. So a mixed GT–solar–wind power plant may be a natural symbiotic relationship. Even more so because GT can supply a kind of subsurface energy storage for peak solar and wind which seems a far better option than utility scale critical mineral batteries. Second, most of the talks at this workshop are hot rock projects in granite. This means there is negligible poro-perm in the host rock and the GT reservoir is a tightly bounded container built by the frac job. In this situation a fluid breakthrough, 'thermal short circuit', is a critical failure of the system. When a short circuit occurs the power production drops precipitously because it acts like a thief zone taking fluid directly from injector to producer with little heating. However, for GT designed in unbounded brine aquifers, with naturally high poro–perm, the short circuit effect would be of minimal concern.
EGS: enhanced geothermal system usually with frac wells to create permeability.
Greenfield: EGS with new wells
Brownfield: EGS with reused wells
Binary plant: power plant driven by hot brine passing through a heat exchanger to flash working fluid with low boiling point.
Closed loop: no-frac EGS with working fluid circulating through boreholes and power plant.
Excellent talk by Phil Vardon describing the very impressive TU Delft on-campus geothermal project followed by Denis Voskov also of Delft reviewing modeling and simulation support for the project. Laudably, TU Delt is committed to open data and source code, impacting geothermal projects worldwide. How delightfully enlightened. Love this cool graphic:
Nice talk this morning on Utah FORGE stimulation by Mark McClure of ReFrac. Some points and phrases: no Digital Fracture Network (DFN) used in simulations but more data may show need for DFN; model used has 22 params, no layering; 'stress shadowing'; frac reach from well bore about 1800 ft lateral and 1500 ft vertical; simulated 20 yr behavior; sim 1 no thermal stress effects (TSE), 2-3 kbbl/d; sim 2 with TSE, 8 kbbl/d and thermal breakthrough (TB) in about 7 months; sim 3 with flow control, 8 kbbl/d, TB in 8 years; sim 4 with CO2, 37% more heat extraction than H2O.
Q: why do fracs propagate up not down from lateral?A: because SHmax increases faster with depth than the pressure gradient.
A couple of high-level thoughts come to mind after listening to so many experts on geothermal (GT). First, GT power plant efficiency is highest when ambient temperature is low and lowest when ambient temperature is high, whereas wind and solar are just the opposite. So a mixed GT–solar–wind power plant may be a natural symbiotic relationship. Even more so because GT can supply a kind of subsurface energy storage for peak solar and wind which seems a far better option than utility scale critical mineral batteries. Second, most of the talks at this workshop are hot rock projects in granite. This means there is negligible poro-perm in the host rock and the GT reservoir is a tightly bounded container built by the frac job. In this situation a fluid breakthrough, 'thermal short circuit', is a critical failure of the system. When a short circuit occurs the power production drops precipitously because it acts like a thief zone taking fluid directly from injector to producer with little heating. However, for GT designed in unbounded brine aquifers, with naturally high poro–perm, the short circuit effect would be of minimal concern.
The 49th Stanford Geothermal Workshop is over and I am packing bags to head back to Arkansas, after a good New York style pizza. The last thing I'll leave you with is the map below based on data from Jamie Woolsey, a subsurface mapping guru and UA geosciences alum. The map shows 1292 wells in Jamie's Petra project that are 9000+ feet deep. All of these wells have raster logs either in the project or available from our MJ Systems database. Part of our geothermal work is to capture these bottom hole temperatures as digital data for further analysis. Much work ahead, but we will very soon know more about subsurface heat in the state of Arkansas than has ever been known before. Stay tuned.
OK, I can’t resist posting one more Arkansas well map while waiting for my flight home. This one shows the 1292 deep wells in Arkansas, but the depth is meters for my European friends, the symbol size is proportional to depth, all the coal power plants are shown with nameplate MW capacity, as well as the lone nuclear power plant AR1 (1800MW unlabeled), and finally the state capital Little Rock and my home town of Fayetteville, AR Total coal power electric generation capacity in Arkansas is about 5.1 GW.
