Geothermal Energy

1. Geothermal Energy Jen Eden ME 258 Fall 2012

2. Location Requirements • Traditional Geothermal Plant • Hottest reservoir regions • Volcanic areas • Recent tectonic activity • High Permeability • Discovered by visible hot springs or other industries • Hydrocarbon • Enhanced Geothermal Systems • Low enthalpy reservoirs • Near the end user

3. EGS Plant • U.S. Department of Energy: http://www1.eere.energy.gov

4. What sets EGS apart • Man-made reservoirs • Created where there is hot rock but little to no natural permeability or fluid saturation • Fluid is injected into the subsurface • At low pressures • Causes less damage to fractures • Which causes pre-existing fractures to re-open • Increased permeability • Allows fluid to circulate throughout the rock • Transport heat to the surface where electricity can be generated.

5. 2. Drilling Injection Well • Understand Geology • Rock permeability • Depth to target temperature is important • Heat at shallow depth is desired

6. 3. Reservoir Enhancement • Thermal Stimulation • Increases Permeability • Hydraulic Fracture • Increases Permeability • Chemical Stimulation • Dissolves Rock • Induced Seismicity • Opening existing fractures • Or creates new ones

7. Extraction Well • Needs to intersect as many fractures as possible • Can have multiple production wells • Hot fluid (brine) is pumped out of the well and into the power plant

8. Types of Power Plants • Dry Steam • First type of plant built • Hydrothermal fluids are primarily steam • Flash Steam • Most common type of plants today • Fluid greater than 360°F (182°C) is pumped at high pressure into a tank • The tank is held at a much lower pressure, causing the fluid to rapidly vaporize, "flash” • Binary Cycle • The future • Brine below 400°F • Uses secondary fluid with lower vaporization temperature • Binary cycle power plants are closed-loop systems and virtually nothing • U.S. Department of Energy: http://www1.eere.energy.gov

9. Binary Power Plant Diagram • Power Generation From Low-Enthalpy Geothermal Resources. by Maghiar and Antal

10. Binary Power Plant SchematicUniversity of Oredea, Romania • Power Generation From Low-Enthalpy Geothermal Resources. by Maghiar and Antal

11. Paper 1:Rock specific hydraulic fracturing and matrix acidizing to enhance a geothermal system-concepts and field results • A major aspect of EGS is enhancing the geothermal reservoir. • This is done on a site–to–site basis taking into account unique geological features. • This paper focused on the GroßSchönebeckfield, a key site for EGS research in the North German Basin • Has 2 lithological units: • volcanic rock on bottom • Siliciclastics on top (from conglomerates to fine-grained sandstone)

12. Paper 1:Rock specific hydraulic fracturing and matrix acidizing to enhance a geothermal system-concepts and field results • Treatments were performed over 6 days • Needed multiple hydraulic treatments done at various depths in order to initiate cross-flow. • Multiple acid treatments were also performed to avoid iron scaling of the injected water and keep the pH at 5. • Additionally, quartz was added in low concentrations to maintain sustainable fracture performance.

13. Paper 1:Rock specific hydraulic fracturing and matrix acidizing to enhance a geothermal system-concepts and field results • Must sustain fracture openings • mostly tensile fractures without shearing displacement: add meshed sand or proppants to support the fracture opening • Higher flow rates lead to an increase in fracture length, lower flow rates lead to an increase in width and height. • Acid stimulation dissolved the residual drilling mud • increased productivity by 30-50% • lead to a total increase in productivity by a factor between 5.5 and 6.2

14. Paper 2: Environmental analysis of practical design options for enhanced geothermal systems(EGS) through life-cycle assessment • Analysis of EGS in central Europe based on life cycle assessment (LCA) of 10 significant design options • Annual electricity output of 10 power plants in central Europe corresponding to different sets of parameters were calculated. • number of wells • well depth and geothermal fluid temp at production wellhead • flow rate • production flow rate • reinjection flow rate • induced seismicity risk

15. Paper 2: Environmental analysis of practical design options for enhanced geothermal systems(EGS) through life-cycle assessment • 2 well cases: • 5 risk categories: • Human Health • Ecosystem Quality • Climate Change • Resources • Seismicity Risk

16. Paper 2: Environmental analysis of practical design options for enhanced geothermal systems(EGS) through life-cycle assessment • EGS achieves environmental performances comparable to other renewable energies (Despite the high amount of energy and resources required to build it) • Drilling has the highest environmental impact because of its use of fossil fuels • Alternative: is to connect to the grid to improve environmental performance. • Without appropriate reinjection strategy, the risk of induced seismicity increases. • Design of the plant and reservoir conditions can greatly change the environmental performance.

17. Paper 3:EGS using CO2 as working fluid • Problems with water use: • water is a sparse commodity and loss of it can be an economic liability • water is a powerful solvent which brings precipitants to the surface • Aim: Utilize supercritical CO2 instead of water as heat transmission fluid to reduce CO2 emissions by

18. Paper 3:EGS using CO2 as working fluid • Wellbore flow: • gravity contribution to pressure gradient is dominant • friction and inertial gradients are decidedly small • at lower depths, temperature increases by surrounding rock and by pressure increase, from compression, of the fluid • this is small for water but higher for CO2. • Difference in wellhead pressures are: • 230.7 bar CO2 • 61.2 bar water • Indicates a stronger buoyancy drive from CO2

19. Paper 3:EGS using CO2 as working fluid • Benefits of CO2: • CO2 is superior to water in its ability to mine heat and • with its larger compressibility and expansive properties its large buoyancy force would reduce power consumption with respect to the wellbore hydraulics, • its lower viscosity would yield higher velocities, • it’s a less effective solvent than water • Thermal extraction rate • 50% larger for CO2 than water • CO2flow rates are larger than water by a factor of 3.7 (This is a result of the enhanced mobility of CO2 at lower temperatures near the injection well.)

20. Paper 4:Performance analysis of hybrid solar-geothermal CO2 heat pump system for residential heating • Aim: to develop a solar-CO2geothermal hybrid heating system • The performance of a heat pump using CO2is lower than that using a subcritical cycle refrigerant due to irreversibilities, so system performance needs to be investigated. • Previous studies have used CFC or HCFC refrigerant, so it’s important to analyze the performance of a hybrid solar-geothermal CO2heat pump system.

21. Paper 4:Performance analysis of hybrid solar-geothermal CO2 heat pump system for residential heating • Setup: • A solar heat unit • A CO2heat pump unit. • The heat is collected and stored in a thermal heat storage tank at a specified operating temperature, when the temperature drops below this, the heat pump starts to operate and supplies heat to the tank

22. Paper 4:Performance analysis of hybrid solar-geothermal CO2 heat pump system for residential heating • Performance of the hybrid system was analyzed under varying operating conditions • Elevation of ground temp can significantly reduce the refrigerant temperature at the outlet of the compressor, thereby improving the system performance and reliability. • When the heat pump operating temperature increases from 40 C to 48 C, the pressure ratio between the inlet and the outlet of the compressor rises by 19.9% and the compressor work increases from 4.5 to 5.3 kW. • The performance of the solar hybrid heat pump is very sensitive to pump operating conditions. • Therefore, design of proper indoor temperature for variable outdoor conditions is very important to maintain high system performance and reliability in the pump system.

23. Paper 5: Shallow geothermal energy applies to a solar-assisted air-conditioning system in southern Spain • Aim: to determine the viability of a shallow geothermal system used in place of a cooling tower for a solar assisted AC system. • Specifically an aquifer thermal storage to solar assisted AC system • Main goal is to propose the application of a new alternative heat dissipation system for the absorption chiller installed in the CIESOL building in Spain

24. Paper 5: Shallow geothermal energy applies to a solar-assisted air-conditioning system in southern Spain • First analyzed the solar-assisted AC system with cooling tower, then with the geothermal system applied. • Cooling Tower: • The water in it can cause corrosion if not treated • The tower circuit is vulnerable because its an open circuit susceptible to scaling from precipitation of dissolved solids and algae growth and microorganisms • Causes Legionella outbreak if not properly maintained. • Also requires a storage tank and distribution pump to provide the needed permanent flow. • Shallow Geothermal System: • Purpose is to provide cooling water to the absorption chiller. • No risk of Legionella. • Does not involve any water consumption or rigorous maintenance. • Requires less space and eliminates outdoor noise levels

25. Paper 5: Shallow geothermal energy applies to a solar-assisted air-conditioning system in southern Spain • Operating for 2 years 2010-2012. During Summer: • Used 31% less electrical energy • Consumed none of the water the cooling tower needed • Saves 116m3 of water in one cooling period.

26. Questions?