1. G EOTHERMAL E NERGY Jen Eden ME 258 Fall 2012

2. L OCATION R EQUIREMENTS 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 P LANT U.S. Department of Energy: http://www1.eere.energy.gov

4. W HAT SETS EGS APART 1. Man-made reservoirs Created where there is hot rock but little to no natural permeability or fluid saturation 2. Fluid is injected into the subsurface At low pressures Causes less damage to fractures Which causes pre-existing fractures to re-open 3. Increased permeability Allows fluid to circulate throughout the rock Transport heat to the surface where electricity can be generated.

5. 2. D RILLING I NJECTION W ELL Understand Geology Rock permeability Depth to target temperature is important Heat at shallow depth is desired

6. 3. R ESERVOIR E NHANCEMENT Thermal Stimulation Increases Permeability Hydraulic Fracture Increases Permeability Chemical Stimulation Dissolves Rock Induced Seismicity Opening existing fractures Or creates new ones

7. E XTRACTION W ELL 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. T YPES OF P OWER P LANTS 1. Dry Steam First type of plant built Hydrothermal fluids are primarily steam 2. 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” 3. 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. B INARY P OWER P LANT D IAGRAM Power Generation From Low-Enthalpy Geothermal Resources. by Maghiar and Antal

10. B INARY P OWER P LANT S CHEMATIC U NIVERSITY OF O REDEA, R OMANIA Power Generation From Low-Enthalpy Geothermal Resources. by Maghiar and Antal

11. P APER 1: R OCK 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 Groß Schönebeck field, 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. P APER 1: R OCK 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. P APER 1: R OCK 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. P APER 2: E NVIRONMENTAL 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. P APER 2: E NVIRONMENTAL 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. P APER 2: E NVIRONMENTAL 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. P APER 3: EGS USING CO 2 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 CO 2 instead of water as heat transmission fluid to reduce CO 2 emissions by

18. P APER 3: EGS USING CO 2 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 CO 2. Difference in wellhead pressures are: 230.7 bar CO 2 61.2 bar water Indicates a stronger buoyancy drive from CO 2

19. P APER 3: EGS USING CO 2 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 CO 2 than water CO 2 flow rates are larger than water by a factor of 3.7 (This is a result of the enhanced mobility of CO 2 at lower temperatures near the injection well.)

20. P APER 4: P ERFORMANCE ANALYSIS OF HYBRID SOLAR - GEOTHERMAL CO 2 HEAT PUMP SYSTEM FOR RESIDENTIAL HEATING Aim: to develop a solar-CO 2 geothermal hybrid heating system The performance of a heat pump using CO 2 is 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 CO 2 heat pump system.

21. P APER 4: P ERFORMANCE ANALYSIS OF HYBRID SOLAR - GEOTHERMAL CO 2 HEAT PUMP SYSTEM FOR RESIDENTIAL HEATING Setup: A solar heat unit A CO 2 heat 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. P APER 4: P ERFORMANCE ANALYSIS OF HYBRID SOLAR - GEOTHERMAL CO 2 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. P APER 5: S HALLOW GEOTHERMAL ENERGY APPLIES TO A SOLAR - ASSISTED AIR - CONDITIONING SYSTEM IN SOUTHERN S PAIN 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. P APER 5: S HALLOW GEOTHERMAL ENERGY APPLIES TO A SOLAR - ASSISTED AIR - CONDITIONING SYSTEM IN SOUTHERN S PAIN 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. P APER 5: S HALLOW GEOTHERMAL ENERGY APPLIES TO A SOLAR - ASSISTED AIR - CONDITIONING SYSTEM IN SOUTHERN S PAIN Operating for 2 years 2010-2012. During Summer: Used 31% less electrical energy Consumed none of the water the cooling tower needed Saves 116m 3 of water in one cooling period.

26. Q UESTIONS ?