Geothermal Energy. Jen Eden ME 258 Fall 2012. 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
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Geothermal Energy Jen Eden ME 258 Fall 2012
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
EGS Plant • U.S. Department of Energy: http://www1.eere.energy.gov
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.
2. Drilling Injection Well • Understand Geology • Rock permeability • Depth to target temperature is important • Heat at shallow depth is desired
3. Reservoir Enhancement • Thermal Stimulation • Increases Permeability • Hydraulic Fracture • Increases Permeability • Chemical Stimulation • Dissolves Rock • Induced Seismicity • Opening existing fractures • Or creates new ones
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
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
Binary Power Plant Diagram • Power Generation From Low-Enthalpy Geothermal Resources. by Maghiar and Antal
Binary Power Plant SchematicUniversity of Oredea, Romania • Power Generation From Low-Enthalpy Geothermal Resources. by Maghiar and Antal
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)
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.
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
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
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
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.
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
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
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.)
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.
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
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.
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
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
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.