GEOTHERMAL ENERGYJen 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

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.

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

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

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 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)

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 CO2 flow 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-CO2 geothermal hybrid heating system

The performance of a heat pump using CO2 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 CO2 heat pump system.

PAPER 4: PERFORMANCE ANALYSIS OF HYBRID SOLAR-GEOTHERMAL CO2 HEAT PUMP SYSTEM FOR RESIDENTIAL HEATING

Setup: A solar heat unit A CO2 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

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.

QUESTIONS?