ENHANCEMENT OF HEAT EXTRACTION FROM GEOTHERMAL RESERVOIRS USING CO2 AS A WORKING FLUIDGSA Colloqium November 1, 2012
University of Wisconsin – Milwaukee SURF Funding Fall 2012
Elise Uphoff
Outline
I. Global Warming
II. Geothermal Investment
and use
I. Geothermal Reservoirs
II. CO2 in Enhanced Geothermal Systems
III. Future of Geothermal Energy
CO2 as a Green House Gas
Carbon Dioxide amplifies the quantity of trapped solar radiation in the atmosphere (radiative forcing) Positive Feedback: Reduces Earth’s release of heat
back to space Temperature continues to rise
*cite data from Ifcc, and enviro txtbk
CO2 as a Green House Gas
CO2 Reduction Drivers in the US Energy demands on technology
improvements
Cap and Trade Legislation in California
One method for mass quantity removal of CO2 is collection and sequestration.
Sequestration Tax Credits (45Q)
Enhanced Hydrocarbon Recovery
Comparable Renewable Energies
Solar
Geothermal
Wind Turbine
Hydropower
Geothermal Energy
Reliable production for many decades. Requires no material consumption. Global Use 78 countries used direct geothermal
application for heat in 2008 24 countries produced electricity in 2008 (IPCC) United States produces the most electricity per
year The Philippines have the most geothermal
electric units (Bertani, 2005)
Global Geothermal Growth Rate
1970-2010 2005-2010
Electricity 7.0% 3.7%
Direct Heat 11.0% (1975-) 12.7%
Installed geothermal electricity capacity (MW) by country in 2009 (IPCC, 2011)
Locations of Geothermal Reservoirs
Source: NETL MGSC Annual Review Meeting 2011
What is a Geothermal Reservoir? A region where heat from Earth's
magma and radioactive decay collects in geologic formations, or in trapped liquid reservoirs. Exploitable reservoirs require water over
240˚CNew technologies are modeling 100˚C< T
<+240˚C
System Types
Two primary types of reservoirs available:
1) Wet Rock: Easily exploited, but geographically limited (Gallup 2009) Fueled by geothermal
gradients and liquid pressures through naturally occurring geologic faults.
System Types
2) Hot Dry Rock - Technology advancements have aided profitable exploitation. (Evans, 2012)
In energy production- known as Enhanced Geothermal Systems (EGS)
CO2 as a Working Fluid
Proposed working fluid in EGS due to its advantageous thermophysical Complementary process to CO2
sequestration.
Operated in the supercritical phase (SCCO2).
SCCO2 is highly pressure dependent at low pressures and high temperatures. (Pruess, 2006)
CO2 Compared to Water
Large expansivity and density buoyancy Larger flow velocities Lower viscosity Less effective solvent reduce scaling in production systems.
Approximately 50% larger heat extraction rates
Especially low to medium grade geothermal heat resources (Randolph, 2011)
Application of CO2 in EGS
Several layers of caprock contain the system.
Injection well is open to the entire reservoir and the production well open to the upper portion to Reduces temperature
decreases from the cold injection fluid. (Pruess, 2008)
PetraSim System Model
Injection
Production
Flow
The simulation injects SCCO2 at 1.25 kg/s (70°C) in an injection well, and produces at 1.75 kg/s (100°C).
Density 2650 kg/m3Porosity 0.12Permeability 6e-14Pressure 8MPaGas Saturation 0.1
Temperature Gradient (55yrs)
Migration of CO2
CO2 Saturation Front
T=0 T=15.5 yrs
T=55 yrs
At 55 years SCCO2 migrates from near saturation at injection, to CO2-brine at production.
Variation of Injection Temperature
T=30°C
Reservoir temperature over simulation length
Heat removal from the reservoir is dependent on CO2 injection temperature.
Disadvantages of CO2
Lower mass heat capacity Viscosity of CO2 is approximately 40% lower than water
in reservoir conditions, so higher temperatures are not required. (Brown, 2000)
As CO2 expands
under lower pressures,
it releases heat
(specific enthalpy). (Pruess, 2006)
Seismic activity during reservoir stimulation. A few sites shut down due to well casing limitations. (Evans,
2012)
Forward Trends of CO2 EGS
Technology Improve EGS, simulations, fracture tracking
through extensive R&D Develop post-injection field dataEconomy Energy Cost: Lower geothermal energy cost
to $0.06/kWh by year 2020 (http://www1.eere.energy.gov/geothermal/about.html)
Political US goal to have 80% ‘clean’ energy by 2035
Thank you
Elise Uphoff University of Wisconsin-Milwaukee Civil
Engineering [email protected]
Research Advisor: Dr. Weon Shik Han University of Wisconsin-Milwaukee Geology
Department [email protected]
Funding University of Wisconsin-Milwaukee Office for
Undergraduate Research (OUR) Stipend for Undergraduate Research (SURF)