Enhancement of Heat Extraction from Geothermal Reservoirs Using CO2 as A Working Fluid

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)