Geothermal Engineering: Fundamentals & Synergies with ... · PDF fileInstitute of Petroleum...

Geothermal Engineering:

Fundamentals & Synergies with Petroleum Engineering

Prof. Dr. Gioia Falcone Institute of Petroleum Engineering Dept. of Geothermal Engineering & Integrated Energy Systems Geneva, 25th April 2013

Prof. Dr. G. Falcone Institute of Petroleum Engineering Geothermal Engineering: Fundamentals & Synergies with Petroleum Engineering 2

Outline • Geothermal within the energy arena

• Fundamentals of geothermal energy

• Types of geothermal resources

• Uses of geothermal energy

• Oil & gas expertise for geothermal exploitation

• Conclusions


Fuel Shares of World Total Primary Energy Supply (2010)

(IEA 2012)


World Electricity Generation (TWh) from Non-Hydropower Renewables by 2030

(ESMAP, 2012)

Concentrating Solar Power

Photovoltaic


Cost-Competitiveness of Renewables


Constant Base Load Production from Geothermal vs. Other Energy Sources

(ESMAP, 2012)


2010 World* CO2 Emissions** by Fuel

(IEA, 2012)


US CO2 Emissions by Primary Energy Source

(ESMAP, 2012)







• Conclusions


The Earth’s Heat -1

(Gupta & Roy, 2007 )


Total heat flow observed on the Earth’s surface (& T distribution within it) is due to:

● Release of heat due to the cooling of the Earth

● Heat produced by radioactivity (amount of radioactive elements present in rocks releases enough heat to account for ~60% of total heat flow for continental crust)



● Earth’s cooling process is very slow ● Temperature of mantle has decreased by 300-350°C in

3 billion years, remaining at ~4000°C at its base ● 99% of Earth is hotter than 10000C ● 99% of the 1% is hotter than 1000C

(Geothermal Education Office)



Direct measurements of T in the Earth’s interior currently limited to a depth of 12.261 km in the Kola super-deep borehole SG-3 (northwest of Russia), with BHT of 180oC. Another reliable measurement of T at great depth is in the 9.101-km deep KTB borehole in Oberpfalz, Germany, with BHT of 265oC.

Proof of temperature at depth…


Plate Boundaries & Geothermal Spots

(Geothermal Education Office )


Plate Tectonics

(Geothermal Education Office )


(Dickson & Fanelli, 2004 )

Geothermal Systems

Convection & conduction


Essential Requirements for a Geothermal System to Exist

(1) a large source of heat (2) a reservoir to accumulate heat (3) a barrier to hold the accumulated heat

(after Gupta & Roy, 2007 )

Analogy with petroleum systems







• Conclusions


Types of Geothermal Systems Vapour-dominated Hot water Geo-pressured Magma Hot Dry rock (HDR) & Enhanced Geothermal

Systems (EGS)


Vapour-Dominated

Most exploited fields contain water at high P & T>100 oC. When this water is brought to surface, P is reduced and a mixture of saturated steam & water is generated. There are only few geothermal fields producing superheated steam with no associated fluids (dry steam fields).



Hot Water Differ from vapour-dominated fields in that they are characterised by liquid water being the continuous fluid phase. Typically, 60 oC<T<100 oC at depths of 1500 to 3000 m.



Geo-pressured Typically form in a basin in which very rapid filling with sediments takes place, resulting in higher than normal pressure of the hydrothermal water. Often saturated with methane. First identified in the deep sedimentary layers underneath the Gulf of Mexico. Wells flow pressurised to the surface. Water T is 90-200°C.

(Gupta & Roy, 2007 ; Texas Renewable Energy Resource Assessment, 2009)


Magma

Magma is the ultimate source of all high-temperature geothermal resources. Typically, magma crystallizes to form igneous rocks at temperatures varying from 600 to 1400 oC. Magma has been encountered in situ 3 times during drilling projects—twice in Iceland, and once in Hawaii. However, up to now, the necessary technology has not been developed to recover heat energy from magma.



Hot Dry Rock (HDR)

Hydrothermal resources restricted to countries with favourable geological conditions (i.e. plate boundaries). HDR resources exist where the heat is stored in hot & poorly permeable rocks at shallow depths within the Earth’s crust, without fluid availability to store or transport the heat.

HDR is the new frontier of geothermal energy and possibly the area closest to petroleum exploitation


Tem

pera

ture

, 0C

Dep

th, m

(MIT, 2006)

HDR Concept


From HDR to „Deep Geothermal“ • Hot Dry Rock concept first implemented at Fenton Hill in 1977 • Heat stored in deep seated, conductive/radiogenic dominated,

tight sediments & hard crystalline basement rocks. • Volcanic, metamorphic, magmatic or sedimentary settings. • Dry / not dry • W-w/o pre-existing fractures or fissures • Also known as: Hot Fractured Rock Hot Wet Rock Enhanced (or Engineered) Geothermal System (EGS) Deep Heat Mining Deep Earth Geothermal


Why Deep?

(Breede et al., 2012)







• Conclusions


Geothermal Energy Uses

1. Direct Use & District Heating Systems

2. Geothermal Heat Pumps

3. Electricity Generation


Geothermal Energy Use vs. Field T

(*) The above are indicative T value only! As technology advances, the T cut-off point changes.

(after ESMAP, 2012)


Direct Use & District Heating

Geothermal Education Office


Geothermal Heat Pumps

Geothermal heat pumps use the stable temperatures of the ground (vertical well typically 100-400 ft deep) as a heat source to warm buildings in winter and as a heat sink to cool them in summer.

Heating Cooling

(DOE)


Deep Borehole Heat Exchanger

(Kohl et al., 2000) (Rybach, 1994)


Geothermal Power Plants

Lardarello (Italy): 1st plant in the world

Still running after 100 yrs!

(Geothermal Education Office)


Geothermal-Electric Installed Capacity by Country in 2009

(IPCC, 2011)


Geothermal Power: Installed Capacity Worldwide in 2010

(ESMAP, 2012)







• Conclusions


Oil & Gas Expertise for Geothermal Exploitation Geology & Geophysics

Flow in Porous Media

Drilling, Completions, Fracturing & Production Ops.

Field Performance (Enel, 2005)


Geo-modelling & Reservoir Simulation Geology & Geophysics

Flow in Porous Media

Basic mass conservation equations governing the flow of multiphase, multicomponent fluids in permeable media

• Fracture imaging and characterization


Geothermal Reservoir Modelling - Issues

• Non-isothermal flow

• Phase change (boiling & condensation)

• Highly non-linear nature of water-steam flow.

• Geologies typically include CO2 & NaCl.

• Fracture-dominated reservoirs cannot be adequately described with single-porosity.

• Significant heat transfer effects on multiphase flow encountered in geothermal applications.


Drilling, Completions, Fracturing & Production Ops.

Multiphase Flow in Wells & Production Lines Drilling & Completions

Fracturing


Drilling & Completions -1

(DOE, 2006)


Drilling & Completions -1

(DOE, 2006)

Success rate for geothermal wildcat wells is only 25 - 40 % a reduction in exploratory drilling costs would be a major incentive for increased geothermal exploitation.

Drilling costs are only a part of the total well expenditure. Tubulars can double total well cost.

Drilling & completions can account for > 1/2 of the capital cost of a geothermal power project.


Drilling & Completions -2 • Geothermal wells need submersible pumps to lift the

heated fluids to surface. • Large-diameter production casing needed in HDR

wells (amount of fluids to be pumped & associated high enthalpy).

• Pumps must be deployed in a straight hole & installed at a certain depth to ensure a sufficient water head.

(SPE 113852)


Drilling & Completions -3 • Drilling fluids are subject to thermal degradation of

chemical additives, which causes highly variable rheological & filtration properties.

Reduced molecular interaction & viscosity in mud. • Even without degradation, viscosity of hydrosoluble

polymer solutions, used in muds, strongly decreases as temperature > 65°C.

• Current experience with HPHT drilling for oil & gas can be readily transferred to the geothermal sector.

• Testing labs already have mud viscometers working up to 275 MPa & 315°C.

(SPE 113852)


Drilling & Completions -4 • Setting depth of production casing

must ensure downhole pump is submerged at max flow rate.

• New geothermal projects need casing diameters larger than 9 5/8”.

• Thermally-induced casing fatigue & cement integrity are key issues for HDR wells as expected life time is longer than for oil & gas wells.

• Premium casing connections offer excellent resistance to axial loads vs. leak resistance, but their high cost impairs the economics of marginal geothermal projects.

Typical completion for a HDR producing well (SPE 113852)


2-phase flow map (Duns & Ros, 1963). Blue points are data from geothermal wells (Garg et al., 2005)

Flow in Wells: Oil & Gas vs. Geothermal Commonly, flow in geothermal wells is water-steam.

2-phase well flow models already widely used in oil & gas industry.

(SPE 113852)


Flow in Geothermal Wells: Issues • Wellbore simulators for fluid & heat flow already

developed, yet limited ability to match field data.

• Geothermal wellbore simulator must handle 2-phase, 3-component mixtures (H2O-NaCl-CO2).

• With relevant salt content in the produced fluids, these become superheated steam ∆P along the well larger than for pure H2O, due to higher fluid ρ & μ and lower specific enthalpy.

• 2-phase P gradients of H2O-CO2 and H2O-CO2-NaCl mixtures smaller than in 2-phase pure H2O flows.


Fracturing Geothermal Wells • Fracturing is key in HDR / EGS projects, where good

hydraulic conductivity must be created between injection & production wells.

• Oil & gas fracturing techniques in HDR geothermal settings have not been fully successful. Open fractures have short-circuited or not connected to existing natural fractures. Also, induced seismicity…

• Need for new developments to incorporate dynamic poroelastic & thermoelastic effects in the formations penetrated by the fractures.

Chemical stimulation also applied to geothermal wells


Conclusions • Geothermal energy, especially HDR/EGS, is a

renewable resource that can help meet the world’s growing demand.

• Oil & gas expertise fully complements geothermal exploitation. Many areas exist where technology transfer between these energy sectors should be enhanced.

Geothermal Engineering:

Fundamentals & Synergies with Petroleum Engineering

Prof. Dr. Gioia Falcone Institute of Petroleum Engineering Dept. of Geothermal Engineering & Integrated Energy Systems Geneva, 25th April 2013

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