Tim Carr - West Virginia University

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Temperature in the Earth

Why Does Temperature Increase with Depth? Geothermal Gradient Sources of Heat Heat Transfer Heat Flow Equation Role of Thermal Conductivity Sedimentary Basins and Salt Domes Heat Transport by Fluids Temperature Measurements in Wells

Knut Bjørlykke, 2010

Heat Flow, Conductivity and Geothermal Gradients

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Evidence Hotsprings

Volcanoes

Deep mines [at 3200m, 150 F (65 C)]

Oil wells

Metamorphic rocks

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http://www.mpoweruk.com/geothermal_energy.htm 5

Change of Temp with Depth

25 C / kilometer (continental average)

~23 F / 1000 feet

Varies with tectonic setting

0

5

10

15

20

25

30

0 100 200 300 400 500 600 700 800

Temperature (C)

Dep

th (

km

)

6

Radioactive elements in rocks produce heat

Uranium (235U) Lead (205Pb)+ heat

Thorium (232Th) Lead (208Pb)+ heat

Potassium (40K) Argon (40Ar) and Calcium (43,44C) + heat

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Heat? Agitation of the atoms Kinetic energy (at the atomic scale)

Heat Flow? Heat transfer per unit area Transfer of the agitation of the atoms Heat moves from hot to cold Conduction (Thermal Diffusion) Convection/Advection (Fluid Flow)

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http://www.aos.wisc.edu/~aalopez/aos101/wk5.html 9

Hot coffee from china, metal and paper cup

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q = -k . dT/dz

Heat flow (mW/m2)

Thermal Conductivity

Thermal Gradient

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T2 (hot)

T1 (cold)

Material Property

(k= conductivity) q

q = -k . dT/dz

Heat Flow

12

Heat transferred per unit area

40 – 70 mW/m2 depending on tectonic setting

~50 mW/m2 continental average

50% from crust, 50% from mantle

13

Range of interest in Petroleum Geology

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15

Range of temperatures where peak maturation occurs:

60o – 120o C

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As Black Shale is buried, it is heated.

Organic matter is first changed by the increase in temperature into kerogen, which is a solid form of hydrocarbon

Around 90°C, it is changed into a liquid state, which we call oil

Around 150°C, it is changed into a gas

A rock that has produced oil and gas in this way is known as a Source Rock

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18

0

1

2

3

4

5

6

7

8

9

10

0 100 200 300

Temperature (C)

Dep

th (

km

)

60o 120o

Range of temperatures where maturation occurs: 60o – 120o C

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K (conductivity) W/moC

Rock Type K

Steel 46

Salt 5.5

Dolomite 5.5

Granite 3.5

Limestone 2.8 - 3.5

Sandstone 2.6 - 4.0

Shale 1.5 – 3.0

Coal 0.3

Water 0.6

~ 3 W/moC

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High K → Rapid Heat Transfer → Low Thermal Gradient

Low K → Slow Heat Transfer → High Thermal Gradient

T2 (hot)

T1 (cold)

High K Low K

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Sandstone

Sandstone

Salt

K=2.5

K=2.5

K=5.5

Temperature → D

epth

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Knut Bjørlykke, 2010 23

K=2.5 Shale

K=3.5 Granite

Constant Heat Flow 24

Colbalt International 25

Water transports heat with it, or takes it away

T T

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Measure bottom hole T during each logging run

T1

T2

T3 27

During drilling, they pump drilling mud down the well to control pressure

Drilling fluid cools the wellbore

Most Wells in the Appalachian Basin are air drilled Rapid Equilibrium

Time

T

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T

e

m

p

log((t+dt)/t)

t= time since end of

mud circulation

dt= time of

circulation at that

depth

Equilibrium

Temp

http://www.zetaware.com/utilities/bht/horner.html 29

Wellbore Environment

Depth, Diameter,

Temperature,

Mud Parameters

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Formation Depth

( Tf )

Total Depth (TD)

Dep

th

Temperature

Average Mean

Surface Temperature (AMST) Tf BHT

Tf = (((BHT-AMST) / TD) * FD) +AMST 31

77

70

63

55

48

41

oF

T.E. Gass, in Geothermal Heat Pumps Geothermal Resources Council Bulletin 11(11), 3-8, 1982 32

Gamma Ray

log Thermal log

low high low high

5550

5600

5650

Gas

Sand

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Take Home Ideas

Geothermal Gradient in Sedimentary Basins Varies Material

Sedimentation/Erosion Rates

Radioactive Elements are Heat Source Uranium, Potassium, Thorium

Oil Window 2-5 km (6,000-10,000 Feet) Dependent on Thermal Conductivity

Low Conductivity Rocks Lead to High Thermal Gradient

High Conductivity Rocks are Cooler Temperature Below and Higher Temperature Above – Than Surroundings

Bottom Hole Temperatures May Need Correction

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Assignments Reading for this week

Chapter 4, Selley

Work on Project on Monday 1/26 to Hand in on Wednesday 1/28

Read Today in Energy for Tuesday (1/27) at http://www.eia.gov/

Discussion Leader Travis Talbott

Quiz Friday 1/30 Quiz Opens at Noon Friday (1/30) and closes at

11:00am Monday 2/2.

Project – Initial Exploration Evaluation Project is Due Wednesday 1/28

You can work in teams 1-3