ENGINE Workshop 4 Reykjavík July 2-5, 2007

Challenges faced in drilling

high-temperature geothermal

wells in Iceland

Sverrir Thorhallsson

Iceland GeoSurvey

July 3, 2007

1

ENGINE Workshop 4 Reykjavík July 2-5, 2007 2

ÍSOR geothermal map of Iceland

ENGINE Workshop 4 Reykjavík July 2-5, 2007 3

The thermal

gradient reflects

the heat flow in

the earths crust.

Outside the

geothermal areas

the gradient is

from 50°C/km in

the oldest crust

up to 170°C/km

in the youngest.

ÍSOR thermal gradient map

ENGINE Workshop 4 Reykjavík July 2-5, 2007 4

Location of wells in Iceland: www.gagnavefsja.is

ENGINE Workshop 4 Reykjavík July 2-5, 2007 5

Temp. profiles - def. of LT and HT

Low temperature High temperature

Ref.: Guðmundur Pálmason

ENGINE Workshop 4 Reykjavík July 2-5, 2007 6

Well Pressures

0 2 0 4 0 6 0 8 0 10 0 12 0 14 0 16 0 18 0 20 0

200 0

180 0

160 0

140 0

120 0

100 0

80 0

60 0

40 0

20 0

0

Boiling point

depth curve

Max WHP measured

in Iceland

Good inflow

perfo rmance

Watertab le in

stagnant w ell

Inflow dP

Boi ling starts

Pressure due to accumulation

of gas in shu t-in w ell

H igh dP, dry steam w ell

re servo ir p ressure a nd we ll in terna l p re ssu re (bu rst)

ORKUS TOFNUN

Ra nnsókna svið

Casing shoe

prod. casing

800-1100 m

SÞ 4 .4 .19 98

Casing Design

Boi ling point depth curve

S vartsengi S G-7, f lowi ng

Svart sengi, reservoir pressure

Nes javelli r NJ -9, wel l c l osed

Nesj avelli r NJ-9, before f lowi ng

Nes javelli r NJ -18, f lowi ng

Ne sj avellir NJ -18, before f lowi ng

K rafl a K G-12, f lowi ng

K rafl a K G-12, c l osed

De

pth

(m

)

P ressure (bar-g)

The figure shows

pressure profiles that

have been logged in

HT geothermal wells in

Iceland.

-Static (solid lines):

well closed

-Dynamic (dotted

lines):

well flowing

ENGINE Workshop 4 Reykjavík July 2-5, 2007 7

Icelandic geothermal wells

High temp. Low temp.

ENGINE Workshop 4 Reykjavík July 2-5, 2007 8

Output curves for wells in Iceland

13 3/8”

9 5/8”

ENGINE Workshop 4 Reykjavík July 2-5, 2007 9

Drilling methods used in Iceland

Rotary Air hammer Odex Holte Pressure bal.

Most

common

ENGINE Workshop 4 Reykjavík July 2-5, 2007 10

Underbalanced or balanced drilling

Two methods used to

“lighten” the water

column by entering

compressed air – mixing

it with the mud or

water.

Water flow similar as

before but air is extra.

ENGINE Workshop 4 Reykjavík July 2-5, 2007 11

Drilling rigs in Iceland 2007

Sleipnir

Trölli

Jötunn

Óðinn JB 4000 m

Geysir JB 4000 m

Jötunn JB 3300 m

Sleipnir JB 2400 m

RFS new 1600 m

Saga JB 1350 m

Trölli RFS 1100 m

Ýmir JB 1000 m

Langþr. RFS 600 m

Glámur RFS 600 m

Einráður RFS 500 m

Hrímnir JB 300 m

Alvarr 300 m

Trítill RFS 120 m

ENGINE Workshop 4 Reykjavík July 2-5, 2007 12

1940

43 HT wells were drilled to less than 250 m from 1940-1958 at:HveragerðiKrýsuvíkHengillNámaskarð

After the arrival of “Gufubors” (The Steam Rig) in 1958 HT deep drilling started.

ENGINE Workshop 4 Reykjavík July 2-5, 2007 13

Depth of HT wells drilled 1958-20061958 1962 1966 1970 1974 1978 1982 1986 1990 1994 1998 2002 2006

0

500

1000

1500

2000

2500

3000

Le

ng

d h

olu

(m

)Ár borað

Samtals 144 háhitaholur lengri en 500 mSverrir 2006-02-17

One line represents each well

ENGINE Workshop 4 Reykjavík July 2-5, 2007 14

180 production wells at “hitaveitas”

Municipal district

heating services tap

heat from 180 wells

with a cumulative

flow of 6397 l/s

corresponding to

1.562 MWt.

Average flow er well

is thus = 35,5 l/s.

Ave. power 8,7 MWt

In addition there are

200 private wells.

Ref: Þorgils Jónasson 2004

www.orkutolur.is/mm/efni/toflur.html

ENGINE Workshop 4 Reykjavík July 2-5, 2007 15

HT Drilling1. Developers/owners: HS, LV, OR

2. Drilling works:

-Jarðboranir hf.: drilling, casing, cementing, fishing etc.

- ÍSOR: geoscientific and logging services.

- VGK-Hönnun: design and supervision.

- Foreign service companies:for directional drilling and aerated drilling.

- Competitive bidding.

3. Summer of 2007 4 drilling rigs are drilling HT wells at:

-Hellisheiði (OR)

-Reykjanes (HS)

-Krafla (LV)

-Þeistareykir (LV)

ENGINE Workshop 4 Reykjavík July 2-5, 2007 16

Geothermal Drilling Problems (USA)

Casing

Rig repair

Sloughing hole

Fishing

Side tracking

Lost circulation

Cementing

Tw ist off

Stuck pipe

0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 0,18

Relative Impact (normalized freq*days)

Casing

Rig repair

Sloughing hole

Fishing

Side tracking

Lost circulation

Cementing

Tw ist off

Stuck pipe

Ref.: Pers. comm. J. Rawley (1990)

ENGINE Workshop 4 Reykjavík July 2-5, 2007 17

ENGINE Workshop 4 Reykjavík July 2-5, 2007

Control lost KR-4

18

• Heavy mud mixed and pumped

into well. ( = 1.8 g/cm3; eq. 450

m in well)

• Po fell from 38 bar to 0 bar.

• BOP opened.

• 10-20 minutes later the well

starts to flow.

• Drill pipe “blown out” of the

well.

• BOP´s fail to close the well.

• Master valve can not be closed

completely (3 cm missing).

• Well out of control. Decided to

move the rig off the well.

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Blowout at Krafla KR-4

2000

1800

1600

1400

1200

1000

800

600

400

200

0

0 50 100 150 200 250 300 350

12-03-2002

BSORKUSTOFNUN

Krafla Well KG-4Temperature (°C)

De

pth

(m

)

Temperature during "blow-out"

Estimated formation temp.

TD: 2003 m

Casg.: 640 m

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Pressure rating of wellhead

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Krafla KR-4

Blow-out crater

ENGINE Workshop 4 Reykjavík July 2-5, 2007

Underground blow-out NJ-11

22

2200

2000

1800

1600

1400

1200

1000

800

600

400

200

0

0 50 100 150 200 250 300 350 400

15-03-2002

BSBorholumælingarORKUSTOFNUN

NESJAVELLIR NJ-11Temperature (°C)

Depth

(m

)

Measured 17-18th of May '85

Temperature measured inside drill

string.

To quench 44-59 l/s pumped down

the well. Residual pressure WHP

=6.5-6.8 bar

In 1900 m and 2200 m full deflection

on the Amerada temperature gauge

T>381°C

Upflow of fluid hotter than 380°C

from the bottom region (2190 m

aquifer ?) to the main feed zone at

1226 m, which also swallows the

injection.

ENGINE Workshop 4 Reykjavík July 2-5, 2007 23

BOP stack

Drilling for

production

casing.

Drilling

production

interval.

Master

valve on well.

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Krýsuvík 1952

Well.

Drilled 1949

Steam eruption 1999

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Krýsuvík

1987 before

Krýsuvík

1999 after

Photo : GÓF

Photo : GÓF

ENGINE Workshop 4 Reykjavík July 2-5, 2007 26

Krýsuvík steam eruption 1999

Rocks and mud thrown 300 m

ENGINE Workshop 4 Reykjavík July 2-5, 2007 27

Krýsuvík

Steam eruption of 1999

Hole where flying

rock came down

Photo : GÓF

Photo : GÓF

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Bjarnaflag after producing lava

ENGINE Workshop 4 Reykjavík July 2-5, 2007 29

Casing collapse – trapped water

A casing collapse in 9 5/8" prod. cas. at 73.5 m depth in well SG-5.

It was removed with a drop-chisel and the well used for another 5 yrs.

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Detection by calliper and CCL

Gap detected by a calliper log

Bad casing connection (coupling)

Normal casing coupling

as shown by CCL

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Leak through a cemented annulus

Path of steam leak through cement

Temporary gland to stop the leak

ENGINE Workshop 4 Reykjavík July 2-5, 2007 32

Temporary repair of

leak on casing

connection @ 11 m

Leak

Seal

ENGINE Workshop 4 Reykjavík July 2-5, 2007 33

Above:Buckling of a threaded casing joint.

Right:Excavation to replace the top 11 mof casing to the first coupling.

Failed connection

ENGINE Workshop 4 Reykjavík July 2-5, 2007 34

HT Wellheads

Wellhead

12” x ANSI 900

Master valve

Expansion spool

Kill line

Casing head

ENGINE Workshop 4 Reykjavík July 2-5, 2007 35

Casing corrosion

7 mm

corrosion

at top of

cement

Kill

line

Rat

hole

Well

with

cellar

removed

Outside corrosion of casing near surface

ENGINE Workshop 4 Reykjavík July 2-5, 2007 36

Wellhead evolution in Iceland

ENGINE Workshop 4 Reykjavík July 2-5, 2007 37

Min. cas. depthAssume boiling point depth

curve (BPD). The reservoir

pressure is shown as “Water in

formation”, and also the

“Overburden” pressure.

•Draw a near vertical line from

well bottom representing the

density profile for saturated

steam (“Steam in well”).

•The minimum casing depth is

where the steam pressure

intersects the “Overburden”

pressure.

ENGINE Workshop 4 Reykjavík July 2-5, 2007

Conclusions

• Lessons have been learned from past failures

• Still not completely resolved is:

– Integrity of the casing

– Cementing procedures and materials

– How to cope with a steam-cap induced by

drawdown

– Problems of underground blow-outs

– Sealing of BOP´s during prolonged HT exposure

• In spite of this most HT wells are completed

successfully

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