high-temperature geothermal wells in Iceland Sverrir Thorhallsson - - PowerPoint PPT Presentation

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high-temperature geothermal wells in Iceland Sverrir Thorhallsson - - PowerPoint PPT Presentation

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Challenges faced in drilling high-temperature geothermal wells in Iceland Sverrir Thorhallsson Iceland GeoSurvey July 3, 2007 ENGINE Workshop 4 Reykjavk July 2-5, 2007 1 SOR geothermal map of Iceland ENGINE Workshop 4 Reykjavk July

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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

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ÍSOR geothermal map of Iceland

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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

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Location of wells in Iceland: www.gagnavefsja.is

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  • Temp. profiles - def. of LT and HT

Low temperature High temperature

Ref.: Guðmundur Pálmason

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Well Pressures

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

Boiling point depth curve Max WHP measured in Iceland Good inflow performance Watertable in stagnant well Inflow dP Boiling starts Pressure due to accumulation

  • f gas in shut-in well

High dP, dry steam well

reservoir pressure and well internal pressure (burst)

Casing shoe

  • prod. casing

800-1100 m

SÞ 4 .4 .19 98

Boi ling point depth curve S vartsengi S G-7, flowi ng Svart sengi, reservoir pressure Nesjavelli r NJ-9, wel l cl osed Nesj avelli r NJ-9, before flowi ng Nesjavelli r NJ-18, flowi ng Ne sj avellir NJ-18, before flowi ng K rafl a K G-12, flowi ng K rafl a K G-12, cl osed

Depth (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

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Icelandic geothermal wells

High temp. Low temp.

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Output curves for wells in Iceland

13 3/8” 9 5/8”

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Drilling methods used in Iceland

Rotary Air hammer Odex Holte Pressure bal.

Most common

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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.

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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

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1940

43 HT wells were drilled to less than 250 m from 1940- 1958 at: Hveragerði Krýsuvík Hengill Námaskarð After the arrival of “Gufubors” (The Steam Rig) in 1958 HT deep drilling started.

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Depth of HT wells drilled 1958-2006

1958 1962 1966 1970 1974 1978 1982 1986 1990 1994 1998 2002 2006 500 1000 1500 2000 2500 3000

Lengd holu (m) Ár borað Samtals 144 háhitaholur lengri en 500 m

Sverrir 2006-02-17

One line represents each well

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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

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HT Drilling

  • 1. 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)
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Geothermal Drilling Problems (USA)

Casing Rig repair Sloughing hole Fishing Side tracking Lost circulation Cementing Tw ist off Stuck pipe 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)

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Control lost KR-4

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  • 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 50 100 150 200 250 300 350

Krafla Well KG-4

Temperature (°C) Depth (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

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Underground blow-out NJ-11

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2200 2000 1800 1600 1400 1200 1000 800 600 400 200 50 100 150 200 250 300 350 400

Temperature (°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

  • n 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.

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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

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Krýsuvík steam eruption 1999 Rocks and mud thrown 300 m

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Krýsuvík Steam eruption of 1999

Hole where flying rock came down

Photo : GÓF Photo : GÓF

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Bjarnaflag after producing lava

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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

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Temporary repair of leak on casing connection @ 11 m Leak Seal

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Above: Buckling of a threaded casing joint. Right: Excavation to replace the top 11 m

  • f casing to the first coupling.

Failed connection

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HT Wellheads

Wellhead 12” x ANSI 900

Master valve Expansion spool Kill line Casing head

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Casing corrosion

7 mm corrosion at top of cement Kill line Rat hole Well with cellar removed

Outside corrosion of casing near surface

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Wellhead evolution in Iceland

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  • Min. cas. depth

Assume 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.

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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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