Challenges faced in drilling high-temperature geothermal wells in Iceland. Sverrir Thorhallsson Iceland GeoSurvey July 3, 2007

Transcription

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

2 ÍSOR geothermal map of Iceland ENGINE Workshop 4 Reykjavík July 2-5,

3 ÍSOR thermal gradient map 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. ENGINE Workshop 4 Reykjavík July 2-5,

4 Location of wells in Iceland: ENGINE Workshop 4 Reykjavík July 2-5,

5 Temp. profiles - def. of LT and HT Low temperature High temperature Ref.: Guðmundur Pálmason ENGINE Workshop 4 Reykjavík July 2-5,

6 Depth (m) 0 re ser vo ir p re ssur e a nd we ll in ter na l p re ssu re ( bu rst) Well Pressures 20 0 Watertable in stagnant w ell Max WHP measured in Iceland The figure shows pressure profiles that have been logged in HT geothermal wells in Iceland Boiling point depth curve Pressure due to accumulation of gas in shu t-in w ell Boiling starts Casing shoe p rod. ca sing m -Static (solid lines): well closed Good inflow p erfo rmance H igh d P, dry stea m w ell -Dynamic (dotted lines): well flowing Boi ling point depth curve Svartsengi SG-7, flowi ng Svartsengi, reservoir pressure Nesjavelli r NJ -9, well closed Nesj av elli r NJ-9, before flowi ng Nesjavellir 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 Inflow dp SÞ P ressure (bar-g) ENGINE Workshop 4 Reykjavík July 2-5,

7 Icelandic geothermal wells High temp. Low temp. ENGINE Workshop 4 Reykjavík July 2-5,

8 Output curves for wells in Iceland 13 3/8 9 5/8 ENGINE Workshop 4 Reykjavík July 2-5,

9 Drilling methods used in Iceland Most common Rotary Air hammer Odex Holte Pressure bal. ENGINE Workshop 4 Reykjavík July 2-5,

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,

11 Drilling rigs in Iceland 2007 Óðinn JB 4000 m Geysir JB 4000 m Jötunn JB 3300 m Sleipnir JB 2400 m Trölli RFS new Saga JB 1600 m 1350 m Jötunn Trölli RFS 1100 m Ýmir JB 1000 m Langþr. RFS 600 m Glámur RFS 600 m Sleipnir Einráður RFS 500 m Hrímnir JB 300 m Alvarr Trítill RFS 300 m 120 m ENGINE Workshop 4 Reykjavík July 2-5,

12 HT wells were drilled to less than 250 m from at: Hveragerði Krýsuvík Hengill Námaskarð After the arrival of Gufubors (The Steam Rig) in 1958 HT deep drilling started. ENGINE Workshop 4 Reykjavík July 2-5,

13 Lengd holu (m) Depth of HT wells drilled Ár borað Samtals 144 háhitaholur lengri en 500 m One line represents each well Sverrir ENGINE Workshop 4 Reykjavík July 2-5,

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 MWt. Average flow er well is thus = 35,5 l/s. Ave. power 8,7 MW t In addition there are 200 private wells. Ref: Þorgils Jónasson ENGINE Workshop 4 Reykjavík July 2-5,

15 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 drilling rigs are drilling HT wells at: -Hellisheiði (OR) -Reykjanes (HS) -Krafla (LV) -Þeistareykir (LV) ENGINE Workshop 4 Reykjavík July 2-5,

16 Geothermal Drilling Problems (USA) Stuck pipe Tw ist off Cementing Lost circulation Side tracking Fishing Sloughing hole Rig repair Casing 0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 0,18 Relative Im pact (norm alized freq*days) Ref.: Pers. comm. J. Rawley (1990) ENGINE Workshop 4 Reykjavík July 2-5,

17 ENGINE Workshop 4 Reykjavík July 2-5,

18 Control lost KR-4 Heavy mud mixed and pumped into well. ( = 1.8 g/cm 3 ; eq. 450 m in well) Po fell from 38 bar to 0 bar. BOP opened 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. ENGINE Workshop 4 Reykjavík July 2-5,

19 Depth (m) Blowout at Krafla KR-4 ORKUSTOFNUN BS Krafla Well KG-4 Temperature ( C) TD: 2003 m Casg.: 640 m Temperature during "blow-out" Estimated formation temp ENGINE Workshop 4 Reykjavík July 2-5,

20 Pressure rating of wellhead ENGINE Workshop 4 Reykjavík July 2-5,

21 Krafla KR-4 Blow-out crater ENGINE Workshop 4 Reykjavík July 2-5,

22 Depth (m) Underground blow-out NJ ORKUSTOFNUN Borholumælingar BS NESJAVELLIR NJ-11 Temperature ( C) Temperature measured inside drill string. To quench l/s pumped down the well. Residual pressure WHP = bar Measured 17-18th of May '85 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,

23 BOP stack Drilling for production casing. Drilling production interval. Master valve on well. ENGINE Workshop 4 Reykjavík July 2-5,

24 Well. Drilled 1949 Steam eruption 1999 Krýsuvík 1952 ENGINE Workshop 4 Reykjavík July 2-5,

25 Photo : GÓF Krýsuvík 1987 before Photo : GÓF Krýsuvík 1999 after ENGINE Workshop 4 Reykjavík July 2-5,

26 Krýsuvík steam eruption 1999 Rocks and mud thrown 300 m ENGINE Workshop 4 Reykjavík July 2-5,

27 Photo : GÓF Krýsuvík Steam eruption of 1999 Hole where flying rock came down Photo : GÓF ENGINE Workshop 4 Reykjavík July 2-5,

28 Bjarnaflag after producing lava ENGINE Workshop 4 Reykjavík July 2-5,

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. ENGINE Workshop 4 Reykjavík July 2-5,

30 Detection by calliper and CCL Gap detected by a calliper log Bad casing connection (coupling) Normal casing coupling as shown by CCL ENGINE Workshop 4 Reykjavík July 2-5,

31 Leak through a cemented annulus Temporary gland to stop the leak Path of steam leak through cement ENGINE Workshop 4 Reykjavík July 2-5,

32 Leak Temporary repair of leak on casing 11 m Seal ENGINE Workshop 4 Reykjavík July 2-5,

33 Failed connection Above: Buckling of a threaded casing joint. Right: Excavation to replace the top 11 m of casing to the first coupling. ENGINE Workshop 4 Reykjavík July 2-5,

34 HT Wellheads Wellhead 12 x ANSI 900 Master valve Expansion spool Kill line Casing head ENGINE Workshop 4 Reykjavík July 2-5,

35 Casing corrosion Outside corrosion of casing near surface Kill line Rat hole Well with cellar removed 7 mm corrosion at top of cement ENGINE Workshop 4 Reykjavík July 2-5,

36 Wellhead evolution in Iceland ENGINE Workshop 4 Reykjavík July 2-5,

37 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. ENGINE Workshop 4 Reykjavík July 2-5,

38 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 ENGINE Workshop 4 Reykjavík July 2-5,