Challenges faced in drilling high-temperature geothermal wells in Iceland Sverrir Thorhallsson Iceland GeoSurvey July 3, 2007 ENGINE Workshop 4 Reykjavík July 2-5, 2007 1
ÍSOR geothermal map of Iceland ENGINE Workshop 4 Reykjavík July 2-5, 2007 2
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, 2007 3
Location of wells in Iceland: www.gagnavefsja.is ENGINE Workshop 4 Reykjavík July 2-5, 2007 4
Temp. profiles - def. of LT and HT Low temperature High temperature Ref.: Guðmundur Pálmason ENGINE Workshop 4 Reykjavík July 2-5, 2007 5
reservoir pressure and well internal pressure (burst) 0 Well Pressures Max WHP measured Watertable in in Iceland 20 0 stagnant well Boiling point depth curve 40 0 The figure shows Pressure due to accumulation of gas in shut-in well pressure profiles that 60 0 have been logged in Boiling starts 80 0 HT geothermal wells in Casing shoe prod. casing Iceland. Depth (m) 100 0 800-1100 m 120 0 -Static (solid lines): Good inflow performance well closed 140 0 High dP, dry steam well 160 0 Boi ling point depth curve -Dynamic (dotted S vartsengi S G-7, flowi ng Inflow dP Svart sengi, reservoir pressure 180 0 lines): Nesjavelli r NJ-9, wel l cl osed Nesj avelli r NJ-9, before flowi ng Nesjavelli r NJ-18, flowi ng well flowing Ne sj avellir NJ-18, before flowi ng 200 0 K rafl a K G-12, flowi ng K rafl a K G-12, cl osed SÞ 4 .4 .19 98 0 2 0 4 0 6 0 8 0 10 0 12 0 14 0 16 0 18 0 20 0 P ressure (bar-g) ENGINE Workshop 4 Reykjavík July 2-5, 2007 6
Icelandic geothermal wells Low temp. High temp. ENGINE Workshop 4 Reykjavík July 2-5, 2007 7
Output curves for wells in Iceland 13 3/8” 9 5/8” ENGINE Workshop 4 Reykjavík July 2-5, 2007 8
Drilling methods used in Iceland Most common Rotary Air hammer Odex Holte Pressure bal. ENGINE Workshop 4 Reykjavík July 2-5, 2007 9
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 10
Drilling rigs in Iceland 2007 Óðinn JB 4000 m Geysir JB 4000 m Jötunn JB 3300 m Sleipnir JB 2400 m RFS new 1600 m Trölli Saga JB 1350 m Trölli RFS 1100 m Jötunn Ýmir JB 1000 m Langþr. RFS 600 m Glámur RFS 600 m Sleipnir Einráður RFS 500 m Hrímnir JB 300 m Alvarr 300 m Trítill RFS 120 m ENGINE Workshop 4 Reykjavík July 2-5, 2007 11
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. ENGINE Workshop 4 Reykjavík July 2-5, 2007 12
Depth of HT wells drilled 1958-2006 Ár borað 1958 1962 1966 1970 1974 1978 1982 1986 1990 1994 1998 2002 2006 0 500 1000 Lengd holu (m) 1500 2000 2500 Samtals 144 háhitaholur lengri en 500 m 3000 Sverrir 2006-02-17 One line represents each well ENGINE Workshop 4 Reykjavík July 2-5, 2007 13
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 MW t 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 14
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) ENGINE Workshop 4 Reykjavík July 2-5, 2007 15
Geothermal Drilling Problems (USA) Stuck pipe Stuck pipe Tw ist off Tw ist off Cementing Cementing Lost circulation Lost circulation Side tracking Side tracking Fishing Fishing Sloughing hole Sloughing hole Rig repair Rig repair Casing Casing 0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 0,18 Relative Impact (normalized freq*days) Ref.: Pers. comm. J. Rawley (1990) ENGINE Workshop 4 Reykjavík July 2-5, 2007 16
ENGINE Workshop 4 Reykjavík July 2-5, 2007 17
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. • 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. ENGINE Workshop 4 Reykjavík July 2-5, 2007 18
Blowout at Krafla KR-4 Krafla Well KG-4 Temperature (°C) 0 50 100 150 200 250 300 350 0 TD: 2003 m 200 Casg.: 640 m 400 600 800 Depth (m) 1000 1200 1400 1600 Temperature during "blow-out" Estimated formation temp. 1800 2000 ENGINE Workshop 4 Reykjavík July 2-5, 2007 19
Pressure rating of wellhead ENGINE Workshop 4 Reykjavík July 2-5, 2007 20
Krafla KR-4 Blow-out crater ENGINE Workshop 4 Reykjavík July 2-5, 2007 21
Underground blow-out NJ-11 Temperature (°C) 0 50 100 150 200 250 300 350 400 0 Temperature measured inside drill 200 string. To quench 44-59 l/s pumped down 400 the well. Residual pressure WHP 600 =6.5-6.8 bar 800 Depth (m) In 1900 m and 2200 m full deflection 1000 on the Amerada temperature gauge 1200 T>381°C 1400 Upflow of fluid hotter than 380°C 1600 from the bottom region (2190 m Measured 17-18th of May '85 1800 aquifer ?) to the main feed zone at 1226 m, which also swallows the 2000 injection. 2200 ENGINE Workshop 4 Reykjavík July 2-5, 2007 22
BOP stack Drilling for production casing. Drilling production interval. Master valve on well. ENGINE Workshop 4 Reykjavík July 2-5, 2007 23
Well. Drilled 1949 Steam eruption 1999 Krýsuvík 1952 ENGINE Workshop 4 Reykjavík July 2-5, 2007 24
Krýsuvík 1987 before Photo : GÓF Krýsuvík 1999 after Photo : GÓF ENGINE Workshop 4 Reykjavík July 2-5, 2007 25
Krýsuvík steam eruption 1999 Rocks and mud thrown 300 m ENGINE Workshop 4 Reykjavík July 2-5, 2007 26
Photo : GÓF Krýsuvík Steam eruption of 1999 Hole where flying rock came down Photo : GÓF ENGINE Workshop 4 Reykjavík July 2-5, 2007 27
Bjarnaflag after producing lava ENGINE Workshop 4 Reykjavík July 2-5, 2007 28
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, 2007 29
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, 2007 30
Leak through a cemented annulus Temporary gland to stop the leak Path of steam leak through cement ENGINE Workshop 4 Reykjavík July 2-5, 2007 31
Leak Temporary repair of Seal leak on casing connection @ 11 m ENGINE Workshop 4 Reykjavík July 2-5, 2007 32
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, 2007 33
HT Wellheads Master valve Expansion spool Wellhead Kill line 12” x ANSI 900 Casing head ENGINE Workshop 4 Reykjavík July 2-5, 2007 34
Casing corrosion Outside corrosion of casing near surface Kill 7 mm line corrosion at top of cement Well with cellar Rat removed hole ENGINE Workshop 4 Reykjavík July 2-5, 2007 35
Wellhead evolution in Iceland ENGINE Workshop 4 Reykjavík July 2-5, 2007 36
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, 2007 37
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, 2007 38
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