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Underground blow-out in wells in Krafla and Nesjavellir

GeoScience Division. ORKUSTOFNUN. Underground blow-out in wells in Krafla and Nesjavellir. Benedikt Steingrímsson Orkustofnun, GeoScience. B.S. 2002. GeoScience Division. ORKUSTOFNUN. Well KG-4 in Krafla. Víti. Power Plant. B.S. 2002. GeoScience Division.

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Underground blow-out in wells in Krafla and Nesjavellir

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  1. GeoScience Division ORKUSTOFNUN Underground blow-outin wells in Krafla and Nesjavellir Benedikt Steingrímsson Orkustofnun,GeoScience B.S. 2002

  2. GeoScience Division ORKUSTOFNUN Well KG-4 in Krafla Víti Power Plant B.S. 2002

  3. GeoScience Division ORKUSTOFNUN KRAFLA WELL KG-4 Drilled 04.08-04.09.1975 to 2003 m depth. Main circulation losses during drilling: 290 m >40 l/s 645 m 3 l/s 1000 m 6 l/s 1132 m >40 l/s 1228 m 10 l/s 1940 m 8 l/s 18 5/8” surface casing 30 m 13 3/8” anchor casing 120 m 9 5/8” production casing 600 m Bottom at 2003 m B.S. 2002

  4. Circulation with drillbit at bottom to clean well. Pumping on kill line for cooling control. Pull drillstring out. Put one stand (2 pipes) in wellhead. Stop water injection. Run Amerada temp. tool (to locate feed zones to select slotted sections of liner. Run liner. Move the rig off the well. Well KG-4 Completion. Circulated for 1 hour. Total loss (>40 l/s) in 20 minutes. Pumped 20 l/s on kill line. Pulled out (10 1/2 hour). One stand (2 pipes) in wellhead. Injection stopped (4 h). Flow from well 1 1/2 h after stop. BOP-closed. 2” valve put on top of pipe. Injected 20 l/s in annulus. Wellhead pressure stable at 28 bar (12h). Temperature logging GeoScience Division ORKUSTOFNUN Well completion in 1975 Program schedule after total depth was reached B.S. 2002

  5. GeoScience Division ORKUSTOFNUN AMERADA Temperature survey of KG-4 Tool floats at 1400 m depth. Underground blow-out in well. Injected water flows into feed zone at 650 to 700 m depth Upflow of some 320°C fluid from a deep feed zone, probably at 1920 m, to a shallow feed zone at 650-700 m. B.S. 2002

  6. GeoScience Division ORKUSTOFNUN Temperature log in well KG-4 during underground blow-out compared to the formation temperature in this part of the Krafla reservoir. Extrapolated inflow temperature to 1920 m in KG-4 320°C. Reservoir temperature 337°C B.S. 2002

  7. GeoScience Division ORKUSTOFNUN Pressure gradient corresponds to fluid density of 150 kg/m3. Density at 310°C Water: 690 kg/m3 Steam: 55 kg/m3 The upflow is mainly steam and gas B.S. 2002

  8. GeoScience Division ORKUSTOFNUN Estimated pressure in well KG-4 during “blow-out” compared to reservoir pressures. • Pressures at 700 m. • 90 bar during blow-out • Reservoir pressure 50 bar • Pressures at feed zone in 1920 m: • Pressure during “blow-out” 103 bar (extrapolated) • Reservoir pressure 140 bar B.S. 2002

  9. GeoScience Division ORKUSTOFNUN “Killing” of KG-4 and loss of control • 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. • Explosive flow out of the well 10-20 minutes after mud injection. • 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. B.S. 2002

  10. GeoScience Division ORKUSTOFNUN KRAFLA WELL KG-4 Large diameter pipe was lowered on to the BOP-stack in order to divert the steam from the derrick and the mast while the drilling rig was removed from the site. B.S. 2002

  11. GeoScience Division ORKUSTOFNUN The history of the KG-4 blow-out • Sept. ´75-Jan. ´76. Discharge through narrow opening of the master valve. Mainly steam. Water chemistry corresponds to the shallow reservoir (200°C) • Early Jan. ´76 Wellhead falls-off. Concrete cellar disintegrates and pieces of casing is blown out. Crater forms around well. Discharge mainly steam. • Late Jan. ´76. Crater fills with water. Outflow 20-40 l/s. • March ´76. First sample of the year. Water pH 1.86 but chemistry of the shallow reservoir. • Summer ´76. Flowrate 150-250 l/s. pH increasing to 7. • Oct-Dec. ‘76. Periodic flow. Probably due to calcite plugging of the well. • The discharged stopped permanently during Xmas 1976. The size of the crater was some 40 m in diameter and some 10 m in depth. B.S. 2002

  12. ORKUSTOFNUN GeoScience Division NESJAVELLIR Eruptive fissures Eruptive fissure BS.2002

  13. GeoScience Division ORKUSTOFNUN NESJAVELLIR WELL NJ-11 Drilled 11.04-17.05.1985 to 2265 m depth. Feed zones in production part: 600-903 m Several minor inflow zones 950 m Inflow 6 l/s Po=2.5 bar. 1226 m Loss 39 l/s. 1350 m T-log. 1575 m T-log. 1750 m Loss increases (>40 l/s). 1820 m Loss increases. 2160 m Possible feed zone. 2190 m Possible feed zone. Circulation returns change color from black to gray. Smell of gas. 18 5/8” surface casing 54 m 13 3/8” anchor casing 183 m 9 5/8” production casing 565 m Bottom at 2265 m B.S. 2002

  14. Circulation to clean well (3-5 h). Pumping on kill line for cooling control through out the completion program. Temperature log during injection (3h) Pull drillstring out (15h). Logging (T + caliper + lithology) (12h). Run slotted liner (24 h). Injection test, 3-5 flow steps (12h). Move the rig off the well. Well NJ-11 Completion. Circulated for 4 1/2 hour. Circulation loss 20 l/s. Pumped 20 l/s on kill line. Flow starts from the well and increases from 10 to 30 l/s in few minutes. BOP closed and switched to circulation. Loss 30 l/s Next four days attempts were made to kill the well by circulation down the pipes or by injection or both using up to 60 l/s of cold water. During injection up to 10 bar wellhead pressure was measured but zero during circulation. GeoScience Division ORKUSTOFNUN Well completion in 1985 Program schedule after total depth was reached B.S. 2002

  15. GeoScience Division ORKUSTOFNUN NESJAVELLIR WELL NJ-11 Temperature log (Go +Amerada) Measured inside drillstring. 44-59 l/s pumped in the annulus. Po =6.5-6.8 bars. In 1900 and 2200 m full deflection on the Amerada T>381°C Underground blow-out in well 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. B.S. 2002

  16. GeoScience Division ORKUSTOFNUN The temperature log in well NJ-11 during underground blow-out compared to the formation temperature later estimated for this part of the Nesjavellir reservoir. B.S. 2002

  17. GeoScience Division ORKUSTOFNUN Estimated pressures in well NJ-11 during underground “blow-out” compared to estimated reservoir pressures. The blow-out seems to have started with the well full of cold water and circulation of cold water could reverse the flow from the deep aquifer. This suggests reservoir pressures in excess of 220 bar at bottom of NJ-11. B.S. 2002

  18. GeoScience Division ORKUSTOFNUN Well NJ-11 Completion, cont. • After 4 days of cold water circulation and injection it was decided to pull the drill string out of the well. This operation took another 4 days. • The bottom section was then plugged by pouring gravel into the well. This stopped finally the underground blow-out. Top of gravel was then at 1585 m depth. • The rest of the completion program was then carried out and the rig moved to next well. • Well NJ-11 has been and still is one of the best producing wells at Nesjavellir. (For further details see the paper “Evidence of a supercritical fluid at depth in the Nesjavellir field) B.S. 2002

  19. GeoScience Division ORKUSTOFNUN Concluding remarks • Underground blow-outs are extremely dangerous and difficult to stop. • Shallow feed zones should be plugged (or sealed behind casing) before drilling into very hot gaseous reservoirs. • The bottom feed zone in KG-4 had a temperature 340°C and pressure of 140 bars. What triggered the underground blow-out was insufficient cooling (cold water injection was stopped). This has led to pressure (water level) drop in the well and heating-up. Also there might have been a gas kick from the deep feed zone. B.S. 2002

  20. GeoScience Division ORKUSTOFNUN Concluding remarks, cont • The bottom feed zone in NJ-11 had a temperatures higher than 380°C and possibly also supercritical pressures. • The underground blow-out might have started already when a feed zone at 2190 was intersected. • NJ-11 is close to a 2000 year old volcanic fracture and the extremely high temperature below 2000 m depth is believed to be related to a magmatic heat source, probably an intrusions. B.S. 2002

  21. GeoScience Division ORKUSTOFNUN B.S. 2002

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