Untitled - Orkustofnun

Depth (m)Depth (m)Pressure Drawdown (Bar)Olkaria reservoir response38Ofwona3020100Pressure Drawdown in well OW-8 and OW-31980 1985 1990 1995 2000 2005 2010YearFIGURE 12: Pressure drawdown at 640 m a.s.l.in wells OW-3 and OW-8Well OW-3 was never connected to theproduction system and has been used for reinjectionexperiments. It was shut in for a longperiod of time before 1992 and can offer somegood pressure drawdown data up to 1992. Otherproducing wells have been logged at differenttimes when opportunity arises during wellheadequipment servicing and unit shut downs duringmaintenance. Figure 12 shows the pressuredrawdown as measured in wells OW-3 and OW-8 at 640 masl (1300 m depth). Maximumdrawdown was 22 bars in June 2000. Thedecrease in pressure drawdown in the year 2003and 2004 is due to shut-in of most wells as aresult of overhaul of Unit 1.From the pressure logs (Figures 13 to 16), it isobserved that the steam zone is expanding downinto the liquid reservoir as exploitation timeincreases resulting in lowering of thesteam/boiling water interface. Pressure logs from well OW-5 suggest that below 1600 m depth, thereservoir is still unexploited. Downhole measurements in well OW-21 shows that it had pressuredecline only up to 1997 and thereafter has been stable suggesting a good pressure support boundary.However, the measurements are done only when the well is temporarily isolated from the system andhas not been shut long enough to attain stable pressure.0200400600800Pressure (bar-a)0 20 40 60 80 10002004006008001000Pressure (bar-a)0 20 40 60 80 10010001200140016001800200029.7.7521.3.75 - 55 days heating8.3.84 - 357 days shut-in21.1.91 - 2 years shut-in31.12.92 - 4 years shut-inInitial formation pressureFIGURE 13: Pressures inwell OW-3120014001600180020002200240014.2.1979 - 20 days heating17.9.1982 - Shut-in20.9.1983 - Shut-in6.3.1984 - 66 days shut-inafter 2 weeks discharge3.9.1984 - 27 days shut-inafter discharge9.10.2001 - Shut-in for 348 daysInitial pressureFIGURE 14: Pressures inwell OW-83.6 Changes due to exploitationFigure 17 and 18 shows production histories of wells OW-2 and OW-19, which represent the behaviorof most production wells in Olkaria I. Generally, there was an initial high decline rate of about 3% –4% up to early 90’s and from then, the wells show either constant production or increase in output.The decline rate is now practically zero. This has been interpreted to imply that the reservoir has