Untitled - Orkustofnun

Olkaria reservoir response36Ofwona3.3 Injection / re-injection in Olkaria IWell OW-3. A tracer and injection test experiment was done in well OW-3 from April to September1993 (Ambusso, 1994). Cold fresh water at 18°C from Lake Naivasha was injected in this wellcontinuously for 172 days at an average rate of 100 t/hr (27.78 kg/s). 125 kg of Sodium fluoresceindye was introduced as a slug after 45 days of injection. Production and chemical changes wereobserved in wells OW-2, 4, 7, 8, 10 and 11. Chloride decline occurred in wells OW-2 and 4 during theinjection period and tracer returns were observed in wells OW-4, 2 and 7 with OW-4 registering thehighest recovered mass of about 38 %, well OW-2, 0.1 % and well OW-7, 0.07 % (Ofwona, 1996).Hot re-injection of separated brine from wells OW-27, 31 and 33 has been going on in this well (OW-3) since May 1995 at approximately 13 t/hr (3.6 kg/s).Well OW-12. Tracer/injection test experiment was done in this well from 12.7.96 to 1.9.97. Coldfresh water from Lake Naivasha was injected continuously at an average rate of 100 t/hr (27.78 kg/s)for 416 days. 500 kg of Sodium fluorescein tracer was introduced as a slug after 20 days of injection.Wells around OW-12 were monitored for chemical and output changes. High tracer returns wereobtained from wells OW-15, OW-16 and OW-19. The same wells also experienced drastic decline inchloride concentration and enthalpies with big increase in water flow.Well OW-R3. Tracer/injection test experiment was done in this well from May 1995 to July 1.9.96.Cold fresh water from Lake Naivasha was injected continuously at an average rate of 100 t/hr (27.78kg/s) over the duration of the experiment. 500 kg of Sodium fluorescein tracer was introduced as aslug after 27 days of injection. Wells close to OW-R3 were monitored for chemical and outputchanges. Very little tracer returns were obtained from wells OW-25, OW-29 and OW-30 and nonefrom the closest wells OW-32 and 34. There was also very little or no change at all in the fluidchemistry as well as production output from the neighbouring wells.3.4 Hot re-injection in Olkaria NortheastHot re-injection in Olkaria Northeast field is infield and is done in wells OW-R2, OW-R3, OW-703and OW-708. By the end of 2004, a total of 4,895,726.5 tones of hot brine had been re-injected intothe field with 1,186,266 tons flowing into OW-R2, 1,057,768 tons flowing into OW-R3, 1,105,296tons into OW-703 and 1,546,397 tons flowing into OW-708 (Mwawongo, G. M., 2004). Tracer testshave been conducted in well OW-708 and returns were observed in wells OW-712. Monitoring ofthese wells for the effect of re-injection is ongoing but preliminary results show that there is positiverespone.Cold condenser blowdown from Olkaria II plant is injected in wells OW-201 and OW-204 in OlkariaCentral field. By end of 2004, a total of 708,261.5 tons had been re-injected into the two wells.3.5 Pressure response due to productionDue to high demand for steam, no wells within Olkaria I production field were available formonitoring pressure response due to production. Only well OW-3 and well OW-9 were consideredunsuitable for production and could have been used for this purpose but well OW-3 was used for fieldinjection experiments and well OW-9 had internal flow and was also later on plugged due to its closeproximity to the project offices. However, well OW-8 offered some good pressure decline history.This well was first drilled to 1080 m in November 1978 and intercepted permeable zones at 600 - 700m and 900 - 1080 m depth. It was then deepened to 1600 m in 1983 intercepting more permeablezones at 1300 – 1400 m. It remained shut-in from 1979 to 1983 and again to September 1985 when it