| Abstract |
Olkaria well OW-202 was drilled as an appraisal well alongside wells OW-201, OW-203 and OW-204 in Olkaria Central Field, which is one of the seven sectors of the Greater Olkaria Geothermal Area. In the Olkaria Central Field other wells drilled are wells OW-101, OW-601, OW-102 and well OW-501. Wells OW-102, OW-203 OW-204 and OW-601 did not discharge when discharge tests were conducted. These wells were drilled as exploration wells in the Olkaria Central Field. Well OW-202 is currently under lease to Oserian Development Company (ODC) for power production since September 2006. This well supplys steam to an Elliot type back pressure turbine rated at a nominal power output of 1.3 MWe, operated by Oserian Development Company (ODC) since March 2007. Generally in the Greater Olkaria Geothermal Area the water composition encountered in the wells is variable, with dilute content and very low salinity. Typically, in the exploited fields of Olkaria East and Olkaria North East operated by Kenya Electricity Generating Company (KenGen), water composition is predominantly chloride while waters in the Olkaria West, operated by Orpower 4 Inc is carbonate dominated. Well waters in Olkaria Central discharge water type that is mixed sodium-chloride bicarbonate. Wells in the Olkaria Central Field mainly discharge liquid dominated fluid with a discharge enthalpy of saturated water temperature and a chloride range of ~ 300 ppm at separation pressures. Processes that could influence the fluid composition and possible predictions for scale forming mineral calcite using the speciation computer code WATCH was evaluated. Scales deposits flushed from the two-phase fluids indicated carbonate dominance after testing using hydrochloric acid. Well OW-202 experienced a drop in steam output since its production and it is thought scales deposition in the well could have contributed to this observation. A down hole dummy run indicated the well was blocked at a depth of ~ 955 metres. A sampler taken down the well recovered a scale sample at 908 meters suggesting the scale could have formed at a much shallower depth. From a steam supply equivalent of 1.3 MWe the well declined to a steam supply equivalent of ~ 400KW. The well has to be stimulated to enable it to discharge. To understand the cause of the steam decline water and gas sampling was done for about one year to establish the cause. |