| Abstract |
After steam decline was experienced in the production field for the Olkaria I plant in the initial five years of its operation, Olkaria well OW-34 was drilled as a make up well alongside OW-33, OW-32, OW-31 OW-30 and OW-29 wells. It was drilled in 1992 and discharge tests were conducted most of 1993, part of 1996 and in February to March of 2003. The well was connected to the production system in March 2001 and after producing for about 18 months its steam output declined significantly. A thick deposit of scale was observed on inspection of the surface piping at the wellhead master valve, in the two-phase line, inside the separator and in the separated water line. This was unusual as no other well in the Olkaria East Field has ever experienced this magnitude of scale deposition. Most wells in the Olkaria East Production Field show dilute content of solute in the fluids. Typically, in the exploited Olkaria East Production Field, chloride concentration of the fluids sampled at the well weir box are in the range of ~ 300 to ~1000 ppm. Most wells in Olkaria East Production Field exhibit "excess enthalpy" conditions. Well OW-34 fluids showed "excess enthalpy" very close to the enthalpy of steam, very low water flow rates and very high solute content in the residual fluids sampled at the weir box. The chloride concentration of well OW-34 fluids is ~ 3000 ppm and differs greatly from the chloride content of other Olkaria wells. Processes that could influence the fluid composition and possible predictions for scale forming minerals using the speciation computer code WATCH were evaluated and an XRD run on the scales was performed. The XRD run showed 23 angstrom on the 2D- scale which is characteristic of amorphous silica. From investigations of flow tests it is thought that a leakage of colder water from shallow depths trickles into the well when it is on discharge. The shallow colder water with a modest silica concentration mixes with upflowing fluids with a much larger steam fraction and gets evaporated after absorbing the heat from the steam and subsequently supersaturating the fluid with respect to silica which leads to silica depositing out of solution. |