Interpretation of Geochemical Well Tests Data for OW-903B, OW-904B and OW-909 - Olkaria Domes, Kenya.

Abstract

Three production wells from the Olkaria Domes field (Kenya) were allowed to discharge for 3 months in early 2009 and this communication describes the chemical composition of the fluids from these three wells (OW-903B, OW- 904B and OW 909). Down hole temperatures range from 250oC to 350oC for these three wells which agree with the solute and gas geothermometers. The wells produce fluids with high pH, deep fluid pH ranges from 6.9 to 8.3. OW 909 has higher deep fluid TDS, pH and concentrations of anions (B, Cl, F), Na and K as compared to OW 903B and OW 904B. Olkaria Domes wells have a sodium bicarbonate water type similar to those of Olkaria west and Olkaria central fields. Concentrations of most dissolved constituents were initially low but then increased with increasing enthalpy, a considerable range in observed concentrations. Deep fluids appear to be close to equilibrium with quartz and calcite. Very low Ca concentrations suggest that calcite scaling will not be a problem for the utilization of the Olkaria Domes geothermal fluids in electricity generation but fluid has to be separated at temperatures above 100°C to prevent silica scaling. There´s also low carbon dioxide emission from these wells.