Interpretation of geochemical well test data for wells OW-903B, OW-904B and OW-909 Olkaria Domes, Kenya

Abstract

Three wells from the Domes field were allowed to discharge for 3 months in early 2009. This report describes the chemical composition of the fluids from these wells, OW-903B, OW-904B and OW-909. Downhole temperatures range from 250 to 350oC 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 values for deep fluid TDS, pH and concentrations of anions (B, Cl, F), Na and K than OW-903B and OW-904B. Olkaria Domes wells have a sodium bicarbonate water type similar to those in Olkaria West and Olkaria Central fields. Concentrations of most dissolved constituents were initially low but increased with increasing enthalpy, a considerable range is observed in 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 in the utilization of the Olkaria Domes geothermal fluids.