Geology and Hydrothermal Alteration of the North and West Exploration Wells in the Olkaria Geothermal Field, Kenya

Abstract

Petrographic, x-ray diffraction and fluid inclusion studies were camed out cores and selected cuttings from ten exploration wells in the north and western sectors of the Olkaria geothermal field. The wells penetrated a thick volcanic pile of alkali and minor lavas and pyroclastics, with rare intersections of high level intrusives. The main permeability in the formation occurs in widely spaced faults with little fracturing occurring within the fault blocks. Lithological permeability is restricted to shallow levels, with hydrothermal mineral deposition sealing the primary porosity at depth. The distribution of illitic and chloritic clays helps to determine the extent of the bicarbonate, and the alkaline chloride fluids encountered in the reservoir. The distribution of kaolinite, smectite and carbonates is used to delineate the extent of cool recharge fluids.