A Geological Review of Olkaria Geothermal Reservoir Based on Structure

Abstract

The geological structure of Olkaria is known to be the main controller of fluid movement in the geothermal reservoir. However, the detailed structure has been elusive due to the substantial cover of the surface geology by ashes, pumice and other pyroclastic deposits from recent volcanic eruptions. The upflowing movement of the deep geothermal fluids in the field appear to be along the north-east to south-west striking Olkaria fault zone and a couple of the east-west striking The other fault structures appear to provide passage to fluids at shallow levels. There appears to be no unique upflow locality in the field. The present reservoir conditions are a result of an interplay of shallow level fluid movement, strongly influenced by the hydrological gradient to the south, the north-south fractures and fluids from depth rising along steeply dipping major fault zones.