Use of Feedzones to Interpret Subsurface Permeability Controls: A Case Study of Olkaria Geothermal System

Abstract

It has been confirmed that the trachyte is the principle reservoir rock at Olkaria. Permeable zones at Olkaria are randomly distributed in the formations from as shallow as a few hundred metres to depths in excess of three kilometres. The distribution is however segmented creating localities for deep production and some areas with only fairly shallow permeable zones. In addition some permeability boundaries are now becoming evident in the larger field. This paper presents an analysis of feedzones in Olkaria wells and how they can be used to map out subsurface structures and their orientations in a geothermal system. In addition an evaluation of reservoir parameters giving indications on well deliverability, targeting and construction that has implications on well productivity are discussed.