Developing a geo-thermometry and measured down-hole temperature to identify feed-zones.

Abstract

Olkaria Geothermal Field is a high temperature geothermal system; the system is characterized by Quaternary volcanic centers in the central Kenya Rift Valley. The surface geology of OlkariaGeothermal Field is mainly dominated by commenditic lavas and pyroclastic. The aim of the paper was to develop a geo-thermometry and measured down-hole temperature profiles to identify feed-zones of OW 924A, OW 923A, OW917A, OW914B, OW731C, OW710C and OW39B wells. Using alteration mineralogy to interpret the paleo-temperature in a geothermal system and measured formation temperatures represent present state of geothermal systems. Alteration mineralogy curves plotted relied on the first appearance of alteration minerals observed in the wells namely chalcedony, quartz, wairakite, prehnite epidote and actinolite. Feed zone locations in Olkaria geothermal wells are located during completion test with a pressure Temperature spinner probe. After drilling a geothermal well and slotted liners landed, completion test is performed immediately with the purpose of identifying and characterizing the feed zones in the well. In Olkaria permeable zones are distributed from shallow depth to three kilometers deep. The feed zones are indicated in the curve by change in gradient. Thermal models in the study area show that the wells around OW 923A and OW 39B have higher temperatures indicators of the up flow zones.