Improvement of Well Test Equipment in Olkaria Geothermal Field, Kenya

Abstract

Geothermal wells are discharge tested after drilling to capture important parameters such as steam and brine output, enthalpy, discharge wellhead pressure and characteristic fluid chemistry at different throttle conditions. These parameters are useful in estimating the power capacity of a well, and for the design of the geothermal power plants and associated steam field infrastructure. The geothermal field in Olkaria is liquid dominated at reservoir pressure, producing both steam and liquid at the wellhead on expansion, which must be separated during a well discharge test. The silencer/separator is used to separate these two phases where the liquid phase is known as brine because it contains mineral salts and other dissolved solids. Noise is generated by conversion of kinetic energy into noise by sonic expansion of steam in the silencer/separator causing turbulence as a result of mixing high velocity mass flow with quiescent air. Wellhead silencers have been undergoing improvements on both separation efficiency and noise reduction since the start of geothermal development in Olkaria. The current silencers used for well testing causes noise generation of more than 107 decibels which is way beyond allowable noise limits for industrial and commercial areas in Kenya. This has predisposed KenGen to conflicts with local community and Kenya Wildlife Service (KWS) who are our stakeholders in Olkaria. Furthermore, these conflicts have resulted in delays in testing drilled wells therefore affecting the field development plans. The separator/silencer must be designed to achieve two requirements; efficient separation of the two phase flow and to attenuate the noise generated to acceptable limits. The design approach in this study is to handle the two challenges separately, by using a lower separation unit and an upper silencing unit. Based on the cyclone and the gravity separation principle, two prototypes were designed and tested. Both separator/silencers achieved permissible noise levels for industrial and commercial areas at the well pads with better brine separation efficiencies.