Abstract

Abstract The geothermal resources of Kenyan are located in East African Great Rift Valley. The sub surface formation has high matrix compressive strength, rapidly changing and complex lithology, abrasive, fractured and high temperatures about 350 degrees Celcius. As a result, there are many challenges encountered in drilling operations including total loss of circulation, low penetration rate, high temperature damage of directional drilling steering tools and mud motors, breakdown of drilling foam structure at high temperatures, high drill string torque, loss of cement slurry and others. By integrating conventional oil and gas drilling technology, implementation of air and foam drilling technology it has been possible to solve the loss of circulation problems, improve on hole cleaning and cuttings recovery and consequently improved the penetration rates. The application of directional drilling technology has produced wells that reach a greater portion of the reservoir by intersecting more fractures increasing geothermal wells productivity. Through proper bit selection, improved hole cleaning efficiency, reduced drill string torque, the penetration rate has been improved and also reduced the total days per well. A total of fifty seven (57) geothermal wells have successfully been drilled between May 2007 and April 2012. The drilling operation has been 100% successful with the wells being 98% productive. The production has increased from 3 - 5Mwe per single well to 16 MW due to application of directional drilling and aerated drilling technology. This is an tremendous increase of over 100%. This integrated high temperature geothermal drilling technology can be implemented in the entire East African Great Rift Valley system to develop the vast geothermal resources for economic development.

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