Challenges of directional well drilling in Kenya : Case study of Olkaria, Kenya and Theistareykir, Iceland geothermal fields

Abstract

Directional drilling in Olkaria geothermal field started in the year 2007. This was necessitated by the need to drill high productivity geothermal wells by intercepting multiple fractures as well as taking advantage of the benefits associated with directional drilling. These advantages include the ability to exploit geothermal resources in an area that would be difficult to access, the ability to drill multiple wells from the same well pad, thereby minimizing surface disturbance among others. Since then, over 100 directional wells have been drilled successfully. All the directional wells in Olkaria employ the build and hold (J shape) design with a target angle of inclination set at 20°. The kick-off point for the wells ranges from 300 to 600 mRKB. Kick-off is achieved by the use of a mud motor to build the required angle after which an angle holding BHA composed of two stabilizers is used to hold the angle to the total depth. Drilling of the wells is done using water based mud for the upper section of the wellbore down to 300 mRKB and then aerated drilling is employed for the remaining section. Directional drilling in Olkaria is facing a number of challenges. This report focusses on the different challenges with emphasis on the BHA design related challenges. Proper BHA design for directional wells is important as it ensures that the wellbore trajectory is contained within the acceptable dog-leg severity. Excessive dog-legs in drilling results in drill string problems such as fatigue failure and worn out tool joints due to excessive torque and drag. A comparison of the different BHA designs and their performance for two wells drilled in Olkaria, Kenya and two wells drilled in Theistareykir, Iceland is used to highlight these challenges and explore how some of them can be addressed.