Determination of optimum drilling parameters using 8.5 inch tricone bits in olkaria geothermal steamfield, Kenya

Abstract

The performance of drilling bits has a direct influence on cost and increase in the rate of penetration translates significantly to cost and time saving. From a total sample of 56 wells, approximately 450 tri-cone bits were consumed at a cost of KSh 200Millions. The primary objective of this study is to analyze and optimize 8½ tricone bits which were used to drill the 8½ diameter hole at Olkaria geothermal field. The pads had three wells each with the intention of exploring t in order to determine resource availability for massive power production. The exercise covered depth from 750m to 3000m using three rigs all with kelly drive systems. The data were compared in average between the daily and sectional drilling range for each well. Evaluation was on weight on bit, rev per minute and strokes in regard to their ROP. Olkaria formation is mainly trachytic and rhyolite with pyroclastic on surface. Also, occasional minor syenitic and deleritic dyke intrusive on bottom with temperatures above 250degrees centigrade encountered at 3000m total depth. From analysis the average parameters which suits olkaria formation are WOB of 11tonnes and RPM of 50 which accounts an average ROP of 5m/hr while maintaining average strokes of 75. Finally, drill off test has been recommended in future so as to get in-depth parameters while maintaining constant geological section and setting