Comparison of Use of Hammer Bits and Roller Cone Bits on Conventional Rigs, a Case Study of the Menengai Field

Abstract

Drilling speed of the top section (26” hole to a depth of 80m and 171/2” from a depth of 80m-400m) has been a challenge in the Menengai geothermal field with low rate of penetration as per intended target. This section is generally hard formation with frequent drilling fluids losses. Use of the standard roller cone bits on these sections causes a lot of vibrations on the rig leading to frequent breakdowns of the equipment (rotary table and top drive system) leading to downtime hence longer drilling periods and high maintenance cost. Loss of circulations while drilling the top section leads to cement plugs to heal the losses, use of more loss circulation material (LCM) and drilling mud. This increases the time taken to drill these sections due to wait on cement to cure and overall well costs. Introduction of the hammer bit on the conventional land rigs in the Menengai geothermal field has proven to have high rate of penetration on the 26” hole and 171/2” hole section, low/minimum vibrations transmitted to the rig equipment, less drilling fluids used and minimum downtime hence minimum maintenance costs.