Investigating the Effect of Lithological Characteristics and Structural Attributes on the Drilling Rate: Casestudy of Olkaria Geothermal Field, Kenya

Abstract

The development of high temperature geothermal systems in Kenya is partly due to the occurrence of shallow magma bodies under volcanoes in the axis of the rift. Drilling of geothermal wells presents a critical development activity of a geothermal project. However, drilling activityfaces numerous challenges which negatively affect drilling rates. The drilling costs are increased since drilling operations are run on tight schedules and any delays come at a high cost. Some of the most common drilling problems can be attributed to lithology and stratigraphy of the formations. This research assessed the effect of lithological characteristics and structural attributes on the drilling rate at Olkaria geothermal field. The study investigated the joint effect of lithostratigraphy, geological structures and hydrothermal alterations on the drilling rate usingwells OW 724B and OW 45V as case study. These wells experienced drilling challenges caused by severe formation problems leading to high non-productive-time and cost overruns. Geological data ofthe wells included structures, and detailed stratigraphy of the sampled wells. From the study, the joint effect of lithostratigraphy, rock secondary structures and hydrothermal alterations on the drilling rate was found to be significant. However, changes in hydrothermal alterations caused the most significant variations in the daily drilled depths when compared to changes in lithostratigraphy and rock secondary structures. The findings revealed that 11% of the variations in the drilled depth could be explained by lithostratigraphy, rock secondary structures, and hydrothermal alterations.