Design of deep geothermal well using the African Union Code of Practice for Geothermal Drilling : A case study of Olkaria, Kenya

Abstract

This report presents the design of a high-temperature deep geothermal well in Olkaria field, using the revised code of practice for deep geothermal wells, The African Union Code of Practice for Geothermal Drilling (AUS, 2016), with a focus on well OW-49. Furthermore, this study will also provide a well design for a hypothetical 4500 m deep geothermal well that will serve as a guideline for future deep drilling projects. The well, OW-49 was drilled to a depth of 3650 m and designed using the New Zealand Standard code of practice for deep geothermal wells (NZS 2403:1991) (NZS, 1991). A review of the well design was done using the revised code basing the design considerations on the exact conditions of the well. Design calculations on casing loads were done to establish the best casing selection for the well by first establishing whether the current well casing design is adequate in terms of strength. The current casing design for well OW-49 comprises of a 20″, 94 lb/ft K55 surface casing, a 13⅜″, 54.5 lb/ft K55 anchor casing and a 9⅝″, 47 lb/ft K55 production casing. The revised design results conservatively in deeper casings and one additional casing string. Additionally, determination of the most suitable wellhead for the well was done. Finally, the report gives the well design for a hypothetical 4500 m deep geothermal well with an emphasis on casing specifications, drilling programme, cementing programme and wellhead specification.