| Abstract |
The intention of this paper is to prepare a well design for the upcoming well at Gale le Goma field, located at the Asal region (P-1) by considering experience from pervious well GLG-1 drilled in 2016. Existing well lithology data was referred in order to prepare an updated well design according to the guidelines in the African Union Code of Practice for Geothermal Wells. Asal-3, Asal-6 and GLG-1 are located at the same area and drilled into the same reservoir. Therefore, they have a close lithological relationship with permeability and enthalpy in the Asal geothermal field. In this regard, same lithology will be used to design the upcoming well P-1. The wells encountered highly saline reservoir fluid of 120000 ppm (120 g/L). The planned depth of GLG-1 was 700 m MD and the resulting minimum depth of the production casing was set at 300 m MD with 12-1/4” production section down to 700 m MD. Correspondingly, the surface casing has a minimum setting depth of 60 m MD. The selected casing steel grade was of API 5CT of material grade J-55 for the surface casing and N-80 for the Anchor casing and J-55 for the production casing. In casing design, the casings are selected based on collection of the available data and assessment on expected subsurface conditions from the wellhead to the well target. These include considerations on geological formations, formation pressures, BHT, geothermal fluid properties, e.g. H2S gas presence and salinity. Casing thicknesses and material grades are selected according to calculated design factors (DF) that are required to be higher than minimum design factors defined in the African Union Code of Practice for Geothermal Wells. The selected casings for the upcoming well in Asal are of API 5CT steel grade K-55 for the surface casing and L-80 for the anchor and productions section which has more control on chemical composition than K-55. L-80 casing grade is also beneficial for the extreme salinity in the Asal area that may lead to an excessive corrosion of the casing in the borehole. The planned depth is 1300 m MD and the resulting minimum setting depth of the production casing is 800 m MD. The surface casing has a minimum setting depth of 250 m MD and the anchor casing of a 450 m MD correspondingly. This paper describes assumption that defines an appropriate casing design with emphasis on safe drilling and reduced risk of casing failure in the well. Choosing suitable materials will determine a safe operation and extended life time of the well. |