MSc defence by Kennedy Kamunya

Kennedy Mativo Kamunya, MSc Fellow in geochemistry at University of Iceland will give a presentation on his MSc project on Friday 25 May, 2018 at 13:30 at University of Iceland, Askja building, room 130.

The title of the project is:

δD and δ18O systematics in geothermal fluids, Olkaria Geothermal system, Kenya

Kennedy's supervisor:

Dr. Andri Stefánsson, Professor, University of Iceland

The external examiner will be Ingvi Gunnarsson, geochemist, Reykjavík Energy.

Everyone's welcome to attend.

Abstract

The δD and δ¹⁸O systematics of geothermal fluids, Olkaria Kenya, were studied.  Samples were collected from well discharges, both liquid and vapor phases collected at the same temperature and pressure, and analyzed for major elemental and δD and δ¹⁸O composition. The measured discharge fluids ranged in δD and δ¹⁸O composition from -3.7 to +16.1‰ and -1.45 to +3.18‰, respectively.  From these data, the reservoir chemical and isotope composition was reconstructed with δD and δ¹⁸O ratios from -2.1 to +14.6‰ and -0.84 to +2.61‰, respectively.  According to boiling modeling, large δD and δ¹⁸O fractionations can occur from the reservoir to sampling at surface, and these changes exceed the range of observed δD and δ¹⁸O variability for fluids.  Accurate reconstruction of reservoir and source δD and δ¹⁸O values requires, therefore, careful sampling, analysis and geochemical and isotope modeling. Based on the composition of the reservoir δD and δ¹⁸O and the local rainwater, surface water, lake water and non-thermal groundwater, and consideration of total geothermal fluid discharge and annual precipitation, it is concluded that the geothermal reservoir fluids at Olkaria are predominantly meteoric origin, locally and from the surrounding mountains.  Upon water-rock interaction, the geothermal waters are further modified, shifting the δ¹⁸O ratios to higher values.