EFFECT OF GRAIN SIZE ON SELECTED PHYSICO-CHEMICAL PROPERTIES OF LOCALLY AVAILABLE BENTONITE IN GEOTHERMAL DRILLING

Abstract

Geothermal operations at Olkaria have been using imported Bentonite for drilling since the beginning of drilling operations in 1958. Mixture of the right proportion of expanding and non-expanding clay to improve plasticity (moldability) of locally available Bentonite which can be used in the drilling industry in Kenya has not been investigated. In addition, little is known on the choice of the right grain size to eliminate or reduce the content of undesirable compounds such as iron oxide (Fe2O3), and aluminium oxide (Al2O3) to improve the strength of mud cake in the drilling process. The objective of this study was to investigate how selected physico-chemical properties of drilling clay relate to grain size of Bentonite available in Kenya. Randomised and probability sampling was employed in the month of February, March, and May on Bentonite from Parminters and Krigers field within the Lewa Wildlife conservancy. Clay samples were refined into 25, 20, 63 μm using size grading method. The mineralogical composition of the samples was determined using X-Ray Diffraction (XRD). The chemical composition, liquid limit, plastic limit and plasticity index were also determined. Firing was done at 800°C in a muffle furnace and the cracks of the samples recorded. The study showed that clay particles with sizes 20 and 25 μm were higher in Loss On Ignition (LOI) and total Carbon (C) than that of 63 μm regardless of grain size, the clay investigated had Quartz (SiO2), Illite-montmorillonite, Anatase (TiO2) and Kaolinite. Grading affected the concentrations of Iron (Fe), Aluminium (Al) and Silicon (Si) as clays with particle sizes 20 and 25 μm had higher contents of the aforementioned elements compared with those of 63 μm. The clay with particles 63 μm had the best strength and this was so because the clay particles had the lowest amount of Fe, Al and Si. Proper grading of clay particles can improve the physicochemical properties of locally available Bentonite and make it a better quality than imported Wyoming Bentonite.