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 ofdrilling operations in 1958. Mixture of the right proportion of expanding and non-expanding clay to improveplasticity (moldability) of locally available Bentonite which can be used in the drilling industry in Kenya hasnot been investigated. In addition, little is known on the choice of the right grain size to eliminate or reducethe content of undesirable compounds such as iron oxide (Fe2O3), and aluminium oxide (Al2O3) to improvethe strength of mud cake in the drilling process. The objective of this study was to investigate how selectedphysico-chemical properties of drilling clay relate to grain size of Bentonite available in Kenya. Randomisedand probability sampling was employed in the month of February, March, and May on Bentonite fromParminters and Krigers field within the Lewa Wildlife conservancy. Clay samples were refined into 25, 20, 63μm using size grading method. The mineralogical composition of the samples was determined using X-RayDiffraction (XRD). The chemical composition, liquid limit, plastic limit and plasticity index were alsodetermined. Firing was done at 800°C in a muffle furnace and the cracks of the samples recorded. The studyshowed 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 comparedwith those of 63 μm. The clay with particles 63 μm had the best strength and this was so because the clayparticles had the lowest amount of Fe, Al and Si. Proper grading of clay particles can improve the physicochemicalproperties of locally available Bentonite and make it a better quality than imported WyomingBentonite.