EVALUATION OF IMO CLAY-SHALE DEPOSIT (PALEOCENE) FROM OKADA, EDO STATE, SOUTHWESTERN NIGERIA, AS DRILLING MUD CLAY

The dependence on the importation of drilling mud has much impact on the drilling operation in the country. Extensive field and laboratory investigation of Okada clay-shale revealed that the clay –shale deposit can be a good alternative to imported drilling mud when properly processed. X-ray diffraction studies carried out on the dis- turbed soil samples collected from the field showed the presence of vermiculite, montmo- rillonite and glauconite peaks, occurring as a mixed layer with traces of chlorite. District peaks of kaolinite, illite and quartz are also very visible. Chemical tests also showed that the SiO2 range from 55.75% to 55.84%, Al2O2 from 20.5% to 20.7%. The ratio of silica to alumina in both Okada shale and drilling mud are high, which is an indication of low quantity of free quartz. The average loss on ignition values for the Okada shale and drill- ing mud are 16.8 and 9.8 respectively. These values are high and indicate high water of crystallinity. The low content of K2O is an indication of the low amount of illite present. The mineralogical and chemical composition of both the Okada clay-shale and the im- ported drilling mud are such that Okada clay-shale can serve as a good alternative. However, the Okada clay-shale may require beneficiation, blending and refining pro- cesses to reduce its loss on ignition and SiO2 values.