Ezekiel Obinna Igwe

The characteristics of clays from Abakaliki Formation, Southeastern Nigeria was evaluated to establish its suitability as drilling mud when compared with commercial bentonite such as Wyoming bentonite. The chemical, mineralogical and geotechnical properties were employed in assessing the suitability of Abakaliki clay as drilling mud. Mineralogically, the clays were all characterized as dominantly Illite as well as montmorillonite with low percentages of kaolinite. The chemical composition of the clays indicates low percentages of Na2O when compared with that of Wyoming bentonite with fairly higher percentages of CaO and K2O than are required for drilling mud clays. The clays are plastic; with liquid limit (LL) of 58.8 to 72.8, plastic limit (PL) of 25 to 30 and plasticity index (API) of 26 to 45.8. They are classified as inorganic clays of high plasticity (CH) according to Unified Soil Classification System (USCS) and as A-7-6 according to American Association of State High and Transportation Official’s (AASHTO) classification systems. The natural pH values are greater than 8.10, while the viscosity values varied from 5.9 to 8.0 centipoises for 10 g clay per 350 ml water. Some of these natural properties (Na2O and CaO contents, LL, PI and viscosity) of these Nigerian clays failed to satisfy the required specifications outlined for clays used as drilling mud when compared with the properties of Wyoming bentonite. This clay will possibly yield low plastic viscosities but with additives such as sodium carbonate and carboxymethyl cellulose, the rheological properties for Abakaliki clay will remarkably improve. Key words: Abakaliki Formation, drilling mud, geotechnical analysis, Wyoming bentonite, Southeastern Nigeria.