Comparative evaluation of clays from Abakaliki Formation with commercial bentonite clays for use as drilling mud

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

Geotechnical and environmental problems related to shales in the Abakaliki area, Southeastern Nigeria

Six (6) samples of shale and five (5) water samples from hand-dug wells and boreholes, from different locations within the Abakaliki shale formation, have been assessed to evaluate the impact of the shale formation to the geotechnical and hydrogeo-environmental problems prevalent in the Abakaliki area (Southeastern Nigeria). Results indicated that the shale samples have Atterberg limits that might be considered moderate to high; while Liquid Limit (LL) ranged from 49 – 54, the Plasticity Index (PI) ranged from 34 – 38. These relatively high LL and PI suggested presence of expansive clays, some swelling of the shale on moisture influx and high compressibility. Natural moisture content (with mean value of 20%) was also significantly high. Hydrochemical analyses, on the other hand, revealed that the water samples had comparatively high content of ions and dissolved particles; Ca2+ ranged from 8.0 – 134.0 mg/l, Mg2+ ranged from 0.2 – 3.3 mg/l, HCO-3 ranged from 21.8 – 1176.1 mg/l and total dissolved solids ranged 56.9 – 1415.0 mg/l. Dissolution of soluble minerals (predominantly calcite and other rock salts) contained in the shale might likely be responsible for the release of these particles. Geotechnical behaviours of the shale and hydrogeochemical characteristics of water samples from the shale formation, thus, provided insights into the probable causes of seasonal waterlogging, consistent poor groundwater quantity and quality, structural and foundation problems that are prevalent in the Abakaliki area.Key words: Abakaliki shale, dissolution, environmental problems, geotechnical analysis, groundwater quality, structural failure