Abstract

Rheological properties of drilling mud formulated from ten samples of Nigerian clay and treated with sodium carbonate (Na₂CO₃) were determined. Four different formulations were made: A (22.5 g / 350 ml of mud + 0% Na₂CO₃), B (22.5 g / 350 ml of mud + 10% Na₂CO₃), C (25 g / 350 ml of mud + 10% Na₂CO₃) and D (28 g / 350 ml of mud + 10% Na₂CO₃). None of the samples tested in their natural state exhibited remarkable improvement in rheological properties. However, as the concentration of sodium carbonate in 22.5 g / 350 ml of mud increased to 10% in all the samples, the highest percent increase of 525% in shear stress at 1022 s^-1 was observed. As clay concentration increased to 25 and 28 g / 350 ml at 10% sodium carbonate concentration, an additional increase in shear stress of 32 and 29% was observed respectively. This resulted in an increase in the apparent viscosity, plastic viscosity and yield point of the mud by 298, 32 and 29% in B, 205, 10 and 7% in C, and 9500, 90 and 61% in D respectively (on average basis for all samples). Four of the samples (NWY 013, 028, 033 and 053) showed strong promising flow properties and can be further improved to qualify as substitute for imported bentonite clay.

Key words: Clay, viscosity, sodium carbonate, beneficiation, flocculation, yield point, drilling, mud.